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This paper presents an appropriate physical parameter for cement admixed clay, termed as the state parameter that combines the influence of void ratio, stress level, and cement content reference to an ultimate (steady) state. Data from a triaxial testing program on Pasak Clay with different stress paths was presented and demonstrated to be dependent on the state parameter. The strength and pore water pressure at the failure of cement mixed clay were directly associated with mean stress and decreasing state parameters. The 3-D surface for deviatoric stress, mean stress, and state parameter at certain distortional strains was proposed based on a stress path triaxial test. The stiffness of cement-treated clay increased with a decreasing state parameter and increase in mean stress. The concept of state parameter is a basic physical concept and has broad application as an empirical normalising parameter and constitutive modelling of soil behaviour. [ABSTRACT FROM AUTHOR]

Suffusion, one of the modes of internal erosion, occurs when fine particles are detached under hydraulic force. More fine particles are washed out with the void growth, which subsequently causes the failure of earthworks. At present, constitutive models considering suffusion are mostly established through DEM simulations and constitutive models that can capture the main features of eroded soils are quite limited. This study aims to establish constitutive equations to model the mechanical behaviour of soils subjected to suffusion by using drained triaxial experimental data. The modified subloading Cam-clay model incorporated with the normal yield surface for the eroded soil is proposed, which can express the variation of the normal yield surface with the loss of fine particles. The determination method of the erosion-related model parameters is also proposed. The erosion-related model parameters are estimated through empirical equations with curve-fitted parameters. Finally, the capability of this modified model is demonstrated through the comparisons with experimental results. [ABSTRACT FROM AUTHOR]

This research consists of two main parts. First, some laboratory and field tests have been conducted on a specific soil. Therefore, a series of laboratory and field data have been obtained that can be used to evaluate numerical analyses. In the second part, an elastoplastic constitutive model is introduced based on Duncan-Chang constitutive model. The steady state concept has been added to this constitutive model using the state parameter. The mentioned constitutive models have been calibrated using laboratory data for the soil. Then, these constitutive models have been applied in the numerical analysis of an excavation problem monitored during construction. Thus, the effect of the state parameter and steady-state concept on the numerical results has been evaluated with a comparison between the numerical analyses and field observation. Finally, according to the numerical analyses and field data, it has been concluded that the steady state concept in constitutive models can play a significant role to improve the numerical simulations of geotechnical structures. [ABSTRACT FROM AUTHOR]

The generation of the disposal and recycling of Polyethylene Terephthalate (PET) has been significantly grown in recent years. The amount of landfill available to contain this material has been decreasing, and there is an urgent need to find appropriate disposal locations for these solid wastes. Using of PET in the sheeted form to improve strength parameters of sand soil offers a viable solution. Therefore, this study was designed to bridge this gap by performing Laboratory triaxial compression on unreinforced and reinforced samples. To accomplish this objective, a series of cylindrical specimens were prepared and subjected to triaxial tests according to the ASTM D 4546–03 standard. The trend analysis of laboratory data underscored the influence of the plastic sheets on the strength properties, friction angle, and cohesion of sandy soils. Additionally, several numerical simulations using finite element software program ABAQUS were conducted to model a reinforced slope with plastic sheets. The numerical analysis revealed that using the plastic sheets into the sandy soil enhances the factor of safety of the slope and improve the stability of the slope due to the high tensile strength of the plastic sheets. [ABSTRACT FROM AUTHOR]

Skempton coefficient B is commonly used to evaluate the saturation of a sample before the shearing stage in a triaxial test. For unsaturated soils, measuring the degree of saturation Sr at the end of the consolidation stage is very difficult whereas measuring Skempton coefficient B is very simple. Using this coefficient to obtain Sr of a sample in a triaxial apparatus without complex procedures might be an improvement, especially as regards testing procedures for unsaturated soils. Different authors have proposed a relationship between these two parameters based on the hypothesis that a variation of B coefficient with Sr is mostly due to the compressibility of air in the pores. However, the presence of air as a fluid phase gives rise to suction after the equilibrium is reached inside the sample leading to an increase in stiffness. Based on this observation, this article presents a new relationship that enables Sr to be evaluated with a given Skempton coefficient taking into account not only the initial void ratio and the isotropic elastic modulus but also the suction and the elastoplastic behaviour of the soil. The results of the proposed approach are then confronted with the original relationship and compared to experimental data. [ABSTRACT FROM AUTHOR]

This paper explores how the discrete-element method (DEM) was found to play an increasingly important role in cone penetration test (CPT) where continuum-mechanics-based analysis tools are insufficient. We investigated several crucial features of CPT simulations in the two-dimensional DEM. First, the microparameters (stiffness and friction) of discrete material tailored to mimic clean, saturated sand, which is used in cone-penetration tests, were calibrated by curve-fitting drained triaxial tests. Then, three series of cone-penetration simulations were conducted to explore (1) top boundary conditions, (2) reasonable size of discrete particles at different initial porosities, and (3) limit initial porosity of the model for a balance between accurate representation and computational efficiency. Further, we compared the cone-penetration resistance obtained in the laboratory and numerical simulations for the range of relative densities. [ABSTRACT FROM AUTHOR]

