The aim of this paper was: (1) to establish soil-specific laboratory calibration equations for two types of volumetric water content sensors (5TE and GS3); and (2) to evaluate their measurement accuracy and precision for estimating the soil moisture contents in sand, based on the established laboratory calibration equations and the corresponding default factory calibration equations provided by the manufacturers. The study revealed that the developed laboratory calibration equations (linear and polynomial) improved the sensors' measurement accuracy compared to that obtained using their corresponding factory calibration equations. Based on the root mean square error (RMSE), the 5TE sensor exhibited higher accuracy (RMSE=1.15%) with the third-order polynomial equation, followed by the second-order equation (RMSE=1.32%) and a linear regression equation (RMSE=1.63%). Thus, the third-polynomial type equation was considered to be the most suitable calibration model for the 5TE sensors in sand. In contrast, the second-order polynomial calibration equation provided highest accuracy for the GS3 sensors with the lowest RMSE of 0.86%.

Considering the heterogeneity of rock, the hydraulic fracturing process of rock specimen due to internal hydraulic pressure was numerically simulated in a meso-scale by RFPA2D2.0 (Realistic Failure Process Analysis). The differences of perforation angle, bedding angle and bedding material of rock specimens are considered. The numerical results showed that the initiation and propagation of hydraulic fractures were controlled by both global pore pressure's distribution gradient and local pore pressure around the crack tip. Both the lateral compressive pressure ratio and the bedding angle could affect the evolution of the hydraulic fractures. The numerically simulated results were in agreement with the experimental results.

A numerical code RFPA2D (Rock Failure Process Analysis), was used to simulate the initiation and propagation of fractures around pre-existing cavities in brittle rock. The dynamic loadings were applied to the rock specimens to investigate the mechanism of fractures evolution around single cavity. In addition, the evolution and interact of fractures between multiple cavities was investigated. The numerical simulated results reproduced tensile and remote fractures due to dynamic loading. Moreover, numerical results suggested that both the compressive wave and tensile wave could influence the propagation of tensile cracks. Especially the reflected tensile wave accelerated the propagation of tensile cracks.

Joints and fractures contained make rock mass complex mechanical and hydraulic properties. The randomicity of fractures shape factors (fracture orientation, dip, trace length, width, and spacing) is considered and Monte-Carlo simulation technique is adopted to develop the digital fractured rock mass model, which can be combined with numerical methods to solve practical engineering problems. FEM is adopted to simulate the mechanical and hydraulic properties of rock mass with different scales. Identifying representative elementary volume (REV) is a fundamental problem in studying rock mechanics and rock hydraulics, and it is a quantitative criterion for identifying if equivalent continuum approach is available for rock engineering problems and what the REV size is if it exists. On the basis of numerical modeling results, REV of fractured rock mass is discussed. The results show that REV size can be determined by the method in this paper and it can reflect the size effect of mechanical and hydraulic properties of rock mass. In addition, for the different research objects, such as mechanical property and hydraulic property, there exists different REV size.

Accurate characterization and quantification of the three-dimensional (3D) stress field and plastic zones around tunnels are vital for predicting potential rock bursts and spalling disasters and providing a quantitative basis for rational support design. However, the 3D stress field and plastic deformations around tunnels cannot be easily quantified experimentally because of the limitations of conventional experimental techniques. In this study, a novel experimental method combining photoelastic stress-freezing, phase shifting, and phase unwrapping techniques was proposed to quantitatively characterize the principal stress difference and shear stress around an arch tunnel model fabricated using 3D printing. The plastic deformation zones and elastoplastic boundaries around the tunnel were quantitatively defined using the Tresca yield criterion and stress-optic law. The experimental results obtained by the proposed method were compared with the simulation results of the 3D stress and plastic deformations around the tunnel. The results indicated that the areas with high stresses were primarily located at the corners, sidewalls, and shoulders of the arch tunnel. The sidewalls are stress disturbance zones, whereas the top and bottom are rapidly changing stress zones, indicating that disasters are prone to occur in these areas. Plastic zones were formed primarily at the sidewalls, corners, and shoulders of the tunnel, and the entire morphology exhibited a butterfly shape. The proposed method demonstrates good potential for validating numerical solutions. This study contributes to the understanding of the failure mechanisms of underground tunnels and enhances the prediction and prevention of tunnel disasters.

The stability of the residual coal pillar is the key to the re-mining above mined-out area. To improve the stability of overburden-coal pillar group, the method of pillar-side backfilling is proposed and the collaborative bearing mechanism for pillar-side backfilling is constructed. The compressive strength of the pillar-side backfilling and lateral restraint force of pillar-side backfilling on the coal pillar are derived. Moreover, this study takes the mining above mined-out area of 6# coal seam in Yuanbaowan coal mine as the actual engineering background. By using the PFC2D numerical simulation software, the stability of the residual coal pillars during mining above mined-out area was studied. The stress distribution of the overlying strata structure and the deformation characteristics of surrounding rock were analyzed under three different modes of pillar-side backfilling: without backfilling, bilateral pillar-side backfilling, and unilateral pillar-side backfilling. The results showed that without pillar-side backfilling, as the mining face advances, the pillar-type residual mining area will experience chain instability under the influence of advancing support pressure. After pillar-side backfilling, as the width of the filling body increases, the concentration stress in the overlying strata of the goaf gradually decreases. The movement and deformation of interlayer rock strata reduce, and the overall stability of the "residual coal pillar group-interlayer rock strata" system continuously strengthens, ensuring the safe re-mining of the 6# coal seam. When the width of the residual coal pillar is constant, the surrounding rock control effect of bilateral pillar-side backfilling is significantly superior to that of unilateral pillar-side backfilling. The reasonable selection of the width and backfilling method of pillar-side backfilling can effectively improve the overall stability of the residual coal pillars, achieving the purpose of preventing and controlling chain instability.

This study develops two mesoscale hydraulic fracturing modelling approaches, combining a hydromechanical coupled cohesive phase-field model with random field (RF) models and random aggregate models, respectively, for simulating complicated 2D/3D mesoscale hydraulic damage and fracture in quasi-brittle materials. The hydromechanical cohesive phase-field model is used to automatically model fluid-driven crack initiation and propagation in the generated mesoscale models without remeshing. Fracking experiments of a concrete cube under hydraulic pressure were simulated and analysed as benchmark examples. Monte Carlo simulations with 2,400 RF-based samples were first carried out to investigate the effects of variances, correlation lengths, and confining stresses on fluid flow and crack propagation. It was found that a higher variance of tensile strength led to lower mean peak pressures, while a larger correlation length and confining stress had an opposite effect. Random models consisting of mortar, polygonal/polyhedral aggregates, and interfacial transitional zones (ITZ), were then simulated, and the predicted linear peak pressure-confining stress relation was found in good agreement with the experimental and published numerical results. Although more validation is needed, the capacity of simulating complex and realistic fracking processes and the potential for engineering fracking design and parametric optimization of the developed approaches is well demonstrated.

The creep-slip behavior of creeping landslides is closely related to the creep characteristics of slope rock. This study analyzed the creep behavior of ultra-soft mudstone from the Gaomiao landslide in Haidong City, Qinghai Province, China. Uniaxial creep tests were carried out on ultra-soft mudstone with various moisture contents. The test results indicated that the creep duration of the rock sample with a natural moisture content of 9% is 2400 times longer than that of the sample with a natural moisture content of 13%, while its accumulated strain is 70% of the latter. For the rock sample with a natural moisture content of 9.80%, the creep duration under 0.5 MPa load is 80% of that under 0.25 MPa load, yet the accumulated strain is 1.4 times greater. Additionally, porosity significantly influences the creep behavior of mudstone. Analysis of the cause of the Gaomiao landslide and field monitoring data indicates that the instability of the Gaomiao landslide is related to the moisture content of the landslip mass and external forces. The creep-slip curves of landslides and the creep deformation curves of rocks share a common trend. Precisely identifying the moment when the shift occurs from steady state creep to accelerated creep is critical for comprehending slope instability and rock failure. Moreover, this study delves deeper into the issue of the consistency between landslide creep and rock deformation.

Rock grouting is an important technique for sealing rock fractures, but it has long been plagued by the lack of a practical approach to delineate the extent of grout propagation inside the facture flow channels. Despite previous attempts to evaluate grout performance, barely any non-intrusive way can directly and accurately reveal the grout penetration region. In this study, a new inversion method is suggested, based on a magnetic forward model, to predict the burial depth, dip angle and lateral (horizontal) projection span of a grouted area in a single rock fracture. It is assumed that the grout flow route inside a rock mass can be magnetically observable when ferromagnetic materials are added to the grout. The method commences by forward modelling the magnetic field caused by an inclined sheet of magnetic material. Based on the analytical solutions for calculating the magnetic field in the presence of the sheet, a relationship between the magnetic anomalies and the geometric parameters of the sheet is established. Following the feasibility study of the forward model, an inversion procedure is proposed to determine the geometric information of the sheet using multiple observations of magnetic data obtained at various levels above the sheet. The results show the applicability of the inverse method for estimating the burial depth at observation distances up to five times the length down dip of the sheet. Moreover, a correction nomogram is proposed to address the sources of error with known approximate parameters, and this greatly improves the model's performance. Finally, some insights into the application of the inversion process in a three-dimensional magnetic field are presented. The current solutions for predicting the geometry of grout intrusion in a rock fracture system are shown to be efficient. Both the forward and inverse models proposed should provide valuable contributions to the problem of addressing the error involved in non-destructive, remote detection of a grout region in a fractured rock mass.

This study proposes a novel hybrid phase-field method for modelling asymmetric tension¿compression mixed-mode brittle fracture in rock-like materials. In this method, the isotropic elastic strain energy is decomposed into tensile, tensile-shear, and compressive-shear components through a combination of orthogonal decomposition and strain spectral splitting. The split components are combined with three fracture energies and integrated with the Mohr¿Coulomb strength criterion to construct a new hybrid driving force for mixed-mode fracture. The driving force is then incorporated into the framework of the standard brittle phase-field model and the resultant governing equations are discretized within the finite element framework and solved using a staggered Newton¿Raphson iterative method, with a history field of driving force and a bound-constrained solver to ensure damage irreversibility and boundness, respectively. The developed method was validated against experimental and numerical data through six benchmark examples of solid fracture under tensile, shear, and compressive loadings, along with an additional case in the appendix to quantitatively verify its prediction of compressive failure. It is found that the new method implicitly incorporates a practical and physically grounded energy¿strength coupled failure criterion, enabling accurate simulation of complex 2D and 3D fractures under various loading conditions and thus holding great potential for structural stability and safety assessments in engineering applications.

