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摘要:
水位升降引起的水气压力变化会导致岩溶土洞塌陷。通过开展物理模型试验与FLAC3D数值模拟相结合的方式，模拟相同供水速率不同排水速率下的水位升降波动对岩溶土洞的致塌过程，分析了水位升降波动过程中不同排水速率对既有土洞内水气压力的变化、覆盖层土压、变形的影响，建立了排水速率，覆盖层变形、塌陷与水气压力的关系，提出了水位波动对土洞塌陷的作用规律。结果表明：（1）排水速率对水气压力变化的影响规律基本一致但变化程度不同。水气压力的变化程度、响应时间与排水速率呈正相关。（2）覆盖层变形量、土压的变化与水气压力变化呈正相关，但影响程度不同，排水速率只是加快了其变化程度。（3）土洞变形、塌陷程度是综合因素所致。排水速率、水位波动次数对既有土洞中水气压力变化、以及土体变形效应均具有不同程度的影响。（4）数值模拟结果与试验室模型试验所得结论基本吻合。这些规律为进一步研究水动力因素对岩溶塌陷的作用规律提供了重要的理论支撑，为合理防治、预测岩溶塌陷提供了依据。
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关键词:
- 土洞塌陷 /
- 物理模型试验 /
- FLAC3D数值模拟 /
- 排水速率 /
- 水位波动
Abstract:The change of water-gas pressure caused by the rise and fall of water level will lead to the collapse of karst soil caves. In this study, we combined the physical model test and FLAC3D numerical simulation to simulate the soil cave collapse caused by water level fluctuation under the same water supply rate and different drainage rates. Besides, we also analyzed the influence of different drainage rates on the variation of water-gas pressure, soil pressure of the overlying soil layer and deformation of soil caves during the fluctuation. We also established the relationship between water-gas pressure and variables such as drainage rates, overburden deformation and cave, and put forward the action law of water level fluctuations on the collapse of soil cave. The results show as follows. (1) The influence of drainage rates on the variation of water-gas pressure is basically the same, but with different degrees. The change degree and response time of water-gas pressure are positively correlated with the drainage rate. (2) The change of overburden deformation and soil pressure is positively correlated with the change of water-gas pressure, but with different influence degrees. The drainage rate can only accelerate the change degree. (3) Degrees of deformation and collapse of soil caves are caused by comprehensive factors. The speed of the drainage rate and the number of water level fluctuations influence the changes of water-gas pressure in different degrees in soil caves and also influence the soil deformation caused by water level fluctuations. (4) The numerical simulation results are basically consistent with the results of laboratory model test. These results provide important theoretical support for further research on the laws of hydrodynamic factors affecting karst collapse and provide a basis for rational prevention and prediction of karst collapse.
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图 15 不同排水速率下竖向位移分布图 (a)排水速率为2.08×10−4 m·s−1; (b)排水速率为2.78×10−4 m·s−1; (c)排水速率为4.17×10−4 m·s−1; (d)排水速率为8.34×10−4 m·s−1 ;(e)排水速率为4.17×10−3 m·s−1
Figure 15.
图 16 不同排水速率下最大剪应力分布图 (a)排水速率为2.08×10−4 m·s−1; (b)排水速率为2.78×10−4 m·s−1; (c)排水速率为4.17×10−4 m·s−1; (d)排水速率为8.34×10−4 m·s−1 ; (e)排水速率为4.17×10−3 m·s−1
Figure 16.
图 17 不同排水速率下塑性区分布图 (a)排水速率为2.08×10−4 m·s−1; (b)排水速率为2.78×10−4 m·s−1; (c)排水速率为4.17×10−4 m·s−1; (d)排水速率为8.34×10−4 m·s−1 ; (e)排水速率为4.17×10−3 m·s−1
Figure 17.
表 1 土体基本物理、力学参数
Table 1. Basic physical and mechanical parameters of soil
覆盖层类型 密度/g·cm−3 孔隙率 剪切模量/kpa 体积模量/kpa 内摩擦角/° 粘聚力/kPa 渗透系数/cm·s−1 红黏土 1.72 0.47 1.354×106 4.22×106 8.8 25.3 3.22×10−4 
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表 2 覆盖层厚度与岩溶塌陷关系统计表
Table 2. Relationship between cover layer thickness and karst collapse
覆盖层厚度/m <2 2~4 4~6 6~8 8~10 10~12 12~14 合计 塌陷个数/个 97 72 69 56 22 2 1 318 占百分比/% 30.41 22.57 21.63 17.55 6.90 0.63 0.31 100
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表 3 模型试验方案
Table 3. Model test scheme
方案 土洞直径/cm 初始水位位置 初始水位高度/mm 水位上升速率/m·s−1 水位下降速率/m·s−1 1 10 土层表面 100 2.78×10−4 4.17×10−3 2 4.17×10−4 3 2.08×10−4
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表 4 不同排水速率下一次水位升降过程中水气压力响应、变化及初始环境温度效应
Table 4. Water-gas pressure response, variation and initial ambient temperature effect during one rise and fall process of water level under different drainage rates
排水速率/m·s−1 试验时环境初始温度/ ℃ 既有土洞内初始气压值/kPa 水气压力响应时间/s 水气压力消散历时/s 水气压力降幅/kPa 4.17×10−3 20.88 101.083 1 010 10 3.7233 4.17×10−4 25.85 99.065 1 260 80 1.1202 2.08×10−4 31.29 98.99 1 510 90 0.8505
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