Study On Relationship Between Stability And Groundwater Table In Slope At South Jingyang Plateau,Shannxi Province

In South Jing-yang Plateau, Shannxi Province, the loess landslides and collapses occurred frequently because of the Change of Groundwater Table which induced by water raising appliances for irrigation since 1976. It shrinked loess plateau area and caused heavy casualties and serious economic losses. According to monitoring data of groundwater and survey of geological hazards, the relationships between law of groundwater table change and geological hazards were studied. Then the Qualitative-quantitative numerical simulation method was used to gain the Relationship between Stability and change of groundwater table in loess slope at south Jing-yang Plateau. The main achievements include:(1)The relationships between law of groundwater table change and geological hazard include:The rise of groundwater table caused by irrigation activities is the major predisposing factor of landslide. After diversion and irrigation in 1976, the groundwater table of slope in South Jing-yang Plateau raised year by year (the average annual rise is as high as 2.31m). The development Law of landslide is divided into three periods:early Irrigation (1976 to 1980), Irrigation water has not been formed through channel in the slope, in this period, the recharge way to groundwater is single, landslide frequency has only once. With irrigation efforts to strengthen (1981 to 2000), the groundwater levels raised continuously, and there were 26 landslides formatted in this 20 years. After 2000, some Control measures were carried out, the water table reproduced a stable period, slope become stable.(2)The influence of underground water level change to slope stability on the tableland edge have been considered., the first factor considered was the reduction of intensity parameter of soil caused by change of groundwater level, and the another factor considered was the hydrostatic pressure and hydrodynamic pressure caused by transfusion inside the slope. Then the stability evaluation method considering the influence of transfusion which is suitable for the unsaturated soil slopes in research area had been analyzed. Then taking the Dong Feng slide as an example, the theory verification of the stability evaluation method was done, and this example verification demonstrated the stability evaluation method is reasonable and feasible.(3)The simulation results of dynamic seepage field of Dong Feng slide from 1993 to 2003 are as follows:the saturation line in the slope rised convexly year by year, and the infiltration front moved continually to the front of the slope; Seepage concentrated in interface and oozed out of the slope at the slope angle; The maximum seepage vector and hydraulic gradient increased continuously, and the maximum seepage vector increased from 0.051m/d at 0a(1992) to 0.137m/d at 11a(2003), the hydraulic gradient increased from 0.056m/d at 0a(1992) to 0.193 at 11a(2003); The affected area of unsaturated zone within the online side 20.0m; The water content and pore water pressure in the scope of 20m above the invasion line were greatly affected, and these in the scope of on the top of slope and beside 20m of the invasion line were weakly influenced.(4)The quantitative relationship between stability and change of groundwater table of Dong Feng slide as follows:①tability decreased with the change of groundwater table,and in good line relation, the correlation coefficient is 0.9655.②The safe waterline of Dong Feng slope was not less than 50.7m, which can ensure the stability of the slope.