Numerical Analysis of Temperature Field of Cup-Shaped Frozen Soil Wall Reinforcement at Shield Shaft

Abstract

Determining the freezing reinforcement required range and reinforcement method, acquiring the development and distribution pattens of frozen soil wall temperature field are the key issues needed to be addressed when using cup-shaped horizontal freezing method for the soil reinforcement of shield tunnel ends. Based on the shield launching project of the west side of Yixianqiao station in Nanjing subway line 2 and the finite element numerical analysis software, the development and distribution patterns of the cup-shaped frozen soil wall reinforcement were studied. The numerical simulation showed that, after freezing for 30 days, the x = -1 section temperature field evenly distributed around the center tube. And the freezing temperatures within the outer tubes were usually below-20°C. The temperature field circled around the center tube and the temperature gradually increased from the inside to the outside to 0°C within the range of about 1 m outside the outer tubes. The freezing temperatures within the range of 2 m thickness of the cup-bottom in the y= 0 section were usually below-10°C and the temperatures changed from inner to outer significantly until rising to 0 °C at the freezing pipe ends of the cup-bottom. Freeze wall formed firstly in the outer tubes, then the intermediate tubes, and lastly the outer tubes. And the freeze wall closure time that closed cup-shaped frozen soil wall formed was 15 days in this designed freezing method.