Study On Deformation Response Of Toppling Deformation Rock By Excavation At Miaowei Hydropower Station On Lancang River

The formation of toppling deformation has experienced a long geological history, generally it has good-stability under the condition of nature. But a large number of engineering cases show that engineering excavation characteristics of slope toe excavation could cause the continued development of toppling deformation. Studying the toppling deformable response to excavation is the basis of stability evaluation. In this paper, dam abutment slope of Miaowei hydropower station was taken as an example, combined with field investigation and monitoring data, the relationship between the deformation and slope excavation is analyzed, established the conceptual model of toppling slope, use discrete element simulation method studied the deformation response of the toppling deformable body under the excavation condition. The mainly achievements include:(1) Dam abutment slope of Miaowei hydropower station located in a “V” type open asymmetric valley. The left bank of dam abutment slope is slower, the natural grade is about 30°,the right bank of dam abutments slope is steeper, the natural grade range of 50°~60°.The slope exposures killas, sand slate, metamorphic quartz sandstone and phyllite, the strike of the rock stratum parallel with the strike of the valley, developed large-scale toppling deformable body on both sides of the mountain.(2) According to the toppling deformation degree of the toppling of rock mass, the righr and left dam abutment slope can be divided into three toppling degree:extremely strong(A), intensity(B) and weak toppling(C). Combined earlier stage of geological prospecting data and the detailed description of the structure in toppling of rock mass slope, the features of toppling slope rock mass partitioning is analyzed: both left and right dam abutment slope has extremely strong toppling area(A area), strong toppling area(B area) and weak toppling area(C area) rock mass. The horizontal depth of A,B,C area in left dam abutment slope is 0~15m,0~135m,0~130m; the horizontal depth of A,B,C area in right dam abutment slope is 0~25m,0~110m,>110m.(3) Slope monitoring data analysis results shows that areal deformation of both left and right dam abutment slope appeared with the form of surface crack, cumulative horizontal displacement and vertical displacement showed a cumulative increase tend, the overall level of displacement rate and cumulative deformation is bigger than vertical displacement. The maximum displacement in deep generally happened within 20 m depth, the overall deformation decrease with the increase of buried depth, after completion of excavation, the deep displacement has a longer period of slow deformation.(4) Using the discrete element particle flow numerical simulation studed deformation response of topping deformation rock on 4 types of excavation option. The results shows the deformation after excavation of toppling rock mass could divide into four stages: ① the excavation surface unloading springback stage; ② slope toe excavation site are destroyed, the upper rock mass sliding down and be dislocated.③ soft rock develop plastic deformation, hard rock develop deformation of “rotation”, along the structure surface is formed within the rock dilatancy or out of the rock mass destruction of parent rock. ④ when the slope toe has no object to prevent sliding, whole slope deformation shows an accelerated state until the whole completely destroyed; when the slope toe has an object to prevent sliding, whole slope deformation shows an deceleration state until reaches the balance.(5) According the result from the analysis to the process of deformation and failure of the right shoulder slope of the dam after the excavation of toe and the mechanism got by digital analogy there is a unload groove happening at the toe and the rock around the opening line get deformation at first with high speed. The excavation of toe and the airport surface formed by the deformation provided the foundation for the deformation of the upper rock. Caused the shear failure of the upper rock, the internal overhead and the slop of the ramp. And caused the tensile fracture at the top of the slope. The continuous deformation of the rock of region A drives the deformation of the rock of region B. Caused the shear diastrophism along the structural surface of the rock of region B and the deepening and the widening of the fissure of the shoulder of the dam. Along with the deformation, the shear failure phenomenon of the region A and region B get worse. Formed the step failure surface and happened Integral sliding failure finally.