| In the burgeoning subway construction nationwide,shield tunneling has become the preferred construction method for urban subway tunnel construction due to its advantages of high efficiency,environmental protection and safety,while shield tunneling in karst developed areas is an engineering problem that must be faced.In the process of tunneling,the shield tunneling machine is prone to deflection,heading and even collapse of surrounding rock,which is bound to have a significant impact on the construction progress,economic cost and life safety of shield tunnel engineering.This paper takes the shield tunnel project between qianyan station and quanshui east station of dalian metro line 5 as the background to carry out the numerical simulation study on the influence of karst cave on the surrounding rock stability of shield tunnel.The results can be used as a reference for the safety assessment of shield tunneling in karst areas and the treatment of karst caves.The main research contents are as follows:1.Summarize the roles and implementation methods of key factors in numerical simulation,such as shield tail synchronous grouting,palm surface pressure,cutter head torque and initial earthly stress balance of karst strata during shield construction.2.In combination with the actual engineering geology and model parameters of shield tunneling,ABAQUS finite element analysis software was used to establish the three-dimensional numerical model of shield tunneling,and the simulation results were compared with the field measured data to further verify the rationality of the model.The displacement change rules of the surrounding rock vault,arch bottom and arch waist point in the process of shield tunneling with and without karst cave are analyzed.When the shield tunneling reaches the upper part of the lower karst cave,the cutter plate will sink,and the maximum settlement can be increased by 60%.At the same time,the influence law of different grouting pressure on the stability of surrounding rock is compared,and it is suggested to pay attention to the treatment of the side karst cave of the tunnel.3.The influence of karst cave location and distribution on the stability of surrounding rock of shield tunnel is studied.By comparing the karst cave tunnel and the azimuth Angle±90“,±60°,±45°,±30°,0°nine condition of surrounding rock displacement field,stress field and plastic strain of the change law of draw water-eroded cave is located in the most easily result in instability of surrounding rock in tunnel below the diagonal.With the increase of the distance between the tunnel and the karst cave,the settlement of surrounding rock at the bottom of the tunnel decreases and the plastic strain value decreases.The greater the distance between the tunnel and the karst cave,the better the safety of shield construction.In addition,based on the strength reduction method,the influence of cutter disc torque on the stability of surrounding rock developed in karst cave is studied.The strength reduction coefficient of surrounding rock failure is reduced by 21%under the action of torque.4.The influence of karst cave shape and size on the stability of surrounding rock was studied.When the cave is located in the lower part of the tunnel,the width of the cave will weaken the stability of the surrounding rock more than the height.With the increase of the width of karst cave,the surrounding rock will produce more settlement and plastic strain in the process of shield tunneling.When the cave is located at the side of the tunnel,the height of the cave will weaken the stability of the surrounding rock more than the width.As the height of karst cave increases,the horizontal displacement and plastic strain of surrounding rock between the tunnel and the karst cave increase,and the circumferential stress of the lining near the waist increases.Finally,the effects of irregular karst caves and fracture-shaped karst caves on the stability of surrounding rocks are compared and analyzed.The plastic strain region of fissured karst cave expands from the tip of both sides.The maximum plastic strain of the surrounding rock of irregular and fractured karst caves is increased compared with that of circular karst caves,but the range of plastic strain is decreased compared with that of cylindrical karst caves. |
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