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暴雨型滑坡灾害因素分析及预测试验研究
Trial Study on Factors Analysis and Prediction of Landslide Hazard Triggered by Extreme Heavy Rainfall
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摘要: 针对暴雨型滑坡灾害预报预警服务的需要, 以江西为研究区域, 从暴雨型滑坡灾害形成机理及预测理论入手, 通过8个滑坡灾害易发点的监测试验, 系统地研究了大气降水对地下水位、孔隙水压力、滑坡土体应力及滑坡稳定性的影响, 探讨了植被覆盖与滑坡的关系。结果表明:滑坡稳定系数与降水量有较好的负相关关系, 当降水量增大时, 滑坡稳定系数减小, 且略滞后于降水量的峰值; 在其他因素一定的条件下, 地下水位升高, 滑坡稳定系数直线下降。经计算得到8个试验点促使滑坡复活的临界指标是24 h降水量为60~203 mm, 值域的变化与滑坡体的土壤结构、力学性质、植被覆盖程度和降水强度的时空分布等因素有关。Abstract: To meet the service needs of predicting and warning landslides triggered by extreme heavy rainfall, based on mechanism of landslide induced by torrential rainstorm and its predicting theory, by monitoring experiment in eight trial grounds, the impacts of rainfall on underg round water table, pore water pressure, soil stress and landslides stability are studied. The influence of vegetation coverage on landslide is discussed. Combining trial data and statistics method, the precipitation values used to predict and warn the landslides are given.The function of precipitation on landslide is a dynamic process. When raining water is injected into landslide mass, water content and volume weight of rock soil mass can be increased, soil is intenerated, rock soil capacity is enhanced, and soil also becomes lubricant while penetrating into bedrock surface under weathering rock mass or layer cutting with water, which diminishes anti-slide force and causes landslide. Surface landslide in torrential rainfall is caused by short time function of violent precipitation. In the case, landslide mass arrives quickly to saturation situation that leads to ground displacement sharply, as water penetrates promptly and soil saturation degree and pore water pressure are increased, slope substance strength is reduced and it ends with landslide which is the surface landslide mechanism.Critical values of precipitation to forecast landslides are investigated, which provide bases to predict and warn landslide disasters. Eight observation sites in sensitive areas in Jiangxi Province are set to monitoring changes of water table, pore water pressure, stress of gliding zone, and landslide mass movement. Based on observational data and historic records, the purpose is to study models of landslides stability and search criteria forpredicting or warning landslide disasters. By monitoring and experiment, it is proved that landslide hazards can be predicted. Critical rainfall value to induce landslide acquired from field trial is in accordance with statistics results. Changes of water table consistent with precipitation are revealed. Water table has negative correlation with landslide stability, but is dependent on precipitation. The fluctuation of water level lags behind the rainfall wave with half to 1 day, the effect of each precipitation process on water table is different from landslide to landslide, some affecting duration lasts 5 days or less, others 15 days.Near the ground surface, water table changes strongly depending on precipitation.Drop speed of underground water varies with water table and rainfall amount. Changing features of pore water pressure in different depths of landslide body are discussed. Pore water pressure is a useful index to represent saturation degree of landslide mass. Research shows that the increase of rainfall and its intensity vary with the decreasing of landslide stability. Pore water pressure declines gradually from March to August till a lowest value and then increases again. Burying depth is in 6 to 7 meters, descending trend becomes weaker, which is related to evaportraspiration. Variations of landslide mass stress having a consistency with landslide movement are studied. Conditions of slope creeping can be well reflected by stress monitoring, indicating the probability of the mass occurring. It is proved that stress-monitoring data have more sensitivity to indicate the creeping of landslide than that of pore water pressure.Effects of vegetation coverage on landslides are derived from the intensity of precipitation. Whether more or less the degrees of vegetation cover and biology amount, or in mountainous areas, landslide disasters would occur, which are determined by the intensity of precipitation. Forest vegetation plays a role in intercepting precipitation, which can relieve water erosion. When rainfall intensity is 50 mm or more, interception amount decreases sharply. In the same geological environment, while precipitation intensity reaches a threat value that can lead to landslide, events of landslide hazard will be sharpened by vegetation weight adding to soil mass.The threat rainfall value to predict landslides in dense forest area is lager than that in sparse zone.
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Key words:
- heavy rainfall;
- landslide hazard;
- factors
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图 1 2004年ZK1(a) 和ZK2(b) 所监测到的大气降水和地下水位历时曲线图
Fig. 1 Time curve of underground water level and precipitation in ZK1(a) and ZK2(b) in 2004
图 2 2004年3—7月铜鼓县何家洞滑坡大气降水渗系数的时间变化
Fig. 2 Time changes of water penetrating coefficient in landslide body in Hejiadong, Tonggu County, Jiangxi Province from March to July in 2004
图 3 2004年铜鼓ZK3孔地下水压力历时曲线图
Fig. 3 Time curve of ZK3 underground water pressure in Tonggu County in 2004
图 4 定南应力盒压应力历时曲线
Fig. 4 Time curve of soil stress in the trail slope body in Dingnan County
图 5 2004年铜鼓ZK1孔埋深6 m处应力盒测定压力与地下水压力对照图
Fig. 5 Curve of soil stress and underground water level in 6 m depth under ZK1 in Tonggu County in 2004
图 6 2004年铜鼓监测点稳定系数波动曲线与降水量对照图
Fig. 6 Curve changes of landslides stability coefficient and precipitation in Tonggu County in 2004
图 7 铜鼓县监测点稳定计算分块示意图
Fig. 7 Fourteen blocks divided in the slope body for calculating stability coefficient in Tonggu County trail ground
图 8 铜鼓县监测点ZK1孔地下水位与滑坡稳定性关系图
Fig. 8 Relationship between underground water level and landslide stability coefficient in ZK1 in Tonggu County
表 1 ZK1孔的地下水位与降水量相关系数
Table 1 Relative coefficient between underground water level and precipitation in ZK1
表 2 ZK2孔的地下水位与降水量相关系数
Table 2 Relative coefficient between underground water level and precipitation in ZK2
表 3 2004年监测期间稳定性系数最小值
Table 3 The minimum values of stability coefficient in eight trail ground in 2004
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