地铁双线盾构下穿对紧邻既有隧道沉降预测方法

Prediction Method for Settlement of Adjacent Existing Tunnel Affected by Double-Track Shield Tunnel of Metro Downward Crossing

随着盾构地铁施工下穿既有隧道的广泛运用,近距离穿越施工案例逐渐增加,风险也越来越大,故研究盾构施工过程中既有地下结构的沉降规律非常有必要.考虑新建隧道与既有隧道之间的夹角等因素,对Peck公式进行修正.以北京地铁12号线西坝河站至三元桥站区间盾构下穿既有隧道10号线为工程背景,将现场实测数据与Peck公式拟合,获得了该工程隧道区间双线隧道开挖引起的天然地层损失率和沉降槽宽度参数,并根据叠加原理建立了适用于本工程区间的双线盾构隧道开挖引起既有隧道沉降的预测公式;采用FLAC3D模拟工程实况,进一步分析了新建双孔隧道开挖对既有隧道的沉降影响规律.结果表明:该工程隧道区间先行隧道和双孔隧道开挖引起的天然地层损失率取值范围分别为1.37%~2.02%和0.33%~0.87%,沉降槽宽度参数范围分别为0.23~0.37和0.28~0.34.Peck沉降预测公式计算规律与数值模拟、实际监测结果基本一致,表明该公式具有很好的实用性,可应用于类似下穿既有隧道工程.

With the extensive use of shield tunnels under the existing tunnels,the construction cases of short-distance tunnels have gradually increased,and the risks have also increased.Therefore,it is necessary to study the settlement laws of existing underground structures during shield construction.In this paper,factors such as the angle between the new tunnel and the existing tunnel are considered,and the Peck formula is modified.Then,based on the engineering background of the shield tunnel passing through the existing tunnel Line 10 from Xibahe Station to Sanyuanqiao Station of Beijing Metro Line 12,the field measured data is fitted with Peck formula,and the double distance of the tunnel in this section of the project was obtained.The loss rate of the natural stratum and the width of the settlement tank caused by the excavation of the line tunnel were analyzed,and the prediction formula for the settlement of the existing tunnel caused by the excavation of the double line shield tunnel is established according to the superposition principle.Finally,FLAC3D is used to simulate the project.According to the actual situation,the influence law of the new double-hole tunnel excavation on the settlement of the existing tunnel is further analyzed.The results show that the loss rate of natural strata caused by the excavation of the leading tunnel and the double-hole tunnel in the tunnel section of the project ranges from 1.37%to 2.02% and 0.33%to 0.87%,respectively,and the range of the width of the settlement tank is 0.23 to 0.37 and 0.28 to 0.34.The calculation law of the Peck settlement prediction formula is basically consistent with the numerical simulation and actual monitoring results,indicating that the formula has good practicability and can be applied to similar tunnel projects.