顺层深路堑边坡滑带土强度特性和基底预留厚度预警分析

Strength characteristics of the sliding zone soil of bedding deep cutting slopes and early warning analysis of the reserved thickness of the base

含软弱夹层的顺层深路堑边坡在边坡工程中普遍存在,滑带土强度和基底预留厚度(开挖边坡基底到软弱夹层的距离)是影响其稳定性的2个关键性因素。以杨宣(杨柳-宣城)高速K42路堑边坡为例,分析了边坡变形演化过程和基底隆起变形特征,通过适合研究大剪切位移下土体抗剪强度的环剪试验揭示了边坡深部滑带土的特性,应用滑带土的饱和残余强度参数进行了边坡开挖基底预留厚度分析。结果表明:K42滑带土有明显的应变软化特性,且法向应力越小滑带土应变软化特性表现越明显;由峰值抗剪强度到残余抗剪强度,黏聚力和内摩擦角均表现出衰减效应,且黏聚力衰减程度大于内摩擦角;滑带土残余抗剪强度参数中的残余黏聚力随剪切速率的变化很小,而残余内摩擦角和剪切速率呈对数函数φ=0.1303ln v+7.3197关系变化,当剪切速率<2 mm/min时,滑带土残余抗剪强度参数对剪切速率较为敏感,反之敏感性较差;最后,依据边坡不同临界状态的回归方程h_(1)、h_(2)、h_(3)将不同坡率下的基底预留厚度分成A(失稳)、B(欠稳定)、C(基本稳定)以及D(稳定)4个区,并且在此基础上建立了基底预留厚度判据和边坡开挖基底预留厚度预警模型。

[Objective]Bedding deep cutting slopes containing weak interlayers are commonly found in slope engineering,whose stability is influenced by two key factors:The strength of the sliding zone soil and the reserved thickness of the base(the distance from the base of an excavated slope to the weak interlayer).[Methods]In this research,taking the K42 cutting slope of the Yang-Xuan Expressway as an example,the evolution process of slope deformation was analyzed,especially the characteristics of basal heave deformation.The properties of the deep sliding zone soil in the slope were revealed by ring shear tests,which are suitable for studying the shear strength of soil that has experienced large shear displacements.Moreover,the residual strength parameters of the saturated sliding zone soil were applied to analyze the reserved thickness of the base.[Results]The results show that sliding zone soils exhibit obvious strain softening characteristics,which become more evident as the normal stress decreases.As the soil shear strength transitions from peak strength to residual strength,both the cohesion force and internal friction angle decrease,with the cohesion force decreasing to a greater extent than the internal friction angle.The residual cohesion force of sliding zone soil varies slightly with the shear rate,while the relationship between the residual internal friction angle and shear rate varies as a logarithmic function.When the shear rate is less than 2 mm/min,the residual shear strength parameter of sliding zone soil is more sensitive to the shear rate and vice versa.[Conclusion]Furthermore,according to the regression equations of the critical states of slope stability,the reserved thickness of the base under different slope rates was divided into four zones:A(extremely unstable zone),B(unstable zone),C(basically stable zone)and D(stable zone),and based on this,the criterion and early warning model of the reserved thickness of the base for slope excavation were established.