The Influnence Of Tunneling On Adjacent Rigid-flexible Piles

The tunnel construction would easily cause foundation’s additional deformation and stress relaxation, which cause additional displacements and inner forces of piles near tunnel. As a result, buildings’tilt settlement and collapse are caused by piles’bearing capacity, which is significantly reduced by the pile’s additional inner force and displacement. Therefore, it has an important theoretical and practical significance to do research on the effect of tunnel construction on existing piles as well as effectively reduce these adverse effects. Firstly, the existing domestic and international related research are investigated, the laws of foundation’s deformation and the mechanical characteristics of piles at three different zones are elaborated in the process of tunnelling. Then, in order to study the influence of adjacent rigid-flexible piles in the third zone during the course of tunnelling, a numerical method that considers different combined loads at pile’top is adopted. The stiffness ratio of pile and soil that is obtained by the ratio of pile and soil’s elastic modulus, pile’s radius and length. Then the stiffness ratio is used as the computational scheme in the method.At first, the uniform finite element model proved by the Loganathan’s example and the elastic constitutive relation are used in the numerical analysis. Some conclusions are obtained from the rules of rigid-flexible piles at vertical loading during the course of tunnelling. The zone of tunneling influence is mainly concentrated in the tunnel face at1time tunnel’s diameter of front-back the pile during the course of tunnelling. With a constant length for a pile at this zone, the additional inner force increases with the stiffness ratio while the additional displacement decreases. At the same time, the laws of additional inner force and displacement are researched at different pile’s section when tunnel face just goes through the pile. With a small stiffness ratio of pile and soil (Kp=0.177), the axial force of pile which has vertical loading has a different characters with other piles. The additional axial force decreases with depth then increases in a small stiffness ratio and soil of pile; while other piles’additional axial increase with depth then decrease, then have a maximum value adjacent to tunnel axis. Secondly, an elastic-plastic constitutive relation and D-P yield criterion are used in a multi-storey finite element model. The rules of piles’additional inner force and displacement are analysed when the piles have horizontal loading and combined loadings during the course of tunnelling. The horizontal loadings have a directional effect to pile’s inner force and displacement during the course of tunneling. The loading at the pile’s top mainly affects the related inner force and displacement that have the same direction with the loading. Meanwhile the loading barely affects the other inner force and displacement. With the comparison of horizontal displacement of pile during the course of tunnelling, the displacement of the pile at combined horizontal and vertical loadings is smaller than the pile only at horizontal loading.Finally, based on the result of analysis, the practical technology that reduces the tunnel’s influence is researched. According to the geological conditions during the course of tunnelling, different protective measures and reinforcement methods should be adopted for different rigid-flexible piles. Some conclusions can be obtained from the partition wall numerical analysis. The adjacent pile of tunnel can be effectively protected by the technology of partition wall, which can effectively reduce the pile’s settlement and reduces pile’s additional inner force.