Study On The Characteristic Of Seepage Field And The Effectiveness Of Drainage Project Of Badu Landslide

The frequency of landslide, especially the giant landslide, is getting higher and higher, and the damage of landslide is becoming bigger and bigger since the 20th century. The influence of groundwater seepage to the stability of giant landslide and the influence of the landslide drainage project to the stress field, the seepage field is an important issue.From the perspective of the theory of seepage characteristics of unsaturated soil, this paper introduces the predecessors research results of unsaturated, saturated soil seepage. Using ABAQUS finite element software to calculate the rainfall numerical case of different scale soil slope and the drainage engineering numerical model of Badu landslide, and analyzing the effectiveness, which is evaluated by Seepage field, displacement field, stress field, and landslide stability coefficient。The research results mainly include:(1) From the calculation of different sizes numerical slope of rainfall can be seen that, within the scope of the rainfall infiltration, pore pressure has an obvious increase, and in the distance far to the rainfall infiltration pore pressure increase to a relatively small value. The bigger slope is, the maximum negative pore pressure of slope is bigger, and the corresponding matrix suction of soil is greater, and the distribution of matrix suction is more uniform in the pore pressure nephogram, this is mainly due to the ABAQUS assumes that pore pressure and the distance of place to surface are linear change. The horizontal displacement nephogram of Slope display an arc from the slope surface to the inside after 72 hours rainfall, and the value is gradually reduce, with the increase of the slope scale, the horizontal displacement of slope is gradually relatively increase, and the proportion of the horizontal displacement is larger. With the increasing scale of slope, slope principal stress increases gradually, the maximum principal stress, the more close to slope surface, is parallel to the direction of the slope, the farther slope in the closer it gets to the horizontal direction, and basically is given priority to with tensile stress, only for compressive stress of the slope and slope toe, the minimum principal stress direction with the maximum principal stress intersection, give priority to with compressive stress, the level of the slope to the vertical effective stress and effective stress with the slope scale increases, the level to give priority to with tensile stress, effective stress only for compressive stress of the slope and slope toe, the vertical effective stress only had part of the tensile stress in the slope form.(2) The calculation results of Badu landslide under rainfall infiltration show that, the saturated zone increases gradually after the rain, and at the interface between the whole rock bed and soil layer formed a larger saturated zone, while the slope matrix suction of the soil decreases. The gravity horizontal displacement are mainly concentrated in the rear of the main landslide, and the maximum displacement is 4.5mm, after 30 rainfall days, the horizontal displacement of slope are apparently increased, mainly concentrated in the rear of main landslide and the front of secondary landslide, and the maximal displacement of secondary landslide is 395mm, BaDu secondary landslide and the maximum principal stress of the main landslide slope front table for vertical slope table tensile stress, and stress is concentrated, and watch the rest of the slope is mainly parallel to slope table vertical section in the direction of maximum principal stress, the tensile stress in the scattered distribution of vertical slope table, so the main and secondary landslide front parts for landslide deformation more easily; At 30 days’rain BaDu level to the effective stress in the main landslide subprime preceding basic with tensile stress is given priority to, other basic position is given priority to with compressive stress, the vertical effective stress basic is given priority to with compressive stress, tensile stress in the slope table there are a few areas.(3) It can be seen from the contours of pore pressure of different drainage scheme that after setting drainage measures, the drainage effect of landslide is very apparent, and most of the slope groundwater is drainaged, landslide displacement and deformation trend gradually slow down, and the effective stress of soil is gradually increase.(4) The displacement nephogram and displacement-precipitation duration curve shows that BaDu landslide displacement is obviously affected by rainfall, namely, BaDu slope sliding displacement increases after the occurrence of rainfall, and the groundwater intensify creep deformation after 5 days. It is concluded from the pore pressure calculation results that the pore pressure and pore pressure-depth curve of scheme two, scheme three and scheme four, scheme one is quite close, and the pore pressure of the scheme two, scheme three are bigger than the scheme one,scheme four, thus scheme four, scheme one are better, after 30 days, landslide deformation apparently is smaller than the situation with no drainage project, and the main landslide deformation significantly less than secondary landslide, and through the displacement comparison of drainage schemes shows that scheme four is best, but the difference between scheme one and scheme four deformation is still small (the main landslide differs by 2 mm, secondary landslide differs by 10 mm). Thus from the perspective of pore pressure, displacement and engineering cost, construction difficulty, scheme one is a good scheme.(5) The slope stability analysis of the four schemes by ABAQUS is concluded that the slope stability Fs of the slope from scheme one to scheme four is respectively 1.06,0.99,0.95 and 0.95, which demonstrates that the scheme four and scheme one are better scheme to drain the groundwater. In the process of the strength reduction, the development of slope plastic zone indicate that secondary landslide form plastic transfixion area earlier than the main landslide, namely the secondary landslide slips earlier than the main landslide in the process of the landslide instability.