Rain-induced slope failure is a worldwide disaster in engineering practice. This paper presents a framework for stability analysis of unsaturated slopes. A fully coupled model of wetting and non-wetting fluid phases with deformable solid phase is used to model hydro-mechanics of unsaturated slopes under water infiltration and discharge. Plasticity of the solid phase is described using the classical non-smooth Mohr-Coulomb (MC) model, which is implemented using a novel subspace-tracking scheme by updating stresses in the principal stress space that is continuously dependent on stresses. The Vector Sum Method (VSM) and Pattern Search Method (PSM) are combined to transform the slope stability analysis into an optimization problem and to determine critical slip surfaces and safety factors simultaneously. Unlike the conventional definition of safety factor, vector characteristics of the sliding and resistance forces are considered. The present framework is implemented using the Numerical Manifold Method (NMM) and is advantageous in modeling complex boundary conditions and discontinuities in geomaterials. Through benchmark slope stability analyses, effectiveness and accuracy of the proposed model are validated. Numerical simulations show that there is a lag between the time instant rainfall ceases and the time instant fluid phases reach equilibrium and the safety factor assumes its minimum.

Recently, foamed polymers have been widely used in the repair of underground engineering disasters by grouting (trenchless technology) due to controllable gelation time and self-expansion. However, the grouting process becomes more complicated due to the complex geological conditions and the self-expansion of slurry. Therefore, this paper adopts a self-made visual experimental device with peripheral pressure and water plugging rate (WPR) monitoring functions to study the influence of main influencing parameters (particle size distribution, grouting amount and dynamic water pump pressure (DWPP)) on the spatiotemporal distribution of slurry WPR and diffusion dynamic response (peripheral pressure). The results show that: When grouting amount is 563 g and DWPP is 0.013 MPa, the expansion force of the slurry in the diffusion process is dominant and can significantly change the local sand and gravel skeleton structure. When grouting amount is 563 g, DWPP is 0.013 MPa, and particle size distribution type is III, the flow time of the polymer is shortened, the pores of the gravel are rapidly blocked. Then, the peripheral pressure decreases rapidly with the increase of the distance, and the time to reach the inflection point WPR is shortened. The instantaneous blockage of the pores leads to the delayed transmission of flow field blockage information.

A two-scale computational homogenization model is developed based on the Numerical Manifold Method (NMM) for modeling nonlinear transient heat conduction in heterogeneous media with imperfectly bonded material interfaces. The extended Hill-Mandel lemma is adopted to establish the micro- and macroscopic weak formulations and cross-scale relations, incorporating the microscale inertia effects. Moreover, to consider imperfectly bonded interfaces, a versatile and efficient procedure is introduced to model the Kapitza-type interfacial thermal resistance. With NMM approximations and the Backward Euler method, the nonlinear transient heat conduction problem is discretized and solved using nested Newton loops for micro- and macroscopic problems. The present model is able to effectively cope with microscale temperature jumps and heterogeneities with complex topologies and morphologies. To validate the accuracy and effectiveness of the proposed model, benchmark examples, including heat flow in heterogeneous functionally gradient materials, are solved and the results are compared with direct numerical simulations. In particular, it is shown that the perfectly bonded interface condition is equivalent to setting the interfacial thermal resistance less than or equal to 10-5. Additionally, influences of the content ratio, size and distribution of inclusions in representative volume elements on the effective thermal response of the heterogeneous media are also investigated.

The 3D-NDDACP method (nodal-based 3D discontinuous deformation analysis method with contact potential) shows its capability to simulate discontinuous deformation of rock block systems. Due to the adoption of contact potential for contact treatment and Newmark method for time integration, 3D-NDDACP method inherits attractive advantages from both FEM-DEM and discontinuous deformation analysis (DDA) method. Furthermore, tetrahedral meshes are adopted to discretize rock blocks to model their deformation. In this study, 3D-NDDACP method is enriched to simulate wave propagation in rock masses. The new enrichments to the 3D-NDDACP method include: 1) a viscous nonreflecting boundary is firstly adopted to absorb wave energy to minimize the negative effects from artificial boundaries; 2) on the basis of viscous nonreflecting boundary, a viscoelastic boundary is adopted to simulate the elastic recovery property of an infinite problem domain; and 3) to accurately input incident wave, the force input method is adopted. To validate the enriched 3D-NDDACP method, a series of typical numerical tests associated with P/S-wave propagation through jointed/homogeneous rock masses are conducted. Results from these numerical tests show that the enriched 3D-NDDACP method is able to correctly and reliably model the processes of P/S-wave propagation across homogeneous and jointed rock masses.

A three-dimensional (3D) numerical model for polymer grouting in rock mass fractures based on reaction kinetics theory is established in this article. The model integrates polymer reaction kinetics, compressible Newtonian fluid control, the energy balance accounting for foaming agent evaporation, and slurry density and viscosity models. A 3D rock fracture model simulates grouting in complex fractures and is validated by conventional viscosity simulations. In this study, the impact of fracture medium parameters on polymer diffusion is assessed, and slurry flow, pressure, viscosity, and density distributions during grouting are predicted. The research results indicated that (1) wider fractures reduce the overall slurry viscosity, rough fractures yield an uneven viscosity distribution, and smooth fractures (Joint Roughness Coefficient, JRC = 0) exhibit symmetrical viscosity. An increased fracture inclination boosts the slurry viscosity and reduces the reaction time. (2) Compared with viscosity, slurry density inversely trends with distance. (3) Larger fractures exhibit lower overall slurry diffusion pressures, which decrease with distance. Rough fractures experience higher pressure and fluctuations. A greater fracture inclination increases the overall diffusion pressure, with a monotonic increase at 60° and a parabolic distribution at 0°, peaking at the grouting port.

The combination of the dipping effect and hydromechanical (H-M) coupling effect can easily lead to water inrush disasters in water-rich roadways with different dip angles in coal mines. Therefore, H-M coupling tests of bedded sandstones under identical osmotic pressure and various confining pressures were conducted. Then, the evolution curves of stress-strain, permeability and damage, macro- and mesoscopic failure characteristics were obtained. Subsequently, the mechanical behaviour was characterized, and finally the failure mechanism was revealed. The results showed that: (1) The failure of the sandstone with the bedding angle of 45° or 60° was the structure-dominant type, while that with the bedding angle of 0°, 30° or 90° was the force-dominant type. (2) When the bedding angle was in the range of (0°, 30°) or (45°, 90°), the confining pressure played a dominant role in influencing the peak strength. However, within ß¿(30°, 45°), the bedding effect played a dominant role in the peak strength. (3) With the increase in bedding angle, the cohesion increased first, then decreased and finally increased, while the internal friction angle was the opposite. (4) When the bedding angle was 0° or 30°, the "water wedging" effect and the "bedding buckling" effect would lead to the forking or converging shear failure. When the bedding angle was 45° or 60°, the sliding friction effect would lead to the shear slipping failure. When the bedding angle was 90°, the combination of the "bedding buckling" effect and shear effect would lead to the mixed tension-shear failure. The above conclusions obtained are helpful for the prevention of water inrush disasters in water-rich roadways with different dips in coal mines.

Due to the presence of natural joints and weak interlayer interfaces in the rock mass, the rock mass will be damaged or even deformed to high degree under the action of dynamic loads such as strong seismic activity, resulting in significant engineering safety accidents and casualties. In light of the aforementioned dynamic issues with rock discontinuities, complete rock samples and interface rock samples containing cemented material (gypsum) underwent a series of SHPB impact compressive and splitting tensile tests. To investigate the dynamic properties and change laws of rocks, theoretical analysis, high-speed camera systems, and "binary method" fracture extraction technology were employed. It¿was concluded that the peak strength of impact tension and impact compression of the samples increased with the¿increase of strain rate in a power function relationship. The cemented material (gypsum) interface causes stress wave and energy dissipation to be attenuated. When compared to an intact rock sample, the interface causes the number, area, and transmission coefficient of the cracks to decrease, preventing further crack development. However, the initial position and development direction of the crack and the overall stress loading of the sample are not affected. When the energy input is too much, the rock crack gradually changes from peritectic to transgranular, showing that the dissipative energy increases and reaches the peak strength. The findings can serve as a guide and a point of reference for major projects involving joined rock mass and broken rock mass in terms of safety design and operation.

This paper intends to identify the safety and stability issues within quay structures, including scouring and hollowing, in the infrastructure for off-shore rubble bed. The three main research approaches are to combine 3D laser scanning technology, particle discrete element method and on-site experiments. The rubble bed model is established using the rigid block (Rblock) element in discrete element particle flow. Combined with the gradation generation method and the calibration of on-site tests, the influencing factors and evolution characteristics of vibratory compaction technique of rubble bed are then numerically investigated. First, the shape of the on-site stones is characterized using 3D mesoscopic extraction by 3D laser scanning technology.Statistics are used to examine the shape charactrization parameters of stone particles, and 3D mesoscopic characterization description and reconstruction techniques are developed for stone particles. Second, the 3D model of rubble bed is then built using the Rblock element in discrete particle flow, and the necessary model parameters are calibrated through a on-site vibratory compaction test. Additionally, the PFC3D program is used to study two types of influencing factors, namely the particle characteristics and vibration conditions during the vibratory compaction process of rubble bed. The results show how the riprap thickness, particle size, grading effect, vibration time, vibration frequency, and effective excitation amplitude affect the vibratory compactory properties of rubble bed. The functional link between various influencing factors with density degree and deformation modulus is proposed after combining experimental tests to examine the relevance between compaction parameters with density degree after vibration and deformation modulus. The suggested discrete element method can serve as a guide for vibratory rubble bed compaction.

