Research On Horizontal Freezing Method Of Plane Oblique Communication Channel

In recent years,with the gradual acceleration of the construction of urban subways in China,the rapid development of the subway has brought many problems to be solved.The connecting channels between the upper and lower tunnels have become an important part of the overall planning and design of the subway,and they have received more and more attention.The freezing theory and related construction technology are becoming more and more mature,which makes the artificial freezing method more and more widely used in the construction of conventional connecting aisles.However,there may be occasions when the construction is improper,resulting in the wrong connection of the steel pipe in the connecting aisle,or the inclined connecting aisle due to the requirements of the engineering environment.Currently,there are very few studies on the design and construction of such connecting aisle.Based on the plane skew connecting aisle between Cuizhu Station and Changzhou Railway Station of Changzhou Metro Line 1.The connecting channel is tilted 31.2° in the horizontal plane.This paper analyzes the development law of both freezing temperature field and surface displacement caused by frost heaving.The finite element numerical simulation of the freezing temperature field,excavation stress field and displacement field of the project is carried out by using ADINA.The conclusions are as follows:The actual measurement results show that:(1)Due to the inclination of the freezing pipe and the temperature measuring hole and the entrance of the connecting aisle is perpendicular to the tunnel,the actual distance from the internal measuring point to the freezing pipe is shorter than the distance of the temperature measuring point at the interface.The temperature drop of the external measuring point of the outer measuring hole on the left side of the main line is slower than that of the internal measuring point,while the temperature drop of the internal measuring point of the inner measuring hole is faster than that of the external measuring point;the right side of the main line is just the opposite.Meanwhile,the distance between different measuring points of the same measuring hole and the excavation edge is different.The internal measuring point on the right side of the main line is closer to the excavation side line,which is opposite to the measuring hole on the left side of the main line.The measuring points with temperature rise during excavation are at the depth of the soil and at the interface.This is different from the uniformity of the temperature variation law of the plane orthogonal connecting aisle.(2)The temperature change of the hole is divided into 4stages,and the surface frost heaving deformation is divided into 5 stages.The fourth stage to the end of excavation of temperature change corresponds to the third stage of surface frost heaving deformation.(3)According to the measured surface settlement,the maximum distribution line of the surface elevation of the oblique connecting aisle is also oblique.Numerical simulation results show that:(1)Due to the large number of reinforced freezing holes in the tunnels on both sides,the temperature at the junction between the tunnel segments and the soil is lower,and the thickness of the frozen wall is larger than that at the center of the connecting aisle.Especially in the frozen area on the right side of the secondary line,the thickness of the frozen wall is doubled.The thickness of the weakest part of the frozen wall is about 2.0m,which is located in the middle of the connecting aisle.The weak position of the frozen wall with the normal orthogonal communication channel is generally different at the junction of the soil and the segment.This is different from the weak position of the frozen wall of the ordinary orthogonal connecting aisle,which is generally located at the junction of the soil and the segment.(2)Due to the inclination of the freezing pipe,The actual distance between the soil between the frozen pipe and the freezing pipe is smaller than that of the orthogonal connecting aisle,which is not the visually observed freezing pipe spacing.Therefore,the time required for freezing cylinders of the plane oblique connecting aisle to intersect is shorter than that of the orthogonal connecting aisle.(3)The surface frost heave deformation of the plane oblique connecting aisle only has one-way symmetry.It is asymmetric and oblique along the longitudinal line of the connecting aisle,and there is still symmetry along the transverse line of the connecting aisle,which is different from the two-way symmetry of the ordinary orthogonal connecting aisle.(4)During the excavation of the connecting aisle,the maximum of the third principal stress of the surrounding soil is located near the freezing pipe at the bottom of the connecting aisle,whose value is 3.95 MPa.As the third principal stress spreads outward,its value gradually decreases.After excavation,the formation stress is redistributed,and the third principal stress value of the soil is slightly reduced.The third principal stress of the soil is slightly reduced.The maximum of the third principal stress of the permanent support and the temporary support occurs at the junction of the lining and the main tunnel segment.This is because there is a stress concentration at the interface of different materials.Due to the change in the shape of the cross section,there is also a stress concentration at the corner of the connecting aisle.