| Compared with open pit coal mines in north China,Xiaolongtan Coal Mine in Yunnan province is located in a typical water-rich district.Taking Xiaolongtan Xindenger coal dump slope as the engineering background,through the hydrogeological survey,its water-rich characteristics of the engineering site was revealed.The stability and failure mechanism of Xindenger coal dump slope were fully investigated by finite element strength reduction method,under the action of gravitity,basement water pressure and pore pressure induced by rainfall or surface water infiltrating.Considering the dynamic development process of waste dump and the changes of supplementary drainage conditions in the catchment area,a spatio-temporal dynamic water control system and its engineering measures were advanced to Xindenger coal dump.The specific research contents include:Firstly,through the analysis of regional geological and hydrogeological characteristics,the hydraulic connection and water-rich characteristics of the Xindenger coal dump engineering site were clarified.The research results showed that the Xindenger dump engineering site was a typical water-rich region,with abundant rainfall and high rainfall intensity.The catchment area was 11.058km2.In the rainy season,the discharge of the vally was about 2-8 times of that in the dry season.There were 17 springs exposed in the vally,and some springs possessed large water outflow.It was 38.8-538.53L/s in the dry season,and it increased to 1795.7-4976L/s during the rainy season.Chemical testing results showed that the groundwater in this site had no corrosion to concrete and steel structure inside of concrete,but it had weak corrosion to exposed steel.Then,based on the strength reduction principle of finite element,the stability and instability mechanism of the dump was simulated under the action of gravity load only,and under the action of additional basement water pressure,rainfall or surface water infiltration.The research results showed that the safety factor FS of Xindenger dump with a dumping height of 250 m was 1.60～1.64,under the action of gravity load.The FS droped with a gradient of0.013/m-0.015/ms as the increase of basement water head or the infiltration depth of rainfall and surface water.The FS also futher reduced at a speed of 0.016/m-0.023/m under the combined action of basement water and rainfall or surface water infiltration.The failure mechanism of the dump under the action of basement water was the circular sliding of the upper slope and sliding along the basement surface of the lower slope.Under the action of rainfall or surface water infiltration,the failure mode is the shallow shear sliding.When the basement water head and rainfall or surface water infiltration depth were large or equal to each other,it is the combined instability mechanism of the above two failure modes.Finally,considering the dynamic development of the waste dump and the subsequent changes of the supplementary drainage conditions in the catchment area,a spatio-temporal dynamic water prevention and control system was presented for the initial,middle and later stages of the construction of Xindenger waste dump.The water drainage and control system mainly included side ditch,cross ditch,blind ditch,drainage tunnel and open channel.The three stages were mutually integrated and closely linked with each other,which can realize the correction,optimization and adding specific drainage engineering measures in time according to the dynamic construction process of the waste dump.The three-stage water drainage and control system can be divided into two drainage systems in space which were ground drainage system and underground drainage system.The two systems were connected and coordinated with each other,forming a three-dimensional drainage system in space.The on-site monitoring results show that since the mid-term water prevention and control system planning in 2014,there has been no water and soil loss events occurred,such as flood irrigation,debris flow and landslide,which affects the stability of the waste dump slope.The waste dump slope is in a safe construction and service state.And the spring water discharging out of the waste dump slope through the water drainage facilities can meet the production and domestic water demand of downstream residents.It not only achieved the goal of stabilizing slope and consolidating soil,but also realized the goal of safe,green,environment-friendly and sustainable mine development.The research results of this paper could provide important theoretical and engineering guiding significance for the safe construction and scientific drainage planning with the similar water-rich conditions. |
