| Since the impoundment of the Three Gorges Reservoir in 2003,a large number of colluvial landslide have been induced,which has caused huge losses to the safety of local residents ’ lives and property.Therefore,it is of great theoretical significance to study the deformation evolution mechanism and displacement dynamic model of reservoir bank colluvial landslide.In this paper,a displacement dynamic model of reservoir bank colluvial landslide considering rainfall,reservoir water level change and mechanical strength of sliding zone soil is constructed for the constant velocity deformation stage in the deformation evolution process of reservoir bank colluvial landslide.Then,Geo Studio software is used to simulate the deformation evolution process of typical reservoir bank colluvial landslide.Combined with the in-situ monitoring data of typical landslide,the applicability of landslide displacement dynamic model is verified and analyzed.The research results have important theoretical significance and engineering application value for the monitoring,early warning and treatment of reservoir bank colluvial landslide,and can provide theoretical reference for the risk control of landslide geological disasters.Firstly,according to the ratio of the elevation difference between the reservoir water level and the elevation difference between the front and rear edges of the landslide,the inundation ratio of the colluvial landslide is defined,and the inundation ratio of the typical colluvial landslide is calculated.Based on the previous studies on the deformation characteristics of each stage in the deformation evolution process of the colluvial landslide,combined with the analysis of the landslide displacement monitoring data curve in the reservoir area,the research on the constant velocity deformation stage of the colluvial landslide is carried out.The calculation formula of groundwater saturation line considering the change of rainfall and reservoir water level and the calculation formula of mechanical strength of sliding zone soil considering viscous resistance are derived.On the basis of the two formulas,the landslide displacement dynamic model considering rainfall,reservoir water level and mechanical strength of sliding zone soil is constructed.Then,the Shuping landslide with a medium inundation ratio(21.35 %)and the Baijiabao landslide with a high inundation ratio(42.97 %)were selected as typical colluvial landslide.The deformation evolution mechanism of the colluvial landslide was analyzed based on the in-situ monitoring data of the landslide,and the typical period was selected for numerical simulation and displacement dynamics model verification.Finally,the applicability of displacement dynamic model is studied for landslides with different submerged ratios.The research work and results are as follows :(1)Based on the statistical analysis of the cumulative displacement monitoring curve of the colluvial layer landslide in the Three Gorges Reservoir area,it is found that the number of landslides with step deformation characteristics accounts for 41.07 %.In order to study the influence of reservoir water level operation on the deformation evolution of the colluvial layer landslide in the Three Gorges Reservoir area,according to the ratio of the elevation difference between the reservoir water level operation and the elevation difference between the front and rear edges of the landslide,the landslide inundation ratio is defined,and the maximum inundation ratio of 8 landslides with obvious step deformation characteristics in the cumulative displacement curve of the reservoir area is calculated to be 1.5 % ～ 46.8 %.Taking 20 % as the gradient,Shuping landslide with medium submergence ratio(21.35 %)and Baijiabao landslide with high submergence ratio(42.97 %)were selected as typical colluvial landslide research cases.(2)According to the previous research on the characteristics of each stage of the deformation evolution of the colluvial landslide,the constant velocity deformation stage of the landslide is selected for analysis,and the groundwater saturation line formula considering the effective infiltration rainfall and the change of reservoir water level is derived.The definition of equivalent internal friction angle and equivalent cohesion is proposed by using the groundwater saturation line formula,and the mechanical strength calculation formula considering the viscous resistance of sliding zone soil is derived.Then,the landslide displacement dynamics model is constructed by combining the groundwater saturation line formula and the mechanical strength formula of sliding zone soil.