# Study on Filling Material Strength and Dam Failure Characteristics of Loess Dam
## 3 Results
### Indoor Triaxial Tests
When a sample has a water content of 10%, the dry density values of 1.4 g/cm\({}^{3}\) and 1.5 g/cm\({}^{3}\) are strain hardened under different confining pressure conditions; when the sample with a dry density of 1.6 g/cm3 was shear under a confining pressure of 50 kPa, the deviator stress remained almost unchanged with the increase in axial strain, showing an approximate ideal plastic failure characteristic. Samples with a dry density of 1.7 g/cm\({}^{3}\) showed different degrees of strain softening under different confining pressures. During the formation of loess, the combination and arrangement of the spatial stacking of scattered particles directly affect the strength and deformation characteristics of the soil. Under a low confining pressure, the confining pressure will compress the pores between the soil particles but does not change the contact mode between the skeleton elements, and the microstructure does not change significantly, so the shear strength is low. When the confining pressure gradually increases, the pores between the soil particles are compressed, and the pores of the supports formed by lapping between the coarse particles are destroyed by external forces, forming a more stable skeleton structure. Therefore, the threshold of resistance to external forces is higher, and the shear strength index also rises. In the triaxial shearing process, changes in the contact mode between the particles and the mutual position of the particles, as well as the secondary structure formation process of re-engagement between the particles, occur. Then, the process from unstable to stable to unstable occurs, followed by the destruction of the dam. It can be seen from Figure 6a that the peak strength increases significantly with the increase in dry density. At a low confining pressure, samples with a dry density of 1.7 g/cm\({}^{3}\) showed strong strain softening, while other dry densities all showed strain hardening under high and low confining pressure conditions, and when confining pressure remained unchanged, the strain-hardening degree gradually weakened with the increase in dry density (Figure 6b). The arrangement of the skeleton element parts is tighter as the dry density is increased, the inter-particle bite force and the joint force are increased, and the number of overhead pores is reduced compared with the low density. The shape variable caused by the pores during the shearing process is small, and deformation is mainly caused by the damage that occurs after the particles contact with each other, so the strength is increased. It can be seen from Figure 7 that the stress-strain curve changes significantly with the moisture content, and the peak stress of the sample decreases with the increase in the moisture content. When the dry density values were 1.4 g/cm\({}^{3}\) and 1.5 g/cm\({}^{3}\), the change in moisture content did not significantly change the failure type of the sample. When the dry density of the sample increases to 1.6 g/cm\({}^{3}\) and 1.7 g/cm\({}^{3}\), the sample changes from brittle failure to plastic failure as the water content increases, and the strain-softening type changes to the strain-hardening type. When the moisture content increases, water fills the intergranular pores in the loess framework, dissolves intergranular suffusion, thickens the water film on the surface of soil particles, decreases the intergranular bonding force and the occlusal friction force, and decreases the strength. Figures 8-11 shows the change rule of shear strength index and moisture content and dry density. The relationship curve between the shear strength index and moisture content and dry density is drawn by using cohesion and the internal friction angle as vertical coordinates and dry density and moisture content as horizontal coordinates, respectively. Scholars divided the cohesion into two parts: original cohesion and solidified cohesion ([PERSON] 2013). The original cohesive force comes from the electrostatic force and van der Waals force between particles.