Dynamic shear modulus and damping ratio tests of Lanzhou loess under different depositional directions

Undisturbed loess is a special geotechnical material with anisotropy, and anisotropy has a greater impact on the stability of slopes, tunnels and underground space projects in loess areas. In order to study the variation rule of loess dynamic parameters under different depositional directions, this paper selects different station samples of Lanzhou Metro Line 1 as the research object, and carries out dynamic triaxial tests on loess samples with different sampling depths and different sampling angles (vertical and horizontal), and obtains the dynamic characteristic parameters of loess under different working conditions. The relationships between the dynamic strength, dynamic shear modulus and damping ratio of loess and the sampling direction and soil depth are analysed, and the results show that: The dynamic constitutive relationships of the Lanzhou loess during the elastic phase in different depositional directions are consistent with the Hardin-Dinevich hyperbolic model. At the same sampling depth, the dynamic strength of loess in the vertical direction is higher than that in the horizontal direction; the dynamic shear modulus ratios in descending order are as follows: Qilihe > Gongxingdun > Chenguanying > Yingmentan. And in the horizontal direction: the dynamic shear modulus ratios in descending order are as follows: Yingmentan > Chenguanying > Qilihe > Gongxingdun. Under the same depositional direction, the sampling depth has a greater effect on the G_d/G_dmax of loess, and the G_d/G_dmax curve shifts upward with the increase of the soil depth. The effect of the sampling depth on the damping is manifested in the fact that the deeper the soil layer is, the weaker the nonlinear characteristics of the soil are manifested, and the smaller the damping ratio is.