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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 face-advance core soil will also cause the arching around it. However, this kind of arch effect is different from the arch effect around the rear excavated area, which is called incomplete arch effect. The incomplete arch effect plays an important role in pre-convergence deformation and extrusion deformation. Based on the incomplete arch effect, the calculation formula of surrounding rock pressure around core soil is proposed. The difference between this formula and the terbutaline formula is that The influence of pre-convergence deformation on the pressure of surrounding rock is considered, and the effect of non-vertical slip surface is taken into account in the derivation of cohesive soils. It is assumed that the angle between rupture surface and vertical direction is θ. The case study shows that with the increase of pre-convergence deformation, the change of vault earth pressure can be divided into rapid decline, slow decline and steady stage of near linearity. The calculation of earth pressure increases with the increase of internal friction angle, buried depth ratio and cohesion But decreases with the increase of dip angle of fracture surface in clay. On this basis, the theoretical calculation formulas for calculating the advanced core soil consolidation parameters based on the new law are deduced, and the applicability of the theoretical formula is verified by an example. The formula is simple and easy to understand and can be used in the preliminary design stage of the new law.