Study On Stability Of Placer Gold Goaf In Duomei In Ludila Hydropower Station After Storing The Water

Placer gold metallogenic environment of the Jinsha River in Yunnan is complex.The sources of the placer gold is rich and extensive. And the Jinsha River is a veritable golden waterways.In history,placer gold mining was very common along the river, especially in the place where placer gold is rich. However,because of the limitations of the economic and technical level in placer gold mining,now deformation have taken place in goaf in different levels, even collapse.Deformation caused surface cracking, the decrease of bearing capacity of foundation,also affected the stability of building.With the development and construction of cascade hydropower station in Jinsha River,gold mining hollows which distributed in reservoir area will be flooded or near normal water level,under the effect of water,whether it could goaf be produced further deformation and failure.Then the building and road abovw goaf will be damaged.These will become the new ploblems of reservoir stability evaluation.This paper chooses the Duomei placer gold goaf as research object. On the basis of analyzing the geological background and the basic conditions of goaf,including distribution,recovery method and deformation,were carried out detailed investigation and statistical analysis. Through consulting a large amount of references on the stability evaluation of old coal mining area,combine the actual condition of engineering geology,and conclude main influencing factors of goaf: geological factors,hydrological factors,mining condition. Geological factors include structure of rock and soil,geological structure,earthquake effect.Hydrological factors is that groundwater affects rock and soil mass by physical action,chemical action and mechanical functions.Mining condition include the shape of tunnel, extension status,mining scale and exploited horizon.After summarizing proceeding results, find it has close relationship with the stability of goaf and existing form of cementation layer.So,the paper analyzes the distribution and structural characteristics of the cementated layer.Moreover,further research on its petrologic characteristics and cemented causes has been carried out. The result showed that cemented layer is a certain thickness of the gravel layer in the place that there are groundwater flow,under interaction between groundwater and rock, pore in loose accumulational was constantlyfilled and cemented.At last, compact and hard cementated layer was formed. The two necessary conditions of formation of cementated are high-salinity wate and good connection in the pores.Do detailed analysis on influence degree,rule and weight of influencing factors, such as mining scale,horizon,thickness and mechanical properties of cementation layer,affecting the stability of goaf by using Phase2 ,which is a soft of two-dimensional finite element. The results show that horizon and thickness and mechanical properties of cementation layer has great influence on stability of goaf significantly. However, mining scale made little influence on stability of goaf. Finally,through tree-dimension Finite Element Analysis on goaf, combining with the results of three-dimensional numerical simulation and geological analysis, assess the stability of goaf after Storing the Water in Ludila Reservoir. The major conclusions are: at present the goaf is stable,but in local area is deforming slightly.After Storing the Water in Ludila Reservoir, the structure of cementation layer will be destroyed ,then goaf will be occurred further deflection, and cause houses which is above the goaf to collape. Therefore,base on engineering geological conditions and predicted results, based on the condition of immediate roof falling and main roof settlement,directed toward different deformation,the goaf is divided into four areas.