| Numerous rockslide deposits occurring in Three Gorges Reservoir area(TGR)threaten safety of local resident,shipping and dam seriously,the influences of the deposit-bedding interface(DBI)morphology and mechanical properties on slope stability and failure mechanism is significant.The aim of this study is to reveal the controlling mechanism of deposit-bedding interface on rockslide deposits stability in TGR,China.Multiple research methods,including statistical analyses,theoretical analyses,laboratory experiments and numerical simulations,are used to clarify the spatio-temporal development law of rockslide deposits,and a preliminarily investigation about the factors affecting the landslide occurrence is conducted.Based on it,the relationship between slope structure and DBI morphology is built,and the landslide stability under the influence of permeability of sliding body,mechanical property and dip angle of DBI are considered.Taking Taping landslide with linear DBI and Outang landslide with steep-gentle dip angle DBI as examples,both the deformation characteristics and failure evolution mechanism under the coupled influence of reservoir water level(RWL)and rainfall are performed.The main works and conclusions of this study are as follows:(1)Based on numerous statistical information about 790 rockslide deposits cases,the development laws of rockslide deposits show good regional sorting in spatial and distinct stage in temporal.The landslide probability density-magnitude distribution exhibits the self-organized criticality,and the critical landslide area is approximately 2.5×10~4m~2.The relationship between the landslide occurrence and the influence factors such as elevation,slope angle,lithology,slope structure,reservoir water level,and rainfall,is qualitatively analyzed.The relationship between landslide area and volume follows power-law function.The adaptability of the Three Parameter Inverse Gamma function is better than that of Double Pareto function in covering the relationship between landslide probability density and landslide magnitude.(2)According to geological information from 560 rockslide deposits cases,the correlations between DBI morphology and slope structure are revealed.Two landslide models having linear and steep-gentle dip angle DBI are proposed,and the stability change laws of these two landslide models under the influence of permeability are presented.For landslide model with steep-gentle dip angle DBI,when the position of fluctuating RWL is corresponding to the gentle segment of the DBI,the relationship between the landslide stability and reservoir operation would transit from positive to negative as the permeability increase.The influence law posed by the permeability of the mobilized materials on the stability of landslide model with linear DBI is basically the same as the above-mentioned.While if the position of fluctuating RWL is corresponding to the steep segment of the DBI,the relationship between the stability and reservoir operation would change from positive to imperceptible as the permeability increase.(3)The change laws of landslide stability and controlling laws of the sliding surface position for these two landslide models influenced by the mechanical parameters of DBI are clarified by numerical simulation.The results show the landslide stability decrease as the degradation of mechanical parameters of DBI.For landslide model with steep-gentle dip angle DBI,with the decrease of strength properties,the sliding surface will first appear in the front part of the landslide near the DBI,then extends toward upslope and connect with the DBI.Finally,the landslide may be cut out from the middle part of the slide body or destroy along the DBI basically.For landslide model with linear DBI,the position of the sliding surface will gradually extend to the upper part from the front near the DBI,and then expand the degree of overlaps with the DBI,and finally develop along the whole DBI.(4)The influence laws affected by the dip angle of DBI on these two landslide models stability are revealed in detailed.Generally,as the rises of the difference of the dip angle between steep and gentle segment of DBI,the factor of safety for landslide having steep-gentle dip angle DBI increases.While the factor of safety for landslide with linear DBI decrease from fast to slow along with the increase of the dip angle of linear DBI.The larger the dip angle of linear DBI is,the more sensitive the safety factor is to the change of strength parameters.(5)Taking Taping landslide as examples,the multi-retrogressive failure evolution mechanism for the rockslide deposit with linear DBI morphology under the coupled influence of RWL and rainfall are analyzed.Based on the long-term multi-type monitoring data,the change laws of groundwater and subsurface displacement are revealed,the characteristics of slope surface displacement are presented spatially and temporally.The deformation mechanism and failure mode are uncovered.The results from UDEC show that the failure evolution could be divided into three stages:the blocks near the ground surface at the toe detached;the rock failure occurred firstly at the front part of landslide and subsequent extension to the upslope with the characteristics of multi-retrogressive process.(6)The Outang landslide is selected as case study,the mechanism of a compounded push-retrogression-type failure process for the landslide with steep-gentle dip angle DBI under the coupled influence of RWL and rainfall are revealed elaborately.The Outang landslide can be divided into three subzones with both the first and second subzone sliding along IL1,and the third subzone slides along IL3,proved by the in-site investigations and inclinometer data.The dominating impact factors for the groundwater could transition from the reservoir water to the rainfall as the elevation increases.The key triggering factors for slope movement at different subzones are ascertained based on long-term monitoring data analysis and correlation theory.The results from UDEC show that the RWL affects slope movement of the front part of the landslide,the effect of rainfall on the slope movement is mainly concentrated in the middle and the upper.The landslide exhibited a composite push-retrogression-type failure evolution with the fluctuating reservoir levels destabilizing rock masses at the front part of the landslide and the precipitation mainly mobilizing materials in the upper part of the slope. |
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