Emeritus Professor John Carter

This paper presents coupled hydro-mechanical modelling of unsaturated soil problems by incorporating some advanced numerical and constitutive models in a general-purpose commercial software package, Abaqus. Two different strategies for the interpretation of unsaturated soil behaviour with respect to the soil volume change are considered and the relevant constitutive models are implemented through user-defined subroutines. The first approach that is commonly used in geomechanics considers suction as an additional variable and uses a constitutive model in the space of effective stress¿suction assuming that soil compressibility is a function of suction. The second approach treats the constitutive model in the space of effective stress and degree of saturation assuming that the soil compressibility is a function of the degree of saturation. The hydro-mechanical behaviour regarding the change in the degree of saturation caused by both suction and net stress changes is also considered, together with the effect of hydraulic hysteresis. Validation of the implemented algorithms is presented through several benchmark problems. Finally, the application and utility of the implemented procedures are illustrated by simulations of two challenging problems of unsaturated geomechanics, including a slope failure due to seepage and rainfall infiltration as well as cone penetration tests in unsaturated soil. A suitable mesh optimisation scheme is also incorporated to handle finite deformations.

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.

Some previous constitutive models introduce many sophisticated concepts and new parameters to characterise cyclic behaviour of saturated soils, while other simpler models show incomplete theoretical developments which limit their applications. This study aims to improve previous studies by revising the way the yield surface responds to cyclic loading under undrained conditions, i.e., the yield surface is assumed to change its shape while maintaining its size during unloading. The proposed hypothesis is used to examine a series of undrained cyclic tests where various cohesive soils are examined with an acceptable agreement. Based on this process, empirical relationships between the model parameters and given load and soil characteristics are formed, thus enabling the input parameters to be determined rigorously. The analysis shows that soil can reach an unstable state where the excess pore pressure (EPP) and axial strain develop rapidly when the cyclic stress ratio reaches a critical degree. A higher loading frequency requires a larger number of cycles but in shorter timeframe to initiate instability of the soil. The lower the plasticity of the soil, the larger and faster the accumulation of EPP and axial strain whereas increasing the initial shear stress can make soil unstable earlier.

This study describes the development and implementation of a numerical procedure for the analysis of coupled geotechnical problems involving finite deformations, changing boundary conditions, multiphase porous media and softening behaviour. The numerical scheme is first validated through a benchmark problem concerning the laying of an on-bottom offshore pipeline, and then some further highlights of the effects of soil softening are presented. The scheme is then specifically employed to study the penetration process of a full flow cyclic T-bar test in soft sensitive clay. An advanced soil constitutive model has been implemented to capture the effects of soil structure and its progressive de-structuring as well as soil fabric anisotropy. Accordingly, the changing soil resistance due to the combined effects of soil softening, remoulding and reconsolidation is illustrated, by considering a T-bar undergoing large amplitude cyclic sequences interspersed with consolidation periods. The results from the numerical simulations reveal the effects of soil softening on the soil deformation pattern, the evolution of shear bands, the generation of excess pore pressures and the process of soil reconsolidation.

An isotach elastoplastic constitutive model devised by Yang et al. (2016) and referred to as the Hunter Clay (HC) model attempts to capture a number of key behaviours of soft soils within a critical state framework, namely destructuration, fabric anisotropy and rate dependency, the latter often manifesting in creep settlement. Finite element implementation of the HC model is a useful means by which its application to practical problems can be facilitated. However, there are a number of significant challenges associated with the translation of isotach elastoplastic models into a finite element setting. In this paper, a detailed discussion of these challenges is undertaken and a new finite element implementation of the HC model is subsequently developed. This includes sophisticated numerical integration algorithms which employ automatic time substepping for solution of the governing finite element equations. The ability of the implemented HC model to predict the mechanical behaviour of soft soils under 1D compression is investigated via simulation of laboratory tests carried out on Ballina clay by Pineda et al. (2016) and Parkinson (2018).

The design of rail tracks is often challenged by the highly compressible behaviour of soft estuarine clays over which they must pass. It is prudent that the realistic long-term behaviour of subgrade materials under repeated loading applied by fast moving heavy haul trains is properly understood. One feature that should not be ignored when estimating the long-term performance of track foundations is the continuous principal stress rotation (PSR) induced by moving wheel loads. The main purpose of this research is to combine the traditional cyclic triaxial test results (fixed axes, no PSR) with those obtained from the dynamic hollow cylinder apparatus (allowing PSR) to examine the relative influence of cyclic stress ratio (CSR) and frequency on the behaviour of soft subgrade subjected to simulated heavy haul train loading. Employing these two types of equipment applying contrasting stress path regimes, a series of cyclic undrained laboratory tests was conducted on reconstituted sandy clay specimens at varying frequencies (f = 0.1¿1 Hz) and cyclic stress ratios (CSR = 0.2¿0.3). The hollow cylinder test results have shown that higher CSR values and lower frequencies induce greater permanent deformations and excess pore water pressures at a given number of loading cycles (N). For CSR = 0.2, pore pressures and axial strains were found to increase even after a large number of cycles (N = 50,000). However, when the higher CSR value of 0.3 was imposed, the soil failed in less than 300 cycles by reaching 5% of axial strain. Undoubtedly, PSR adversely affected the accumulation of axial strains and soil degradation, whereas in contrast, the development of pore water pressure was less influenced by PSR.

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.

Background: Incidence of lymphedema appears to be higher in women with vulvar/vaginal cancer than in those with other forms of gynecological cancer. The objective of this work was to determine the point prevalence and incidence of lymphedema in women with vulvar/vaginal cancer and to describe symptom burden and quality of life (QOL). Methods: Prospective longitudinal cohort study conducted in Brisbane, Australia, including adult women with newly diagnosed vulvar/vaginal cancer. The primary outcome was selfreported swelling of the legs, vulvar area, or pelvis/abdomen or a clinical diagnosis of lymphedema. Severity of associated symptoms and QOL (Functional Assessment of Cancer Therapy-General) were also reported. Assessments were conducted over 2 years. Results: All participants (vulvar: n = 20; vaginal: n = 2; mean [SD] age = 57 [12] years) received surgical treatment, and 8 (36%) also received adjuvant therapy. By 24 months postdiagnosis, only 2 (9%) women had no evidence of lymphedema; all others self-reported swelling (n = 10; 45%), had a clinical diagnosis (n = 1; 5%), or both (n = 9; 41%). Three or more symptoms of moderate or greater intensity were reported by 7 (44%) women at 2 years. The presence of lower limb symptoms (including mild intensity) was associated with reduced QOL (any symptom: QOL estimate = -13.29; 95% CI, -19.30 to -7.27; P < .001). Limitations: Small sample size limits interpretation of findings. Conclusion: These findings demonstrate that the majority of women receiving treatment of vulvar/vaginal cancer experience lymphedema and symptoms of swelling are associated with lower QOL. Monitoring of swelling via patient self-report may identify women at risk of low QOL outcomes after treatment of vulvar/vaginal cancer.

Naturally occurring materials such as jute and coir have some favorable engineering characteristics and also degrade over time, so they have increasingly been used in engineering applications in recent years. The efficient way that naturally prefabricated vertical drains made from those materials help accelerate soil consolidation has been shown in previous studies, but they also tend to decompose rapidly in adverse environments, where cellulose-degrading bacteria cause a serious deterioration of their favorable drainage properties. This study presents a laboratory investigation into the biodegradation of prefabricated vertical jute drains in saturated soft soils, where the tensile strength of jute and coir fibers and the discharge capacity of drains decrease in response to different environments. Micro-observation also shows a transformation of the jute fibers and destruction of the drain structure due to biodegradation. DNA extraction and sequencing techniques to determine the microbial properties of these decayed fibers indicate that bacteria such as species of the genera Clostridium and Bacillus can cause rapid decomposition of cellulose-based material (i.e., jute), whereas other organic matter-consuming microbes such as sulfate-reducing bacteria do not directly contribute to the biodegradation of jute. In response, an analytical approach that incorporates various forms of drain discharge capacity over time is proposed to predict soil consolidation. The results indicate there is considerable deviation in dissipating the excess pore pressure when the drain degrades in different ways.

