Centrifuge modeling of excavation effects on a nearby tunnel in soft clay
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摘要: 为研究软黏土地层基坑开挖对旁侧隧道的影响,开展了相似比为1∶120的离心模型试验。试验获得了基坑开挖引起的地层不排水抗剪强度、土体孔隙水压力、隧道周围地层水平向土压力、地表沉降、隧道沉降和弯矩响应规律。试验结果表明：①基坑底暴露导致坑底和隧道周围土体超孔压长时间演变,并伴随着隧道周围地层水平向土压力大小和分布形式的持续变化；②基于竖向有效应力衰减程度的土体扰动度评价方法,发现位于坑底下方0.3倍和0.7倍开挖深度处的土体扰动度分别达到了0.33,0.21；③因既有隧道的约束作用,围护墙外侧地表沉降主要位于Peck（1969年）预测的地表沉降Ⅱ区；④基坑开挖完成后,地表沉降、隧道沉降和弯矩持续发展,开挖完成815 d后隧道总沉降达到了开挖期间沉降的1.6倍。固结和蠕变变形是开挖卸载后隧道变形和内力持续发展的主要原因,实际工程中应尽量减少坑底暴露时间。Abstract: The centrifuge modeling with a similarity ratio of 1∶120 is carried out to investigate the impacts of an excavation on a nearby tunnel in soft clayey strata. The responses of undrained shear strength, pore water pressures, horizontal earth pressures around the tunnel, ground settlements, tunnel settlements and bending moments are obtained. The test results show that: (1) The exposure of the excavation base leads to the continuous evolution of the excess pore water pressures of soils below the excavation base and around the tunnel, together with both the magnitude and distribution changes of horizontal earth pressures around the tunnel. (2) Using the effective vertical stress reduction ratio-based equation for soil disturbance degree (SDD), SDD of soils with vertical distances of 0.3 and 0.7 times the excavation depth below the excavation base are 0.33 and 0.21, respectively. (3) Due to the existing tunnel, the ground surface settlements behind the diaphragm wall mainly locate at Zone II predicted by Peck (1969). (4) After excavation, the ground surface settlements, tunnel settlements and bending moments develop continuously. The tunnel settlement at 815 days after excavation is 1.6 times that during excavation stage. The consolidation and creep may be the main reasons for the continuous development of tunnel deformations and internal forces after excavation, implying that the exposure time of the excavation base should be minimized in real projects.
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Keywords:
- centrifuge modeling /
- excavation /
- tunnel /
- soft clay /
- settlement
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图 5 基坑底T1和T2测点超孔压演变过程
Figure 5. Development of excess pore water pressure at T1 and T2
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图 7 隧道周围地层水平向土压力变化曲线
Figure 7. Evolution of horizontal earth pressure of soils around tunnel
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图 8 隧道右侧地层水平向土压力变化量沿深度分布
Figure 8. Distribution of increments of horizontal earth pressure of soils at right side of existing tunnel
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图 10 围护墙外侧地表沉降分布
Figure 10. Distribution of ground surface settlement behind diaphragm wall
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图 12 隧道纵向弯矩分布
Figure 12. Distribution of tunnel bending moment in longitudinal direction
表 1 离心模型试验参数相似关系（模型/原型）
Table 1 Relevant scaling laws in centrifuge models (model/prototype)
物理量 相似比 物理量 相似比 重力加速度/(m·s-2) 120 质量密度/(kg·m-3) 1 几何尺寸/m 1×120-1 弹性模量 1 面积/m2 1×120-2 弯矩/(N·m-1) 1×120-3 应变 1 抗弯刚度/(N·m-2) 1×120-4 应力/kPa 1 时间/s 1×120-2 
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表 2 试验模型和对应原型尺寸
Table 2 Dimensions of test model and corresponding prototype
模型 变量名 模型尺寸/mm 原型尺寸/m 围护墙 长×宽 300×150 36×18 围护墙板厚度 5 0.6 开挖深度 100 12.0 插入深度 160 19.2 隧道 与基坑距离 110 13.2 隧道外径 50 6 隧道长度 1100 132 隧道厚度 1 0.12 隧道拱顶埋深 100 12
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