This paper presents particle breakage and its influence on soil behavior under undrained shear condition. First the pre-crushed sand was produced by triaxial tests under 3MPa confining pressure on dense samples. It was revealed that particle breakage increased with increasing axial strain and particle breakage in shear band was found to be much more substantial than outside shear band. Thereafter the pre-crushed sand and original sand were used separately in new traixial tests under 0.2MPa and 3MPa confining pressures to investigate the influence of particle breakage on soil behavior under undrained condition. It was found that particle breakage deteriorated the stress-strain curves in reduction of peak strength of soil and resulted in more substantial development of excess Pore Water Pressure (PWP) with a higher residual excess PWP. Particle breakage resulted in more contractive behavior of soil in depression of dilatancy. The effective friction angle at peak strength and the deformation modulus at 0.002 axial strain were analyzed with respect to particle breakage. It was concluded that the particle breakage resulted in reduction of friction angle and deformation modulus.

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Soil parameters, e.g., strength coefficients c and phi, are very important factors for stability inspections of river levees against seepage failure. However, large differences have been found among the phi_cu obtained by CU triaxial tests, the phi' obtained by CU-bar triaxial tests, and the phi_d obtained by CD triaxial tests. In the present paper, a series of CU-bar and CD triaxial tests for various soil materials is carried out in order to confirm the difference in strength coefficients obtained under different triaxial test conditions. The test results suggest that CU tests are susceptible to the sample dispersion and that it is difficult to consider the c_cu and phi_cu of natural soils with these tests. On the other hand, CD and CU-bar triaxial tests are not influenced by the sample dispersion, and therefore, easy to confirm the strength coefficients.

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Carbonate sediments which covered approximately 40% of the ocean surface, are located in temperate and tropical areas. This type of soil is typically observed near offshore hydrocarbon Industries. Understanding the mechanical behavior of these sediments was studied in recent decades. Intra-void ratio and particle breakage are two important parameters which affect shearing response of carbonate sediments. In this study two originally different carbonate sands obtained from the Persian Gulf were used. A series of undrained monotonic triaxial tests in different initial relative densities and confining pressures were performed to evaluate the mechanical behaviour of the used sands. The effect of particle breakage on the contraction and dilation phases of the carbonate soils was studied. The input energy done per unit volume of soils was calculated to investigate the effect of this important parameter on mechanical behavior of these soils.

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It is well established that the main mechanism for the occurrence of liquefaction under seismic loading conditions is the generation of excess pore water pressure. The growth of the excess pore water pressure of saturated sand is dependent on several factors. Changing the inclination and magnitude of the major principal stress with respect to the depositional direction in most cases will increase the collapse potential and brittleness as well as reduce the shear strength and shear stiffness. An experimental program was carried out to study the variation of pore water pressure of cross-anisotropic deposits under anisotropic cyclic loading. A total of 30 undrained cyclic tests were performed at a constant mean confining stress, σ0m, constant intermediate principal stress ratios, as indicated by b= (σ2-σ3)/(σ1-σ3), and principal stress directions, α. The experiments were performed on hollow cylinder specimens prepared by moist under compaction technique; with a height of 20cm, outer diameter of 10cm, and a wall thickness of 2cm. The applicability of an empirical model for predicting pore water pressure generation in clean sand during anisotropic cyclic loading has been studied. Results showed that inclination of the major principal stress with respect to the depositional direction had no significant effect on the residual pore water pressure. The residual pore water pressure was increased by increasing b parameter and confining stress. Moreover, increases of confining stress increased the effects of stress anisotropy on the excess pore water.

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As well-known, depending on density and effective mean principal stress levels, sandy soils behave in a different way under undrained shearing. For instance, loose sand usually exhibits a contractive behavior with strain-softening. Instead, dense sand typically shows a dilative response with strain-hardening. Generation of excess pore water pressure is also greatly affected, being negative during contractive state and positive during dilative state. In view of this complex behavior, to predict in a consistent way the sand shearing response over a wide range of initial void ratios and effective mean principal stress levels without the need to change the soil model parameters is not an easy task. In this paper, by using an extended general hyperbolic equation (GHE) combined with an empirical density-dependent stress-dilatancy relation, a newly developed model for describing monotonic undrained torsional shear behavior of sands using a single set of soil parameters is presented. Its validity is demonstrated for the case of Toyoura sand specimens consolidated at various levels of void ratio and effective mean principal stress.

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This paper presents an experimental investigation revisiting the anisotropic behavior of geomaterials in drained monotonic shear using Hollow Cylinder Apparatus. The test program has been designed to cover the effect of material anisotropy, pre-shearing and material density on the behavior of Leighton Buzzard sand. Experiments have also been performed on glass beads to understand the effect of particle shape. The test results demonstrate that the stress-strain-strength behavior of the specimen shows strong dependence on the principal stress direction. The pre-shearing history, material density and particle shape are found to be influential. The deformation non-coaxiality, i.e., non-coincidence between the principal stress direction and the principal strain rate direction is observed. In particular, it was found that non-coaxiality is more significant in presheared specimens. This paper also explains the phenomenological observations based on the recently acquired understanding in micromechanics, with attention focused on strength and deformation non-coaxiality.

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