Dr Congying Li

To address the challenges of cumbersome calibration procedures, high computational demands, and limited material diversity associated with current parameter calibration in rock modeling with the finite-discrete element method (FDEM), this paper introduces an advanced numerical parameter calibration framework. This framework integrates machine learning with the FDEM to enable efficient and simultaneous calibration and prediction of numerical parameters for various rock types, including highly, moderately and slightly weathered rocks. Extensive batch calculations using the finite-discrete numerical model generated a dataset comprising uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) values for weathered rocks. This dataset was employed to establish a mapping between the numerical parameters and UCS/BTS results using a backpropagation neural network (BPNN). By applying the nondominated sorting genetic algorithm II (NSGA-II), we identified an optimal set of numerical parameters that align with UCS/BTS experimental outcomes. Notably, the optimization process incorporates an adaptive correction function formulated as a Dirichlet piecewise type function, as this study proposes. This framework enables precise calibration of numerical parameters across diverse rock masses. Simultaneously, the alignment between the UCS/BTS simulation outcomes, derived from the predicted parameters, and laboratory test results underscores the framework's potential for efficiently calibrating numerical parameters employed in the FDEM.

Calcareous sand, a distinctive granular material in geotechnical engineering, has garnered significant interest due to its irregular particle shapes, internal porosity, susceptibility to breakage, and critical role in island and offshore construction. Despite its importance, the influence of loading paths on its mechanical behavior and particle breakage remains underexplored. This study addresses this gap through an extensive experimental program, including isotropic consolidation and both drained and undrained triaxial compression tests, systematically varying loading paths and initial densities. The findings demonstrate that the strength and deformation characteristics of calcareous sand are profoundly affected by loading paths, initial densities, and particle breakage. A novel breakage evolution model is proposed, effectively capturing gradation changes under diverse testing conditions. Furthermore, the study quantifies the impacts of these factors on critical mechanical properties, including peak friction angle, dilatancy, secant modulus, and critical state parameters. These results provide a robust theoretical foundation for the development of constitutive models that integrate particle breakage and initial density effects. The insights are essential for optimizing geotechnical designs, enhancing stability, and improving infrastructure reliability in coastal and marine environments, particularly in island and reef development projects.

Particle morphology is critical in affecting the crushing behavior of rockfill materials. In contrast, most current single particle simulations lack satisfactory morphology accuracy, and the resulting crushing modes deviate from observations to some extent. Therefore, we reconstruct the real particle morphology with the spherical harmonic (SH) method and employ the finite-discrete element method (FDEM) to simulate the one-dimensional (1D) compressive crushing process of basalt particles commonly used in rockfill. The influences of four main morphological parameters, i.e. sphericity, aspect ratio, roundness, and convexity, on the single particle strength and the crushing modes are discussed. The results show that with the SH degree set to 15 and a mesh number of 20,480, the FDEM models of reconstructed particles achieve sufficient morphology accuracy and high computational efficiency. Based on the model, the simulation results demonstrate that the aspect ratio has the most significant impact on single particle strength, followed by sphericity. In contrast, roundness and convexity have a weaker effect than the above two parameters. Also, it is revealed that single particle strength decreases with increasing aspect ratio and sphericity, while it increases with higher roundness and convexity. Furthermore, aspect ratio significantly changes the initial crushing position, sphericity dominates post-crushing fragment size and quantity, and roundness mainly affects post-crushing morphology. The model results have been employed in establishing a support vector regression (SVR)-based predicted model, exhibiting good predictive performance and advantages for the optimization of rockfill particles in engineering.

The variability in particle morphology significantly impacts the mechanical properties of rockfill materials. To enhance the understanding of this influence, this study collected basalt rockfill particles from 6 different site sources, with their morphology captured by 3D scanning technology, and then the morphological characteristics categorized through cluster analysis. True triaxial tests for these 6 particle groups were simulated using discrete element method (DEM), and the effects of elongation, flatness, convexity, and intermediate principal stress coefficient on the stress-strain relationship and peak strength were qualitatively assessed through principal component analysis (PCA). Further, by controlling the elongation, flatness, and convexity, 3D reconstructed particle models were created by spherical harmonics (SH) analysis, and the true triaxial tests on these models were simulated to quantitatively clarify the influence of morphological parameters on the macroscopic stress-strain relationship, peak strength, microscopic contact, anisotropic evolution, and other characteristics. Considering the size effect in rockfill materials, multi-scale models incorporating particle morphology were further evaluated across four sample scales. The results indicate that, on the macro scale, the three morphological parameters and the middle principal stress coefficient each have substantial effects on peak strength independently, while the interaction among these parameters does not have a notable influence on the strength. With increasing convexity, the peak strength of samples gradually decreases, while an increase in elongation and flatness leads to a trend of initially increasing and then decreasing strength. On the micro scale, the increase in both elongation and flatness results in a more uniform fabric in the main and lateral directions, while the coordination number shows a trend of initially increasing and then decreasing before stabilizing gradually. The influence of elongation on the main direction fabric is slightly smaller than that of flatness, while convexity has minimal effect on these microscopic features. Additionally, the morphological parameters not only impact the deformation capacity of samples but also demonstrate heightened sensitivity to the strength-size relationship of the sample due to interlocking and boundary constraints between particles. This underscores the pivotal role of morphological parameters in governing the mechanical motion of particles during the sample size scaling process, consequently influencing the strength of the material.

