Auxiliary pile group closed to foundation pit can improve the stiffness of soil mass and decrease foundation pit’s transformation effectively to guarantee foundation pit’s stability. Drucker-Prager model is used and matched with Mohr-Coulomb model’s circumcircle, which can solve the problems of uncertain viscoplasticity strain rate and discontinuous in cones vertex, compared with Mohr-Coulomb model. Also, numerical simulation software FLAC3D is applied to help analyze foundation pit’s horizontal displacement caused by auxiliary pile group, and sensitivity analysis is done about pile spacing and stiffness. The calculation results compared with monitoring data show that Drucker-Prager model is appropriate to simulate foundation pit. Stiffness of soil mass can be improved obviously by auxiliary pile group. Auxiliary pile group of CFG mainly reduce foundation pit’s upper horizontal displacement while bored piles mainly cut down deep layer’s horizontal displacement of soil mass. The results can provide references to both design and management of foundation pit.

The relationship between the peak strength of rock masses and joint inclination angle is closely, to study its relationship, experiment on pre-existing persistent jointed rock cylindrical standard specimens was made under uniaxial compression by high stiffness servo control testing machine, experiment found that: the residual peak intensity and peak strength are increased with the decrease of jointed and nonlinear. Analysis on the peak intensity changing with the fissure inclination using Kulun strength theory, theory analysis conclusion is consistent with the experiment, prove the conclusions of experiments and theoretical analysis all can reflect the law of rock masses with transfixion joint failure strength well.

Xiaohegou tunnel is an under construction shallow expansive loess tunnel with Large Pipe Roof Support. Large Pipe Roof Support construction and excavation of the tunnel was simulated by the Fast Lagrangian finite difference software Flac3D. The pipe roof loading states and the deformation of surrounding rock in front of the tunnel face was obtained in each step of excavation, and the results was compared with a simulation without Large Pipe Roof Support. The results show that the reinforcement effect of Pipe Roof was to restrain the plastic flow of soft soil, and Pipe Roof help to share soil pressure, which could decrease the tunnel deformation effectively.