In order to understand the mechanical behaviours of the surrounding rocks in the underground caverns of the Wudongde hydropower plant, triaxial tests are performed on a type of dolomite. It is revealed that damage induced by crack development is the main factor controlling the nonlinear plastic deformation and failure behaviour of the dolomite in both pre- and post-peak regimes. Based on this understanding, a coupled elastoplastic damage model is developed for capturing the dolomite’s mechanical behaviours. In the model, the effects of plasticity and damage on rocks is described by introducing plastic hardening and damage softening commonly in the plastic yield surface. Which are both derived from a suitable Helmholtz free energy function. The model is used to simulate the triaxial tests. Comparisons between test results and the numerical modelling show that the developed model is capable of describing the macro mechanical behaviours of the Wudongde dolomite. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of cross-anisotropic elastic parameters of Bangkok Clay. The study programme consists of both laboratory experiments and parametric analysis. A set of isotropically consolidated undrained and drained triaxial compression tests is performed on vertically- and horizontally-cut undisturbed specimens. The triaxial apparatus is equipped with local strain measuring systems and bender element which enable the measurement of stiffness at small to intermediate strains. The anisotropic stiffness parameters obtained from both undrained and drained triaxial tests are assumed to follow the three-parameter cross-anisotropic elastic model proposed by Graham and Houlsby (1983). Moreover, the elastic moduli are also assumed as power functions of isotropic confining stress. The cross-anisotropic elastic parameters are then derived as functions of these relevant simplified parameters. The least-square method is used to define the optimised elastic parameters from all tests. Finally, a complete set of cross-anisotropic elastic parameters of Bangkok Clay is proposed and discussed against reported values from other soils. [ABSTRACT FROM AUTHOR]

This paper presents a re-appreciation of the ground characterisation and the criteria to select the most representative geomechanical parameters to consider in a numerical model to predict the behaviour of a retaining wall of a deep excavation in highly weathered granite rock masses and residual soils. This study was focused in the construction of a deep station of Metro do Porto, which involved a cut and cover solution, with unusual proportions (in plant and in depth), built in the typical Oporto's granite weathered profiles, being the excavation conducted with retaining walls consisting of multi-anchored concrete piles. Specific sections were carefully instrumented, due to the presence of historic buildings in the vicinity. The definition of representative model parameters was based on precise laboratory tests over high quality soil samples, including oedometer and high-precision triaxial tests. Geotechnical and geological characterisation of all the area for the original design, was initially based on in situ tests, such as SPT and rock masses classification, and on the local experience on this type of ground. After this construction, the assumptions of parameterisation, using a constitutive modelling based on new laboratory tests over high quality block samples, allowed a reanalysis of the assumptions on the design phase. A back-analysis of monitored displacements and forces during the construction was made, assuming the designed structural solutions, which were in fact implemented in construction, but considering the new approaches on the definition of the geomechanical parameters for the prevailing weathered rock masses, necessary for the numerical simulation based on the commercial software Plaxis®, using the Mohr-Coulomb and “Hardening-Soil” models. Some specific changes of the constructive sequence during the excavation and activation of supporting system were attained, by looking at the information found during the construction. The results of this parametrical re-approach and analysis of the singularities of highly weathered granite and corresponding residual soils masses for modelling of retaining walls of large excavations are discussed. [ABSTRACT FROM AUTHOR]

The performance of a new constitutive model called 'kinematic hardening modified Cam clay' (KHMCC) is presented. The model is described using the 'continuous hyperplasticity' framework. Essentially this involves an infinite number of yield surfaces, thus allowing a smooth transition between elasticity and plasticity. The framework allows soil models to be developed in a relatively succinct mathematical form, since the entire constitutive behaviour can be determined through the specification of two scalar potentials. An implementation of the continuous hyperplasticity model is also described. The model requires eight parameters plus a viscosity coefficient for rate-dependent analysis. The model is defined in terms of triaxial stress-strain variables for this study, and is used to model monotonic triaxial tests on Bangkok clay. Comparisons of the theoretical predictions with the results of cyclic undrained triaxial compression tests on Bangkok clay are also presented. [ABSTRACT FROM AUTHOR]

The void distribution of saturated specimens of Ottawa sand is presented. The presence of water inside the sand specimen is detected using the magnetic resonance imaging (MRI) technique. The void distribution of the sample was determined from the image. The specimen was prepared in a non-metallic triaxial cell and was put insie a MRI apparatus to obtain the image. Two sample preparation methods (wet tamping and dry pluviation) were used to illustrate the uniformity of the samples in the initial state. The void distribution along the height of the sample and the three-dimensional orientational void distribution at different locations inside the sample were analysed. The results indicate that the sample generated by the dry-pluviation method is more uniform than the sample generated by the wet-tamping method. When the wet-tamping sample preparation technique is used, the dense sample is more uniform than the loose sample. The development of voids was investigated by a sample loaded inside the MRI device under drained compression condition. The void distribution along the height of the sample at different stages was observed. This work has demonstrated the feasibility of using the MRI technique to examine void distribution in granular material. [ABSTRACT FROM AUTHOR]