盾构法联络通道T接头局部冻结加固效果及影响因素研究

Partial Freezing Reinforcement Effect and Influencing Factors of T-Junction of Connection Gallery Bored by Shield

为研究盾构法联络通道T接头局部冻结区域的薄弱位置,探究主隧道管片材料、洞门间隙注浆体热导率、是否注浆改良土体和冻结管环数等因素对局部冻结的影响,依托天津地铁10号线某联络通道T接头局部冻结加固工程,采用数值模拟对局部冻结温度场的分布规律进行分析。研究结果表明:1)对于沿洞门处的土体,联络通道顶底部冻结效果差于联络通道侧面;主隧道钢管片向主隧道底部比向顶部延伸的更长,因而联络通道底半环冻结效果略差于顶半环。2)影响局部冻结时间的主要因素为主隧道管片材料和洞门间隙注浆体的热导率。3)主隧道部分采用钢管片工况,钢管片起到通道壁后远近土体导热“桥梁”的作用;当洞门间隙注浆体的热导率较低(如0.93 W/(m·K))时,注浆体不能及时地向主隧道钢管片输送冷量,联络通道壁后近处土体中大量冻结冷量沿钢管片传递至远处土体,使通道壁后较近处土体温度较高,因而比主隧道全部采用钢筋混凝土管片工况冻结时间长。4)随着洞门间隙注浆体热导率的增大,其向主隧道管片输送冷量的效率得到提升,主隧道附近土体的冻结效果得到改善,冻结时长有所缩短;间隙注浆体热导率由0.93 W/(m·K)提升至1.8 W/(m·K)时,可以将主隧道部分采用钢管片工况冻结时间由17 d缩短至12 d,所需冻结时长相比主隧道全部采用钢筋混凝土管片工况反而缩短1 d,即主隧道部分采用钢管片工况的冻结时间对洞门间隙注浆体热导率的改变更为敏感。

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.