考虑黄土结构性的浅埋隧道松动压力极限分析

Analysis on Limit of Loosening Pressure on Shallow Tunnel Considering Structure Characteristics of Loess

隧道围岩松动压力值是隧道设计计算的重要参数之一,而黄土区浅埋隧道的围岩松动压力计算必须考虑黄土强度的结构性特点。首先针对现有描述强度参数和结构性参数的方法存在的问题,引入结构性发挥度的概念,对黄土强度描述方法进行了改进。根据黄土区浅埋隧道的工程特点,构建出浅埋黄土隧道的破坏模式。在此基础上,引入考虑黄土结构性发挥度的强度,基于改进的摩尔-库伦准则和极限分析上限法,导出了浅埋黄土隧道上覆松动围岩压力计算公式,并通过Matlab算法求得了最优上限解。将计算值与现场试验值进行了对比。分析了相关参数对隧道松动支护压力和破坏模式的影响规律。黄土在不同含水量和围压下的应力应变关系表明:黄土的抗剪强度指标黏聚力和结构性发挥度之间近似呈线性关系,而内摩擦角基本不随结构性发挥度的变化而变化。对比分析结果表明:浅埋隧道围岩松动压力受黄土的结构性发挥度影响明显,其随结构性发挥度的增大而减小;该值随着隧道埋深和围岩重度的增加而线性增长,但随着侧压力系数的增加,松动围岩压力呈非线性减小的趋势,且减小趋势先快后慢,这说明前期侧压力系数的变化对支护压力影响更大;计算值与实测值吻合良好,验证了该方法的可行性。

The loose pressure value of tunnel surrounding rock is one of the important parameters for tunnel design and calculation,and the structural characteristics of loess strength must be considered in the calculation of the surrounding rock loosening pressure on shallow tunnel in loess area.First,in view of the problems existing in the existing methods of describing strength parameters and structural parameters,the concept of structural extent is introduced to improve the description method of loess strength.According to the engineering characteristics of shallow loess tunnel in loess area,the failure mode of shallow loess tunnel is constructed.On this basis,by introducing the strength considering the loess structural extent,based on the improved Mohr-Coulomb criterion and the upper bound method of limit analysis,the calculation formula of the overburden loosening surrounding rock pressure on shallow loess tunnel is derived,the optimal upper bound solution is obtained through Matlab algorithm.The calculated values are compared with the field test result.The influence rules of related parameters on the tunnel loosening support pressure and failure mode are analyzed.The stress-strain relationship of loess with different water contents and confining pressures shows that there is an approximate linear relationship between the cohesion of shear strength and the structural extent of loess,while the internal friction angle does not change with the change of structural extent.The comparative analysis result shows that(1)the surrounding rock loosening pressure of shallow tunnel is obviously affected by the structural extent of loess,and it decreases with the increase of structural extent;(2)this value increases linearly with the increase of tunnel buried depth and surrounding rock weight,but with the increase of lateral pressure coefficient,the pressure of loosening surrounding rock shows a nonlinear decreasing trend,and the decreasing trend is first fast and then slow,indicating that the change of lateral pressure coefficient in the early stage has a greater influence on the support pressure;(3)the calculated values are in good agreement with the measured values,which verified the feasibility of the method.