The interface is the weakest region of the coal-backfilling composite structure (CBCS) for underground mines, the sawtooth angles of which is one of the most critical concerns to be accounted. However, limited studies have focused on the deformation and failure behaviours of CBCS with different interface sawtooth angles under double shearing. To investigate the effect of interface sawtooth angles on the damage characteristics of CBCS under double shearing, CBCS with different interface sawtooth angles (i.e., 0°, 15°, 30°, 45°, 60°) were prepared and double shearing tests were carried out in the present research. Macroscopic failure characteristics (i.e., failure mode, failure process, and shear strength) of the CBCS were experimentally investigated via the digital image correlation (DIC), acoustic emission (AE), and 3D scanner system, whereas microscopic feature of which, including the contact force¿microcrack evolution, and displacement vector of CBCS were numerical simulated by the discrete element modelling (DEM) method. The results showed that the failure modes of the CBCS can be classified into three types (e.g., climbing failure, cutting failure, and sliding failure). Among them, the climbing failure was only occurred when the loads on the sawtooth surfaces exceeded its shear strength, while the cutting failure occurred if the load on the sawtooth end of the coal element or backfilling element exceeded its shear strength. The sliding failure occurred, because the load applied to the interface exceeded the shear strength of the specimen interface. Moreover, the peak shear stress, the degree of strain concentration, and the extent of the strain concentration zone of the CBCS increased with the enlarged sawtooth angle. The research outcomes will contribute to obtain an in-depth understanding about the mechanical response of the coal-backfill composites under double shear loading.

Polymer grouting can effectively improve the stability of surrounding rock fractures. However, in practical construction, it is difficult to judge the degree of coupling between the slurry and the rock, and the effective grouting range after grouting. Therefore, early prediction of the effect of grouting on the surrounding rock is crucial. In this paper, a new artificial intelligence method is proposed to predict the polymer fracture grouting effect. The genetic algorithm optimized back propagation neural network (GA-BP) is employed to construct an intelligent prediction model. To acquire a substantial dataset for constructing the model, an easily assembled/disassembled test apparatus for polymer fracture grouting is designed. The maximum coupling degree of the fractures and slurry diffusion distance are chosen as the evaluation metrics for the grouting effectiveness. The influences of the fracture characteristic parameters and grouting volume on the grouting effect are investigated. Furthermore, a comprehensive analysis is conducted on the spatiotemporal diffusion characteristics and slurry-rock coupling mechanism of polymer grouting. Compared to traditional BP neural networks, and three other machine learning algorithms (decision trees, random forests and gradient boosting decision trees), the GA-BP model outperforms them in terms of R2 (coefficient of determination), MSE (mean squared error), MBE (mean bias error), MAE (mean absolute error) and RMSE (root mean squared error) in both the test and training sets. The GA algorithm significantly improves the accuracy and robustness of the prediction model. The optimized model demonstrates significant accuracy in predicting grouting results and assessing efficiency, providing a practical reference for grouting construction.

With increasing loading rate, the layer-activated fractures tend to occur. Under high strain rates, cracks generally develop along diversified directions inclined to the bedding planes. Five typical failure patterns of transversely isotropic shales under dynamic Brazilian splitting were concluded. The modified Nova¿Zaninetti criterion considering strain rate effect was proposed.

Pull-out load and the cement-sand ratio (CSR) can affect the non-destructive testing (NDT) results of anchor bolts. Therefore, in this article, NDT experiments were conducted on both fully and defectively grouted anchor bolts, and variation patterns of key dynamic testing signal parameters were analyzed. A longitudinal vibration model of defectively grouted anchor bolts considering dynamic and static damping was proposed, and simulated NDT of anchor bolts with varying qualities. The results indicated that grouting defects resulted in an increase in wave velocity, along with a decrease in the fundamental frequency and dynamic stiffness of anchor bolts. When grouting defects and pull-out load acted concurrently, the fundamental frequency, and dynamic stiffness of the defectively grouted anchor bolts were consistently smaller than those of fully grouted ones during the initial loading phase. With pull-out load increasing, wave velocity decreased first, then increased; fundamental frequency increased, followed by a decrease; dynamic stiffness rose. When the CSR of defectively grouted anchor bolts was reduced, wave velocity decreased, fundamental frequency increased slightly, and a substantial increase in dynamic stiffness was observed. Pull-out loads were more sensitive to anchor bolt key dynamic signals than defects and CSR. Simulated validation demonstrated the reliability of the proposed theory.

In an anchor support system, once the soil strength is improved by grouting with a geotextile, the pull-out force of anchors increases. To investigate the improvement of surrounding soils due to the grouting with a geotextile, a series of filtration and penetration tests under various parameters such as different initial degrees of compaction, water content and soil types were conducted via a self-developed device. In addition, microscopic tests were then carried out to obtain the soil's structure before and after grouting. The main conclusions are as follows: (1) The strength of surrounding soils is improved by grouting with a geotextile through the compaction effect and the slurry infiltration, while its strengthening effect gradually declines with the increase in the initial degree of compaction. (2) As the initial water content increases, the strengthening effect derived from the compaction effect and the cohesive substances infiltration decreases, while this improved efficiency of the soil strength declines due to the water infiltration during grouting. (3) Although the effect of grouting with a geotextile on different soils is obviously different due to the different efficiency of slurry (i.e., water and cohesive substances) infiltration, it can improve the soil strength regardless of soil type, especially for sandy soils. (4) Under the filtration of geotextile, a hardened layer is formed at the grout¿soil interface due to the accumulation of cohesive substances, which is beneficial to the performance improvement in applications such as the capsule-type anchor.

Permeation grouting is one of the important methods of anti-seepage reinforcement when the drainage pipes crosses loose diseases caused by leakage. With the development of grouting materials, permeable polymer slurry is widely used in engineering practice. Due to its low viscosity, fast reaction and micro-expansion, the diffusion and reinforcement law of slurry in loose area of drainage pipeline is more complex. To better understand the effects of water head pressure, grouting pressure, sand particle size and clay content on the anti-seepage and reinforcement effect of permeable polymer grouting in loose area of drainage pipeline, several types of tests, including permeability and uniaxial compressive strength tests, were performed. Then, based on the model test results, a BP neural network prediction model for the anti-seepage reinforcement effect of permeable polymer grouting in loose area of drainage pipeline is constructed, and the research results are applied to the treatment project of loose area of drainage pipeline for verification. The results show that: 1) after grouting, the order of magnitude of permeability coefficient of the consolidated body is reduced to 10-7cm/s, the anti-seepage performance of the sand layer is greatly improved, and the grouting pressure is the main controlling factor affecting the anti-seepage performance of the consolidated body. 2) The compressive strength of the consolidated body is obvious different under different working conditions. The water head pressure is the main controlling factor affecting the strength of the consolidated body. 3) Due to the limitation of test conditions, the relative error between the predicted value of BP neural network model and the actual value is about 20%, which can meet the general prediction needs.

A backfilling body-coal pillar-backfilling body (BPB) structure formed by pillar-side cemented paste backfilling can bear overburden stress and ensure safe mining. However, the failure response of BPB composite samples must be investigated. This paper examines the deformation characteristics and damage evolution of six types of BPB composite samples using a digital speckle correlation method under uniaxial compression conditions. A new damage evolution equation was established on the basis of the input strain energy and dissipated strain energy at the peak stress. The prevention and control mechanisms of the backfilling body on the coal pillar instability were discussed. The results show that the deformation localization and macroscopic cracks of the BPB composite samples first appeared at the coal-backfilling interface, and then expanded to the backfilling elements, ultimately appearing in the coal elements. The elastic strain energy in the BPB composite samples reached a maximum at the peak stress, whereas the dissipated energy continued to accumulate and increase. The damage evolution curve and equation agree well with the test results, providing further understanding of instability prevention and the control mechanisms of the BPB composite samples. The restraining effect on the coal pillar was gradually reduced with decreasing backfilling body element's volume ratio, and the BPB composite structure became more vulnerable to failure. This research is expected to guide the design, stability monitoring, instability prevention, and control of BPB structures in pillar-side cemented paste backfilling mining.

The aim of the study is to explore the failure response characteristics of the "backfilling body-coal pillar" cooperative bearing structure(BP coal-backfilling structure) in the pillar-side backfilling. Firstly, six groups of uniaxial compression tests were carried out for different types of BP coal-backfilling structure samples, the three-dimensional optical speckle monitor and acoustic emission system were used to capture the surface deformation information and sample fracture signal. Secondly, the damage model of BP coal-backfilling structure was constructed based on the acoustic emission characteristics. Finally, the failure mechanism of BP coal-backfilling structure under uniaxial compression was revealed. The results show that with the increase of coal volume ratios, the bearing capacity of BP coal-backfilling structure samples gradually decreases, the elastic modulus firstly decreases and then increases, and the peak strain firstly increases and then decreases. During the uniaxial loading process of BP coal-backfilling structure samples, the strain concentration zone appears earliest at the interface position, then appears in the element with the larger volume ratio, and the appearance relatively lags behind in the element with a small volume ratio. In addition, the maximum acoustic emission energy value occurs in element with large volume ratio. The BP coal-backfilling structure samples experience a gradual damage process, which mainly includes the initial damage stage, the damage development stage and the damage attenuation stage. The larger the volume ratio of coal elements, the faster the damage value of the BP coal-backfilling structure samples increases, and the more likely the sudden instability is to be caused. On the contrary, the damage rate of BP coal-backfilling structure samples can be slowed down by increasing volume ratio of the backfilling body element. The failure of the BP coal-backfilling structure sample is firstly induced by the shear failure or tensile failure of coal-backfilling interface, then, the coal element or the backfilling body element suffers the linkage failure, resulting in the loss of overall bearing capacity of BP coal-backfilling structure samples, and the eventual destabilization is caused.

