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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。
The sensitivity of silt clay is high. Analyzing the range and characteristics of formation disturbance caused by shield propulsion is conducive to adopting proper construction technology. In this paper, based on the measured surface subsidence induced by shield tunneling in metro tunnel section, the formation loss rate of monitoring section is calculated as an index to measure the disturbance of strata, so as to characterize the longitudinal disturbance to the front strata caused by shield propulsion. Literature research shows that the variation of the engineering geological characteristics of the silt clay in Shanghai is not large, and the change characteristics of the loss rate of the monitoring strata converted by the subsidence are generally similar, and thus the formation disturbance of the shield can be divided into three areas: 1) to promote the disturbance zone, the shield tail to the front of the shield incision 1.16 ~ 1.35 (H + D); (2) enhanced disturbance zone, shield tail to the rear of the shield tail 10 ~ 12D; 12D behind. Analysis of the formation loss rate data shows that the formation loss in the disturbance zone is positive or negative, but the magnitude is small (<1.0 ‰), indicating that the positive pressure of the shield advance in the silt texture layer is effectively controlled; and the formation loss in the disturbance enhancement zone The rate shows a linear trend of linear increase. The rate of formation loss gradually stabilizes within 4 ‰ in the zone with moderate disturbance, which meets the construction control target of 5 ‰, which shows that it is appropriate to control the formation disturbance after shield tail prolapse.