Effect of shield tunneling construction on bearing capacity of foundation of existing buildings and stability analysis of reinforced soil

The current foundation reinforcement of existing buildings (structures) in shield tunneling construction depends on experience and lacks perfect theory as support. To better this situation, this paper studies the influence mechanism of bearing capacity of existing buildings (structures) in shield tunneling and after leaving and the stability of soil after reinforcement. In order to understand the shear state of cement-soil reinforcement, the triaxial test of cement-soil is carried out. The results show that before the deviating stress reaches the yield point, the relationship of (σ₁-σ₃)-ε₁ is approximately linear and the strain is very small, and the shear strength of the reinforcement is far from that of the unreinforced soil. In stability analysis, the displacement of the reinforcement body and the share of shear force of the unreinforced soil outside the reinforcement body are not taken into account. In shield tunneling, the squeezing of the surrounding soil to produce shear stress diffuses to the pile side to form additional positive friction resistance, and thus increases the bearing capacity of the pile. After the shield tunneling leaves, the soil unloads, the negative friction resistance occurs at the pile side, and the bearing capacity of the pile decreases. In shield tunneling construction, the upper part of reinforcement body is subjected to passive or active earth pressure, the outer part and the lower part are subjected to static earth pressure, the difference of earth pressure produces shear stress, the potential sliding interface produces tension and compression stress, and the formula of safety factor of composite sliding surface of soil after reinforcement is derived. The strength of reinforcement body and the stability of soil after reinforcement are checked through engineering examples.