The grouting sequence and spatial layout of grouting holes are key technical problems in the treatment of underground drainage pipeline defects. An unreasonable grouting parameter design will lead to slurry running or bulging during pipeline defect repair. In this paper, based on the discrete element particle flow numerical simulation software PFC and maximum value characteristics of different shapes, a new multiple hole grouting model is established. In the multiple hole grouting model, the variation law of soil porosity and soil stress around the grouting hole was analyzed under two operating conditions of successive grouting with adjacent double holes and interhole grouting with three holes. Meanwhile, the variation law of soil porosity and stress around the grouting hole is analyzed under triangular and rectangular spatial layouts of the grouting hole. Then, the results obtained from the multiple hole grouting model are applied to an engineering site. The results show that the grouting effect in the interhole is better than that of successive grouting in adjacent holes, and the grouting effect of the triangular hole layout is better than that of the rectangular hole layout. In addition, it can be concluded that the triangular hole pattern is suitable for transverse joints or longitudinal joints.

This paper presents a work to define four fundamental concepts, namely, buoyant force, submerged unit weight, seepage force, and critical hydraulic gradients, for saturated geomaterials including soils, rocks, and concrete under normal and high pressures using the general effective stress (GES) concept along with Terzaghi's effective stress. In particular, four typical GES expressions are used for this purpose, and their impacts on the definition of the four concepts are compared based on available experimental evidence in the literature. The results suggest that (1) Terzaghi's effective stress can be physically validated in the context of Archimedes' principle for soils under normal conditions; (2) the generalized buoyant force on the unit volume of saturated geomaterials is the product of the unit weight of pore fluid and the GES coefficient tensor; and (3) the generalized seepage force theoretically acts in the direction of pore fluid flow only when the GES coefficient tensor is proportional to the permeability coefficient tensor. These four fundamental concepts have a profound significance for geotechnical applications with GES and thus merit further validation with adequate laboratory and in situ observations.

Slope bearing capacity is one of the most important characteristics in slope engineering and is strongly influenced by weak planes, loading conditions, and slope geometry. By presenting the evolution of slip surfaces, this paper explored how the slope bearing capacity is affected by widely observed influencing factors. The initiation and propagation of slip surfaces are presented in laboratory model tests of slope using the transparent soil technique. Shear band evolution under various weak planes, loading conditions, and slope geometries were experimentally presented, and slope bearing capacities were analyzed with the process of shear band evolution. This paper verified that slip surface morphologies have a strong relation with the slope bearing capacity. The same slip surface morphology can have different evolutionary processes. In this case, it is the shear band evolution that determines the slope bearing capacity, not the morphology of the slip surface. The influencing factors such as pre-existing weak planes, loading conditions, and slope geometry strongly affect the slope bearing capacity as these factors govern the process of shear band evolution inside the slope.

This study deals with rock-bit interaction mechanism in rotary drilling to assess rock drillability for hard rock formations. A serial of drilling tests with different thrusts and rotary speeds were separately conducted on the cylindrical specimens of granite, marble and limestone by a newly developed drilling monitoring equipment. During the test, the rock-bit interaction performance and drilling parameters (e.g., thrust, rotation speed and torque) were recorded by a high-speed camera and the drilling monitoring equipment respectively. The mass and size distribution of rock chips were finally measured to analyze the factors controlling rock fragmentation. The results of this study show that the drill bit presents a helicoidal trajectory in rock because of the simultaneous indentation and cutting process, resulting in rock crushing, shearing, and tensile cracking respectively. Some of the large size chips burst due to large absorbed cutting energy, but most of chips accumulate in the cutting path of the drill bit and increase the cutting friction energy. Additionally, the applied thrust is the essential factor in rock fragmentation, the rock compressive strength and tensile strength contribute significantly to the mass of rock chips and size of rock chips respectively during rock fragmentation. There is also a positive linear correlation between torque and thrust. The magnitude of this linear slope is affected by the cutter movement condition, but not by the rotation speed. A higher linear slope specifically means bigger rock abrasivity and rock intrinsic energy. A new rock drillability theoretical model was finally proposed on the basis of those rock-bit interaction results, which is not only related to rock intrinsic specific energy and friction coefficient but also independent of drilling parameters, such as thrusts and rotation speeds. The validity of this theoretical model in practical engineering applications was also verified by drilling data available in the literature.

This paper describes test apparatus developed to evaluate, at model scale, the behaviour of a pressure grouted soil nail system. The apparatus allows the grout to be injected at different injection rates. A latex membrane is used as a liner around the grouting outlets of the pressure-grouted soil nail to form a Tube-a-Manchette (TAM) for direct injection of grout into the surrounding soil, in some tests entering the soil voids. Pure cement and water were used as the grout (w/c = 0.5). A special screw jack pump system was developed, automated and instrumented to control the injection rate of the grout, as well as to monitor the injected grout volume over time. In addition, an overburden pressure system was designed to apply surcharge pressure using a water-filled rubber bag, which also allowed the settlement of the soil mass to be inferred directly from the volume of pressurized water. In this study, a series of laboratory-scale pullout tests were conducted with the newly developed apparatus to investigate the performance of pressure grouted soil nails with the grout being injected at different rates. The experimental results show that more grout can be injected at higher rates. Accordingly, the pullout resistance of the pressure grouted soil nail also increases with the injection rate.

The configuration of slip surface is conventionally regarded as a key characteristic to distinguish slope failure modes that are embedded in the limited equilibrium method and the bearing capacity theories. However, few studies indicated that a different way of propagating a slip surface with the same configuration might affect the mechanical behaviour and failure mode of the slope. In this paper, the mechanical behaviour is studied in two slopes that have a similar configuration of slip surface with different processes of shear band evolution. Advances in transparent soil technology allow the non-intrusive observation of shear band development in the laboratory slope models. This paper presents shear band development inside slopes using the transparent soil technique and then analyse the mechanical behaviour via the discrete element method (DEM). In order to reproduce the laboratory results, the real shape of transparent soil particles is used in the DEM model, and the microscopic parameters are calibrated by response surface methodology (RSM). The mechanical parameters such as movement, stress, void ratio and energy dissipation are measured in different stages of shear band evolution and are measured in four regions: the weak plane, the shear band, the slope mass above the slip surface, and the slope mass below the slip surface. This paper presents the role of shear band propagation in the mechanical behaviour of slope and discusses the possibility of monitoring the mechanical behaviour of slope to predict the coalescence of slip surface.

Fracture toughness of anisotropic shale is an important parameter in shale-gas exploitation technology. Currently available literature is mainly focused on Mode I fracture toughness (KIC) of anisotropic rock under tensile loading. Although there are the cracked straight through Brazilian disk and crack ring disk used to determine Mode II fracture toughness (KIIC) of anisotropic rock under pure shear stress, their fracture trajectories are deviated from the original crack plane and cannot be regarded as the true Mode II fracture. In this paper, shear-box test was firstly adopted to measure KIIC of anisotropic shale. New physical factors YI0 and YII0 were proposed to describe effects of both the geometry and the material parameters on stress intensity factors (SIFs) of the original crack plane (KI0 and KII0) and to derive the calculation formulae of SIFs on arbitrary (KI¿ and KII¿). Calculated results show that KII¿ reaches its maximum absolute value at ¿ = 0¿10° where KI¿ is negative, which promotes occurrence of Mode II fracture. The predicted planes of Mode II fracture agree well with the tested fracture trajectories (amostly along the original crack plane). The KIIC is increased with increase of ß (ß = 0¿90°). KIIC is 3¿4 times as large as KIC and can be regarded as the true Mode II fracture toughness of anisotropic shale. The shear-box test is an effective method for measuring KIIC of anisotropic rock.

To investigate the influence of the fissure morphology on the dynamic mechanical properties of the rock and the crack propagation, a drop hammer impact test device was used to conduct impact failure tests on sandstones with different fissure numbers and fissure dips, simultaneously recorded the crack growth after each impact. The box fractal dimension is used to quantitatively analyze the dynamic change in the sandstone cracks and a fractal model of crack growth over time is established based on fractal theory. The results demonstrate that under impact test conditions of the same mass and different heights, the energy absorbed by sandstone accounts for about 26.7% of the gravitational potential energy. But at the same height and different mass, the energy absorbed by the sandstone accounts for about 68.6% of the total energy. As the fissure dip increases and the number of fissures increases, the dynamic peak stress and dynamic elastic modulus of the fractured sandstone gradually decrease. The fractal dimensions of crack evolution tend to increase with time as a whole and assume as a parabolic. Except for one fissure, 60° and 90° specimens, with the extension of time, the increase rate of fractal dimension is decreasing correspondingly.

Chain instability of residual coal pillars can lead to the dynamic disaster, such as the overburden caving, surface collapse, dynamic shock, gas leaking and water releasing.Revealing the chain failure mechanism of residual coal pillars is the basic prerequisite for its accurate control.Starting from the chain instability source, the weakest failure model of residual coal pillars was firstly proposed.The basic concept of key pillar was defined and its characteristics was analyzed.The determining method of key pillar was developed and the chain failure of residual coal pillars was revealed.Then, the key pillar theory in the instability of residual coal pillars was formed.At last, the potential application scope and field of key pillar theory was discussed.Results show that ¿ the differences in the internal physical-mechanical properties and external environmental factors have led to the weakest instability model of residual coal pillars.When any form of instability models appears in the residual coal pillar system, the weakest instability model must have occurred.That is, the coal pillar with the weakest stability factor fails inevitably when the chain instability of pillar system occurs.¿ The key pillar refers to the pillar that the local instability occurs earliest in the pillar system.Only the local failure of key pillar appears, the collapse of adjacent coal pillars with stronger stability can be activated.And the chain failure of residual pillar system can occur.¿ The pillar with the smallest safety factor can be determined as the key pillar in the pillar system.Four principles of regionality, relativity, dynamics, and compound should be followed in determining the position of key pillar.¿ Linear increase of load for the nearest adjacent coal pillar is triggered by the gradual reduction of load for key pillar.That is, the local instability of key pillar will cause the shift of overburden stress, which will transfer to the nearest coal pillars and lead to further instability and damage.Eventually, the chain failure and destruction of residual pillar system may also be caused.¿ The key pillar theory can be used in the fields, such as the adjacent seams mining in the pillar areas, the strong pressure behavior controlling, the coal pillar designing, the backfilling mining, the gas extraction and the water disaster prevention.It can also be applied to the controlling of rock pillars in the non-coal resources mining.The key pillar theory in the instability of residual coal pillars is expected to promote the development of the theories and technologies of Chinese green mining.

