Numerical Study On The Impact Of Freezing Temperature Decreasing On Joint Of Subway Shield Tunnel

With property closes to subway developing strongly, a growing number of foundation pit engineering above subway tunnel appear. In impermeable stratum, there are many successful construction of foundation pit above subway. However, in the strong permeable stratum, waterproof system cannot be formed in regular way in the foundation pit engineering because of the waterproof curtain cannot across the subway tunnel. And it may endanger the safety of foundation pit and the subway tunnel structure and operation. Using freezing method to decrease the temperature in the permeable stratum, outsides which the two sides of supporting structure of foundation pit cannot be inserted into the impermeable stratum, will stop water and protect the safety of subway structure effectively in similar case. The mechanical behavior of subway shield tunnel will be changed because of the freezing temperature decreased, such as splaying amount of joint increases, and then it may lead to leakage. However, related research about impact of freezing temperature decreasing on splaying amount of subway tunnel joint in similar case is very less.Taking operation subway shield tunnel under a foundation pit engineering in which using freezing method as the object of study, a 3D numerical model of subway shield tunnel is established by using Midas FEA finite element software. The impact of freezing temperature decreasing on splaying amount of longitudinal and circular joint of shield tunnel and deformation and force of the segment is studied. The reason of leakage is also analyzed preliminarily. The main works of this paper are as follows:(1) With the structural feature of shield tunnel segment connected by longitudinal and circular bolts, the 3D numerical model of single transverse and three longitudinal segments is established. This model considers the detailed structures such as segment joint, connecting bolts, hand hole and rubber gasket, etc.(2) The temperature field and impact of freezing temperature decreasing on structure of longitudinal joints and deformation and force of single segment are studied under four kinds of freezing scopes. The splaying amount of longitudinal joints and the law of deformation and force of single segment are analyzed under two conditions when the thermal conductivity of concrete and minimum freezing temperature changes.(3) The impact of freezing temperature decreasing on structure of circular joints and deformation and force of three longitudinal segments are studied under different kinds of freezing scopes. The splaying amount of circular joints and the law of deformation and force of three longitudinal segments are analyzed under the temperature condition when the thermal conductivity of concrete and minimum freezing temperature changes.(4) With the shield tunnel joint leakage case, the impact of freezing temperature decreasing on splaying amount of longitudinal and circular joint of tunnel is analyzed. And the reason of leakage is analyzed preliminarily.