The prediction of lymph node metastasis using clinic-pathological data and molecular information from endometrial cancers lacks accuracy and is therefore currently not routinely used in patient management. Consequently, although only a small percentage of patients with endometrial cancers suffer from metastasis, the majority undergo radical surgery including removal of pelvic lymph nodes. Upon analysis of publically available data and published research, we compiled a list of 60 proteins having the potential to display differential abundance between primary endometrial cancers with versus those without lymph node metastasis. Using data dependent acquisition LC-ESI-MS/MS we were able to detect 23 of these proteins in endometrial cancers, and using data independent LC-ESI-MS/MS the differential abundance of five of those proteins was observed. The localization of the differentially expressed proteins, was visualized using peptide MALDI MSI in whole tissue sections as well as tissue microarrays of 43 patients. The proteins identified were further validated by immunohistochemistry. Our data indicate that annexin A2 protein level is upregulated, whereas annexin A1 and a actinin 4 expression are downregulated in tumours with lymph node metastasis compared to those without lymphatic spread. Moreover, our analysis confirmed the potential of these markers, to be included in a statistical model for prediction of lymph node metastasis. The predictive model using highly ranked m/z values identified by MALDI MSI showed significantly higher predictive accuracy than the model using immunohistochemistry data. In summary, using publicly available data and complementary proteomics approaches, we were able to improve the prediction model for lymph node metastasis in EC.

The development of a numerical procedure for the finite element analysis of anchors dynamically penetrating into saturated soils is outlined, highlighting its unique features and capabilities. The mechanical behaviour of saturated porous media is predicted using mixture theory. An algorithm is developed for frictional contact in terms of effective normal stress. The contact formulation is based on a mortar segment-to-segment scheme, which considers the interpolation functions of the contact elements to be of order N, thus overcoming a numerical deficiency of the so-called node-to-segment (NTS) contact algorithm. The nonlinear behaviour of the solid constituent is captured by the Modified Cam Clay soil model. The soil constitutive model is also adapted so as to incorporate the dependence of clay strength on strain rate. An appropriate energy-absorbing boundary is used to eliminate possible wave reflections from the artificial mesh boundaries. To illustrate the use of the proposed computational scheme, simulations of dynamically penetrating anchors are conducted. Results are presented and discussed for the installation phase followed by 'setup', i.e., pore pressure dissipation and soil consolidation. The results, in particular, reveal the effects of strain rate on the generation of excess pore pressure, bearing resistance and frictional forces. The setup analyses also illustrate the pattern in which pore pressures are dissipated within the soil domain after installation. Hole closure behind a dynamic projectile is also illustrated by an example.

The aim of this paper is to address a number of significant challenges in the analysis of multiphase unsaturated soils when subjected to both static and dynamic loading. These challenges include the non-linear behaviour of the solid skeleton of the soil as well as the means by which the unsaturated nature of the multi-phase soil is dealt with. A review of some fundamental issues in partially saturated soils as well as the governing equations are presented and then the application of the generalised-. a algorithm for time integration of the global equations of motion for unsaturated soils is demonstrated. Solutions to these equations obtained by the finite element method are validated by recently presented analytical solutions. A description of the selected constitutive model and its integration is also presented, together with a strategy to verify the numerical implementation. Finally, solutions for the classic problem of static loading of a rigid footing resting on a partially saturated (three-phase) soil and a fully saturated (two-phase) soil are presented.

Background The current Australian National Health and Medical Research Council guidelines discourage the use of 'see and treat' colposcopic management due to concerns regarding over-treatment. However, this approach has been shown to have benefits in several studies, including cost savings, elimination of loss to follow up and decreased patient anxiety. Aims To provide Australian data on treatment outcomes for women presenting with a high-grade Pap smear to a large metropolitan colposcopy unit and to determine whether a 'see and treat' approach would meet specified standards. Materials and methods Retrospective review of women referred to the Royal Prince Alfred Hospital colposcopy unit with a high-grade smear. Patient data, colposcopy findings, treatment and pathology results were collated and analysed to determine treatment outcomes using the current 'biopsy and treat' approach. The feasibility of 'see and treat' was assessed by determining which women with high-grade colposcopy findings had high-grade disease confirmed on biopsy or excisional specimens. Results One hundred and thirty-seven women underwent either excisional or ablative treatment. Of those undergoing excisional procedures, 81.3% had high-grade dysplasia or invasive cancer, 11.6% had CIN1 and 7.1% had no dysplasia on histopathology. One hundred and twenty-one with high-grade colposcopy findings had histopathology results available. Using a 'see and treat' approach, 92.6% would have had confirmed dysplasia of any grade, while 91.7% had confirmed high-grade dysplasia. Conclusions 'See and treat' colposcopy is feasible in the Australian setting when applied to selected patients with high-grade cytology and high-grade colposcopic findings.

The time and strain rate dependency observed in natural soft clays is formulated within the framework of conventional elastoplasticity. Creep of soft clays is essentially like the response of an overdamped oscillatory system, i.e., the strain rate decays in an exponential manner. A characteristic strain rate and time relationship is presented based on data from creep tests on a large number of different soft clays. The evolutionary change of strain rate is found to affect the mechanical response of soft clays in an isotach manner. Taking strain rate as another stress-like variable, a loading-isotach (LI) yield curve is proposed, which describes the combined hardening mechanisms of loading and variation of strain rate. Incorporation of this LI yield curve into critical state soil mechanics results in an isotach elastoplastic (IEP) model in triaxial stress-strain-strain rate space, which has been dubbed 'Hunter Clay'. The effects of fabric anisotropy and inter-particle cementation, which are typical features of natural soft clays, are also introduced to produce an advanced hierarchical constitutive model for soft clay. Qualitative predictions are first described and compared with the characteristic behaviour of natural soft clays. Experimental validations using test data for two soft clays are then carried out, and comparisons of the model predictions and experimental data demonstrate the capability of the model in reproducing realistic behaviour of natural soft clays. This work confirms that the complex mechanical behaviour of natural soft clays can be reproduced satisfactorily within the general framework of classical plasticity theory.

A finite element algorithm for frictionless contact problems in a two-phase saturated porous medium, considering finite deformation and inertia effects, has been formulated and implemented in a finite element programme. The mechanical behaviour of the saturated porous medium is predicted using mixture theory, which models the dynamic advection of fluids through a fully saturated porous solid matrix. The resulting mixed formulation predicts all field variables including the solid displacement, pore fluid pressure and Darcy velocity of the pore fluid. The contact constraints arising from the requirement for continuity of the contact traction, as well as the fluid flow across the contact interface, are enforced using a penalty approach that is regularised with an augmented Lagrangian method. The contact formulation is based on a mortar segment-to-segment scheme that allows the interpolation functions of the contact elements to be of order N. The main thrust of this paper is therefore how to deal with contact interfaces in problems that involve both dynamics and consolidation and possibly large deformations of porous media. The numerical algorithm is first verified using several illustrative examples. This algorithm is then employed to solve a pipe-seabed interaction problem, involving large deformations and dynamic effects, and the results of the analysis are also compared with those obtained using a node-to-segment contact algorithm. The results of this study indicate that the proposed method is able to solve the highly nonlinear problem of dynamic soil-structure interaction when coupled with pore water pressures and Darcy velocity.

