非连续边界荷载影响下隧道围岩压力计算方法

浅埋隧道施工中经常面临堆载、孤石等工况，为了确定其形成的非连续边界荷载对围岩压力取值的影响，以隧道上覆岩体破坏迹线建立压力模型，将堆载、孤石按照作用范围、位置等效为均布或者集中边界荷载，以其随岩体深度变化及偏压情况为条件，按照太沙基理论建立轴对称边界荷载影响下围岩压力微分方程，以非连续边界荷载和为条件求解方程，将求解的压力值与附加弯矩在半无限空间体中产生的应力组合，形成非连续偏压边界荷载影响下围岩压力计算方法。通过与拉林铁路隧道群围岩压力监测值的对比，验证模型的可行性。得到以下结论： 1）非连续边界荷载在岩体分布的有效长度可作为围岩压力计算方法的选取依据。2）在非连续边界荷载影响下，围岩压力取值与隧道衬砌不同位置的角度呈线性关联。3）将孤石等效为集中或者均布边界荷载，2种围岩压力计算值存在一定的偏差，压力差值与隧道埋深有关；当埋深小于7 m时，将孤石作为非连续均布荷载的围岩压力计算值与监测值相近； 当埋深大于8 m时，将孤石作为非连续集中荷载的围岩压力计算值与监测值较为接近。

Calculation Method of Surrounding Rock Pressure of a Tunnel under Noncontinuous Load Effect

Discontinuous boundary loads formed under various working conditions, such as surcharge loads and boulders, during shallow buried tunnel construction might affect the surrounding rock pressure. The rock mass between the slip oblique line and excavation tracking line can be considered as the calculation model of surrounding rock pressure according to the slippage characteristic in the surrounding rock failure of the shallow buried tunnel. Surcharge loads and boulders are equivalent to uniformly distributed or concentrated load according to the action range and position. These loads are divided into two working conditions according to the depth variation and bias of the surrounding rock. The differential equation of confining pressure under axisymmetric condition is established in accordance with the Terzaghi confining pressure theory. Given that the sum of discontinuous boundaries is constant, the equation for ordinary solution to surrounding rock pressure is established and combined with the surrounding rock pressure generated by additional bending moment in the semi infinite half space to calculate the surrounding rock pressure under the influence of discontinuous eccentric load. The conclusions are drawn based on the theoretical and monitoring values of the surrounding rock pressure of a tunnel group of the Lhasa Nyingchi railway line. (1) The effective length of the noncontinuous load in the surrounding rock can be used as the basis for calculating the surrounding rock pressure. (2) Surrounding rock pressure is related to the angle of the tunnel lining, which is linearly dependent on the difference position of the surrounding rock. (3) A certain deviation that is related to the buried depth of the tunnel can be found on the premise of equalizing boulder to models of concentrated or uniformly distributed load according to the comparison. The uniformly distributed load is close to the actual monitoring value when buried depth <7 m, and the concentrated load is close to the actual monitoring value when buried depth > 8 m.