Conventional rock mechanics testing faces significant limitations, including destructive testing conditions, time-intensive procedures, the inability to directly observe internal plastic zone expansion, and limited generalization capability. To overcome these challenges, this study uses granite with varying weathering grades as a case study, establishing a connection between uniaxial compressive strength (UCS)/Brazilian tensile strength (BTS) test results and X-ray Fluorescence (XRF) data through a particle swarm optimization-backpropagation neural network (PSO-BPNN). Numerical parameters are further optimized and redistributed by integrating weight factors using a multi-objective particle swarm optimization algorithm (MOPSO) to model weathered rock numerically. This approach successfully reproduces the three stages observed in UCS/BTS tests during loading: the elastic stage, plastic stage, and fracture stage. The numerical results show good agreement with experimental findings, revealing that the mineral composition of weathered rock exhibits distinct patterns corresponding to varying weathering degrees. As the weathering degree increases, the rock failure pattern transitions from single shear plane failure to crushing damage. The proposed method enables database construction with minimal pre-testing, facilitating rapid calibration and prediction of numerical parameters for diverse weathered rocks based on XRF field test results. Consequently, this method quantitatively correlates microscopic mineral composition with macroscopic mechanical behavior, surpassing traditional classification methods based on empirical estimation. It also provides a robust framework for accurately determining numerical parameters of weathered rocks, thereby enhancing the safety assessment of weathered rock formations.

While experimental research on laser rock-breaking is extensive, numerical simulations, especially for thermal fractures, are limited, and the thermal rupture mechanism remains poorly understood. This study addresses these gaps by introducing a novel approach that combines Voronoi diagrams and Weibull distributions with the coupled cohesive zone model and thermomechanical damage (CZM-TMD) approach. The developed numerical model accurately predicts the temperature and stress distributions, as well as the formation and propagation of thermal cracks and craters. Validation against theoretical analyses and past experiments confirms its accuracy. Thermal cracks originate at the interface between irradiated and nonirradiated areas and propagate bidirectionally. Shear damage is prominent at the crater, whereas tensile damage is more common in cracks. With continued irradiation, the crater diameter increases rapidly before stabilizing, and the depth follows an S-shaped curve after a rapid increase, similar to the water cushion effect in water jet rock-breaking. These insights enhance the theoretical understanding of laser rock-breaking and provide a key reference for future simulations.

Erosion and entrainment significantly increase the volume and destructive potential of high-speed long-runout landslides. Previous studies seldom quantitatively address these effects, and even fewer incorporate the extent of slope weathering into the analysis of landslide dynamics. This study addressed this gap by developing a framework for dynamic analysis, combining Finite Element Method-Smoothed Particle Hydrodynamics-Finite Discrete Element Method (FEM-SPH-FDEM), and applying it to the Shuicheng landslide. Simulation results closely matched field data, revealing substantial sliding mass deviation and velocity variations influenced by rocky ridges and valleys. According to the simulation, the weathering degree of rock slope significantly affects landslide dynamic processes. The interparticle friction coefficient is crucial for accurately modeling these processes using the SPH-FDEM method. Additionally, by incorporating landslide erosion behavior into the framework, the case study indicates that the volume of landslides in Shuicheng County increased by approximately 0.6 times. Three stages of evolution mechanisms of high-altitude landslide-induced erosion behavior are proposed in this paper, highlighting the effectiveness of this framework in understanding landslide mechanisms and providing information for prevention strategies in high-altitude, highly weathered areas.

The stress¿strain behavior of coarse-grained materials is significantly influenced by the initial grain size distribution (GSD). However, limited research on constitutive models for coarse-grained materials considers this influence. In this study, we introduced an initial GSD index, ¿, measuring the distance between the initial GSD and the ultimate GSD, which associates the initial GSD with the ultimate GSD. We explored the influence of ¿ on the critical state friction angle fcs and the location of the critical state line (CSL) on the e- (pcs'/pa)0.7 plane for coarse-grained materials. The results show that a decrease in ¿ leads to a downward movement and counterclockwise rotation of the CSL and an increase in fcs. The effect of initial GSD was incorporated into the state parameter, bounding stress ratio, dilatancy stress ratio and plastic modulus. Then, a state-dependent bounding surface model for coarse-grained materials has been proposed, highlighting the effect of initial GSD. The high accuracy of this model is evidenced by a good agreement between the modelling results and the experimental counterparts under drained and undrained conditions. This finding demonstrates the importance of initial GSD on granular materials, the effect of which can be well simulated by our proposed model.