Dynamic penetrometers have been used for offshore oil and gas industry applications such as pipeline feasibility studies and anchoring systems, and military applications including naval mine countermeasures and terminal ballistic studies. The main challenge of using dynamic penetrometers is the interpretation of their test results in order to deduce the mechanical properties of the penetrated soil via empirical or theoretical relations. Recently, a robust numerical method based on the Arbitrary Lagrangian-Eulerian (ALE) technique has been developed for analysing dynamic penetration problems and used to investigate a smooth penetrometer free falling into a uniform layer of clayey soil. Numerical as well as experimental results indicate that the penetration characteristics, including the impact energy, total time, and total depth of penetration, depend on the mechanical properties of the soil including its stiffness and strength parameters as well as the geometry of the penetrometer and its initial impact energy. In this study, the ALE method is employed to study the effect of shear strength increasing with depth (a common condition of seabed deposits) on the penetration characteristics of a free falling penetrometer. Conducting more than two thousand numerical simulations has shown that there is an approximate quadratic relation between the final embedment depth of a FFP penetrating into a non-uniform clay soil and the combined kinetic energy on contact with the soil and subsequent loss in potential energy of the penetrometer.

In this paper high-order triangular elements are implemented in the framework of the Arbitrary Lagrangian-Eulerian method for the analysis of large strain consolidation problems in geomechanics. The theory of consolidation, as well as details of the high-order elements, including cubic (10-noded), quartic (15-noded), quantic (21-noded) and sextic (28- noded) elements are discussed. The accuracy and the efficiency of high-order elements in the analysis of consolidation problems are demonstrated conducting a small deformation analysis of the soil under a strip footing as well as a large deformation analysis of a vertical cut subjected to a surcharge loading. Based on the numerical results, it is shown that high-order elements not only improve the accuracy of solution but can also significantly decrease the required computational time. It is also demonstrated that assuming identical order for displacement shape functions and the pore water pressure shape functions does not affect the stability of the time-marching analysis of consolidation nor the accuracy of the numerical predictions.

The behaviour of a test embankment constructed on a soft clayey deposit in Saga, Japan, was simulated by both three-dimensional (3D) and two-dimensional (2D) finite element analyses (FEA). Floating soil-cement columns had been installed in the clay prior to construction of the embankment. Comparing the results of 3D and 2D FEA indicates that 2D analysis predicts incorrect results in terms of the lateral displacement and bending moment in the columns under the toe of the embankment. In the 2D analysis, the rows of columns were modelled by continuous walls, which partially block the interaction between the soil layers and the columns and influence the simulated lateral displacement and bending moment in the column. It has been postulated that compaction of fill material during the construction process has a significant influence on both the magnitude and pattern of the lateral displacement of the column under the toe of the embankment. Pragmatically, this influence can be indirectly simulated by reducing the stiffness and increasing Poisson's ratio of the embankment fill material. Finally, both the measured and FEA results indicate that the columns not only reduced the total settlement but also accelerated the settlement rate of the deposit under the embankment loading, due to the much higher stiffness of the column material.

Experimental data on Lower Cromer Till (LCT), a sandy silty-clay, are re-evaluated enabling a study on the effects of plastic anisotropy of soil fabric. The results of virgin constant stress ratio consolidation tests reveal that an equilibrium state is achieved and maintained under any specific radial loading path, with characteristics of a unique anisotropic fabric and a unique straining mode. The inclination of the plastic dilatancy and the yield surface from the hydrostatic axis provides a means of quantifying this equilibrium state of the soil fabric. A unique fabric anisotropy at critical state is naturally obtained. Rotational hardening laws are then proposed to quantify the changes in plastic anisotropy of soil fabric for all stress ranges. Constitutive relations are formulated within the framework of Critical Sate Soil Mechanics, with a non-associated flow rule logically determined from experiments. The proposed rotational hardening laws have been systematically validated against a large bank of laboratory tests on LCT samples, covering a variety of deposition conditions, stress histories, and overconsolidation ratios. Comparisons illustrate the feasibility and efficiency of the proposed framework in describing the plastic anisotropy of LCT, which may suggest possible application to other types of clays.

Whilst next generation sequencing can report point mutations in fixed tissue tumour samples reliably, the accurate determination of copy number is more challenging. The conventional Multiplex Ligation-dependent Probe Amplification (MLPA) assay is an effective tool for measurement of gene dosage, but is restricted to around 50 targets due to size resolution of the MLPA probes. By switching from a size-resolved format, to a sequence-resolved format we developed a scalable, high-throughput, quantitative assay. MLPA-seq is capable of detecting deletions, duplications, and amplifications in as little as 5ng of genomic DNA, including from formalin-fixed paraffin-embedded (FFPE) tumour samples. We show that this method can detect BRCA1, BRCA2, ERBB2 and CCNE1 copy number changes in DNA extracted from snap-frozen and FFPE tumour tissue, with 100% sensitivity and >99.5% specificity.

This paper compares predictions, made using selected soil constitutive models, of the anisotropic plastic response of a sandy silty-clay, viz., Lower Cromer Till (LCT). The performance of four elastoplastic models, designated as MCC (Roscoe and Burland, 1968), S-CLAY1 (Wheeler et al., 2003), SANICLAY14 (Dafalias and Taiebat, 2014) and YANG2015 (Yang et al., 2015), are systematically evaluated based on a series of drained triaxial stress path tests, including virgin constant-stress-ratio (CSR) compression tests, probing stress path tests on initially K<inf>0</inf> consolidated samples, and also various transitional CSR tests. Comparison of the various predictions shows that the isotropic MCC model cannot properly describe the mechanical behaviour of LCT due to its neglect of fabric anisotropy. The other three anisotropic models differ in their definition of the rotational hardening laws, particularly in the description of the equilibrium state of fabric anisotropy achieved under CSR loading. While significant improvements in model predictions can be observed from the three anisotropic models, for LCT S-CLAY1 generally tends to underestimate the volumetric deformation and both S-CLAY1 and SANICLAY14 are likely to overestimate the ratio of the deviatoric and volumetric strains for more anisotropic stress states. YANG2015 exhibits the most consistent performance in reproducing the mechanical behaviour of LCT among the four models under comparison. The importance of the virgin CSR tests to properly understanding the plastic anisotropy of soil fabric is highlighted.

This paper presents a new constitutive model for cyclic loading of soil to predict the behavior of soft clays under undrained cyclic triaxial loading. It is inspired by the modified Cam-clay theory, and a new yield surface for elastic unloading is proposed to capture the soil behavior under cyclic loading. Only two additional parameters that characterize the cyclic behavior are used together with the traditional parameters associated with the modified Cam-clay constitutive model. The details of the relevant soil properties, initial states, and cyclic loading conditions are presented, and a computational procedure for determining the effective stresses and strains is demonstrated. The new model is used to simulate cyclic triaxial tests on kaolin, and the model predictions are generally found to be in agreement with the measured excess pore pressures and axial strains. Furthermore, numerous factors that influence the cyclic performance of soft soils can be considered in the new model, such as cyclic stress ratios, preshearing, and cyclic loading frequency. The critical cyclic stress ratio is also predictable using the proposed model in terms of excess pore pressures and axial strains.

A rate-independent anisotropic elastoplastic constitutive model for natural soft clays is proposed, with emphasis on the effects of cementation or structure and fabric anisotropy. The characteristic non-linear normal compression line for structured soils is described by defining a variable compressibility as a function of plastic straining. No reference to the 'intrinsic' reconstituted state is required. The effect of plastic anisotropy is investigated from virgin constant stress ratio consolidation tests, which provide an accurate description of the equilibrium states of soil fabric. The change of fabric anisotropy is correlated with the change of inclination of the yield and plastic potential surfaces via a pair of improved rotational hardening laws. Experiments on Otaniemi clay samples in both natural and reconstituted states are simulated. Comparisons of numerical predictions with experimental data illustrate the feasibility and advantage of the proposed methodology to describe the mechanical behaviour of natural soft clays.

