关键词: 局部冻结, 盾构法联络通道, T接头, 温度场, 有限元分析

Abstract:  In order to study the weak position of local freezing area for Tjoint of connection gallery bored by shield, and explore the influences of main tunnel segments material, thermal conductivity of grouting body in the gap of the tunnel opening, whether the soil is improved by grouting and the number of frozen pipe ring on partial freezing. Based on a partial freezing strengthening project of Tjoint of the connection gallery of the Tianjin metro line 10, the distribution law of temperature field in the partial freezing is analyzed by numerical simulation. The results reveal the following: (1) At the tunnel opening, the freezing effect is better on the side of the connection gallery than on the top and bottom. The steel segments extend further toward the bottom of the main tunnel than toward the top, indicating a slightly inferior freezing effect on the bottom half ring of the connection gallery compared to the top half ring. (2) The primary factors affecting partial freezing time are the material of the main tunnel segments and the thermal conductivity of the grouting body in the gap of the tunnel opening. (3) When the grouting body in the gap has a low thermal conductivity (0.93 W/(m·K)), the cooling energy cannot be transferred timely through the grouting body to the main tunnel steel segments. Consequently, the cooling energy in the soil behind the connection gallery transfers to distant soil along the steel segments, resulting in a higher temperature of the soil near the connection gallery, leading to a significantly longer freezing time compared to cases with all reinforced concrete segments. (4) Increasing the thermal conductivity of the grouting body in the gap improves the cooling transfer efficiency, enhancing the freezing effect of the soil near the main tunnel and reducing the freezing time. Elevating the thermal conductivity of the grouting body in the gap from 0.93 to 1.8 W/(m·K) reduces the freezing time from 17 to 12 days under the condition that steel segments are partially used in the main tunnel, and the required freezing time is 1 day shorter than that under the condition that all reinforced concrete segments are used in the main tunnel. It is concluded that the thermal conductivity of the grouting body in the gap significantly affects the freezing time when steel segments are partially used in the main tunnel.

Key words: partial freezing, connection gallery bored by shield, Tjunction, temperature field, finite element analysis