Study On The Characteristics Of Ground Pressure Activity And The Filling Effect Of Goaf Under The Action Of Open-pit To Underground Mining Of Inclined Medium Thick Orebody

The research on the compound action mechanism of open roof slope and underground mining is the key scientific problem for safe and effective deep mining.Based on the project supported by NSFC(NO.41702327),"study on the evolution characteristics and dynamic effect of rock mass response under the coupling action of slope and underground mining",this paper takes a phosphate mine around Dianchi Lake as the engineering background,and uses the method of numerical simulation and similar model test to study the characteristics of ground pressure under the action of open-pit to underground mining of gently inclined medium thick orebody The characteristics and their dynamic effects are systematically studied,and different filling structures are used to prevent and control the possible dynamic disasters.The main research results are as follows:1.The engineering geology,hydrometeorology,mining status and other conditions of the mining area are systematically investigated.The main rock masses in the mining area are sampled on site and the mechanical properties are measured in the room.The mechanical parameters measured are reduced by Hoek Brown empirical formula,and the basic mechanical parameters of the rock and roof and floor surrounding rock of the mining area are obtained.2.Similar model proportioning test shows that the similar materials made of quartz sand,gypsum,calcium carbonate,water and borax have great influence on the elastic modulus and compressive strength of the simulated materials by changing the content of each component.When the content of quartz sand is 75% and 80%,the simulated elastic modulus and uniaxial compressive strength range are 0.015-2.8 GPA and 0.08-8.4 MPa respectively,which can effectively match the mechanical properties of the main rock mass in the mining area.3.The results of similar model tests show that: in the open pit mining,affected by the excavation,there is a certain rebound phenomenon at the side slope adjacent to the model.The stress and deformation of the side slope and the overburden of the stope are in a complex dynamic change process,but on the whole,the change law decreases with the increase of the distance from the side slope.The maximum settlement displacement at the slope angle position is 0.28 M,and the maximum water appears at the slope waist position.The horizontal displacement is 0.22 m.When the open-pit is transferred to underground mining,the maximum settlement displacement is 1.1m at the slope angle,and the maximum horizontal displacement is 0.44 m at the slope waist;the pressure relief area of slope rock is mainly concentrated at the slope waist.The stress of the same measuring point on the overburden of the stope changes with the advance of the access road.The stress in the central part of the roof increases before the roof collapses,and the roof collapses backward.The roof of the goaf shows pressure relief.The stress is transferred to the two ends of the goaf,and the stress decreases.With the continuous increase of the goaf area,the overlying strata of the goaf develops from insufficient mining to full mining.After the completion of the mining,the stress on the goaf increases The overburden has reached the state of ultra full mining,and the horizontal displacement of the overburden in each stage is relatively complex.The maximum horizontal displacement at the upper corner of the first stage of the goaf is 0.32 m,and the maximum settlement displacement at the upper part of the second stage of the goaf is 2.4m.After the completion of underground excavation,macro cracks appear at the slope waist,and the roof falls seriously in each stage,with the maximum crack height up to 32 m.The existence of stage pillars is of great significance to the stability of the mining area.4.The numerical simulation results of the characteristics of ground pressure activity under the mining of medium thick and gently inclined ore body in the open pit show that: in the process of open pit mining,due to the unloading effect,the stress in the open pit slope and adjacent slope rock mass decreases and the displacement rebounds,and after the mining,the slope angle position appears obvious tensile failure.In the process of underground mining,the maximum subsidence of the open-pit slope rock mass occurs at the slope angle position of 1.01 m,and the maximum lateral displacement occurs at the slope waist position of 0.45M;the internal pressure stress of the slope rock mass decreases,and the pressure relief area is concentrated at the slope waist,and the maximum pressure relief amplitude can reach 34%.The maximum lateral displacement of overburden is 0.55 M at the right corner above the first stage goaf,and the maximum subsidence displacement is 2.10 m at the center of the second stage goaf roof.With the increase of the scope of goaf,the roof of the stope collapses,and the pressure relief range,degree of pressure relief and the stress concentration coefficient of the ore body on both sides of the goaf increase with the increase of the upper part of the goaf The height of the strata is inversely proportional.The safety factor of open-pit slope decreases rapidly under the influence of underground mining.After mining,the safety factor of slope is close to the lowest value of allowable safety factor.Both numerical simulation and model test show the same change trend in stress and displacement,the error range is within 15%,and the location and range of rock deformation and failure are similar.5.The numerical simulation software is used to study the effect of goaf treatment under different filling structures.The results show that the overburden of the stope under the four filling structures does not break in a large range,the peak stress changes tend to be gentle,the roof of the model does not appear obvious subsidence movement,and the filling effect is significant.Generally speaking,the use of "strip" filling structure with filling rate of 19.6% can not only effectively control the movement of overburden and reduce the stress concentration of surrounding rock in the stope,but also has less filling materials,lower economic cost and the most ideal effect.