Abstract:

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.