桩-岩界面粗糙度量化模型及其剪切机制研究

Roughness Quantization Model and Shear Mechanism of Pile-rock Interfaces

为考虑桩-岩界面粗糙度对其剪切强度的影响,提出一种能描述粗糙体起伏高度变化的量化模型。该模型在现有规则三角形粗糙体模型的基础上将岩体表面的粗糙起伏用不同高度的等腰三角形粗糙体进行量化,其优点在于能同时考虑各个局部粗糙体在界面总体剪切位移下所表现出来的剪胀与剪断2种机制。通过结合常法向刚度条件(CNS)下桩-岩界面的剪切特性,建立了局部粗糙体的剪切模型,并采用对所有局部粗糙体剪切响应求和的方法获取界面的整体剪切响应。基于局部粗糙体的剪胀-剪断两相机制和三角形粗糙体的几何特征推导了界面在剪切过程中处于两阶段粗糙体个数及剪切应力的演化方程;在此基础之上,根据位移控制条件将界面剪切过程划分为:剪胀、渐进破坏及剪断3个过程,并求解了各过程的剪切强度发挥函数,同时提出了完备的参数确定方法。最后,通过室内剪切试验对所提理论模型进行验证,结果表明:①各工况下试验曲线存在明显的3个剪切过程,验证了理论模型的合理性;②所提理论模型可较为精确地预测界面峰值剪切应力τu,预测误差在2%~10%之间;③理论模型高估残余应力τr误差在17%~25%之间的概率为50%,误差在17%~32%之间概率为81.25%;④峰值应力和残余应力与最大粗糙体高度hmax、初始法向应力σn0及法向刚度K成正比。

To consider the effect of the roughness of pile-rock interfaces on the shear strength,a quantitative model is being proposed to describe the variation in the asperity height.Based on the existing regular triangular asperity model,the roughness of pile-rock interfaces is quantified by the isosceles triangular asperities using different heights.The model has the advantage that it can simultaneously consider the different shear mechanisms(sliding dilatancy and residual shear)of each local asperity under the overall shear displacement.The shear model of the local asperity is established by combining the shear characteristics of the pile-rock interface under the condition of constant normal stiffness(CNS).The global shear response of the interface was obtained from the summation of the shear responses of all local asperities.Based on the dilatation-shear two-phase mechanism and the geometric of the local asperity,the evolution equations of the asperities number and shear stress in the two stages were derived.On this basis,the shearing process was divided into three stages according to the shear displacement:sliding dilatancy,progressive failure,and residual shear.The shear functions of the three shear stages were then solved and a complete method for determining the parameters was proposed.Finally,the theoretical model was verified by shear tests.The results show that:①There are three shear stages in the test curves under various conditions,which verifies the rationality of the theoretical model;②The theoretical model can accurately predict the peak shear stress,τu,with an error of a 2%-10%;③The theoretical model overestimates the residual stress,τr,by 17%-25%with a 50%probability,and 17%-32%with a 81.25%probability;and④The peak stress and residual stress are proportional to the maximum asperity height,hmax,the initial normal stress,σn0,and the normal stiffness,K.