This paper investigates the application of high-order elements within the framework of the arbitrary Lagrangian-Eulerian method for the analysis of elastoplastic problems involving large deformations. The governing equations of the method as well as its important aspects such as the nodal stress recovery and the remapping of state variables are discussed. The efficiency and accuracy of 6-, 10-, 15-, and 21-noded triangular elements are compared for the analysis of two geotechnical engineering problems, namely, the behavior of an undrained layer of soil under a strip footing subjected to large deformations and the soil behavior in a biaxial test. The use of high-order elements is shown to increase the accuracy of the numerical results and to significantly decrease the computational time required to achieve a specific level of accuracy. For problems considered in this study, the 21-noded elements outperform other triangular elements.

In this paper high-order triangular elements are implemented in the framework of the Arbitrary Lagrangian-Eulerian method for the analysis of large strain coupled consolidation problems in geomechanics. The theory of coupled consolidation, as well as details of the high-order elements, including quadratic (6-noded), cubic (10-noded), quartic (15-noded) and quantic (21-noded) elements, are discussed. The accuracy and the efficiency of high-order elements in the analysis of undrained problems are presented by solving two classical geomechanics problems. These include the bearing capacity of soil under a footing and the large deformation analysis of a vertical cut subjected to a surcharge loading. Based on the numerical results, it is shown that high-order elements not only improve the accuracy of the solution, but can also significantly decrease the required computational time.

The excess pore water pressure distribution (u) induced by the penetration of a piezocone into clay and its dissipation behaviour have been investigated by laboratory model tests, theoretical analysis and numerical simulation. Based on the results of the tests and the analysis, a semi-theoretical method has been proposed to predict the piezocone penetration-induced pore pressure distribution in the radial direction from the shoulder of the cone. The method can consider the effect of the undrained shear strength (su), over-consolidation ratio (OCR) and rigidity index (Ir) of the soil. With a reliably predicted initial distribution of u and the measured curve of dissipation of pore water pressure at the shoulder of the cone (u2), the coefficient of consolidation of the soil in the horizontal direction (ch) can be back-fitted by analysis of the pore pressure dissipation. Comparing the back-fitted values of ch with the values directly estimated by a previously proposed method indicates that the previously proposed method can be used reliably to estimate ch values from non-standard dissipation curves (where u2 increases initially and then dissipates with time). © 2014 Elsevier Ltd.

This study identifies the relative magnitude of horizontal stress change below a series of parallel longwall panels as a consequence of multi-seam mining. The investigation method yields an upper bound to the horizontal stress change by assuming that the fractured and caved overburden above the supercritical longwall panels is not able to support any lateral load. Finite element modelling was conducted to consider the effects of the following variables on the horizontal stress redistribution: the ratio of the equivalent width of the extracted area to the overburden depth, the ratio of the original horizontal to vertical in situ stress components, and anisotropy in the rock mass behaviour. The key findings of this research are that the maximum horizontal stress induced as a consequence of extracting multiple supercritical longwall panels will be within approximately 10% of the original in situ horizontal stress for the case of isotropic rock strata. The magnitude of this horizontal stress may be larger in a stiff stratum if the overall sequence of strata consists predominantly of softer rocks. Anisotropy in the strata underlying the extracted longwall panels also causes an increase in the maximum horizontal stress induced into the immediate floor of the first extracted seam, and an increase in the rate of dissipation of horizontal stress change with depth. These findings indicate that a significant increase in horizontal stress relative to the original in situ horizontal stress should not be expected in multi-seam mining situations. The results from this study need to be considered in conjunction with predicted vertical stress distributions in order to accurately predict the overall stress environment likely to be encountered when conducting multi-seam mining. © 2014 Elsevier Ltd.

The design of foundations on soft ground reinforced by columns usually involves two important verifications, namely, checking for adequate bearing capacity and checking for acceptable settlement performance. This paper details a comprehensive methodology for determining the optimized portion of the ground area that should be improved by the installation of columns. The optimization is required to avoid an overly conservative design and, consequently, the use of uneconomical quantities of material to construct the columnar reinforcement. The basis of the suggested methodology consists of first estimating the minimum improvement area ratio (IAR) required to ensure attainment of the required design bearing capacity of the reinforced soil and then determining an upper-bound or maximum value of IAR by considering the issue of allowable settlement. Optimization is then performed on the IAR within the range defined by these bearing capacity and settlement limits. Analysis of three case studies provides an illustration of the implementation of this novel design methodology, which has been incorporated into software recently developed to assist in the design of soil foundations reinforced by columns and to provide cost-effective solutions for this type of foundation.

A method has been developed for the consolidation analysis of dredged mud or clayey soil deposits containing strip-type, prefabricated horizontal drains (PHDs), based on either the axisymmetric or plane strain unit cell theory. An approximate consolidation theory has also been proposed for a surface soil layer subjected to vacuum pressure applied through the PHDs at a shallow depth from the surface. The proposed method and the consolidation theory have then been applied to the analysis of a field project in Japan involving dredged mud consolidated by vacuum pressure with PHDs. By comparing the field-measured and analyzed results in terms of water content distributions with depth and the thickness variation of the deposit, the usefulness of the proposed method has been demonstrated.

Two methods, namely the air-tight sheet method and the vacuum-drain method (sheetless), are generally used to conduct vacuum consolidation in the field. The advantages and disadvantages of both methods and the techniques for preventing vacuum leakage through a middle sand layer in a deposit, as well as the method for maintaining vacuum pressure when large settlement occurs, have been described. Vacuum pressure is an isotropic consolidation pressure applied to a soil deposit, and the deformation induced is different from that induced by a surcharge (e.g. the weight of an embankment). Two typical case histories in Japan are presented and deformation analyses were conducted. In one case history the vacuum-drain method was used with vacuum pressure alone, and in the other a combination of embankment loading and vacuum pressure was applied employing the air-tight sheet method. It is shown that under vacuum pressure loading, the ground deformation (settlement and lateral displacement) can be calculated reliably using a method proposed previously. For the case involving a combination of vacuum pressure and embankment load, the settlements under the embankment centreline can be estimated reasonably assuming one-dimensional deformation conditions.

Based on examination of existing field results, an empirical equation has been suggested for estimating the likely range of the maximum value of the net lateral displacement (dnm) of ground improved by the installation of prefabricated vertical drains (PVDs) and subjected to the combined effects of vacuum pressure and embankment loading. The effects on lateral displacement of the magnitudes of embankment loading, as well as the vacuum pressure, the loading rate, and the undrained shear strength and consolidation properties of the soil deposit, have been explicitly included in a newly defined parameter, which is given by the ratio of an index pressure to the representative soil shear strength (RLS). The ratio of dnm to the surface settlement under the embankment centreline, Sf, is also defined as the normalised maximum (net) lateral displacement (NLD). A direct relationship between RLS and NLD has been proposed, with a prescribed range, based on the results of 18 field case histories from 12 different project sites in five countries. It is suggested that the proposed relationship can be used as a preliminary design tool for preloading projects involving combinations of a vacuum pressure and an embankment pressure as well as PVD improvement.

