| Rainfall infiltration and groundwater could increase the pore water pressure of the slope and reduce strength of the rock and soil.Especially for the inner dump of open pit coalmine,the influence of rainfall and groundwater is even more obvious.Study on the slope failure mechanism induced by rainfall and groundwater has become urgent problem to be solved in open pit mine,which is of great significance for ensuring the slope stability and safe production in open pit coalmine.In this paper,the methods were used to to analyze slope stability including the in-situ hydrological test,the analytical solution of the safety factor based on the circular failure slope,the theoretical solution of the slope safety factor considering the strength reduction of the waste,slope model of the combined action of groundwater and rainfall models.Three slope stability mechanics models(progressive relations)were established and solved.The correctness of the model results was verified by numerical calculation and model test.The obtained model results were applied to the open pit mine site,combined with radar and anchor stress monitoring results.The slope is stabilized for verification.For the existing open pit slope geometry,theoretical model were used to quantitatively evaluate the safety factor variation results and evaluate the stability of the open pit slope by the rainfall and groundwater hydrological changes.The main work and research results are as follows:1.Study on field insitu test of inner dump in open pit mine(1)The field insitu test has the advantages of simple operation and objective data,such as hydrologic drilling,tracer connectivity test,stratified water pressure test,which are of great significance for hydrogeological parameters of inner dump in open pit mine.(2)The distribution of groundwater flow field is ascertained and the groundwater mainly infiltrated from the east site of internal waste dump and the water level gradually decreased.The linear direction between ZK7 and ZK3 is closer to the mainstream direction of groundwater.2.Analytical solution of the safety factor for circular arc damage caused by groundwater permeability is given(1)The analytical solution of the safety factor considering the influence of groundwater seepage on the slope stability is given by improving the Swedish arc method.The analytical solution is simple and easy to analyze field slope stability.The analytical equations show that the slope angle,groundwater level and the mechanical properties of the material affect the slope stability.(2)The parametric study shows that,as the groundwater level increases,the F.S of a dump slope decreases until a stable value is reached.The reduction of F.S along with groundwater level increase can be described by an inverse function in which F.S=1 may be taken as the inflection point of the reduction rate change,i.e.,when RS>1,FoS declines at a higher rate;when F.S<1,FoS reduces at a smaller rate and eventually levels off.The F.S of the dump slope calculated by the strength reduction method in FLAC3D,limit equilibrium method in SLOPE/W and our analytical solution consistently agreed with each other very well in all the scenarios.3.Water transfer function in the process of rainfall and the analytical equation of safety factor considering material strength reduction are obtained(1)The function of wetting front is given considering the elliptical variation of water content.The results of parameter analysis indicate that the wetting front depth increases by linear function with the increase of the rainfall time and the increasing rate is constant in non-compressive infiltration stage.While,the wetting front depth increases with the increasing of the rainfall time and the increasing rate gradually decreased in compressive infiltration stage.The increasing rate of the wetting front decreases with the increase of the slope angle.(2)The improved analytic solutions of safety factor is obtained considering the strength reduction with water content in rainfall transition layer.The improved analytic solutions is closer to the actual safety factor under rainfall conditions.The form of analytical solution is simple,calculation convenient,and efficiency.(3)A depth of minimum safety factor exists and it is not in the wetting front,but in the position close to the wetting front.The depth(hmin)of the minimum safety factor increases by linear function with the increase of the wetting front(hf)and increases with?.The ratio(?)of the depth of the minimum safety factor to the wetting front depth increases by exponential function with ?.The critical failure depth and the potential sliding surface of slope can be converse solved the improved analytic solutions of F.S when Fst=1.The method can be used for pre-evaluating the slope stability and the potential sliding surface under the rainfall condition in advance and providing corresponding guidance to the reinforcement scheme.4.Stratification model of rainfall and groundwater is put forward and solved(1)The safety factor is inversely proportional to the depths of saturation layer of rainfall,transitional layer and groundwater.The safety factor decreases following an inverse proportional function with the increase of ration ? and the wetting front depth.The influence of ratio ? and the wetting front depth on the safety factor of saturation surface of rainfall,wetting front and basement surface reduced gradually.(2)The strength reduction and seepage force caused by rainfall and groundwater affect the slope stability.The main factors of slope instability induced by rainfall and groundwater change with the change of groundwater and rainfall.There exist critical wetting front and critical groundwater depth where the dominant factors inducing slope failure change.(3)The expression formulas of critical wetting front depth and groundwater depth are given.The critical wetting front depth increases with the increase of groundwater depth,and the increasing rate increases gradually.As the ratio ? of the saturated layer of rainfall increases,the critical wetting front depth decreases,and the rate of decrease continuously reduces.When the ratio ? and the wetting front depth are smaller and the groundwater depth is larger,there is no critical wetting front depth.The critical groundwater depth increases with the increase of the wetting front depth and the ratio ?,and the increasing rate gradually decreases.The corresponding critical safety factor decreases with the increase of the wetting front depth.When the ratio ? and the initial wetting front depth gets larger,there is no critical groundwater depth.The corresponding critical safety factor decreases with the increase of groundwater depth.5.Modeling test and field applications tudy on combined influence of rainfall and groundwater on dump slopeThrough laboratory model test,the combined action of groundwater action,rainfall action and groundwater known rainfall change is compared.Considering the stress displacement and failure form of slope under four kinds of groundwater and rainfall supply modes,it is considered that the action of groundwater leads to piping and deformation in the lower part of slope,and rainfall mainly causes shallow deformation and sliding of slope body,and the combined action of groundwater level change and rainfall supply mode is considered to cause piping and deformation in the lower part of slope,and rainfall mainly leads to shallow deformation and sliding of slope body.When the combined action,the increase of groundwater level and rainfall intensity to a certain extent,will cause large-scale landslide in the deep part of the slope.That is to say,when the local situation and rainfall pattern change,the leading factors of slope failure and the potential sliding surface and scale of slope instability will change. |
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