The mechanical response of a soil-rock mixture (SRM) is crucial in railway, airport, highway, and dam engineering. However, existing studies of the SRM often fail to account for the effect of its components (e.g., fine content) and particle crushing. This paper aims to develop a thermodynamically consistent constitutive model that can simulate the mechanical behaviour of the SRM. Based on the initial fine content (FC0), we quantify the components of the SRM and explore the effect of FC0 on the mixture's mechanical responses. The FC0-related energy dissipation due to particle crushing is highlighted in the proposed model. The model is validated by three experimental cases with different FC0, which shows that our model satisfactorily captures the complex SRM behaviours with only eight physically identifiable parameters. The model also confirms the experimental phenomenon that the FC0 has a substantial effect on both the shear strength and energy dissipative ratio of soil-rock mixtures.

This paper proposes a gradation-state-dependent constitutive model to capture the granular materials' mechanical behaviours considering the granular crushing's influence. Firstly, a gradation evolution law is developed to reflect the change in grain size distribution (GSD) with the growth of stress levels, and then, based on the evolution law, the elastic compliance matrix is modified to reflect the effects of particle breakage. Secondly, as the critical state line (CSL) exhibits gradation dependence, a novel method is developed to describe the family of CSLs under different fixed gradations. Subsequently, by combining the gradation evolution law with the CSL equation, the paper explains the steepening of the slope of the critical state line when the crushing is activated. With the improvement of CSL, the material's shear dilatancy and contraction properties are better reflected, assisting in establishing a plastic compliance matrix. Employing the derived elastic and plastic compliance matrix, the elastic¿plastic model reflecting the influence of gradation and state effects is established and verified with a series of experimental and discrete element method (DEM) simulation results.

This research develops an energy-driven constitutive model designed to tackle the complex phenomenon of grain crushing in porous rocks. Initially, a novel coupled relationship is proposed to integrate various energy dissipation mechanisms, including both plastic and crushing effects, using spherical polar coordinates. This approach results in a robust coupling of energy dissipation, providing a comprehensive depiction of the influence of grain crushing on plastic deformation. An energy-based yield criterion is then formulated by comparing elastic potential energy contours with experimental findings, and the behaviour of crushing hardening is examined through energy evolution. Flow rules are subsequently derived, both independently and with consideration of plasticity-crushing coupling. Finally, validation against a range of experimental tests highlights the model's versatility. The proposed model enhances the understanding of rock-crushing issues from an energy perspective and demonstrates simplicity with only 4 or 5 easily calibrated parameters.

Granular crushing significantly changes mechanical behaviours, especially under elevated stress levels. Therefore, this study aims to develop a model to simulate the constitutive behaviours of granular materials at the crushing-dominant stage. Firstly, the contour of elastic potential energy is demonstrated and employed to derive the yield surface or function, acknowledging that the stored elastic energy dominates the breakage yield criterion. The versatility of the proposed yield function in accurately capturing the features of yield surfaces is verified with three cases, including Cam-clay models, test results, and an empirical yield function. Next, a hardening parameter, H, is formulated, considering the extent of crushing, B, and the void ratio, e, to reflect the expansion of the yield surface during hardening. The proposed simple hardening formulation favourably represents compression characteristics under elevated stress levels. Combining the above results of yield and hardening functions, a new elastic¿plastic-crushing constitutive model is developed; the model's capability to describe crushable granular material behaviours is validated against experimental counterparts.

Over the last 20¿30¿years, there has been an evolution in urban stormwater management towards the use of stormwater control measures (SCMs) at or near the source of the runoff. These approaches aim to protect or restore natural elements of the flow regime. However, evidence of the success of such approaches is to date limited. We reviewed attempts to both model and monitor the catchment-scale hydrological consequences of SCMs. While many catchment-scale studies on the hydrologic effects of SCMs are based on computer simulation, these modeling approaches are limited by many uncertainties. The few existing monitoring studies provide early indications of the potential of SCMs to deliver more natural flow regimes, but many questions remain. There is an urgent need for properly monitored studies that aim to assess the hydrologic effects of SCMs at the catchment scale. In future monitoring studies, these hydrologic effects need to be characterized using appropriate flow metrics at a range of scales (from site scale to catchment scale), and changes to flow metrics by SCMs need to be assessed using robust statistical methods. Such studies will give confidence to stormwater and river managers of the feasibility and benefits of "low impact" approaches to stormwater management.