To reveal the influence of water content on the strength characteristics and brittle-plastic failure process of Xiashu loess, the direct shear test and unconfined compressive strength test of Xiashu loess with different water content were carried out, and the influence of water content on its strength characteristics and brittle-plastic failure transformation characteristics was studied. Eight kinds of Xiashu loess with different moisture contents were designed, and a direct shear test and uniaxial compression test were carried out, respectively. The results show that with the increase in water content, the shear strength and unconfined compressive strength of Xiashu loess decrease continuously. The influence of water content on cohesion in the shear strength index is greater than that of the internal friction angle. The relationship curve between cohesion and internal friction angle and water content shows obvious segmentation. When approaching the optimal water content, the downward trend is slowed down. When the water content is constant, the shear strength of the sample will also increase with the increase of normal stress. When the water content is 12% to 15%, the failure mode of Xiashu loess is a brittle failure, and the unconfined compressive strength decreases by 43.23%. When the water content is 15% to 16%, the failure mode of Xiashu loess is a transitional failure, and the unconfined compressive strength decreases by 60.38%. When the water content is greater than 16%, Xiashu loess shows plastic failure, and the unconfined compressive strength decreases slightly.

To reveal the influence of cementation degree on the mechanical properties of bimrocks with different particle sizes under different types and contents of cement, indoor direct shear tests as well as numerical tests were conducted. The variation law of mechanical properties and the development law of internal force chain distribution of bimrocks under different conditions are fully studied. The specimens with three particle sizes, two cementing types (cement and gypsum), and three cementing contents were prepared for indoor shear tests under different normal stresses. The results show that the fluctuation of shear stress-displacement curve of bimrocks with round gravels of large particle size is relatively gentle, and the fluctuation of residual strength is relatively small. Under low normal stress, the peak shear strength of bimrocks with round gravels of large particle size can be increased by 115.2% under the action of cementation. Compared with the cohesion of samples without cementation, the maximum improvement of the cohesion of the samples containing large particle size, small particle size, and mixed particle size with different cementing materials is 143.2%, 149.0%, and 141.9%, respectively. The results show that, compared with the internal friction angle of samples without cementation, the maximum increases of the internal friction angle of the samples with large particle size, small particle size, and mixed particle size for adding different contents of cementing materials are 15.7%, 18.5%, and 21.2%, respectively. Numerical tests show that, with the increase of cementation degree, the gathering of force chain is more obvious and more concentrated near the shear surface.

No abstract