3D visual model tests on stability of tunnel excavation surface based on transparent soil
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摘要: 为研究承压渗流条件下复合地层盾构开挖面失稳破坏模式及支护压力,自行研发了一种可以自由施加多种渗流承压作用的三维可视化盾构开挖面稳定性模型试验系统。该系统首次采用两种不同透明土材料模拟黏土-砂砾石复合地层,不仅可以消除原样砂砾的粒径效应,而且可以清晰演示复合地层内部变形过程,并基于数字图像测量技术和自行编写的三维地形位移场重构程序可精准获取开挖面三维破坏体视图。应用该设备进行了7组盾构隧道不同埋径比（C/D=0.5,1.0,2.0）的模型试验,系统研究黏土-砂砾石复合地层有无承压水渗流条件下盾构隧道开挖面稳定性。试验结果表明：有无承压水渗流条件下,支护压力随开挖面后撤位移曲线均存在明显3个阶段；临界破坏状态下,模型试验得到的破坏体形态与隧道埋径比C/D有关,隧道浅埋与深埋时破坏体形态存在不同,此外,破坏体形态还与土层类别息息相关,不同土层中土体破坏形态也不尽相同；相比无渗流条件,承压渗流条件下开挖面土体失稳破坏区域影响范围更广。同时,以上试验也表明了该试验系统可形象地再现盾构开挖面失稳破坏演化过程,具有采集精度高、稳定性好和可操作性强等优势,适用于各种复杂工况下复合地层开挖面稳定性研究。Abstract: To study the supporting pressure and instability failure modes of shield tunnel face in composite soil strata under seepage and confined water, a three-dimensional visualized model test system for tunnel face stability is invented to freely exert multiple seepage and confining effects. For the first time, the system uses two different transparent soil materials to simulate a clay-gravel composite stratum, which can eliminate the particle size effect and demonstrate the internal deformation of the composite stratum clearly. Based on the digital image measurement technology and a self-written 3D reconstruction program, the 3D failure mode view of the excavation surface can be obtained accurately. A series of model tests are carried out to investigate the failure modes of the tunnel face with three different cover-to-diameter ratios of 0.5, 1.0 and 2.0 under seepage and confined water in clay-gravel composite strata. The test results show that the curve of the supporting pressure can be divided into three phases. In the critical failure state, the shape of the failure modes is related to the tunnel diameter ratio C/D obtained by the model tests. The shape of the failure modes is different when the tunnel covered depth is relatively small or large. In addition, the shape of the failure modes is also related to the type of soil strata. Compared to that under no seepage, the soil failure zone of the excavation surface under seepage confined water has a wider influence range. At the same time, the test system can vividly reproduce the evolution process and development law of the failure zone on the tunnel face. It has the advantages of high sensitivity, good stability and strong operability. It can be used to study the stability of the tunnel face under various complex conditions.
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Keywords:
- shield tunnel /
- composite stratum /
- tunnel face stability /
- transparent soil /
- model test
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图 1 承压渗流作用下开挖面稳定模型试验系统
Figure 1. Model test system for excavation face stability under seepage and confined water
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图 9 支护压力比与相对位移曲线（饱和无渗流）
Figure 9. Curves supproting pressure ratio and relative displacement pressure (Undrained)
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图 11 开挖面失稳等值线图（饱和无渗流）
Figure 11. Contour map of excavation face instability (Undrained)
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图 12 支护压力比与相对位移曲线（承压渗流）
Figure 12. Curves of supporting pressure ratio and relative displacement pressure (seepage and confined water)
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图 13 复合地层变形过程（承压渗流）
Figure 13. Deformations of composite soil strata (seepage and confined water)
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图 14 开挖面失稳等值线图（承压渗流）
Figure 14. Contour map of excavation face instability (seepage and confined water)
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图 15 开挖面失稳区域三维重构视图
Figure 15. Three-dimensional reconstruction view on failure zone of excavation face
表 1 隧道开挖面稳定试验方案
Table 1 Schemes of tunnel face stability
工况 地层 渗流/承压水 埋深/直径（C/D） 工况1 黏土-砂砾石 无 0.5 工况2 黏土-砂砾石 无 1 工况3 黏土-砂砾石 无 2 工况4 黏土-砂砾石 有/3D 0.5 工况5 黏土-砂砾石 有/3D 1 工况6 黏土-砂砾石 有/3D 2 工况7 黏土 无 1 注： C为隧道上覆土层厚度,D为隧道直径。
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