Research And Application Of Soil Reinforcement Method At The Originating End Of Pipe Jacking

With the continuous development of urban underground space engineering,underground pipe jacking tunnel engineering is increasing.The entrance and exit tunnel of pipe jacking is the most dangerous stage of pipe jacking construction safety,especially in the large diameter pipe jacking tunnel and parallel pipe jacking construction in water-rich sand layer.How to select a reasonable reinforcement method of pipe jacking end soil to ensure the safety of pipe jacking construction has become an important research topic.In this paper,based on the background of the three-row pipe jacking project of the external drainage of Meilan Airport Phase II reconstruction and expansion project in Haikou City,aiming at the instability and construction technical problems of the water-rich sand layer pipe jacking（group）in and out of the tunnel end,the reinforcement range of the pipe jacking in and out of the tunnel end soil in the water-rich sand-bearing soft stratum is studied by theoretical analysis,numerical simulation and field monitoring,and the reinforcement construction scheme and process are designed.The influence of the pipe jacking（group）starting section on the stability of the end soil under different reinforcement ranges is discussed,and the general laws of the surface deformation and soil stress of the pipe jacking（group）starting section are summarized.The main work and results of this paper are as follows :（1）The change of soil disturbance property and the mechanism of soil deformation caused by pipe jacking construction are studied.The causes of stratum loss and the reinforcement of soil at the beginning of pipe jacking are briefly analyzed,and the range of reinforcement structure of soil at the end of pipe jacking is further determined.The theoretical analysis of soil reinforcement at the end of pipe jacking is carried out from three aspects of soil strength,static balance and anti-slip to determine the range of theoretical reinforcement.（2）Through numerical simulation,the displacement field of the improved reinforced soil when the pipe jacking starts to break the tunnel is analyzed,and the soil sliding surface is located above the front of the tunnel door.The reinforcement of 1 ～ 5 m in the end soil layer can effectively reduce the slip value of the stratum and improve the stability of the soil layer.The maximum slip value of the soil at the front end of the portal is 13.48 mm when the reinforcement is 5 m.When the reinforcement length exceeds 5m,the reinforcement effect is weakened.Under different reinforcement lengths,the tensile stress and shear stress of the soil layer when the initial hole is broken changes little,and the change range is basically maintained between 0 ～ 0.05 MPa.The change of compressive stress is relatively large,and the overall range is 0.762 ～ 1.013 MPa.The increase of longitudinal reinforcement length is more obvious to improve the compressive stress of soil.（3）Combined with the three-row pipe jacking project,the numerical analysis method is used to explore the influence of different reinforcement construction parameters on the reinforcement effect in the process of pipe jacking.The longitudinal reinforcement of the soil at the end of the pipe group can effectively reduce the disturbance of the soil caused by the initiation of the pipe jacking.With the increase of the longitudinal reinforcement length,the settlement deformation groove decreases continuously,and the improvement effect of stratum stability is remarkable.When the length exceeds 7 m,the reinforcement effect is weakened.The lateral reinforcement of the end soil is mainly to provide a certain section area for the solid to improve the ability of the soil to resist external water and soil pressure,and has little influence on the formation caused by the initiation of the pipe jacking.The lateral reinforcement length is 2 m to meet the end face requirements.The improvement of the cohesive force of the reinforced soil can effectively reduce the disturbance to the surface soil caused by the initiation process of the jacking tunnel breaking.The cohesive force of the reinforced soil is negatively correlated with the surface settlement on the whole.When the rotary jet grouting pile is completed,attention should be paid to the construction technology and material selection to ensure that the measured soil cohesive force is between260 ～ 300 k Pa.（4）After the numerical analysis of various construction reinforcement parameters,it is finally determined that the soil reinforcement at the origin of the three-row pipe jacking in this project is 7 m in the longitudinal direction and 2 m in the transverse direction,and the designed cohesion of the soil is 280 k Pa.The combined reinforcement method of highpressure rotary jet grouting pile and horizontal grouting can meet the requirements of the stability of the water-rich sand layer pipe jacking and have a large safety redundancy.（5）The deformation stage of pipe jacking construction soil is demonstrated by analyzing the measured surface settlement data;the comparison between the numerical simulation results and the field measured data shows that the numerical simulation results are basically consistent with the field measured data graph curve,which plays a certain reference role in the analysis of the monitoring results and verifies the applicability of the simulation.Figure [57] table [12] Reference [63]...