The diffusion of cement slurry in a fracture with flowing water is an important factor ensuring the grouting effect and a key factor influencing the environment, including natural and social traffic. To better understand the influence of the characteristic fracture parameters and the water flow rate on the cement slurry diffusion law, first, diffusion testing of a cement slurry in a simulated tortuous fracture with flowing water is carried out. Then, the results obtained from these tests are applied to an engineering site. The results of the experimental and engineering tests support the following conclusions. 1) At a low water flow rate, the sealing efficiency of test points near the grouting source increases rapidly with time, while the sealing efficiency of test points far from the grouting source exhibits little change with time. 2) Near the grouting source, the sealing efficiency corresponding to a high fractal dimension of fracture tortuosity is higher than that corresponding to a low fractal dimension of fracture tortuosity; far from the grouting source, this pattern is reversed. 3) When the inflection point of the grouting pressure is reached at a test point, the sealing efficiency of the fracture at this test point is the greatest.

Prestressed anchor support is one of the most important support methods for coal mine roadways. As the coal mining depth increases, the adaptability of existing prestressed anchor has become weaker and weaker, which is mainly reflected in the current anchor prestress is much smaller than the support resistance required for the stability of the roadways and makes it difficult to effectively control the roadways. In order to solve the problem, a group anchor structure was proposed to realize higher prestressed anchor support technology and improve the support status of deep roadways. For coal mine roadways, group anchor structure is a new technology and new topic, and the design method and theoretical basis of the group anchor support are lacking. Therefore, the paper studied the bearing capacity of the group anchors through physical tests and numerical simulations. Among them, a special set of group anchor drawing tooling was designed and processed to match the physical test. The test results show that the group anchor structure can double the bearing capacity and bearing rigidity compared with traditional anchors, and the group anchor support can further optimize the support parameters to improve the bearing capacity of the surrounding rock. Therefore, the group anchor support is helpful to the stability control of the surrounding rock of the deep roadway.

By utilizing wave velocity imaging technology, the uniaxial multi-stage loading test was conducted on siltstone to attain wave velocity imagings during rock fracture. Based on the time series parameters of acoustic emissions (AE), joint response characteristics of the velocity field and AE during rock fracture were analyzed. Moreover, the localization effect of damage during rock fracture was explored by applying wave velocity imagings. The experimental result showed that the wave velocity imagings enable three-dimensional (3-D) visualization of the extent and spatial position of damage to the rock. A damaged zone has a low wave velocity and a zone where the low wave velocity is concentrated tends to correspond to a severely damaged zone. AE parameters and wave velocity imagings depict the changes in activity of cracks during rock fracture from temporal and spatial perspectives, respectively: the activity of cracks is strengthened, and the rate of AE events increases during rock fracture; correspondingly, the low-velocity zones are gradually aggregated and their area gradually increases. From the wave velocity imagings, the damaged zones in rock were divided into an initially damaged zone, a progressively damaged zone, and a fractured zone. During rock fracture, the progressively damaged zone and the fractured zone both develop around the initially damaged zone, showing a typical localization effect of the damage. By capturing the spatial development trends of the progressively damaged zone and fractured zone in wave velocity imagings, the development of microfractures can be predicted, exerting practical significance for determining the position of the main fracture.

Numerous tunnel excavation projects have been undertaken in China to address the ever-increasing demand for tunnels, which is driven by the rapid development of urban cities. Tunnel excavations generally induce the settlement of existing tunnels and sometimes result in the derailment of metro vehicles. In this study, the Nanyan Fourth Circuit Transmission Reconstruction, located in Dalian City in China, was selected to investigate the local settlement of a metro station caused by an underlying tunnel excavation project. The theoretical solution of the stochastic medium theory was calculated for a horseshoe-shaped tunnel based on the Gauss¿Legendre integral in a non-uniform convergence situation. Results were compared with data measured at the metro station. A three-dimensional model was developed to further explore the variations in stress and deformation, which were difficult to measure during the excavation. The results showed the existence of a settlement gradient of the metro station in the direction of the excavation after the underlying tunnel was excavated. The numerical results were in good agreement with the data measured onsite. The non-uniformity of the settlement in the direction of the excavation was investigated. The findings of this study can provide a reference for predicting and controlling the impact of undercrossing tunnel excavation on the deformation of metro stations.

Fracture mechanism of hydraulic fracturing for anisotropic shale is of very importance in shale gas mining technology. The classical fracture criteria can better predict tensile (Mode I) fracture under arbitrary loading condition (pure tensile, pure shear and mixed-mode), but have difficultly in predicting shear (Mode II) fracture. In this paper, a new mixed-mode fracture criterion (modified K-ratio criterion) of anisotropic rock is established based on the ratio of stress intense factors (SIFs) and fracture toughness of arbitrary plane to predict both the crack initiation angle and fracture mode. New physical influencing factors are proposed to describe effects of both the geometry and the material parameters of anisotropic rock on the SIFs of the original crack plane, KI(0) and KII(0), in order to calculate the SIFs on arbitrary crack plane, KI(¿) and KII(¿). Prediction results show that under the pure tension, pure shear and tension-shear loads applied onto the original plane, Mode I fracture can occur on the sedimentary plane or on the plane of KI(¿)max. Mode I or Mode II fracture can occur under compression-shear load. The semi-circular bend (SCB) test results of anisotropic shale specimens with different ¿ (crack inclined angle) and ß (sedimentary plane angle) are in good agreement with the predicted results and can verify the validity of the modified K-ratio criterion.

In order to understand the influence of brittleness and confining stress on rock cuttability, the indentation tests were carried out by a conical pick on the four types of rocks. Then, the experimental results were utilized to take regression analysis. The eight sets of normalized regression models were established for reflecting the relationships of peak indentation force (PIF) and specific energy (SE) with brittleness index and uniaxial confining stress. The regression analyses present that these regression models have good prediction performance. The regressive results indicate that brittleness indices and uniaxial confining stress conditions have non-linear effects on the rock cuttability that is determined by PIF and SE. Finally, the multilayer perceptual neural network was used to measure the importance weights of brittleness index and uniaxial confining stress upon the influence for rock cuttability. The results indicate that the uniaxial confining stress is more significant than brittleness index for influencing the rock cuttability.

Ore recovery and dilution in caving mines are strongly determined by the flow characteristics of broken rock, especially under inclined boundary conditions. A physical draw model was designed and used to investigate the gravity flow characterization of granular materials during longitudinal sublevel caving. The three-dimensional (3D) shapes of flow axis, isolated extraction zone (IEZ) and ore remnants under inclined walls were obtained using the discharged quantity method and 3Dmine software, which indicated that stope boundary conditions and orebody dip have an impact on the characteristics of gravity flow. The experimental results also showed that the gravity flow characteristics of 3D draw experiments under the inclined walls were significantly different from those of the two-dimensional (2D) draw experiments. The flow axis is a line segment and lies in the same plane and only the width of the IEZ can be displayed in 2D experiment. However, the flow axis is a space curve segment in 3D draw experiment. Since being cut off by the front and inclined upper walls simultaneously, the 3D IEZ is more complicated than the 2D IEZ and both the width and thickness of the draw body are displayed simultaneously in 3D state. The shape and location of ore remnants in 3D state are also different from that in 2D state. Therefore, the 3D IEZ is more consistent with the actual situation than 2D IEZ for sublevel caving stope. The 3D gravity flow presented may be used to determine the design of the extraction layout and improve ore recovery during longitudinal sublevel caving.

Stress conditions and preflaws are prominent conditions influencing the cuttability of deep hard rock. This study aims to investigate the cuttability of intact, prefractured, and drilled rocks under biaxial confining stress, uniaxial confining stress, and stress-free conditions using a conical cutter in rock fragmentation tests on true triaxial loading apparatus. Peak cutter force and penetration depth at rock initial fracture and final failure of the rock specimen were used to reflect rock cuttability. The results show that the rock cuttability increases with stress in one direction decreasing under biaxial confining stresses, and presents a decreasing trend followed by an initial increase as uniaxial confining stress increases. The prefractures and boreholes in rock can further improve the rock cuttability, compared with intact rock. A series of cuttability improvement measures were proposed to provide a suitable condition for the application of nonexplosive mechanized mining in hard rock. Finally, comparative field tests were performed on a single-face entryway and a peninsula-shaped pillar, in which the mean value of cutting efficiency increased from 32.6 to 107.7 t/h, and the dust production and cutter wearout failure reduced significantly.

In this study, numerical simulations of uniaxial compression, biaxial compression, and biaxial unloading were performed on granite specimens that contained different prefabricated defects. The microscopic parameters in numerical models were verified by the uniaxial compression experiments on the intact standard cylindrical granite specimen and the square granite specimens with prefabricated defects. The influences from different stress paths, different shapes of prefabricated defects, different numbers of defects, and different distribution of defects on the strength, deformation, and crack initiation stress characteristics of the rock specimens were investigated. Furthermore, the initial cracking and cracking stage distributions, cumulative crack amounts, ultimate failure modes, and crack propagation fractal dimensions of specimens with different prefabricated defects under biaxial unloading conditions were analyzed and compared. The experiment was divided into three stages to analyze crack evolution mechanisms. The results show that most cracks appeared after peak strength, and different shapes, the number of defects, and the relative defect positions significantly affected crack initiation, crack propagation, and crack coalescence.

This paper describes an experimental investigation of a newly developed driven and grouted soil nail (x-Nail), which combines the capabilities of a purely frictional driven nail and a compaction-grouted nail. The innovative design allows the x-Nail to be driven into the ground with a latex balloon attached that is subsequently used for compaction grouting. A grout bulb is thus formed at the driven end of the nail to improve its pull-out resistance. For compaction grouting, a special type of additive mixed cement grout was used in this investigation because of its zero bleeding and high bond strength. A series of pullout model tests was conducted to examine the performance of the x-Nail compared to a purely frictional soil nail. It was found that more than 90% of the pullout force of the x-Nail was resisted by the expanded grout bulb and the end bearing resistance of the grout bulb increased with the increment of the injected grout volumes. The experimental results revealed that the pullout force of the x-Nail increased approximately 1800%, 1550%, 1200%, and 900% compared to the purely frictional soil nail for the injected grout volumes of about 350, 270, 220, and 170 mL, respectively.

