For the lack of accurate test results in design and maintenance of desert-crossing highways in the Tengger Desert of western China, the GDS true-triaxial system was used to conduct the drained test on dense sand. Under the condition of different intermediate principal stress ratio b-value, the results showed that the stress-strain relationships in three orthogonal directions had significant differences, presenting significant anisotropy. The peak of the generalized shear stress increased with the increase of b-value. Except under the condition of b = 0, the specimen contracted firstly and then dilated, while the others dilated. The results of the different confining pressures showed that the stress-strain relationships appeared as a hardening type at low confining pressures, and as the confining pressure increased, the stress-strain relationships exhibit hardening, peaking, softening, and stable deformation characteristics. At low confining pressure, the contractive behaviors were not obvious, mainly as dilatancy, and as the confining pressure increased, the dilatancy increased gradually. The specimen transformed contract to dilatancy, and when the confining pressure reached 800 kPa, the specimen exhibited contractive behavior. The test results will provide data for subgrade design and construction in desert area.

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Aimed at the characteristics of aeolian sand under rapid construction conditions in desert geotechnical engineering, a series of the true triaxial undrained test were carried out on the GDS apparatus. The 3D deformation, failure, and other characteristics of the dense sand are obtained. Under the condition of same p c , the state transition point where the void water pressure changes from increasing to decreasing appears earlier and leads to enhanced dilatancy with the increase of b, which means the enhanced dilatancy of dense sand caused the increase in strength. The results of the same b shows that the void water pressure generally indicates a decrease at low confining pressure and an increase at high confining pressure, indicating that the aeolian sand shows dilatancy at low confining pressure and contraction at high confining pressure. The state transition point increases with the increase of p c , but all points tend to the same critical state line and state transition line. When b = 0, the critical state line is q = 1.57 p ′ , and the state transition line is q = 1.23 p ′ . When b = 1, the critical state line is q = 1.24 p ′ , and the state transition line is q = 1.04 p ′ . The results at same b obtained the unified critical state line and the state transition line. Therefore, the true triaxial test can obtain the unified relationship of void ratio, p c and b, which overcomes the fact that the existing test cannot consider the influence of b. The test results provide a basis data for the design, construction, and maintenance of geotechnical engineering in Tengger Desert.

Based on the principle of stereology to describe void fabric, the fabric tensor is redefined by the idea of normalization, and a novel quantitative description method for the orthotropic fabric of granular materials is presented. The scan line is described by two independent angles in the stereo space, and the projection of the scan line on three orthogonal planes is used to determine the plane tensor. The second-order plane tensor can be described equivalently by two invariants, which describe the degree and direction of anisotropy of the material, respectively. In the three-dimensional orthogonal space, there are three measurable amplitude parameters on the three orthogonal planes. Due to the normalized definition of tensor in this paper, there are only two independent variations of the three amplitude parameters, and any two amplitude parameters can be used to derive the three-dimensional orthotropic fabric tensor. Therefore, the same orthorhombic anisotropy structure can be described by three fabrics, which enriches the theoretical description of orthotropy greatly. As the geometric relationship of the stereoscopic space scan line changes, the three sets of orthotropic fabrics degenerate into different forms of transversely isotropic and isotropic fabrics naturally and have a clear physical meaning. The novel fabric tensor is quantitatively determined based on mathematical probability and statistics. The discrete distribution of voids in space is projected as a scalar measurable parameter on a plane. This parameter is related to the macroscopic constitutive relationship directly and can be used to describe the effect of microscopic voids on the macroscopic phenomenon of materials.

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As a special road-building material widely distributed in desert areas, critical state soil mechanics is used to study the mechanical properties of sand and make up for the lack of research on its engineering characteristics. A series of drained and undrained triaxial compression tests with a loading rate of 0.12 mm/min medium-density aeolian sands taken from Tengger Desert in the northwest of China was carried out to obtain the three-dimensional state boundary surface. The test results reveal that the strength gained from drained and undrained tests increased, respectively, linearly and non-linearly with the increase of the effective confining pressure. Affected by the variation of pore pressure and shear rate, the undrained strength was higher than the drained strength at low effective confining pressures, and the two types of strengths tend to be consistent when the effective confining pressure becomes greater than 800 kPa. The volumetric changes of the aeolian specimens transition from dilatation to contraction when the effective confining pressures increase. The investigation of the strength, deformation and failure characteristics gives rise to the shape parameters of its state boundary surface, which provides not only a basis for the constitutive modelling of the aeolian sand, but also a reference for roadbed construction and other foundation engineering in desert areas.

In order to better simulated the anisotropy of granular materials, the anisotropic state variable was introduced into the micropolar hypoplastic constitutive model, and the simulation of biaxial compression tests were carried out. The influences of fabric on the width and inclination of the shear band were studied by the FEM and DEM. The following results were found. With the increase of anisotropic state variables, at the same vertical strain, the width and inclination of the shear band remained basically unchanged and the element rotation angle at the same position was increased.

The drained shear tests of aeolian sand in Tengger Desert were carried out by using the British GDS true triaxial apparatus, and the shear strength and stress-strain relationships of aeolian sand were studied under the conditions of constant average principal stress and different intermediate principal stress coefficients. The test results showed that the variation trends of principal strains in the three principal stress directions were correlated with the variation of the intermediate principal stress coefficient, and the stress-strain relationships in the three principal strain directions were hardening type. With the increase of intermediate principal stress coefficients, the shear strength of the specimen decreased, and the peak value of shear strength was the lowest when b = 0.8.