Numerical Analysis Of Geomechanical Model Test And Study Of Pile Cutting Principle For Shield Receiving Tunneling

Shield construction method has many advantages and has been widely used in the process of tunnel construction.Shield receiving is the most accident prone link in shield construction,which is directly related to the smooth implementation and timely connection of shield tunnel.In the process of shield receiving,due to the decrease of soil mass in front of the shield,the stress and displacement of the soil mass in front of the shield and the stress of the retaining structure have changed,as well as the mechanism of shield cutting GFRP reinforced concrete retaining pile is not clear.In order to solve the above problems,this paper uses theoretical analysis,numerical simulation and on-site monitoring based on the shield receiving of Changchun Bridge Station of Beijing Metro Line 12 Data comparison and analysis;provide reasonable parameter "Preview" for the three-dimensional geomechanical model test of shield receiving tunneling,use different tunneling parameters for simulation comparison,provide theoretical basis for guiding the model test,improve the test accuracy and reduce the error.The specific results of the research are as follows:1.Study on the inversion of formation parameters and numerical simulation of shield receiving processThrough the numerical calculation of shield receiving tunneling,the lateral displacement of GFRP reinforced concrete retaining pile is 32.7mm,in which the lateral displacement of pile caused by shield receiving tunneling is 15.71 mm,accounting for 48% of the total deformation.Combined with the field monitoring and numerical analysis of the retaining pile,it can be seen that the influence on the GFRP reinforced concrete retaining pile at the tunnel portal starts from around the 17 th to 12 th ring of the tunnel portal,the stress state of the soil in front of the shield changes,from the semi infinite soil to the limited soil,and when the excavation is within the 12 th ring of the retaining pile,it starts to enter the limited soil state.2.Numerical simulation of geomechanical model test for barrier free receiving of shieldCombined with the second chapter,the process of shield receiving tunneling is divided.When the model shield machine starts to excavate,it needs to establish the earth chamber pressure quickly.When the shield tunneling is about 10 rings away from the tunnel portal,the stress field and displacement field of the soil at the tunnel portal begin to change,and the soil begins to enter the limited soil state gradually.The lateral pressure on the cutter head of the control shield is not less than 30 KN,and the control speed of the normal driving section(before the 10 th ring of the tunnel portal)is about 6mm / min;the control speed of the receiving driving section(within the 10 th ring of the tunnel portal)is about 3mm / min.3.Mechanism of shield cutting GFRP reinforced concrete retaining pileAt the same speed,the greater the rotating speed of the cutterhead,the greater the radial force on the pile,the more obvious the pile cutting effect,and the greater the torque of the cutterhead;at the same rotating speed of the cutterhead,the greater the advancing speed,the greater the tangential pressure on the pile,and the pile is prone to collapse towards the free side of the foundation pit.During pile cutting,the principle of "large rotation speed,small torque and small thrust" shall be followed.The breaking process of GFRP reinforced concrete retaining pile can be simplified as the generation,expansion and connection of cracks(the cracked pile can be peeled off).