Investigation On The Strain Rate Effects On The Shear Strength Of Saturated And Unsaturated Loess

Given the complexity and diversity of soil instability,research attention has been directed towards investigating the time-dependent damage behavior of soils,particularly the strain rate effect on soil shear strength.This study employs a combination of triaxial mechanical tests and intrinsic relationships for unsaturated soils to:(i)examine the deformation characteristics and shear strength differences of unsaturated soils under varying strain rates through triaxial consolidation and drainage(CU)and consolidation and undrainage(CD)tests for unsaturated remodeled loess;and(ii)scrutinize the impact of strain rate on pore water pressure and peak strength of saturated remodeled loess using CU tests for saturated remodeled loess with the same test parameters.The research also investigates the effect of strain rate on the pore water pressure and peak strength of saturated and unsaturated remodeled loess by conducting a CU test of saturated remodeled loess with the same test parameters thereby comparing the mechanism of strain rate on saturated and unsaturated remodeled loess.The findings obtained are summarized as follows:(1)Within the range of strain rate from 0.005mm/min to 0.011mm/min and a dry density of 1.7g/cm~3,the shear stress-axial strain curve of non-saturated remolded clay CD in a shear test exhibits a strain-softening behavior.In the strain rate range of0.03mm/min to 0.3mm/min and a dry density of 1.7g/cm~3,the shear stress-axial strain curve of non-saturated remolded clay CU also shows a strain-softening behavior,but the same dry density saturated remolded clay CU in a shear test displays a strain-hardening behavior.(2)The drainage strength of unsaturated remodeled loess decreases with an increase in strain rate.Additionally,the specimens demonstrate shear shrinkage before experiencing shear expansion during drainage shear at varying strain rates.The maximum shear shrinkage reduces as the strain rate increases,with the shear drainage following a similar trend to the change of peak strength with strain rate.When subjected to the same surrounding pressure,the total cohesion and effective internal friction angle of unsaturated remodeled loess similarly decrease with increasing loaded strain rate.(3)During undrained shear of unsaturated remodeled loess,the peak strength decreases with an increase in strain rate.Notably,the strain rate effect of peak strength reduces at high envelope pressure.The maximum shear shrinkage and its corresponding axial strain similarly decrease as the strain rate increases.Moreover,the pore water pressure during undrained shear increases with an increase in strain rate,whereas the total cohesion of unsaturated remodeled loess decreases concomitantly.Surprisingly,the effective internal friction angle increases as the strain rate increases.(4)The super-pore water pressure of both saturated and unsaturated remodeled loess without drainage damage is positive.With an increase in strain rate,the super-pore water pressure resulting from shearing saturated remodeled loess increases,while its peak strength reduces.The decrease in shear strength of compacted saturated remodeled loess with a dry density of 1.7g/cm~3 is mainly due to the decline in effective stress caused by the increase in pore water pressure.(5)The effect of strain rate on the tangential deformation modulus parameter of the Duncan-Zhang model is pronounced.The initial deformation modulus of both saturated and unsaturated remodeled loess decreases with an increase in strain rate while relying on the peak strength.When determining parameters in the nonlinear elastic intrinsic model based on triaxial test results,the impact of strain rate must be considered.