Study On Cracking Temperature Effect For Underground Structure Of Rail Transit Station In Soft Soil

Ningbo rail transit construction is in full swing,there is also a series of engineering problems to be solved,especially the large-scale structure of the main station through the cracks occur remains unresolved.Since the main structure of the rail transit station is made of large-volume concrete,a large amount of heat is released during the condensation and hardening process.Under the action of the external temperature and the temperature field of the concrete itself,the concrete of rail transit station will be subjected to the action of temperature load,and under the constraint conditions,a large tensile stress will be generated,which is prone to cracking and seepage.This study combines the test section of Xingningqiao East Station of Ningbo Rail Transit Line 4,through theoretical analysis and experimental study,laying strain sensor and temperature sensor in test section,monitoring temperature and displacement fields in the whole process of concrete construction,analysis of the variation of temperature field and displacement field of main structure,the law of fracture development is also studied.The main conclusions are as follows:(1)In the early stage of concrete pouring,along the length direction of the side wall,the strain of the wall is closely related to the temperature difference.The larger the temperature difference between the inside and outside of the wall structure,the greater the strain of the wall in this part.(2)In the early stage of concrete pouring,along the height of the wall,the temperature stress of the wall is related to the degree of constraint of the wall.The tensile strain of the wall near the interface of the construction joint is greater than that of the middle horizontal section.(3)After the wall is demolded,the temperature outside the wall is higher than the atmospheric temperature,and the sudden drop in the temperature of the wall causes a sudden change in temperature stress.The inside of the wall is located inside the concrete,and the ability to sense the outside air temperature lags behind.(4)In the later stage of temperature stress,the wall strain is mainly affected by the external temperature.For example,in the later stage,the outside temperature of the wall is affected by the external temperature,which keeps periodic change,while the inside temperature of the wall changes uniformly.(5)Different season construction has a great influence on the temperature of the main structure.The maximum temperature of the side wall in summer construction is 20.65 °C higher than the temperature of the side wall in winter construction.The temperature difference of the wall in summer construction is higher than that of the winter construction wall.The body temperature difference is high.Also reflected in the strain of the wall,the wall strain during winter construction is smaller than the wall of the same part.(6)If there are cracks near the wall,the tensile strain around the wall will decrease,which is due to the redistribution of temperature stress caused by cracks.(7)Roof cracks mostly occur at the junction of side wall and roof,because this part is a variable cross-section,and stress concentration will occur during the whole construction process.Far from the end of the side wall interface,the roof is evenly stressed.(8)In the whole process,the internal and external strain values of the side wall are close to the outside wall,so the cracks gradually extend from the outside wall to the inside wall until they become penetrating cracks.(9)The crack of the wall gradually extends from the interface of the construction joint to the intermediate horizontal interface.The strain of the XW13 strain gauge is-8.73?? at 784 h,and the strain value becomes 73.91?? at 2056 h.Finally,the paper gives the suggestions for prevention and treatment of cracks in the concrete structure of the main body of rail transit stations.