The effect of hydraulic hysteresis inherent in soil water characteristic curves is explored stochastically in seepage analysis of engineered soil covers. A multi-layer soil cover with random top boundary flux conditions is simulated with the First Order Second Moment method. Water inflow and outflow at the top boundary are chosen as two random variables. The capillary barrier mechanism is taken into account, and the breakthrough hydraulic head at the bottom boundary of the soil cover is adopted as the performance function. Results show that the hysteretic hydraulic model predicts a more conservative result than does the traditional nonhysteretic hydraulic model when simulating seepage in unsaturated, multi-layer soil covers. The dependence of the soil cover performance on its exterior environment during construction is also identified, with a relatively arid season significantly improving the soil cover's functionality. Furthermore, multi-layer soil covers with a proper selection of geotechnical materials provide better performance than a single layer of soil cover of the same thickness. The importance of hydraulic hysteresis in soil covers subjected to alternative climatic actions is emphasized. © 2013 American Society of Civil Engineers.

The Cam Clay model and most models subsequently developed within the critical state framework are normally formulated to represent the behaviour of soils reconstituted in the laboratory, where the soil structure, if present, is standardised by the sample preparation method. However, as seen from both laboratory and in situ tests, soil behaviour may depend significantly on its structure. The structures of soils found in situ vary greatly, depending on their formation processes and their mechanical, electro-chemical and biological histories. The authors have proposed a relatively simple predictive model, known as the Structured Cam Clay (SCC) model, for solving practical geotechnical problems. In this paper a review of the performance of the Structured Cam Clay model is presented. The paper contains the following four parts. (1) A summary is made of the generalisation of the critical state framework into a new four dimensional space, consisting of the current stress state, stress history, the current voids ratio, and the current soil structure. The key assumption of the theoretical derivation is that both the hardening and destructuring of natural clays are dependent on plastic volumetric deformation. (2) The main concepts and the formulation of the Structure Cam Clay model are introduced within the generalized framework and an explicit stress-strain matrix is obtained for SCC. (3) The capacity of the model for describing laboratory single element tests is evaluated and the main features of the model are summarised. (4) Techniques for refining the Structured Cam Clay model are also discussed.

An exponential finite-element model for multiple-porosity contaminant transport in soils is proposed. The model combines three compartments for dissolved contaminants: a primary compartment of diffusion-advection transport with nonequilibrium sorption, a secondary compartment with diffusion in rectangular or spherical soil blocks, and a tertiary compartment for immobile solutions within the primary compartment. Hence the finite-element model can be used to solve four types of mass-transfer problems which include: (1) intact soils, (2) intact soils with multiple sources of nonequilibrium partitioning, (3) soils with a network of regularly spaced fissures, and (4) structured soils. Hitherto, mobile/immobile compartments, fissured soils, and nonequilibrium sorption have been treated separately or in pairs. A Laplace transform is applied to the governing equations to remove the time derivative. A Galerkin residual statement is written and a finite-element method is developed. Both polynomial and exponential finite elements are implemented. The solution is inverted to the time domain numerically. The method is validated by comparison to analytical and boundary element predictions. Exponential elements perform particularly well, speeding up convergence significantly. The scope of the method is illustrated by analyzing contamination from a set of four waste repositories buried in fissured clay. © ASCE.

The nonhomogeneous behavior of structured soils during triaxial tests has been studied using a finite element model based on the Structured Cam Clay constitutive model with Biot-type consolidation. The effect of inhomogeneities caused by the end restraint is studied by simulating drained triaxial tests for samples with a height to diameter ratio of 2. It was discovered that with the increase in degree of soil structure with respect to the same soil at the reconstituted state, the inhomogeineities caused by the end restraint will increase. By loading the sample at different strain rates and assuming different hydraulic boundary conditions, inhomogeneities caused by partial drainage were investigated. It was found that if drainage is allowed from all faces of the specimen, fully drained tests can be carried out at strain rates about ten times higher than those required when the drainage is allowed only in the vertical direction at the top and bottom of the specimen, confirming the findings of previous studies. Both end restraint and partial drainage can cause bulging of the triaxial specimen around mid-height. Inhomogeneities due to partial drainage influence the stress-strain behavior during destructuring, a characteristic feature of a structured soil. With an increase in the strain rate, the change in voids ratio during destructuration reduces, but, in contrast, the mean effective stress at which destructuration commences was found to increase. It is shown that the stress-strain behavior of the soil calculated for a triaxial specimen with inhomogeneities, based on global measurements of the triaxial response, does not represent the true constitutive behavior of the soil inside the test specimen. For most soils analyzed, the deviatoric stress based on the global measurements is about 25% less than that for the soil inside the test specimen, when the applied axial strain is about 30%. Therefore it can be concluded that the conventional global measurements of the sample response may not accurately reflect the true stress-strain behavior of a structured soil. This finding has major implications for the interpretation of laboratory triaxial tests on structured soils. © ASCE.

Foundations of oil and gas platforms and drilling rigs are constructed on carbonate sands. For economy of foundation design and construction it is necessary to understand their mechanical behaviour and characterise the same. This paper proposes two critical state models and investigates their appropriateness for characterising the behaviour of carbonate sands.

The influence of the natural (or artificially induced) structure of a geomaterial on its compression behavior is investigated. An approach for modeling this influence for various structured geomaterials is proposed by using the disturbed state concept. An isotropic compression model is formulated on three basic assumptions. A special version of the proposed model is also described for situations where the compression is one-dimensional. The proposed compression model is used to simulate the behavior of a variety of structured geomaterials such as clays, sands, calcareous soils, clay-shale, soft rock, unsaturated soils, and soils artificially treated by adding chemical agents or mechanical reinforcement, and the model is evaluated on the basis of these simulations. A general discussion on the influence of the structure of geomaterials on their mechanical properties is also presented. © ASCE.

This note presents the results of a study on the variation of the strength of geomaterials. A general isotropic strength criterion is proposed which unifies the peak strength and critical state (or steady state) strength into one strength criterion. The proposed criterion describes the strength of a geomaterial in terms of its current stress state, its current voids ratio, and the bonding of its constituents. The proposed criterion has been applied to sand, clay, cemented sand and rocks. Based on comparisons presented between theoretical simulations and experimental data, it is seen that the proposed criterion describes successfully the isotropic strength of all these materials for general stress conditions. © ASCE.

A theoretical framework to describe the behavior of natural clay is proposed in a new four-dimensional space, consisting of the current stress state, stress history, the current voids ratio, and a measure of the current soil structure. A key assumption of the proposed framework is that both the hardening and the destructuring of natural clay are dependent on plastic volumetric deformation. Two different assumptions about how this destructuring occurs are proposed, based on which two versions of a complete constitutive model have been formulated. The behavior of reconstituted soil can also be simulated by the proposed model as a special case where the structure of soil has no effect on soil deformation. Characteristics of the proposed model are demonstrated through systematic simulations of the influence of soil structure on clay behavior. The simulated behavior of natural clay is compared qualitatively with widely available experimental data. It is seen that the proposed model successfully represents the main features of natural clays with various soil structures. © ASCE / DECEMBER 2003.

Professor John Robert Booker died in Concord Hospital in Sydney on 13 January 1998, after a long and courageously-fought battle against cancer. His death cut short a brilliant academic career and deprived the Australian geotechnical and engineering mechanics communities of one of its most eminent members. At the time of his death John Booker held a personal chair in engineering mechanics in the Department of Civil Engineering at the University of Sydney, and he was widely regarded as one of the finest researchers of his generation working in the field of theoretical geomechanics. His long battle with cancer did not deflect him from his life's work. While understandably, he was unable to hold formal classes during the last months of his life, it is significant that he was active in research until his very last weeks, such was his love for and dedication to his work. John Booker was a warm, friendly, caring man who touched many lives. He was mentor to most with whom he came into close contact, students and colleagues alike. He is survived by his second wife Elizabeth, daughters from his first marriage, Katie and Lucie, sister Judith and mother Joan. © Australian Academy of Science 2002.

