The fabric anisotropy in granular soils is a very important character in soil mechanics that may directly affect many geotechnical engineering properties. The principal objective of this study is to develop an efficient approach for assessing the degree of fabric anisotropy as a function of grading, particles shape and weighting specifications. By assuming cross-anisotropy, the anisotropic shear stiffness values of 1042 implemented tests on 200 various sandy and gravelly soil specimens from 43 different soil types were collected from the literature. Those were combined with their corresponding void ratios, stress conditions, grading parameters, particles shape and weighting attributes to generate a global database of anisotropic shear moduli in terms of testing conditions. The magnitudes of fabric anisotropy ratio were obtained using a well-known empirical equation, and they were plotted against the relevant soil grading and particles information to examine the dependency level of this ratio to the particularities. A series of multiple regression analyses were carried out to develop a global correlation for evaluating fabric anisotropy ratio in granular soils from grading, particles shape and weighting characteristic. The results showed that reliable quantities of fabric anisotropy ratio can be estimated using the surface appearance soil specifications. The findings may serve as an appropriate technique to yield good approximations for fabric and shear stiffness anisotropies using soil grading and particle properties.

In this paper, the tunnelling-induced deformation in anisotropic stiff soils is analysed using FE modelling. The influence of material description is investigated rather than an advanced simulation of the tunnelling method. A new hyperelastic-plastic model is proposed to describe the anisotropic mechanical behaviour of stiff highly overconsolidated soil. This model can reproduce the superposition of variable stress-induced anisotropy and constant inherent cross-anisotropy of the small strain stiffness. Additionally, a Brick-type framework accounts for the strain degradation of stiffness. Formulation of the novel model is presented. The tunnelling-induced deformation is first investigated in plane strain conditions for a simple boundary value problem of homogeneous ground. The influence of initial stress anisotropy and inherent cross-anisotropy is inspected. Later, the results of 2D simulations are compared with the analogous results of 3D simulations considering different excavated length of the tunnel sections. The tunnelling process is reproduced by introduction of a supported excavation and a lining contraction stage in undrained conditions. Finally, the tunnelling case study at St James Park is back analysed using the proposed material model in plane strain conditions. The obtained calculation results are compared with the field measurements and discussed.

Although the internal stress state of soils can be affected by repetitive loading, there are few studies evaluating the lateral stress (or K0) 0 ) of soils under repetitive loading. This study investigates the changes in K0 0 and directional shear wave velocity (Vs) s ) in samples of two granular materials with different particle shapes during repetitive loading. A modified oedometer cell equipped with bender elements and a diaphragm transducer was developed to measure the variations in the lateral stress and the shear wave velocity, under repetitive loading on the loading and unloading paths. The study produced the following results: (1) Repetitive loading on the loading path resulted in an increase in the K0 0 of test samples as a function of cyclic loading number (i), and (2) Repetitive loading on the unloading path resulted in a decrease in K0 0 according to i. The shear wave velocity ratio (i.e. Vs(HH)/Vs(VH), s (HH)/V s (VH), where the first and second letters in parentheses corresponds to the directions of wave propagation and particle motion, respectively, and V and H corresponds to the vertical and horizontal directions, respectively) according to i supports the experimental observations of this study. However, when the tested material was in lightly over-consolidated state, there was an increase in K0 0 during repetitive loading, indicating that it was the initial K0, 0 , rather than the loading path, which is responsible for the change in K0. 0 . The power model can capture the variation in the K0 0 of samples according to i. Notably, the K0 0 = 1 line acts as the boundary between the increase and decrease in K0 0 under repetitive loading. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

The stiffness anisotropy of soil is a critical factor that influences the deformation characteristics of soil in landform evolution, geological disaster mitigation and engineering applications. However, the effects of freeze-thaw cycles on the stiffness anisotropy of soil have not been clearly understood. In this study, a new thermal boundary-controlled triaxial testing system equipped with bender elements is developed to investigate the effects of cyclic freeze-thaw on the stiffness of a sandy silt under both unidirectional and all-round freezing modes. It is revealed that under all-round freeze-thaw cycles, the shear wave velocity in the horizontal and vertical planes undergoes a continuous increase of 14% and 8%, respectively. In contrast, unidirectional freeze-thaw leads to a non-monotonic evolution of shear wave velocity, eventually resulting in a 3% reduction in the horizontal plane and a 16% reduction in the vertical plane after 10 freeze-thaw cycles. The increase in shear stiffness anisotropy of the sandy silt after freeze-thaw cycles is more significant in the unidirectional freeze-thaw condition (from 1.11 to 1.49) compared with the all-round freeze-thaw condition (from 1.13 to 1.19). This study illustrates the significance of unidirectional freeze-thaw in the evolution of mechanical anisotropy of soils in cold regions.

For the characterization of soil stiffness anisotropy at small strains and the calculation of soil elastic constants derived from the cross-anisotropic model, it is important to obtain stress wave phase velocities of soils in both principal and oblique directions. This study developed an original eight-prismatic shape apparatus equipped with disk-shaped shear plates to measure shear (S-) wave phase velocities (V-phase) in multiple directions, and four granular materials of various shapes were tested by this apparatus under isotropic confinement. Experimental results confirm the capability of the new apparatus and reveal that both S-wave propagation and oscillation directions are sensitive to soil inner fabric, i.e., V-s changes with the variation of either S-wave propagation or oscillation direction. Based on the experimental observations, it is suggested to keep the same S-wave oscillation direction when measuring V-s in multiple propagation directions so that the corresponding shape of the S-wave surface (polar plots of V-s in arbitrary propagation directions) is more precise to reflect the small-strain stiffness anisotropy of soils.