(3)Taking Shuping landslide as an example,based on the monitoring data of water level,rainfall and surface displacement of the landslide reservoir,combined with the calculation results of the displacement dynamics model and the numerical simulation results,the results show that for the Shuping landslide with a submerged ratio of 21.35 %,the accuracy of the displacement dynamics model calculation results is between 94.56 % and 99.82 %,and the accuracy of the numerical simulation results is between 93.13 % and 99.42 %.The groundwater level of Shuping landslide is more sensitive to reservoir water level,which is 0.965,and less sensitive to rainfall,which is 0.0011.The internal cause is mainly controlled by the permeability coefficient of landslide rock and soil,and the sensitivity coefficient of landslide groundwater level to the permeability coefficient is 0.0028.(4)Taking Baijiabao landslide as an example,based on the monitoring data of landslide rainfall,reservoir water level and surface displacement,combined with the calculation results of displacement dynamics model and numerical simulation results,the results show that for Baijiabao landslide with a submerged ratio of 42.97 %,the displacement accuracy calculated by displacement dynamics formula is between 87.62 % and 95.03 %,and the displacement accuracy obtained by numerical simulation is between 78.96 % and 90.25 %.In addition,there is a strong correlation between the low water level operation of reservoir water and the deformation of Baijiabao landslide.When the reservoir water level is lower than 155 m,the deformation displacement of Baijiabao landslide is the most significant.The sensitivity coefficient of the deformation of the Baijiabao landslide to the change of the reservoir water level is 1.241,the sensitivity coefficient to the rainfall is 0.0039,and the sensitivity coefficient to the permeability coefficient is 0.231.Therefore,the change of the reservoir water level is the main factor for the resurrection of the Baijiabao landslide.The size of its permeability coefficient restricts the response of landslide deformation displacement to rainfall and reservoir water level changes.(5)The applicability of the landslide displacement dynamic model under different submerged ratios is verified.The applicability of the dynamic displacement model decreases with the increase of the maximum submerged proportion of the landslide.For the Shuping landslide with low submergence ratio,the accuracy of the results calculated by the groundwater saturation line formula is between 98.52 % and 99.86 %.For the Baijiabao landslide with a high proportion of inundation,the accuracy of the groundwater saturation line formula is between 98.6 % and 99.49 %,but the overall accuracy has been decreasing.In addition,the deformation of Baijiabao landslide is concentrated in the period when the dynamic inundation ratio of the landslide is less than 5.12 %(the water level of the reservoir is less than 160 m),and the maximum deformation rate of the landslide calculated by the displacement dynamics formula occurs during the period when the dynamic inundation ratio of the landslide decreases,which is 4.49 mm / d.At this time,the dynamic inundation ratio of the landslide is 1.35 %(the water level of the reservoir is 149.03 m);for Shuping landslide,the deformation of landslide is concentrated in the period when the dynamic submergence ratio of landslide decreases.The maximum deformation rate of landslide calculated by displacement dynamics formula also appears in this period,which is 5.64 mm / d.At this time,the dynamic submergence ratio of landslide is 2.75 %(reservoir water level is 161.71m).The applicability of the landslide displacement dynamic model under different wading degrees is verified.The applicability of the displacement dynamics model decreases with the increase of the maximum wading degree of the landslide.For the Shuping landslide with low wading degree,the accuracy of the calculation results of the groundwater saturation line formula is between 98.52 % and 99.86 %.For the Baijiabao landslide with a high degree of wading,the accuracy of the groundwater saturation line formula is between 98.6 % and 99.49 %,but the overall accuracy has been decreasing.In addition,the deformation of Baijiabao landslide is concentrated in the period when the dynamic wading degree of the landslide is lower than 5.12 %(the water level of the reservoir is lower than 160m),and the maximum deformation rate of the landslide calculated by the displacement dynamics formula appears during the period when the dynamic wading degree of the landslide decreases,which is 4.49 mm / d.At this time,the dynamic wading degree of the landslide is 1.35 %(the water level of the reservoir is 149.03m).For Shuping landslide,the deformation of landslide is concentrated in the period when the dynamic wading degree of landslide decreases.The maximum deformation rate of landslide calculated by displacement dynamics formula also appears in this period,which is 5.64 mm / d.At this time,the dynamic wading degree of landslide is 2.75 %(reservoir water level is 161.71m). |