The compaction grouting is an important factor in enhancing the performance of the newly developed compaction-grouted soil nail. Based on the self-developed large-scale model system, two series of pull-out tests with and without compaction grouting are carried out, and their results are compared to study the influences of compaction grouting on the enhancement of the pull-out force of the new soil nail. In addition, a hyperbolic model that can well describe the evolution of pull-out force with displacement is proposed. The study shows that: (1) The compaction grouting has significant influence on the pullout force within small pullout displacement, while it has small influence on the final pullout force. Moreover, when the soil conditions change, the compaction grouting (leading to soil densification) on the performance of soil nails depends on the grouting pressure rather than the diameter of the grout bulb. (2) The differences in soil responses caused by the compaction grouting, including vertical dilatation, the vertical and horizontal squeezing effects, are the main causes that lead to the difference in the increase rate of the pullout force of soil nails. (3) By introducing two parameters, the compression modulus and the ultimate pullout stress, a hyperbolic pullout model is proposed. After verification, the pullout forces can be calculated for the given diameter of grout bulb and pullout displacement.

The mechanical behavior evolution characteristics of sandstone are important to the application and practice of rock engineering. Therefore, a new method and concept of deep rock mechanics testing are proposed to reveal the mechanical behavior evolution mechanism of deep roadway surrounding rock after excavation with a depth over 1000 m. High stress-seepage coupling experiments of deep sandstone under various confining pressures are conducted using GCTS. Stress ¿ strain and permeability curves are obtained. The three-stage mechanical behavior of deep sandstone is better characterized. A platform and secondary compaction phenomena are observed. With the confining pressure increasing, the platform length gradually decreases, even disappears. In the stade I, the rigid effect of deep sandstone is remarkable. In the stage II, radial deformation of deep sandstone dominates. The transient strain of confining pressure compliance is defined, which shows three-stage evolution characteristics. In the stage III, the radial deformation is greater than the axial deformation in the pre-peak stage, but the opposite trend is observed in the post-peak stage. It is found that the dynamic permeability can be more accurately characterized by the radial strain. The relations between the permeability and stress-strain curves in various stages are revealed.

The surrounding rocks of underground engineering are usually subjected to the coupling of compressive and shear stresses. The variable angle shear tests (VASTs) and direct shear tests (DSTs) are two types of lab tests that can easily achieve different compression-shear stress states. The VASTs and DSTs on cubic rock specimens were conducted to analyze the shear strength parameters and acoustic emission (AE) characteristics during rock failure process. The test results show that it is more reasonable to use the test data in VASTs with shear angles greater than 45° for calculating the shear strength parameters of rocks. The essence of changing the shear angles in VASTs or the normal loads in DSTs is to change the micro-crack component produced in the compression-shear failure mode, in which the shear cracking mainly trigger the AE signals with low peak frequency around 100 kHz, and the tensile cracking mainly induce the AE signals with relatively high peak frequency around 300 kHz. Although the main type of micro-crack produced by shear failure and compression failure are both shear micro-crack, the micro-cracks generated by shear failure have higher efficiency in generating AE energy compared with compression failure, which means that the large-scale micro-crack expansion activities are more intense in shear failure than that in compression failure.

A series of dynamic fracture experiments on semicircular bend (SCB) marble specimens were conducted to characterize the loading rate effect using the INSTRON testing machine and the modified SHPB testing system. The fracture toughness of the marble specimens was measured from a low loading rate to a high loading rate (10-3106 MPa·m1/2s-1). The results show that the fracture toughness will increase with the loading rate. Since the fracture toughness at a magnitude of 10-3 MPa·m1/2s-1 is regarded as the static fracture toughness, the specific value of DIFf (the dynamic increase factor of fracture toughness) can be obtained at the other loading magnitudes from dynamic fracture tests. To describe the variation in DIFf from low to high loading rates, a new continuous model of DIFf was put forward to express the quantitative relation between the loading rate and rock dynamic fracture toughness. It is shown that the new DIFf model can accurately describe the loading rate effect on the dynamic fracture testing data for rock materials.

Aiming at the shortcomings of the existing micro-source localization algorithm based on the uniform speed assumption and the iterative method leading to large amount of calculation and poor robustness, a new method of micro-source location considering the velocity anisotropy was proposed through the transformation of time-distance equation. The new method used six effective detector data to implement positioning. Stochastic simulation method was applied to produce a large number of source alternative solutions considering the complexity of wave velocity characteristics. Final source solution was discussed from the angle of information fusion, the gross error criterion and the clustering analysis method was used to obtain the source solution. The examples show that the analytical method is correct and reasonable, and the information fusion method is scientific and reasonable, and suggest the final micro source is determined through gross error criterion.

Prediction of rock burst tendency is one of the basic tasks of disaster prevention and reduction in underground engineering. In view of the existing mathematical models, there are some shortages in the necessary inspection process determining the comprehensive weight of the rock burst index, and there is low accuracy for predicting the rock burst. An improved cloud model for predicting rock bursts is proposed. The improved model is fused with the index weight through cloud atomization conditions in the cloud theory. And the comprehensive weight of the index after the test is obtained. By modifying the standard cloud model and generating the hierarchical integrated cloud by comprehensive cloud algorithm, the deficiencies that the standard cloud model is too sensitive to the average grade range are made up. A number of rock burst examples are used to verify the proposed model. The results show that a more reasonable comprehensive weight can be obtained using the weight fusion method based on the cloud theory. The improved model can be well applied to the prediction of rock burst tendency.

The quality classification of rock mass is a basic geotechnical engineering issue. The classification of rock mass quality shows the uncertainty due to the fuzziness and randomness of the rock mass parameters. The effect of parameter uncertainty on the classification results is ignored in the existing classification model. The reliability method was thus introduced into the classification of rock mass quality, and a coupled model of Monte Carlo simulation(MCS) and technique for order preference by similarity to ideal solution(TOPSIS) was proposed, which can consider the effect of the parameter uncertainty on the classification. The model consists of two parts. One part is to obtain the weight of classification system index with the game theory and to determine the limit-state equation of the reliability with the TOPSIS model, and the other part is to perform uncertainty analysis and to provide the final classification result based on the probability function. The TOPSIS model was tested with 25 sets of samples. The analysis results of the MCS-TOPSIS model indicate that the misjudgment ratio of the model is 0. The quality classification of the surrounding rock at Shuibuya underground powerhouse is examined based on the certainty and uncertainty methods using Matlab programs. The results demonstrate that it is feasible to use the MCS-TOPSIS model to classify the rock mass quality and the model has high accuracy and is easy to use.

Micro-seismic source location is crucial for the micro-seismic monitoring technology. The existing algorithms usually minimize the function of time arrival values(time difference) from all detectors to obtain the location of micro-seismic source. The positioning results deviate usually from the actual locations of the sources because all the known micro-seismic parameters have errors. To overcome the shortcomings of the present algorithm, a two-step inversion method for the micro-seismic source location is thus proposed. The first inversion is to identify the abnormal detector, and the second inversion is to search the exact location from the space coordinates of sources. The 3-parameter, 4-parameter and 5-parameter inversion models on the assumption of uniform velocity are established and compared. A multi-objective genetic algorithm(Non-dominated Sorting Genetic Algorithm-II, NSGA-II) is used for the first inversion. A single objective optimization algorithm is suggested in the second inversion in order to achieve the accurate source searching and to reduce the computing time. The results from a case study indicate that the proposed method can effectively identify the abnormal detectors and the positioning is greatly improved compared with the results with the abnormal geophone. The 4-parameter inversion model is better than the 5-parameter inversion model.

The creation of microfractures within rock is commonly observed as rock is strained. The presence of these microfractures constitutes damage to the rock, and this damage can reduce the rock's strength. This paper explores the evolution of rock strength as microfractures within a rock accumulate. Two approaches involving different laboratory tests are used to study how cohesion and internal friction evolve during progressive damage to rock. The mobilized cohesion and friction angle are measured for intact and damaged rock specimens. Intact rock specimens tested under compression were used to determine the peak values of cohesion and friction angle for two types of rock. Specimens of rock with varying amounts of accumulated microfracture damage were tested under direct shear or multi-stage triaxial compression to measure the Coulomb strength parameters for damaged rock. The laboratory testing shows that cohesion decreases with strain as the rock accumulates internal damage caused by microfracturing before the peak strength. The frictional component of the rock strength starts to be mobilized as strain causes internal microfractures. The mobilized internal friction angle increases up to and slightly beyond the peak strength. A small amount of post-peak strain is required to initiate macroscopic slip surfaces, and until these are created, high frictional resistance is mobilized between the many interacting and interlocked pieces of rock in the test specimen. With further post-peak strain, the friction angle decreases as the macroscopic slip surfaces in the rock become well established.

In geotechnical engineering, when the strength of soft soils is relatively low, a rapid loading rate can lead to ground failure. In this situation, a multi-stage loading scheme can be utilized to achieve higher soil strength by consolidating the soil layer to a certain degree before applying the next, larger load(s). Additionally, the total stress in the soil layer usually varies, and, in many cases, this variation is not uniform with depth, for example, when the loading is applied within a small area over a thick soil layer. In this study, a thorough, explicit analytical solution is presented for the consolidation of a single soil layer using a multi-stage loading with depth-dependent total stress. The particular case of a two-stage loading scheme is selected to investigate the consolidation behavior of a soil layer. Finally, the convergence of the analytical solution is assessed by comparing the calculated results using the various terms of the series to facilitate the use of the solution by engineers and to provide sufficient accuracy.

