剪切速率对黄土力学性质及邓肯 张参数的影响

为探究加载速率对原状黄土强度和变形特性及其邓肯-张模型参数的影响，采用SLB-1型三轴剪切渗透试验仪，开展原状黄土在不同围压和剪切速率下的不固结不排水三轴剪切试验，并通过微观试验验证其宏观力学性质。结果表明：在试验参数设定范围内，剪切速率对原状黄土的力学性能有显著影响，不同剪切速率下原状黄土的偏应力－应变关系基本符合双曲线关系；初始变形模量随围压的增大而增大，随剪切速率的增大呈现先增大后减小的规律，原状黄土的黏聚力c、无因次基数K、应力破坏比Rf和破坏强度与剪切速率之间存在明显的临界剪切速率转折点1.7 mm?min-1，此时各参数均达到最大值，无因次指数n无明显规律可循；当剪切速率小于此临界值时，黏聚力c、无因次基数K、应力破坏比Rf和破坏强度随着剪切速率的增大而增大，当超过剪切速率临界值时又有一定程度的降低，总体上呈现先增大后减小的规律，而内摩擦角随着剪切速率的增大而逐渐增大且增大幅度甚微；试样的偏应力－应变曲线无明显的峰值点，呈应变硬化型；通过拟合曲线，得到了原状黄土试样的抗剪强度指标和破坏强度与不同剪切速率之间的拟合公式，以期更好地研究剪切速率的变化对西宁原状黄土力学性能的影响。

Effect of Shear Rate on Mechanical Properties of Loess and Duncan-Chang Parameters

In order to explore the influence of loading rate on the strength and deformation characteristics of undisturbed loess and the parameters of Duncan-Chang model, the SLB-1 triaxial shear permeability tester was used to carry out the unconsolidated and undrained triaxial shear test of undisturbed loess under different confining pressures and shear rates, and verify its macroscopic mechanical properties through microscopic tests. The results show that within the setting range of the test parameters, the shear rate has a significant effect on the mechanical properties of the undisturbed loess. The deviator stress-strain relationship of the undisturbed loess under different shear rate basically conforms to the hyperbolic relationship, and the initial deformation modulus increases with the increase of confining pressure, and with the increase of shear rate, it increases first and then decreases; There is an obvious critical shear rate turning point of 1.7 mm?min-1 between the cohesive force c, dimensionless base number K, stress failure ratio Rf and failure strength. At this time, each parameter reaches the maximum value, and the dimensionless index n is no obvious rule to follow; When the shear rate is less than this critical value, the cohesion force c, the dimensionless base K, the stress-to-failure ratio Rf, and the fracture strength increase with the increases of the shear rate and decrease to a certain extent when the shear rate exceeds the critical value, and generally appear to increase first and then decrease, the internal friction angle gradually increases with the increase of the shear rate ,but the increase amplitude is little; The deviator stress-strain curve of the sample shows a strain hardening type without obvious peak point; By fitting the curve, the fitting formula between the shear strength index and the failure strength of the unmodified loess sample and the different shear rate was obtained so as to better study the influence of the changes of shear rate on the mechanical properties of Xining undisturbed loess.