The problem of cavity expansion from zero radius has no characteristic length and therefore possesses a similarity solution, in which the cavity pressure remains constant and the continuing deformation is geometrically self-similar. In this case, the incremental velocity approach first used by Hill [7] to analyze cavity expansion in Tresca materials may be extended to derive a solution for limiting pressure of cavity expansion in Mohr-Coulomb materials. An analytical solution for cavity limit pressures in Mohr-Coulomb materials was suggested by Carter et al. [2]. However, the solution of Carter et al. may only be regarded as approximate since the convected part of the stress rate was neglected in their derivation. By including the convected part of the stress rate, Collins and Wang [4] later derived a semi-analytical similarity solution for cavity expansion in purely frictional soils. The solution of Collins and Wang [4] was, however, obtained from numerical integration as their solution could not be expressed in explicit form. In this article, a rigorous closed-form solution is derived for the expansion of cavities from zero initial radius in cohesive-frictional soils. The solution procedure adopted here follows the Hill incremental velocity method, which is different from that used by Collins andWang [4]. In particular, the plastic radius c is used in this article as the time scale. Unlike the solution of Collins and Wang [4], it is shown that by using a series expansion the similarity solution can be expressed in closed form. © 2003 ASCE.

The bearing behavior of footings on layered soils has received significant attention from researchers, but most of the reported studies are limited to footings resting on the surface of the soil and are based on the assumption of small deformations. In this article, large deformation analyses, simulating the penetration of strip and circular footings into two-layered clays, are described. The upper layer was assumed to be stronger than the lower layer. The importance of large deformation analysis for this problem is illustrated by comparing the small and large deformation predictions. The bearing behavior is discussed and the undrained bearing capacity factors are given for various cases involving different layer thicknesses and different ratios of the undrained shear strengths of the two clay layers. The development of the plastic zones and the effect of soil self-weight on the bearing capacity are also discussed in the article. © 2003 ASCE.

This paper reviews the phenomenon of volumetric hardening, which is a common feature of the mechanical behaviour of many geo-materials. Three different material idealizations have been proposed to describe this hardening, and the paper contains the corresponding mathematical formulation. These idealizations vary in their complexity and hence their ability to capture different aspects of real material behaviour. Any of the three postulates can be implemented into most constitutive models. As a demonstration of their capabilities, the postulates have been implemented into the well-known modified Cam Clay model, and computations are made with the resulting new constitutive models. It is seen that the new models can successfully represent important features of soil behaviour such as plastic yielding associated with loading inside the current virgin yield surface, the loosening or densifying of granular soils caused by shearing, and the accumulation of both volumetric and distortional deformation caused by repeated drained loading over a large number of cycles. Copyright (C) 2000 John Wiley and Sons, Ltd.

The aim of this note is to quantify the influence of soil structure on the compression behaviour of natural soils using the disturbed state concept (DSC). The behaviour of the fully adjusted state is chosen to be that of the corresponding soil in a reconstituted condition so that the disturbance function is a direct measure of the effects of soil structure. A new DSC compression model is proposed. This model is able to describe the compression behaviour of structured soils under loading, swelling and reloading. Special versions of the proposed model are also described for situations (a) where the compression behaviour of the corresponding reconstituted soils is linear in the e-ln p' space and (b) where the compression is one-dimensional. The ability of the proposed model and its various versions to describe the compression behaviour of structured soils has been verified. The aim of this note is to quantify the influence of soil structure on the compression behaviour of natural soils using the disturbed state concept (DSC). The behaviour of the fully adjusted state is chosen to be that of the corresponding soil in a reconstituted condition so that the disturbance function is a direct measure of the effects of soil structure. A new DSC compression model is proposed. This model is able to describe the compression behaviour of structured soils under loading, swelling and reloading. Special versions of the proposed model are also described for situations (a) where the compression behaviour of the corresponding reconstituted soils is linear in the e-ln p' space and (b) where the compression is one-dimensional. The ability of the proposed model and its various versions to describe the compression behaviour of structured soils has been verified. Copyright (C) 2000 John Wiley and sons, Ltd.

The purpose of this study was to evaluate patient selection, local control, survival and late toxicity of posthysterectomy adjuvant radiotherapy and compare adjuvant external beam therapy and high-dose rate (HDR) brachytherapy versus HDR brachytherapy alone. A retrospective analysis was performed on a series of 225 patients with endometrial cancer treated with external beam radiotherapy and HDR brachytherapy or HDR brachytherapy alone posthysterectomy from 1985 to June 1993. Of these 225 patients, 82 received external beam radiotherapy and brachytherapy and 143 received brachytherapy alone. The HDR fraction size was 8.5 Gy prescribed to the mucosal surface; two fractions were given after external beam and four fractions if brachytherapy alone was used. The median follow-up was 6.9 years. The patients who received combined external beam and brachytherapy had higher stage and grade tumors. The survival outcome was similar for either group when matched for stage. Overall relapse-free survival at five years was 96% and 81%, respectively for brachytherapy alone and combined adjuvant therapy. Pelvic recurrence was seen in 2.7% of patients. Toxicity was more common with external beam radiotherapy and brachytherapy compared to brachytherapy alone (45.1% vs 23.1%, P = 0.003). However, moderate or severe toxicity was rare but again was more common in the combined radiotherapy group (8.5% vs 2.1%, P = 0.04). There was a non-significant trend to increased toxicity after lymphadenectomy and external beam radiotherapy compared with patients who did not have a staging lymphadenectomy prior to external beam radiotherapy (62% vs 38%, P = 0.16). Adjuvant radiotherapy can be individualized and be based upon the information provided by the pathological specimens, which excluded external beam radiotherapy if a lymphadenectomy was performed and there was no evidence of extra-uterine disease. This study found more toxicity associated with adjuvant radiotherapy compared with other studies, but this may reflect different reporting criteria. There was more toxicity related to external beam radiotherapy and brachytherapy compared to brachytherapy alone. The two HDR brachytherapy protocols used in this series appear effective and safe.

Purpose: To evaluate the outcome of post-hysterectomy adjuvant vaginal high-dose-rate (HDR) brachytherapy. Methods and Materials: A retrospective analysis was performed on a series of 143 patients with endometrial cancer treated with HDR brachytherapy alone post-hysterectomy from 1985 to June 1993. Of these patients, 141 received 34 Gy in four fractions prescribed to the vaginal mucosa in a 2-week period. The median follow-up was 6.9 years. Patients were analyzed for treatment parameters, survival, local recurrence, distant relapse, and toxicity. Results: Five-year relapse free survival and overall survival was 100% and 88% for Stage 1A, 98% and 94% for Stage IB, 100% and 86% for Stage IC, and 92% and 92% for Stage IIA. The overall vaginal recurrence rate was 1.4%. The overall late-toxicity rate was low, and no RTOG grade 3, 4, or 5 complications were recorded. Conclusion: These results are similar to reported international series that have used either low-dose-rate or HDR brachytherapy. The biological effective dose was low for both acute and late responding tissues compared with some of the HDR brachytherapy series, and supports using this lower dose and possibly decreasing late side- effects with no apparent increased risk of vaginal recurrence.

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%.

Suction caissons are being used increasingly for the anchorage of large compliant offshore structures. Uplift capacity of the suction caissons under inclined loading is a critical issue in these applications, and reliable methods of predicting the capacity under this form of loading are required in order to produce reliable designs. An extensive theoretical investigation has been carried out of suction caissons in uniform soils subjected to inclined uplift loading for cases where the behaviour of the seabed soil is undrained. A brief review of previous research on the behaviour of suction caisson under uplift loading is included, and results of finite element modelling are presented. A simplified method for the estimation of the uplift capacity for suction caissons is described, based on the results of the finite element study. The expressions developed in this paper take into account the influence of the aspect ratio of the caisson, the point of application and angle of inclination of the loading, and the undrained shear strength of the soil.

