Research On Trigger Mechanism Of Strong Toppling Deformation Of Reservoir Bank Near Dam Of A Hydropower Station Of The Yellow River

Stability of reservoir slopes have been one of the main problems of the Hydropower Engineering Geology for its popularity,harmfulness and particularity.So the further study of its trigger mechanism and evolution process is great significant for evaluating reservoir slope stability,predicting their development trend and developing cost-effective treatment measures.In this paper,taking a slope at the right bank of a hydropower station in upstream of the Yellow River for the study.On the basis of identifying its engineering geological conditions,reservoir slope deformation characteristics and deformation monitoring data.Using the engineering geology analysis method to analyse the deformation of reservoir slope toppling inducing factors and its mechanism.And through the numerical simulation on reservoir slope deformation evolution process is simulated.Specific contents and results are as follows:(1)Reservoir slope is a product of the composite deformation under the condition of long geological history,mainly composed of granite.Slope body with complex structure and a large number of structural plane which the main genetic types are tectonic structural planes and supergene structural planes.The rock mass of reservoir slope has a high degree fragmenting under the action of the structure cutting,weathering and unloading.By the table to the inner the slope can be divided into five belts: granular structure,cataclastic structure,tabular structure,mosaic block structure and block-integral structure.(2)Reservoir slope with typical dump deformation characteristics,the deformation and fracture of slope table mainly for toppling-tensile fracture,fracture and disintegration-caving of three basic forms.By the table to the inner thedeformation and fracture of rock mass for five types,they are toppling-disintegration,toppling-fracture,toppling-tensile fracture,toppling-relaxation and weak unloading-relaxation.Combined with the development of dump deformation and its engineering geological properties,the dump deformation intensity of rock mass is divided into four types of engineering geology rocks: A is extremely strong toppling disintegration,B is strong toppling tensile fracture,C is weak toppling relaxation and deep original rock mass.In posterior edge of active slope form a "tensile fracture-scattered" scarp,along a series of nearly NS-trending dipping joint track development.At the top there are four developmental slope deformation controlled by the large-scale topping of "pull-collapse" deformation bands,respectively,controlling the slope of the deformation and failure.(3)The analysis of displacement monitoring data of reservoir slope play a show that the stability is better in early stage and in a stable state.But after the construction of the dam at the slope crest and destroyed in 2004,the slope deformation is triggered.Trailing edge scarp vertical offset of 1.5m and has the feature of continuity.And the displacement deformation monitoring data after the impoundment show that the slope deformation development intensified.The large deformation displacement at the top of the slope turn,toe’s deformation small.And internal deformation is concentrated in the same slope position,the deformation gradually decreased with depth.All of these are in conformity with the field investigation of deformation phenomenon,further confirms the deformation pattern for toppling.Reservoir slope deformation affected by water level is obvious,synchronized with the reservoir water level.The correlation is obvious and no obvious lag phenomenon.(4)The results of discrete element numerical simulation(UDEC)of geological evolution process show that: the toppling deformation was occurred at the early stage under the action of gravity.Under the control of the Hf104 fault and jointed intensive,deformation is mainly concentrated in the 2700 m elevation above.In posterior edge of slope form a berm,but the whole deformation body is stable.And the top surface water infiltration triggered to deformation,crack development at the top of the platform and toppling deformation development.The reservoir impoundment changedthe mechanical environmental conditions of toe’s rock mass.The lower rock mass begin to deformation and failure,providing the upper rock mass deformation space.Due to the high slope of the "cumulative effect" is very obvious,so the whole slope toppling of degeneration and the largest deformation displacement in protruding parts.While the whole 3# ridge is stable with the reservoir water level stability,only local rock mass of strong toppling deformation parts and fracture zones are still in the sustainable development.The numerical simulation results of the deformation and failure of 3# ridge under the condition of different reservoir water level show that: once the reservoir impoundment will have a larger impact on the whole slope.Toppling of degeneration of the 3# ridge began to intensify which tends to stabilize and the deformation range extends to below 2700 m elevation.Every time the water level rise will make the realization of 3# ridge increased,especially for the first,the third and the fifth time.The degree of fitting is good which the calculation results and the actual monitoring results.This also verify the rationality of the calculation model and parameters selection.(5)Toppling deformation of reservoir slope integrated control of multiple factors such as landform,formation lithology,rock mass structure combination,weathering unloading,rainfall and reservoir water level rise,etc.Through the numerical simulation proved that water is predisposing factor of slope deformation and failure again.It not only reduce the physical and mechanical parameters of the fault fracture zone and jointed intensive in rock and soil.Also makes the increase of pore water pressure in saturated rock mass,reduce the effective stress.The original equilibrium condition of rock mass is broken,so deformation and failure to occur.The toppling deformation stages of development of slope can be mainly summarized as: weak toppling rock plate dislocation-relaxation,strong topplingtensile fracture,strong toppling-broken or cut layer tensile shear fracture,extremely strong toppling-collapse landslide.With the development of progressive deformation and failure,the slope forms the current shape eventually.