Study On The Load Transfer Mechanism Induced By The Failure Of Anchors In Excavations Retained By Pile-anchor Structure

As a common excavation retaining structure method,pile-anchor structure is widely used in geotechnical engineering because of the advantages of internal force and deformation control.However,collapse accidents of excavation are often caused by anchors failure.The numerical simulation method and model tests on partial failure of retaining structure caused by the breakage of anchors are adopted in this study.And,the load transfer mechanism induced by partial anchors failure is researched.The principal results are as follows:The model tests of pile anchor excavation are carried out,and the influence of excavation depth on load transfer coefficient is studied.Meanwhile,the results of experimental and numerical results are qualitatively compared.The load transfer coefficient induced by anchors failure is preliminarily obtained in pile-anchor excavation.The increase ratio of pile bending moment and anchor axial force caused by the failure of anchors,are defined as load transfer coefficients I_m and I_t,which raise with the increase of the excavation depth.The Fast Lagrangian Analysis of Continua(FLAC)method is used to establish the pile-anchor excavation model which is retained by single row anchor,and the partial failure of the pile-anchor excavation was simulated.When partial failure occurred in anchors,the influence of consequent soil pressure redistribution on the internal forces of the retaining structure is studied.The research reveals the load transfer mechanism induced by single row anchor failure.Also,according to the change trend of the pile bending moment,the damage influence zone is divided into the core failure zone and the edge failure zone.In the sand,both the load transfer coefficients of pile and the load transfer coefficients of anchor raise with the increase of the excavation depth,and the growth of I_m is more fast than that of I_t.The failure of anchors is easier to result in the damage of the retaining piles when the excavation depth is larger.The load transfer coefficient of members decrease with the increase of soil strength,which is different with that in cantilever retaining system.The numerical analysis model of pile-anchor excavation retained by double row anchors is established,and the internal force change of pile and anchor is given during of bolt failure stage.The groth of the load transfer coefficient of anchor in vertical direction is more obvious than that in horizontal direction when the anchors failure occur.Both the change law of capping beam internal force and pile head shear force is analyzed,and the reason for the increase of pile bending moment is obtained.In addition,the most vulnerable location is at the shared node of the anchor and the breast beam when anchors failure occurs.