© 2014 Elsevier Ltd. The consolidation behavior of ground with vertical drains is known to be greatly affected by the finite permeability of the sand drains, also called the effect of well resistance. However, up to now, no analytical methods have been reported for evaluating this effect on the nonlinear consolidation behavior of vertical drains. In this paper, by considering the nonlinear compressibility and permeability of soil during consolidation, the effect of well resistance was incorporated into the derivation of the equations that govern the nonlinear consolidation of a vertical drain with coupled radial-vertical flow. In addition, the smear effect was considered by assuming three decay patterns for the radial permeability coefficients of the soil toward the sand drain in the smeared zone. After obtaining the governing equations, a simplified analytical solution is derived for a general time-variable surcharge loading. Based on the general solution obtained, detailed solutions are provided for three special types of loading schemes: constant loading, single-stage loading, and multi-stage loading. The validity of the solution is verified by reducing it to several special cases and comparing these to existing solutions. Finally, the effect of the well resistance, the ratios of the compression index to the radial and vertical permeability indices, various loading schemes, and various variation patterns of the radial permeability coefficient of the soil in the smeared soil zone are investigated using parametric analysis.

The 3D fracture field distribution model of goaf and overlying strata was derived on the basis of the continuous surface mathematical model of overlying strata. The applicability of 3D model was verified through practical examples. The overlying strata fissure changes in proportion coupled form of double hump. The porosity in external area is small and convex front-like, while the porosity in the internal region is large and hollow. The junction point of ionosphere porosity exists in the vertical direction, with depth increases the side of the porosity increases, and the other side gets lower. The distribution of porosity appears shovel-like in the Caving zone of the goaf. The porosity is large in the periphery of the goaf, but small in the internal range.

In this paper, a coupled thermal-mechanical-damage model, Material Failure Process Analysis for Thermo code (abbreviated as MFPA-thermo), was applied to investigate the formation, extension and coalescence of cracks in FRCs, caused by the thermal mismatch of the matrix and the particles under uniform temperature variations. The effects of the thermal mismatch between the matrix and fibers on the stress distribution and crack development were also numerically studied. The influences of the material heterogeneity, the failure patterns of FRCs at varied temperatures are simulated and compared with the experimental results in the present paper. The results show that the mechanisms of thermal damage and fracture of the composite remarkedably depend on the difference between the coefficients of thermal expansion of the fibers and the matrix on a meso-scale. Meanwhile, the simulations indicate that the thermal cracking of the FRCs at uniform varied temperatures is an evolution process from diffused damage, nucleation, and finally linkage of cracks.

One small-scale physical model test on the PVD (Prefabricated Vertical Drain) treated Hong Kong marine clay was simulated using finite element method (FEM) in this study. A User MATerial (UMAT) subroutine describing an Elastic Visco-Plastic (EVP) constitutive model was developed and incorporated into one commercial finite element code ABAQUS. A degressive permeability of the PVD strip was included to consider variations of its permeability during the consolidation process. The UMAT and the adopted reducing technique were demonstrated to be effective by good agreement between the observed consolidation settlement and excess pore water pressures and the simulated ones.

A series of numerical model tests were performed to investigate the behaviour of the anisotropic rock surrounding circular excavations under high confining pressures. The aim was to provide information on the formation of fractures and failure around deep level rock tunnels under controlled conditions. Solid cubes containing a circular hole were confined to a vertical pressure with same as the confinement in the horizontal directions. In this modeling, the inhomogeneous rock is generated by using Weibull parameters which are related to the microstructural properties determined by crack size distribution and grain size. The fracture angle is assumed to be 45°. The observed failure zone around the excavation was simulated using both the maximum tensile strain criterion and Mohr-Coulomb criterion respectively (as the damage threshold). And RFPA (Realistic Failure Process Analysis) code was used as the calculating tool in this modelling, three opening modes are simulated and compared. Computational model predictions that include crack propagation and failure modes of rock show a good agreement with those of the observation in site. It is pointed out that the damage evolution of EDZ strongly depends on the inhomogeneous, the excavation mode, anisotropic property, and the various loading conditions. Concerning the existence of a weak plane, the amount of displacement at the side wall of the tunnel was quite large, since the shear deformation occurred in EDZ. The model is implemented in RFPA code and is able to represent the change in fracture patterns between the solid and jointed parts. This provides confidence for the application of the numerical model to the design of rock tunnels at great depth.

Soil nailing is a widely used technique for stabilizing slopes and excavations. In all current design methods, the nail-soil interface shear strength, that is, the pull-out resistance of a soil nail is an important parameter which controls the design and safety assessment of the soil nailing system. The pressure grouting is a cost effective method for increasing the soil nail pull-out resistance and in turn improving the performance of the nailed structure. In this paper, a three dimensional (3-D) finite element (FE) model for pull-out tests is established and verified by comparing simulated results with measured data. This model is then used to simulate the effect of grouting pressure on the soil nail pull-out resistance.

In this paper, a Material Failure Process Analysis code (MFPA) was employed to investigate the interaction of end effect zone of specimen with the wing crack propagation inside the brittle specimen containing pre-existing flaws under uniaxial compression comparing with the experimental results. The numerical results show that the shorter the distance between the pre-existing flaw and the specimen's end, the slower the crack propagation process and the shorter wing propagation length is, and vice versa. In addition, the end effect zone was also influenced by the wing crack propagation.

An Elastic Plastic-Damage (EPD) model is developed to model the softening behaviour of the cement-soil admixture based on continuous damage mechanics. The softening behaviour is considered to be characteristic outcome of the material degradation due to damage in material. Material degradation is modelled by reducing progressively the stiffness and yield stress of the material when the damage variable has attained a critical index. The basic equations of the model are derived and presented. A Fortran program for this model has been developed and implemented into a finite element code ABAQUS. In order to evaluate the applicability of this model, several unconfined compression tests are simulated using ABAQUS with this model. The computed results are compared with measured data and good agreement is achieved.

In numerical simulation of engineering problems, it is important to properly simulate the interface between two adjacent parts of the model. In finite element method, there are generally three methods for simulating interface problems: interface element method, surface based contact method and the method by using a thin layer of continuum elements. In this paper, simulation of interface problems is conducted using continuum elements and surface based contact methods. The results from each method are presented and compared with each other.

Since non-stationary signal of hydro-power unit can be analyzed by using continuous wavelet transform (CWT), implicated information about the operational status can be extracted in the scale domain using the CWT. Power rate of each frequency is proposed to be refined to deal with the CWT coefficient figure pixel brightness. Gray moment is then introduced to quantitatively indicate the characteristics of the CWT coefficient figure. It is demonstrated that the gray moment is effective to be a hydro-power unit vibration symptom for the hydro-power unit analysis and diagnosis.

Laboratory compact grouting was performed using a modified triaxial test on Hong Kong CDG (completely decomposed granite) soils to investigate the effect of effective confining pressure and grout injection rate on the compact grouting effect. In this study, compaction grouting was simulated by expanding a latex balloon inside a triaxial sample using de-aired water. When the balloon is expanded, it first needs to overcome the effect of the confining pressure of the soil; further expansion will compact and density the surrounding soil. The compact grouting effect can be control by measuring the total void ratio change during injection and the following consolidation. The injection rate was controlled by a GDS using a volume control technique. The results of the experiments showed that the effective confining pressure on soil specimen plays an important role in the effect of compaction grouting, and the injection rate has an effect on the rate of excess pore pressure dissipation but minor effect on soil density. © 2007 Taylor & Francis Group.

Based on cusp-type catastrophe theory, a sample rock-rock model for studying the pillar rockburst mechanism is presented in this paper. It is shown that the stiffness ratio, K, of the roof and floor to the pillar plays an important role in the outbreak of instability. Additionally, simple formulae for the deformation jump and the energy release are derived. Based on the assumption that there exists a proportional relationship between the number of microseismic events and microfractured elements, the theoretical microseismic event rate produced by the double rock sample, loaded in series under uniaxial compression, is obtained. Using a newly developed numerical code, RFPA 2D, the progressive failure process and associated microseismic behavior of the twin rock samples are simulated, which shows that the spatial distribution of microseismic events develops progressively from disorder at the initial loading stage to order prior to the main shock. The numerically simulated results also confirm that a soft roof and floor promote an unstable failure or collapse of pillars, while a stiff roof and floor can lead to a stable failure of pillars. Additionally, the simulated results reproduce the deformation jump and the energy release that occur during a pillar rockburst. It is demonstrated that the proposed model properly simulates the pillar failure process. © Springer-Verlag 2006.

Rock is a very heterogeneous material, containing various types of weaknesses such as gain boundaries, pores, and cracks and other defects. When rock is subjected to surrounding loading or the increase of hydraulic pressure due to rainstorm, the pre-existing fractures will initiate or propagate at the point of least resistance, which may cause failure of the entire structure of slope, dam and so on. By using Flow-Rock Failure Process Analysis code, F-RFPA2D. Firstly, a numerical simulation and similar materials experiment on rock samples with two pre-existing cracks without hydraulic pressure were conducted to investigate the initiation, propagation, coalescence of cracks and failure mechanism of rock considering the heterogeneity of rock; secondly, another sample with two pre-existing cracks subjected to hydraulic pressure under the loading conditions of different k0 is used to investigate the behavior of hydraulic fractures evolution, and their coupling action. Numerical results reproduce the process of pre-existing cracking evolution process which agreed with the experimental results.

Many stiff clays forming part of natural slopes and earth dams exist in the fissured state. When these cracks are subjected to gravity induced normal and shear stresses they may propagate. The present discussion presents a numerical method to study the propagation direction of cracks under stress fields similar to those found in the field. Not only did the results on one crack propagation direction obtained from the numerical method and the analytical results agree well, but numerical results have been used to investigate the mechanisms of the whole process of two horizontal cracks initiation and propagation and coalescence in stiff soils.

Rock and concrete are typical heterogeneous material that the meso-scale heterogeneity may have a significant effect on their macro-scale mechanical responses. In this work, a digital image-based (DIB) technique is employed to characterize and quantify the heterogeneity of concrete, and the obtained data is directly imported into a numerical code named RFPA (Rock Failure Process Analysis) to study the effect of heterogeneity on the failure process of concrete. The upgraded RFPA is capable to simulate the progressive failure of brittle materials such as rock and concrete, representing both the growth of existing fractures and the formation of new fractures, obviating the need to identify crack tips and their interaction expl icitly. The simulated results are in reasonable agreement with experimental measurements and phenomenological observations reported in previous studies.

