基于不完全拱效应的隧道预处理机制与计算方法

The pretreatment mechanism of tunnels and its calculation method based on the incomplete arch effect

隧道开挖中,掌子面–超前核心土的变形同样会使其周围产生拱效应,但该种拱效应不同于后方已开挖区域周围的拱效应,称之为不完全拱效应。不完全拱效应的发挥与预收敛变形和挤出变形有很大的关系,基于不完全拱效应提出了超前核心土周围围岩压力的计算公式,此公式与太沙基公式的不同在于考虑了预收敛变形对围岩压力的影响,并在黏性土的推导中考虑了非垂直滑移面效应,假定破裂面与垂直方向存在夹角θ。算例分析显示,随着预收敛变形的增加拱顶土压力的变化可分为近线性快速下降、缓慢下降及稳定阶段,计算土压力随内摩擦角、埋深比及黏聚力的增大而减小,且在黏性土中随破裂面倾角的增大而增大。在此基础上,推导了计算基于新意法的超前核心土加固参数的理论计算公式,结合算例验证了理论公式的适用性,该公式计算简单,便于理解,可用于新意法的初步设计阶段。

In the tunnel excavation,the deformation of the soil core in front of the surface of tunnel excavation may stimulate the arch effect in the surrounding soil ahead of the tunnel face. This kind of arch effect is different from the one produced behind the tunnel face and is called the incomplete arch effect. The performance of the incomplete arch effect is closely related to the pre-convergence deformation and extrusion. The formulas for calculating the soil pressure around the front soil core considering the incomplete arch effect are proposed and are different from Terzaghi formula,because in the proposed method,an angle between the fracture face and vertical direction is assumed and the effect of the pre-convergence deformation on the surrounding soil pressure and the non-vertical sliding surface effect of cohesive soils are taken into consideration. The results show that as the increase of the pre-convergence deformation,the earth pressure exhibits three stages：the rapid near-linear decrease,the slow decrease and the stable ones. The earth pressure decreases with the increase of internal friction angle,thickness-span ratio and cohesion. However,the earth pressure increases with the increase of the angle of rupture surface. The formula for calculating the reinforcement parameters of the front soil core based on ADECO-RS is deduced and its applicability is verified in a case study.