Study On Bearing Characteristics Of Dentate Row Bamboo Pile-composite Soil Nailing System

With the rapid development of my country's economy and the acceleration of urbanization,a large number of shallow foundation pit projects have appeared in soft soil areas.Due to the shallow excavation depth of the shallow foundation pit and weak support awareness,it is easy to cause engineering accidents.The conventional pile-supporting structure has the limitation that the pile spacing is limited by the instability of the soil slip between the piles,the safety factor is relatively low,the stability of the foundation pit is poor,and the support deformation of the soil nail wall is difficult to effectively control,the support depth is limited,etc.problem.At the same time,the traditional construction materials have the problems of waste of resources and environmental pollution,especially in the temporary soft soil shallow foundation pit support.Phyllostachys pubescens is a green,environmentally friendly,renewable and easily degradable building material with relatively short-term strength.Under this background,this paper selects bamboo pipe as the main material of the supporting system.In order to study the working mechanism,stress state and deformation characteristics of the bamboo pile-anchor system in the foundation pit supporting project,two sets of indoor model tests and Corresponding numerical simulation,based on the conventional single-row pile-soil nail composite support,a toothed bamboo pile-soil nail composite support system is proposed.The main work and results are as follows:?1?Through the scaled physical model test,the process of excavation and step-by-step loading of the foundation pit under the single-row bamboo pile and soil nail composite support system was simulated.The stress state and deformation process of a single row of bamboo piles and soil nails in each stage are revealed.The study found that the deformation of the pile body is similar to that of the cantilever beam under bending.The bending moment transition point is close to the excavation surface,and gradually decreases with the increase of the excavation depth.The axial force of soil nails is distributed in the form of "large in the middle and small on both sides".The maximum axial force appears in the middle area of the soil nails.The change of the axial force of soil nails is proportional to the excavation depth and loading.The surface settlement in the excavation phase is small,and the settlement value in the loading phase gradually increases with the increase of the load.The maximum settlement value is 1.35 mm,and it is within a reasonable settlement interval.?2?Through the scaled physical model test,the process of excavation and step loading of the foundation pit under the action of the toothed bamboo pile-soil nail composite support system was simulated.In comparison with the test results of the composite support model of single-row piles,the stress and deformation characteristics of the bamboo pile support system with tooth arrangement are analyzed.The study found that above the bottom of the foundation pit,the earth pressure behind the pile decreases first and then stabilizes with the increase of the excavation depth;below the bottom of the foundation pit,the fluctuation of the earth pressure is small,and the earth pressure after the pile during the loading stage increases and The overall change range is smaller than the single-row pile composite support system.The displacement of the pile top in the area of the pile is greater than the displacement of the pile body on both sides.The maximum settlement of the composite support system of the toothed bamboo pile is 0.87mm.It is concluded that the new pile type composite support design has a greater impact on the horizontal displacement of the pile top and the settlement of the foundation pit.The binding ability is relatively strong.In the toothed bamboo pile support system,the macro deformation of the pile body is small,the compression and bending distribution is even,and the bending moment value is much smaller than the maximum bending moment of the single row pile,which can resist more lateral loads.The placement of soil nails has a certain inhibitory effect on settlement and surface displacement,improves the distribution of stress field in the soil,and improves the overall strength of the foundation pit.In general,the soil nail anchoring effect in the new pile support system is better,and the foundation pit Strong stability.?3?Through FLAC^3D numerical simulation,comparative analysis of the deformation law and bearing characteristics of the two supporting systems under ideal conditions.The study found that the simulation results are consistent with the model test results and regular characteristics.The toothed bamboo pile-soil nail composite supporting system greatly improves the bearing capacity of the supporting structure,and has good restraining ability to control foundation pit settlement,pile top displacement and horizontal movement of surface layer.At the same time,the mutual synergy between the pile and the soil nails improves the distribution of the stress field in the soil,improves the support capacity of the support structure and the stability of the foundation pit,which strongly illustrates that the new support system is shallow in soft soil.The feasibility and applicability of the foundation pit field is a better form of support.