Research On Construction Effect Of Local Over-excavation Of Internal Support Foundation Pi

The internal support structure is a commonly used form of support in excavation engineering,especially for deep excavations.This structure uses support piles or diaphragm walls and supporting structures to jointly resist the internal force of the surrounding rock and ensure the stability of the excavation.In recent years,the use of internal support for deep excavations has been increasing,especially in urban built-up areas.However,due to limited construction space,complex surrounding environments,tight schedules,and other factors,partial over-excavation frequently occurs.The larger the length and depth of the partially excavated area,the more convenient it is for construction and the shorter the construction period.However,excessive partial over-excavation can cause structural deformation,instability,and other problems.Therefore,controlling the amount of partial over-excavation and its effects on construction is an urgent issue to be addressed.In actual engineering,partial over-excavation often occurs in internal support excavations.Studying partial over-excavation can effectively reduce engineering accidents and improve construction efficiency.This article takes the construction effects of partial over-excavation under an internal support system as the research basis and mainly studies the laws of the influence of partial overexcavation on the internal forces and deformations of the surrounding structures and soil in the excavation and the derivation of relevant theories.Considering the needs of actual engineering,based on engineering cases,the deformation and internal force monitoring data of the support system are summarized as safety evaluation indicators.The concept of quantifying the construction effects of partial over-excavation is proposed,and the feasibility of the method is verified through indoor model experiments,numerical model simulations,and actual engineering exercise system analysis.The main work and conclusions of this article are as follows:(1)Based on the Mindlin pure soil slope theory,virtual stress is applied to simulate partial excavation in the excavation.Then,using the Mindlin solution and the finite element method,combined with programming in MATLAB,the additional stress and deformation generated by the horizontal unloading near the partial over-excavation zone on the surrounding unexcavated soil are calculated.The deformation theory under partial over-excavation under the internal support structure is deduced,and the spatial distribution law of the internal force and deformation under the influence of construction effects in the partial over-excavation zone is analyzed.The effectiveness of the method is verified through calculation examples.(2)Through indoor model experiments of partial over-excavation under internal support excavations,the internal forces and deformations of the support system(including settlement of surrounding soil,displacement of the top of the support structure,the axial force of the support,soil pressure,and bending moment of the support structure)are studied under different partial over-excavation and external loading conditions.The characteristics of the support system under partial over-excavation conditions are further analyzed based on engineering cases.(3)By establishing a 3D model of the internal support excavation,the excavation process under different conditions of partial over-excavation length and depth is simulated.The evolution of the horizontal lateral deformation,bending moment,and axial force of the support structure during the construction process is studied and compared under different conditions of partial over-excavation.The construction effects and influence range of different partial overexcavation conditions on the internal forces and deformations of the excavation support structure are explored to determine the optimal range of partial excavation.