Structured soils exhibit an apparent non-linear normal compression line in the semi-log compression plane, which dominates the difference in the mechanical behaviour between structured soils and their reconstituted counterparts. The effect of soil structure is investigated via the change of compression stiffness with structure degradation. A differential expression of the normal compression line is then established and applied to a large number of different types of soil. Satisfactory results are obtained, illustrating the validity and applicability of the proposed approach. © 2015 Taylor & Francis Group, London.

The main aim of this study is to apply a robust time integration technique for simulating the behaviour of unsaturated soils subjected to dynamic loads. The governing equations of the three soil phases and their interactions are derived based on the mass conservation law, linear momentum balance and energy conservation of each phase in an isothermal environment. In addition, a number of experimental equations are employed to represent the hydraulic conductivity and the drainage characteristics of the soil, such as the suction-saturation relationship and the dependency of the hydraulic conductivity on suction. The global system of equations is then solved by using an implicit time-stepping algorithm based on the Generalised-a integration scheme. The accuracy of the numerical model and the finite element code is verified by comparing the numerical results with results obtained by an analytical solution. © 2015 Taylor & Francis Group, London.

This study outlines the development of a computational scheme which accounts for large deformation dynamic behaviour of saturated porous media and models soil-structure interaction using a high-order frictional contact algorithm. The numerical scheme is employed to analyse a dynamic coupled problem of pipeline-seabed interaction in two steps, including the simulation of the dynamic embedment process as well as the subsequent consolidation stage. The analysis considers a frictional interface between the pipe and the soil which is normally ignored in most analyses due to numerical difficulties. The nonlinear behaviour of the solid constituent is captured by the Modified Cam Clay soil model, allowing the incorporation of shear-induced pore water pressures during the embedment process. The results of this study indicate that the proposed method is able to solve the highly nonlinear problem of dynamic soil-pipe interaction coupled with pore water pressures and Darcy velocity. The results also show that a dynamic approach is necessary for coupled problems of pipe-seabed interaction involving very fast loading. © 2015 Taylor & Francis Group, London.

Dynamic compaction is known as one of the most cost-effective soil improvement techniques. In this method the soil at the ground surface or at a relatively deep depth is compacted by repeatedly dropping heavy weights on the ground. Since its introduction, dynamic compaction has exhibited its versatility and simplicity of use in different types of civil engineering projects, including building structures, container terminals, highways, airports, dockyards, and harbours. However, despite the abundance of experimental data and field observation reports, few numerical approaches have been established in the literature to effectively deal with soil behaviour under dynamic compaction. This is mainly due to the dependence of soil dynamic response on variations in the moisture content. Therefore, to achieve a comprehensive understanding of dynamic compaction the soil should be modelled as a three-phase porous medium. The presence of a non-wetting and a wetting phase, together with the existence of inertia forces in each phase, makes the solution of the coupled dynamic system computationally demanding. Moreover, large deformations often take place during dynamic compaction; hence the infinitesimal strain theory cannot be employed for higher impact loads. In this paper a finite element approach is introduced to numerically simulate the problem of dynamic compaction under the framework of unsaturated soil mechanics. The governing equations are derived based upon the overall momentum balance of the mixture, the mass balance of the liquid phase, and the mass balance of the gas phase. Phase changes and chemical reactions are not considered. Among other important parameters, the effect of the degree of saturation on the soil response will be addressed.

The dynamic penetration of anchors into the seabed is an important problem in offshore geomechanics and one of the most challenging for geotechnical analysts. Complications due to the nonlinear material response of the soil, the large deformations caused by the insertion of the object, and the changing boundary conditions at the contact between the soil and the anchors must be taken into account. Moreover, the presence of a pore fluid, and the pressure that it may exert, requires a fully coupled displacement-pore pressure analysis. Recent work has facilitated the modelling of the dynamic penetration of objects into soil. The finite element method is one of the most commonly used techniques for tackling problems of soil penetration because the resulting solutions satisfy the equation of dynamic equilibrium and the method can incorporate sophisticated soil models as well as complex boundary conditions. This study discusses a number of challenging aspects of the numerical simulation of dynamically embedded anchors, particularly torpedo anchors, and presents a robust analysis strategy for such problems. This technique is based on the Arbitrary Lagrangian-Eulerian method and rigorously incorporates displacements, velocities, and accelerations of the solid phase along with the pore pressure and velocities of the fluid phase.

This paper addresses the application of high-order elements in the analysis of soil penetration problems, particularly those involving inertia forces and large deformations. Among others, 15-node triangular elements are formulated within an Arbitrary Lagrangian-Eulerian finite element method. Preliminary studies indicate that high-order elements can significantly decrease the analysis time without significant loss of accuracy. © (2014) Trans Tech Publications, Switzerland.

The plastic anisotropy of reconstituted soft soils is described from the compression behaviour observed during radial loading paths in stress space. A unique relationship is established between the orientation of the yield surface and the corresponding normal compression line, which indicates that a stabilized fabric is maintained under continuous loading along radial stress paths. The equilibrium orientation angle of the plastic potential surface is obtained explicitly. A new rotational hardening law is proposed by considering the dependence of the evolution of anisotropic fabric with the current stress condition and plastic strain. An elastoplastic constitutive model for anisotropic soil is formulated within the framework of Critical State Soil Mechanics. Validation with experimental data and predictions from other models demonstrate the feasibility of the basic concept and the capacity of the proposed new model. © 2014 American Society of Civil Engineers.

This paper presents the development of a numerical framework based on the finite element method and its application in the analysis of torpedo anchors. The procedure is based on a mixture theory for the dynamic behaviour of saturated porous media. The nonlinear behaviour of the solid phase of soil is represented by the Modified Cam Clay material model and the interface between the soil and the structure is modelled by a mortar segment-to-segment frictional contact method. An Arbitrary Lagrangian-Eulerian (ALE) method is adopted to avoid mesh distortion throughout the numerical simulation. The generalised-a method is utilised to integrate the governing equations of motion in the time domain. Results obtained from the installation phase of a torpedo anchor reveal that the anchor decelerates at a constant rate during most of its penetration. Analysis results show a typical distribution of excess pore-water pressure during free falling installation, having higher magnitudes at the face and lower magnitudes along the shaft. The computational results for the setup phase indicate that for soil elements located within a radial distance of approximately one diameter from the centreline of the torpedo, 90% of consolidation takes place in a few days after installation, depending on the value of soil permeability.

Atheory describing the consolidation of a uniform clayey deposit with and without prefabricated vertical drain (PVD) improvement under the combination of a vacuum pressure and a surcharge load has been developed and expressed as closed-form equations. For the case of a soil layer without PVD improvement, both one-way and two-way drainage boundary conditions are considered. Laboratory consolidation tests using combinations of vacuum pressure and surcharge load were conductedunder oedometer conditions with vertical or radial drainage. The measured excess pore water pressures are compared with values predicted by the theory presented in the paper. It has been demonstrated that the theory is valid and can be used for designing preloading projects that involve the combination of a vacuum pressure and a surcharge load.

The characteristics of vacuum consolidation and the advantages of preloading soft clayey deposits by combining vacuum pressure treatment with embankment loading are discussed. Laboratory oedometer test results show that vacuum pressure induces less or about the same settlement compared to an applied surcharge load of the same magnitude. If the applied vacuum pressure is larger than the lateral stress required to maintain a ko condition (no horizontal strain), there will be inward lateral displacement and the vacuum pressure will induce less settlement. In cases where the bottom of the soft clayey deposit is drained (e.g., where the clay overlies a sand or gravel layer), application of a vacuum pressure will cause less consolidation than an equivalent surcharge load because that at the bottom drainage boundary effectively the vacuum pressure can not be applied. For this type of subsoil condition it is suggested that if vacuum consolidation is combined with the use of prefabricated vertical drains (PVDs) for ground improvement, the PVDs should not penetrate the entire clayey layer. An equation for calculating the optimum penetration depth has been derived for this case. The advantages of combining vacuum pressure with embankment loading are discussed in terms of increasing the effective surcharge loading, reducing construction time in the case of road construction, and reducing the preloading-induced lateral displacement of the subsoil. Copyright ASCE 2006.

