Study On The Development Law Of Temperature Stress Field Of Freezing Curtain In Freezing-Excavation Process Of Connecting Passage

Subway has been favored by more and more cities because of its convenience and safety.As the life channel of the subway,the importance of the contact channel is self-evident.Because of the special geological conditions in the coastal areas,the freezing method is often used for the construction of underground projects.Based on a section project of Fuzhou subway connection channel,this paper obtains the compressive and flexural strength of silty soil by frozen soil test of silty soil at different temperatures,and fits the temperature and corresponding parameter equations.Secondly,by establishing the numerical model of the excavation of the connecting passage,the simulation results of the temperature field are compared with the field measurement to verify the rationality of the numerical simulation.Finally,based on the established numerical model,the displacement and stress variation of the frozen curtain under different excavation steps and different supporting time during the excavation process of the connecting passage are discussed.The specific research results are as follows :1)The strength of artificial frozen soil increases with the decrease of temperature.After reaching the peak stress,the specimen continues to be destroyed,but the stress value increases slowly,indicating that the muddy soil shows obvious plastic characteristics.The average uniaxial compressive strength of mucky soil at-5 °C,-10 °C and-15 °C is 2.22 MPa,3.15 MPa and 4.75 MPa,respectively.The fitting formula of temperature and compressive strength is =0.84-0.25 T;the average values of elastic modulus are 38.74 MPa,71.85 MPa and 106.38 MPa respectively,and the fitting formula is E = 4.68-6.76 T.The average values of flexural strength of muddy soil are 1.02 MPa,2.35 MPa and 3.88 MPa respectively,and the fitting formula is =-0.44-0.29 T.2)The freezing curtain of the left and right lines intersects for 32 days.At the end of the active freezing,the weakest part of the freezing curtain is located at the junction of the cross section of the freezing pipe and the normal section.The thickness of the freezing curtain in the cross section of the freezing pipe is more prominent,and stress concentration may occur.3)The largest part of the displacement change during the excavation of the connecting passage is the bottom of the frozen soil curtain,and as the excavation footage continues to increase,the uplift displacement at the bottom of the frozen curtain continues to increase,but the cumulative displacement value does not exceed 10 mm,within the safety control range.After the excavation of the connecting passage is completed,the left line displacement and the right line displacement of the tunnel are symmetrical with the middle line.4)After the excavation of the connecting channel is completed,the first principal stress is in a compressive state as a whole,and local tensile stress occurs at the side wall and vault,with the maximum tensile stress value of 0.78 MPa.The flexural strength obtained from the frozen soil test is 2.35 MPa,and the empirical safety factor is 3.01.The maximum tensile stress of the third principal stress appears at the angle of the bottom plate and the side wall of the freezing curtain,the maximum value is 0.24 MPa,and the safety factor is 13.The maximum shear stress value corresponds to the position of the first principal stress,the maximum shear stress value is 0.89 MPa,and the safety factor is 3.6.5)The maximum displacement of the freezing curtain during the excavation of the connecting passage is located at the vault and the arch bottom.The displacement of the vault decreases gradually along the vertical direction,and the displacement of the arch bottom increases gradually.The earlier the supporting time,the smaller the displacement change of the freezing curtain;when the excavation step is different,the deformation at different positions of the freezing curtain is different,and with the increase of the excavation step,the vertical displacement and stress at different positions show an increasing trend;when the excavation step is 1.5 ～ 2m,the vertical displacement and stress increment of the monitoring point are less than the excavation step of 2 ～ 2.5m.