The purpose of this paper is to investigate shear behaviors (failure progress, failure pattern, failure mechanism and shear resistance) of rock specimens containing four joints with different joint azimuth angles using RFPA2D (rock failure process analysis) code. Specimens are placed in a direct shear box. The upper surface of shear box is loaded with a constant normal stress 0.5 MPa, and the left surface is controlled by a constant increasing horizontal displacement at 0.002 mm/step. The whole shear failure process is visually represented and the failure pattern in reasonable accordance with other experimental results is obtained. In general, the failure pattern is mostly influenced by joint azimuth angle while shear strength is closely related to failure pattern and its mechanism. Two phases of shearing can be identified. Wing cracks firstly initiate from the tips of pre-existing joints with an initiation angle, and then propagate towards another joint through rock bridge. The second phase of shearing is characterized by friction process and volume increase in shear zone. The shear resistance obtained is a function of joint azimuth angle.

A geo-material failure process analysis, considering the coupling of stress distribution, fluid flow, and element damage evolution, has been used to investigate the mechanisms of crack initiation and propagation around a 2-D cylindrical cavity in heterogeneous stiff soils during grouting. Numerical simulations were performed using the specifically developed computer software F-RFPA2D. The results indicate the analysis is a powerful tool for the studying of soil behavior during fracture grouting. Moreover, they give us a better understanding of the crack initiation and propagation mechanisms during hydrofracturing.

A numerical model is developed to study hydraulic fracturing in permeable and heterogeneous rocks, coupling with the flow and failure process. The effects of flow and in-situ stress ratio on fracture, material homogeneity and breakdown pressure are specifically studied.

By investigating the influence of hydraulic pressure on the deformation of north side slope of Fushun open cast, the slide and inclination deformation mechanism of high steep slope in the area W200-W600 are presented, as well as the evaluation of effect of reinforcement for anti-slide pile and dewatering. The results show that most of the maximum deformation appears in layers No.1 and No.2, and the deformation decreases greatly after being reinforced. Otherwise, the slide depth will get into layer No.5 and this will lead to the slide of the whole layer No.5. Finally, some practice effects are introduced and it can provide references to the prediction and control of failure and instability of the similar slopes.

The changing rule for infrared thermal image boding of the rock with crack is essential for the geotechnical engineering, especially for the underground engineering. In order to study the rule, infrared thermal images for the failure process of rock with fracture are carried out. The size of the rock sample is 20 cm × 10 cm × 2 cm with a crack of 45° to the horizontal direction at the center and with the length of 2 cm. Considering the fact that sample will effect the results of the observation for infrared thermal image during the experiment, the laminated granite sample is used to replace the cylinder or cuboid sample. The achieved results under uniaxial compression indicate that intensity of the microruptures has close relation with the thermal effects. When the main fractures happen, there is a strip of high temperature that will appear at the destructive local area. During loading process, the abnormality of infrared temperature has three kinds of behaviors as follows: (1) temperature falls first and rises just before fracture; (2) temperature rises and falls alternately, and rises before the fracture; and (3) temperature rises slowly at first, and then rises quickly before the fracture appears. Even for the same rock sample, the behaviors of the infrared phenomenon may be different during failure process.

The coupling action of seepage and fracture on crack coalescence process under loading and hydraulic pressures are investigated. Numerical results demonstrate that the trend and magnitude of the permeability variations are controlled by the stress and the damage evolution developed in rocks. This includes the induced stress evolution of flow properties, and the regions of both diminished and enhanced flow depending on which the rock is in the linear-elastic, nonlinear, or post-failure portions of the stress-strain curves are presented. In elastic deformation region, rock permeability reduces when the rock compacts, and the decrease rate of the permeability starts to slow down or gradually to increase again when micro fractures begin to nucleate. Dramatic permeability increase occurs as soon as the macro-fracture forms in the rock.

The numerical simulations on the influence of mesoscopic structures on the macroscopic strength and fracture characteristics are carried out based on that the concrete is assumed to be a three-phase composite composed of matrix (mortar), aggregate and bond between them by using a numerical code named MFPA. The finite element program is employed as the basic stress analysis tool when the elastic damage mechanics is used to describe the constitutive law of meso-level element and the maximum tensile strain criterion and Mohr-Coulomb criterion are utilized as damage threshold. It can be found from the numerical results that the bond between matrix and aggregate has a significant effect on the macroscopic mechanical performance of concrete.

Based on cusp-type catastrophe theory, a sample rock-rock (hypocenter surrounding the rock) model for studying the pillar rockburst mechanism is presented in this paper. It is expounded theoretically that the stiffness ratio, K, of the roof and floor to the pillar plays an important role in the outbreak of instability. Using a newly developed numerical code, RFPA2D, the progressive failure process and associated microseismic behavior of the twin rock samples are simulated. The numerically simulated results also confirm that a soft roof and floor promotes an unstable failure or collapse of pillars. Additionally, the simulated results reproduced the deformation jump and the energy release that occur during a pillar rockburst. It is demonstrated that the proposed model properly simulates the pillar failure process.

Disastrous rock slope failures have been posing a hazard to people's lives and causing enormous economic losses worldwide. Numerical simulation of rock slope failure can lead to improve the degree of understand of such phenomenon so as to predict and avoid the occurrence of these disastrous events. In order to simulate the global behaviors of rock slope failure under the high seepage pressure and the local behaviors of the occurrence of hydraulic fracture in the pre-existing rock joints effectively, a powerful finite element tools F-RFPA2D, is adopted. The simulation takes into account of the growth of existing fractures and the initiation of new fractures under various of hydraulic pressure in different heterogeneities medium. The behavior of fluid flow and damage evolution, and their coupling action are studied in small specimens that are subjected to both hydraulic and biaxial compressive loadings. The influence of the ratio (the initial horizontal stress to the initial vertical stress) and the distance between the two existing cracks on the fracture propagation behaviors are investigated. Moreover, based on the fundamental study of hydraulic fracture, the progressive failure of rock slope under the influence of the increase in hydraulic pressure was also studied in the paper.

Borehole breakout is the process by which portions of borehole or tunnel wall fracture or spall when subjected to compressive stresses. The stress-strain characteristics of rock during loading and unloading confining pressure are studied firstly. To overcome the difficulties in analytical model studies, a numerical code, RFPA2D (Rock Failure Process Analysis), developed by CRISR, Northeastern University, China, is used to investigate the progressive failure of breakout around tunnel. The heterogeneity of rock was also taken into account in the software. The numerical simulation reproduces the formation notch in rocks by the growth, interaction and coalescence of randomly distributed macrocracks. It is illustrated from the numerical simulated results that breakout direction of tunnel is parallel with the minor stress tensor in the plane perpendicular to the borehole axis. Specifically due to the inclusion of heterogeneity, some peculiarities are studied both in the evolution of fracture and the influence of borehole on the peak intensity of specimen as well as the AE event patterns.

By using numerical code RFPA2D (Rock Failure Process Analysis), the evolution of fracture around cavities subjected to uniaxial and polyaxial compression is examined through a series of model simulation. It is shown from the numerical results that the chain of events leading to the collapse of the cavity may involve all or some of the fractures designated as primary tensile, shear and remote fracture. Numerical simulated results reproduce the evolution of three types of fractures. Under the condition of no confining pressure, the tensile mode dominates with collapse coinciding with the sudden and explosive appearance of the secondary tensile fracture; at moderate higher confining pressure, the tensile mode is depressed, comparatively, the shear effect is strengthened. Nevertheless, tensile fractures especially in remote fractures stage still play a role; at higher pressure, the shear fracture dominates the remote fractures, In addition, the evolution and interact of fractures between multiple cavities is investigated, considering the stress redistribution and transference in compressive and tensile stress field.

Using a Material Failure Process Analysis (MFPA2D) code, the influence of crack continuity in heterogeneous materials containing two existing parallel flaws under uniaxial loading is numerically studied. The numerical simulation reproduces the stress field in the vicinity of cracks and the processes of propagation and coalescence of cracks during compression. The numerical simulation results showed that, with the decrease of the crack continuity, the stress field between the tips of internal cracks gradually changes from tensile stress to compression stress and the propagation mode of cracks also changes from tensile mode(T), tensile-shear mode(T-S) to compressive mode(C), and the initiation angle between the flaw and the direction of the maximum compression increases gradually as well. In addition, the initiation stress on the tips of cracks is about l/2-1/3 of the failure strength of the specimens.

This study is to evaluate the effect of the heterogeneity on the failure processes and strength characterization of brittle rock containing the single pre-existing crack (or flaw) under uniaxial compression loadings. The numerical simulation reproduces the evolution of the stress and strain fields in flaw propagation process, the mode of acoustic emission related to the heterogeneity of rock and the phenomenon related to discontinuous. It is shown that the lower the value of the homogeneous index, the more influence of local variation on the propagation process of the pre-existing flaw, and there occurs more randomly distributed microfractures throughout the specimen. Studying the details of macrofracture formation in relatively homogeneous specimens, it is interesting to find that there exists a "constant jump" propagation pattern of the wing crack, which is responsible for the formation of the pre-existing flaw. The numerical results also demonstrate that the stress-strain relation and strength characterization depends strongly on the heterogeneity of the specimen. The heterogeneous rock has a gentler post-peak behavior and lower strength, while the more homogeneous specimen has a higher strength, accordingly, the curve becomes more linear and the strength loss is also rapidly.

By using the code RFPA2D (Rock Failure Process Analysis), the influence of the excavation of No.2 subway of Guangzhou on the new south supermarket was simulated. The simulation reflects macroscopic damage-evolution process induced by microscopic fracture and the spatial-temporal distribution characteristics of acoustic emissions event hypocenter. Both the sedimentation of the cavity gore and the sedimentation of the building were analyzed, and the future evolution of the fragmentation belt was forecasted. The data of the in-cave observation is in agreement with the results of the analytic method.