Investigation of the kinematic characteristic of Lijie Beishan landslide through surface displacement monitoring and rainfall response numerical simulation
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摘要:
速度倒数法(INV)是基于坡表变形特征的滑坡启滑预测工具, 其与滑坡内部多物理场演化的关系仍需进一步明晰。开展了甘肃省舟曲县立节北山滑坡的勘察与坡表变形监测, 采用基于速度倒数法、速度阈值法、以非饱和土理论为基础的边坡降雨响应模拟3种方法, 对该滑坡的运动特征与失稳的内在机制展开了研究。研究结果表明: 边坡变形速度倒数-时间曲线有明显的加速起始点。速度倒数在2021年6月3日达到最低值后, 进入约60 d的平稳期, 在9月20日突然加速, 并在20 d内速度达到200 mm/d以上, 变形不再收敛。基于速度倒数法得到的滑坡生命周期结束点, 与实际的失稳点相差8 d, 提前约130 d对该突发性滑坡进行了预报。根据全过程速度时程曲线, 存在20, 60, 100 mm/d的多级速度阈值。边坡应力场、变形场、渗流场的数值模拟结果显示, 变形时程曲线的拐点与降雨强度的增加相关, 累计降雨量与安全系数呈指数负相关。数值模拟得到的累计变形为2 250 mm, 变形速度为10~35 mm/d, 速度倒数为0.03~0.12 d/mm, 与实际监测数据接近。综上所述, 速度倒数法对立节北山滑坡的生命周期进行了有效预测, 基于速度的预警阈值受长时序变形时程曲线波动的影响, 采用以非饱和土理论为基础的数值模拟明晰了立节北山滑坡变形对降雨的响应机制。
Abstract:Slope kinematics is normally used to evaluate the temporal and spatial evolution of landslides. The inverse velocity method (INV) is an important tool for predicting the initiation of landslide, but its correlation with the physical and mechanical mechanisms of multiple physical fields inside the landslide need to be further clarified. In this paper, the slope deformation and geological characteristics of the Lijie Beishan landslide in Zhouqu, Gansu Province was investigated. The inverse velocity method, velocity threshold method and numerical simulation based on unsaturated soil theory were used to study the kinematic characteristic of slope. The results showed that after the lowest value of the inverse velocity on June 3, 2021, a stable stage lasted for approximately 60 days and then suddenly accelerated on September 20. The velocity became more than 200 mm/d over 20 days, and the deformation did not converged. There was an obvious acceleration point in the time-dependent inverse velocity curve. The end of the landslide life cycle was obtained by extending the straight line after the onset of the acceleration point. The prediction period was within 8 days compared to the actual instability startup, and the landslide was predicted 130 days in advance. According to the post analysis of the whole time-dependent velocity curve, the multi-level speed thresholds of
v 1=20 mm/d,v 2=60 mm/d, andv 3=100 mm/d were set up. Because there were two peaks of velocity, the prediction of landslide triggering was lagging compared to the inverse velocity method. The coupling of slope stresses, deformation and pore water transportation was simulated. The results showed that the inflection point of the time-dependent deformation curve was correlated with the increase in precipitation intensity, and the cumulative precipitation was negatively exponentially correlated with the safety factor. The cumulative deformation obtained by numerical simulation was 2 250 mm, the velocity of deformation was 10-35 mm/d, and the inverse velocity was 0.03-0.12 d/mm, which were close to the actual monitoring data. However, there was still a deviation between the prediction of the inflection point of slope deformation and the actual situation. -
图 1 2021年1月20日-10月30日单日降雨量与累计降雨量历时曲线
Figure 1. Time-dependent precipitation intensity and cumulative precipitation from January 20 to October 30, 2021
图 2 立节北山滑坡分布与监测设备布置图
Figure 2. Spatial distribution of Lijie Beishan landslide and setup of the monitoring system
图 5 2021年1月20日-6月3日GNSS1前期监测数据
Figure 5. Preliminary data of GNSS1 from January 20 to June 3, 2021
图 6 2021年1月20日-10月30日GNSS1全周期数据
Figure 6. Data of GNSS1 in complete period from January 20 to October 30, 2021
图 10 数值模拟得到的坡表变形时程曲线
Figure 10. Time-dependent slope deformation based on numerical simulation
图 12 累计降雨量-安全系数相关性分析
Figure 12. Correlation analysis of cumulative precipitation and safety factor
图 13 监测数据与数值模拟结果的对比分析
Figure 13. Correlation analysis of monitoring data and numerical calculation results
表 1 速度阈值预警等级
Table 1. Warning level and velocity threshold
变形速度 v < v1 v≥v1 v≥v2 v2≥v≥v3 v≥v3，Δv>0 预警等级 正常监测级 注意级 警示级 警戒级 警报级 注：v1用于识别滑坡开始出现异常变形时的状态；v2用于判断滑坡异常变形是否进入加速阶段；v3用于判断变形是否达到临界状态。另外, 采用速度增量Δv来判断滑坡变形趋势 
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表 2 岩土体物理力学参数取值
Table 2. Mechanical and physical parameters of the soil and rocks
名称 重度/(kN·m-3) 黏聚力/kPa 内摩擦角/(°) 饱和含水率/% 渗透系数/(m·s-1) 泊松比 弹性模量/MPa 堆积体 15~18 15 10~15 45 2.2×10-6 0.30~0.35 10~20 基岩 26~27 6×103 — — 0.20~0.25 4×104
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