In this paper attempts have been made to find the effects of sequential loadings on the ultimate uplift capacity of a typical horizontal plate anchor loaded vertically. A series of finite element analyses was performed where the anchor was subjected to different initial loading under undrained conditions followed by consolidation under sustained loading. The anchor was then loaded under undrained conditions up to failure. The anchor is idealised as a circular plate embedded in a homogeneous soil. The soil is represented by the Modified Cam Clay material model with an undrained shear strength varying linearly with depth. No allowance has been made to model break away between the soil and the anchor. The results of the finite element analyses show that if a low value of the initial loading is applied to the anchor under undrained conditions followed by consolidation, the ultimate undrained uplift resistance of the anchor increases. However, for relatively high values of the initial loading the soil fails during the consolidation period. © 2005 Taylor & Francis Group.

This paper examines the undrained bearing capacity of shallow circular foundations on structured soil deposits. Guidelines are given to identify the importance of structural features of the soil when assessing its bearing resistance. Results obtained using a finite element model have been compared with those from existing bearing capacity formulae based largely on plasticity theory. A new bearing capacity equation has been proposed incorporating critical state soil parameters and additional parameters that quantify the effects of soil structure on its mechanical behaviour. © 2005 Taylor & Francis Group.

This paper presents the results of a series of numerical analyses of caisson foundations embedded in a homogeneous soil deforming under undrained conditions. The performance of a typical caisson foundation under separate axial, torsional and lateral forces is investigated, followed by the interaction of these forces with each other. The lateral force is applied at various points along the skirt of the caisson so that the effects of overturning moments are also included in the analyses. The ultimate capacity of the caisson under combined loading is presented in the form of failure envelopes in the axial-lateral, axial-torsional and lateral-torsional loading planes and the axial-lateral-torsional loading space. The results of this study show that although the capacity of the caisson under lateral load depends on the location of the padeye along the caisson skirt, a unique failure envelope, in a non-dimensional form, can be presented for the caisson regardless of the location of the padeye. © 2005 Taylor & Francis Group.

In this paper, simulations of the behaviour of calcareous soils are made using a simple predictive model proposed previously by the authors and known as the Structured Cam Clay model. It is demonstrated that this simple model has the capacity to describe many important features of the complicated behaviour of these soils. © 2005 Taylor & Francis Group.

The Sydney Soil Model is formulated within the framework of Critical State Soil Mechanics. In the proposed model, the behaviour of a soil is divided into two parts, that at a reference state and that attributed to the influence of soil structure. The reference state behaviour is formulated according to soil properties at the critical state of deformation based on the concept of plastic volumetric hardening. The influence of soil structure is introduced by formulating the variation of the additional voids ratio, associated with soil structure, for any general stress or strain path. The proposed model is employed to simulate the behaviour of a natural sensitive clay and a dense sand under conventional undrained triaxial tests. It is shown that the model can provide good simulations for the behaviour of structured soils.

This paper presents the results of a numerical study of the problem of bearing capacity of shallow circular foundations under combinations of vertical load, horizontal load and moment. The motivation for the study comes from the fact that the existence of a unique or exact solution to this problem has not yet been demonstrated. This study includes the performance of the foundation under large overturning moments and large horizontal loads. The contact between the foundation and the soil is unable to sustain tension. The results of the numerical analyses are compared with the conventional equations commonly used in bearing capacity calculation. The bearing capacity of the foundation, obtained from finite element analyses, are presented in the form of a failure locus in the vertical, horizontal and moment loading space.

This paper presents results of a theoretical investigation of suction caissons installed in seabed deposits composed of dense sand and subjected to inclined uplift loading under fully drained conditions. Consideration is given to the effects of caisson embedment, load application point, load inclination angle, friction angle of the soil, dilatancy and the initial stress state, as defined by the value of K0. Simplified expressions for the inclined uplift capacity of suction caissons are developed, based on the results of the finite element study.

A general failure criterion for clays is proposed. For intact clays the proposed formula unifies the three identifiable strengths of soils, i.e., peak strength, critical state strength and residual strength, into a single isotropic failure criterion. By the introduction of two new parameters, describing the anisotropy and the degree of fissuring, the criterion may be extended to model the anisotropic strength of fissured clays. The capabilities of the proposed criterion are demonstrated and evaluated by comparing its predictions with experimental data. It is obvious that soils with different structures need different numbers of parameters to define their failure criteria. Indeed, the complexity and accuracy of the criterion can be selected to match the available data.

Cemented and uncemented carbonate sediments are encountered in many offshore regions of Australia and the world. These sediments are biogenic in origin, highly compressible, angular in shape, and usually have high friction angles. This combination of factors can lead to existing empirical methods of analysis for sandy soils giving poor predictions for carbonate soils. To investigate the behaviour of foundations in carbonate soils a new constitutive model has been developed by modifying and generalising the Modified Cam Clay model. In this model the plastic potential function is identical to that for Modified Cam Clay, but the yield function is obtained by scaling down the plastic potential function by a 'spacing ratio'. The spacing ratio is the only additional parameter introduced in this model, and it results in general in a non-associated flow rule. The model has been used to predict the triaxial behaviour of uncemented and artificially cemented carbonate sands, as well as the behaviour of a model footing on cemented carbonate sands. Typical predictions are shown to illustrate the usefulness of the model.

The conventional bearing capacity factor N(¿) generally makes a relatively large contribution to the overall bearing capacity of a frictional material, but no analytic solution has been found for the case of either a fissured or a non-fissured material. An efficient numerical method to evaluate N(¿), based on the method of characteristics, is presented in this paper. The method has been employed to generate new results for materials weakened by the presence of vertical and horizontal fissures or joints. Values of N(¿) have been calculated for a variety of friction angles for the fissures and the matrix material. The accuracy of bearing capacity calculations using these values of N(¿) combined with the conventional Terzaghi bearing capacity equation is discussed.

A limited theoretical investigation has been made of the problem of the bearing capacity of shallow circular footings subjected to inclined loading with no applied moment. The soil has been modelled as a cohesive-frictional (Mohr-Coulomb) material, and predictions of the bearing capacity have been made with a semi-analytical finite element procedure, thus avoiding the need for a full three-dimensional treatment. The investigation has been primarily concerned with the behaviour of foundations on calcareous sediments, and only a limited range of values of the material properties, representative of weakly cemented carbonate soils, has been investigated. The results show that increasing cohesion and friction angle both have significant and similar effects on the bearing capacity and its variation with load angle.

The compression behaviour of sands has been investigated, and it is proposed that a linear relationship between voids ratio, e, and mean effective stress, p', instead of the more widely employed e-lnp' relationship, can best describe this behaviour. A general equation is presented describing the compression behaviour of sands under first loading. The proposed compression equation has been applied to ten different types of sand and one crushed rock with the compression pressures reaching 850 MPa. It is seen that the proposed equation can describe very satisfactorily the behaviour of all these materials. A simplified model for virgin compression loading, unloading and reloading of sands is then formulated. It contains only four material parameters and describes a linear variation between the voids ratio and the compression stress for both virgin yielding and purely elastic behaviour. Based on the comparison between predictions of the model and experimental data, it is seen that the proposed model captures important features of sand behaviour, including the response to cycles of load, and provides a simple, yet realistic, material idealization for constitutive modelling of sand behaviour.