ABSTRACT
For a loess-mudstone interlayer tunnel project, a dry mixed cement gravel pile was innovatively used to strengthen the mudstone foundation of the tunnel, which reduces the adverse effects of softening mudstone. In this paper, the mechanical mechanism of this method is studied by the finite element method, which is used to simulate the different conditions respectively. The construction conditions with different degrees of softening of mudstone and the reinforcement conditions of tunnel elevation piles are established. The mechanism and force characteristics of the interaction between dry mixed cement gravel piles and tunnel surrounding rock under softening conditions were investigated. Using the field measurement results for comparison, it was observed that under the condition of mudstone softening without reinforcement pile, the overall increase of bending moment of the tunnel substructure and the deformation of the tunnel structure are obvious. The value of the axial force of the reinforcement pile is greatly related to the location of pile placement, the pile near the foot of the arch is the main load bearing pile, and the pile near the center of the elevated arch is almost not load-bearing, which can optimize the design here. Numerical simulation results and monitoring data show that dry mixed cement gravel pile has a good reinforcement effect on the tunnel mudstone foundation.
