Study On Interaction Between Pipe Jacking Caisson And Surrounding Soils

The pipe jacking construction actually consists of two parts: 1)the excavation and construction of the working well;2)the construction of the pipe jacking advancement process.During the jacking process,the soil around the working well forms a active zone and a passive zone separately.On the one hand,studying the extent of soil cracking and uplift has positive significance in reducing the impact of pipe jacking construction on the surrounding environment;The resistance is also of great significance to the guidance of practical engineering.By using theoretical analysis,model experiment,numerical simulation and other methods,combined with the actual situation of the project,the working well and surrounding soil construction mechanics,deformation characteristics,and the reinforcement characteristics of jetting piles are discussed in depth.In the existing research,there are few studies on the loss of the surrounding strata during the jacking process.For the situation where there are rotary jetting piles around the caisson,a simplified method is generally used for calculation.The research on the reinforcement effect of rotary jetting piles is insufficient.The piles and working wells are combined to carry out numerical simulation operations and other issues to analyze,so the following specific contents are studied:(1)Provide laboratory test data for actual engineering by measuring the friction parameters between different soils and caisson walls.The measured results are that the friction coefficient of granite residual soil is 0.501;the friction coefficient of undisturbed soil is 0.448;the friction coefficient of silty soil is 0.309;the friction coefficient of standard sand is 0.617,and the reasons for the results are analyzed to a certain extent.Finally,the obtained parameters are used for numerical calculation.(2)Small model box to simulate caisson jacking test By establishing an indoor small model box test model and carrying out the test,the simulation situation under certain working conditions is analyzed,and the impact of pipe jacking on the surrounding soil is qualitatively understood.When local cracks extending to the surface do not appear,the surface influence range of active zone and passive zone is small.After the jacking reaches a certain distance,the shape of the passive side soil failure surface in the horizontal direction is a continuous arc shape,the influence range of the ground surface is an ellipse,and the ellipse long axis direction is the direction of the jacking axis.If the top force continues to increase,the scope of influence will continue to expand.Finally,the results are compared with the numerical simulation analysis to obtain certain rules.(3)Combined with an actual engineering project in Xi'an,use the ABAQUS software to establish a working well jacking process model with piles,and compare the results with other simulation results and projects.It is believed that the foundation pit excavation and the working well did not sink.During the entry stage,the soil body at the bottom of the pit produces a large uplift.When the well body sinks and stabilizes,the horizontal displacement of the lateral soil mass and the vertical uplift of the soil body at the bottom of the pit decrease.After the top thrust is applied,the back wall and the soil are both deformed by a large force,and the soil is squeezed to form a wedge-shaped horn-shaped failure body.The soil body on the forward side is displaced into the pit to form a three-dimensional space body shaped like half an hourglass,and the shape of the uplift on the surface of the back surface is an elliptical arc.After verifying that the model is correct,combined with the reinforcement construction method of rotary jet piles around a power caisson in Shunde,a working well model with piles under different jacking forces is established.For soil deformation,the basic laws are summarized by analyzing the mechanical deformation characteristics of the working well,the rotary jet pile and the surrounding soil in detail.Finally,the soil was replaced with silty soil,and it was found that the effect of rotary jetting piles in preventing soil cracking was more obvious than that in soft soil layers.