淤泥质黏土层盾构推进的地层扰动分析

淤泥质黏土的灵敏度高,分析盾构推进在该土层造成的地层扰动范围和特征有利于采取合适的施工技术对策。本文中根据地铁区间隧道盾构推进的实测地表沉降,计算监测断面的地层损失率作为衡量地层扰动的指标,以表征盾构推进对前方地层的纵向扰动。文献资料调研表明,上海淤泥质黏土层的工程地质特性变异性不大,用沉降换算的各监测地层损失率的变化特征总体相近,进而可将盾构推进的地层扰动划为3个区域:(1)推进扰动区,盾尾至盾构切口前方1.16~1.35(H+D);(2)扰动增强区,盾尾至盾尾后方10~12D;(3)扰动平缓区,盾尾10~12D后方。分析地层损失率数据发现,推进扰动区的地层损失或正或负,但量值较小(<1.0‰),表明在该淤泥质地层中盾构推进的正面压力控制有效;扰动增强区地层损失率总体呈线性增大趋势,扰动平缓区地层损失率逐渐稳定在4‰以内,符合5‰的施工控制目标,表明盾尾脱出后控制该地层扰动的技术措施是恰当的。

Statistical Analysis of Ground Disturbance Induced by Shield Tunneling in Muddy Clay Stratum

Muddy clay is prone to be disturbed due to its sensitivity. Shielding a tunnel in this stratum would induce heaven or subsidence of the ground. This paper gives an overall statistics of ground disturbance, in the term of Ground Loss Ratio (GLR). It is found that the ground disturbed by shielding can be marked as three zones: (1) Front Zone,1.16~1.35(H+D) in front of cutterhead to the end of a shield machine, where ground disturbance exhibits heaven or subsidence by fluctuation of pushing pressure; (2) Tail Zone, (10~12)D behind shield tail, where ground disturbance is overall intensified; and (3) Even Zone, after Tail Zone, where ground disturbance becomes stable. Statistical analysis of 11 cross-sectional measurements indicates that, GLR in Front Zone can be positive or negative, but its value is less than 1.0‰. It implies that the control of shield pressure in this clay stratum is successful. Although GLR in other zones increases to 4.0‰ and it is still under the limit of 5.0‰. It may symbolize that the measures in control subsidence during shielding are reasonable.