Study on Force Mechanisms of Support Systems Combined by Long and Short Piles in Soil-Rock Composite Strata

To demonstrate the interactive mechanical mechanisms between long and short piles in the long-short pile composite support system in the soil-rock composite stratum, according to the force analysis on long and short piles in the soil-rock stratum, the calculation methods for the forces and deformation of long and short piles were proposed respectively:When the rock layer under the soil layer was intact, the forces acting on short piles should meet the stability requirements of the foundation excavation in the soil layer, and the long piles were only used as a safety reserve. Therefore, the long and short piles in the soil layer could be simplified as elastically supported continuous beams. When there was a weak structural plane in the rock stratum, the long pile must meet the stability requirements of the foundation excavation in the rock stratum, and the lateral earth pressure of long piles was obtained according to the force requirements of sliders. Simultaneously, combined with the arrangement form of supports, the long pile was also simplified as the elastically supported continuous beam. Eventually, the calculation methods of long and short piles in two working conditions were given, and based on a real engineering project, the analytical solutions by the proposed methods were compared with numerical solutions by the finite element method to verified the correctness of the proposed. The results indicated that if the long-short pile support system in the soil-rock composite stratum was divided into two types of support system for foundation excavation in the soil layer and rock strata and the long and short piles were simplified into elastically supported continuous beams,the analytical solutions of the support system were basically consistent with the numerical calculation results, and the results were basically reasonable.