Study On Deformation Controlling Of Existing Composite Foundation Under Lateral Excavation

Composite Foundation (especially the CFG composite foundation) is widely used in the actual projects as a foundation treatment approach.Since foundation pit engineering is gradually processed in the city center strip, the composite foundation under existing buildings will be affected by lateral excavation in a passive state. At this moment vertical load and soil lateral couples to form a P-Δ effect, increasing additional deformation and internal force of the pile. But at the design stage, the composite foundation is just to meet the vertical bearing role, not taking security problems into account which are caused by the effect of lateral soil movement.In this paper, the finite difference software FLAC3D is used to establish numerical models including foundation pit and existing composite foundation. The lateral deformation and internal force distribution of CFG composite foundation under four typical deformation modes of supporting structure is discussed and the unfavorable position is judged.Then make parameter sensitivity analysis aiming at the complex deformation mode and propose control methods.The simulation results show that under the effects of different deformation modes of supporting structure with the same maximum deformation, the lateral deformation of existing composite foundation is less than the deformation of supporting structure.It decreases with increasing distance from the foundation pit, but the deformation mode is different.Through the analysis of deformation combined with internal force, the CFG pile which is closest to the foundation pit is in the most unfavorable position under each mode of deformation.And vertical loads increases the deformation and internal force of pile, which threat the security of the pile. In the four deformation modes, skirting deformation mode is the greatest threat to the security of composite foundation, followed by the convex deformation mode.Under the situation of composite deformation mode, length of pile puts greatest effect on lateral deformation of CFG pile, followed by the pile spacing, addition is the modulus of elasticity, with the minimal impact of pile diameter. Different from the pile spacing, the increase of the value of the remaining three parameters within a certain range is conducive to reducing the pile deformation.Finally, propose the control measures of lateral deformation of existing composite foundation under lateral excavation, such as avoiding the appearance of skirting deformation mode of supporting structure, improving the supporting structure stiffness, which has some great significance to the actual project.