| A special sedimentary stratum is widely distributed in Sichuan Basin,Southwest of China,which is composed of interbedded thick sandstones and thin mudstones layers.Translational landslides are often developed in this type of rock combination.With a small angle of the slip surface,the internal friction angle of slip soil in this type of landslides is often greater than the sliding surface inclination.These landslides are extremely stable evaluated by a traditional limit equilibrium theory method.It is characterized for their complex formation mechanisms,highly concealed,suddenly happened,and serious destruction.For such rainfall induced landslide,the main influence factor of the stability is groundwater.In order to establish the monitor-warning system in a translational landslide,it is required to study the dynamic characteristics of the groundwater flow.In this paper,multi-tracer test,injection test and electrical resistivity tomography were used to investigate the hydrogeological characteristics in the fracture medium of a typical translational landslide(Kualiangzi),which is located in the Sichuan Basin,China.There are some understandings below.(1)The groundwater flow in the Kualiangzi landslide is mainly controlled by vertical preferential flow pathway(concentrated mode)of which the direction is perpendicular to the sliding direction of this landslide approximately.It is developed from structural fracture.The groundwater flow migrating along the weathered sandstone and mudstone medium in the vicinity of slip surface is very slow(dispersed mode)compared with the groundwater flow in the preferential flow pathway.(2)The preferential flow pathway made the observed BTCs(Breakthrough Curve)concentration higher in the nearby wells of the preferential direction.The dominant permeate direction is verified by the direction of preferential hydraulic conductivity indicated by hydraulic conductivity ellipse,which is obtained by analyzing injection test.The orientation of maximum hydraulic conductivity(K?=33.865m/h)is 65.34 o east by north.The direction of minimum hydraulic conductivity(K?=0.009m/h)is perpendicular to the direction of preferential hydraulic conductivity.The hydraulic conductivity in the preferential direction is more than 3750.52 times larger than that perpendicular to the preferential direction.Based on the analysis of engineering geological conditions,these concentrated flow pathways are subvertical cracks space in the sandstone layer,which are developed from the joints with the trend of WN10°–20° and dipping angle of 80-85°.The reason for this development is the different deformation rate between the hard sandstone and the weak mudstone and landslide movement.These subvertical cracks provide well space for groundwater flow.(3)The main discharge direction along the preferential flow pathway is southwest in the middle of the landslide according to the electrical resistivity tomography and sodium chloride tracer test.The northeast direction is the secondary discharge direction.The mean and maximum velocities in main discharge direction in flood period were up to 29.87-35.75m/h and 127.59m/h respectively.The mean and maximum velocities in the secondary discharge direction were 0.04m/h and 5.08m/h respectively.(4)The dispersion parameters in study area are estimated by Qtracer2 program.The range of longitudinal dispersivity is 0.03~0.05 m,dispersion coefficient is 3.58E-6~5.60E-6m2/s and Pelect number is 187.46-1657.1. |
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