基于NSM分析双线隧道下穿对既有隧道影响

Effects of New Twin Underneath Tunneling on Existing Tunnels Based on NSM Study

为探究新建双线隧道下穿对既有盾构隧道纵向位移的影响,采用Pasternak双参数弹性地基及Euler-Bernoulli梁模型,考虑新建隧道与既有隧道轴线夹角以及隧道开挖引发土体损失等因素,通过Loganathan-Poulos解和叠加原理计算新建双线隧道开挖引起周围土体自由场竖向位移,基于零空间法对既有隧道沉降变形进行求解。以深圳地铁9号线下穿地铁4号线为工程背景,将现场实测数据与零空间法的结果进行对比,进一步分析双线隧道水平距离、土体损失、新旧隧道轴线间夹角以及新建隧道埋深对隧道沉降的影响。结果表明:新建隧道双线间距在其外径7倍范围内时对既有隧道沉降影响显著,沉降量随间距增大而减小,沉降范围随间距增大而增大,沉降形态由“V”型向“W”型转变。当间距大于7倍新建隧道外径,沉降量与沉降形态均趋于稳定。此外,土体损失、新旧隧道夹角及新建隧道埋深对沉降的影响显著,沉降量随土体损失增大而增大,随新旧隧道夹角和新建隧道埋深的增大而减小。

In order to investigate the effects of new twin tunneling on the longitudinal displacement of existing shield tunnel,Pasternak double parameters of the elastic foundation and Euler-Bernoulli beam model is employed to consider the new tunnel,existing tunnel skew angle and the tunnel excavation causing factors such as ground loss.The new double line tunnel excavation caused by free field vertical displacement of surrounding soils is determined by Loganathan-Poulos solution and superposition principle,and null space method is used to calculate the settlement deformation of the existing tunnel.Taking Shenzhen Metro Line 9 passing under Metro Line 4 as an example,the predicted results by the null space method is compared with the field-measured data.The effect of horizontal distance,ground loss,skew angle and depth of the new tunnel on existing tunnel settlement is further analyzed.The results show that the distance between the two lines of the new tunnel significantly affects the settlement of the existing tunnel in a range of 7 times its outer diameter.The settlement decreases with the increase of the distance,the settlement domain increases as the distance increases.The settlement pattern changes from"V"to"W".When the distance is larger than 7 times the outer diameter of the new tunnel,the settlement and pattern tend to be stable.In addition,ground loss,skew angle and the depth of the new tunnel significantly influences the settlement.It increases with the increase of ground loss,and decreases with the skew angle and the depth of the new tunnel.