Damage Mechanism And Stable Operation Technology For Coal Pillar Dams Effected By Stress And Water Immersion In Underground Reservoir

The mining area with fragile ecological environment in the Yellow River basin is facing the key problem of coordinated development of safe and efficient development of coal resources and ecological environment protection.The proposal of the engineering technical system of coal mine underground reservoir has become an important way to solve this problem.As its main bearing structure,the coal pillar dam is not only special in structure,but also in a complex stress environment.Therefore,the study of the damage mechanism of the coal pillar dam under the action of water leaching and stress will have important engineering significance for the long-term safe service of the underground reservoir project.In this thesis,taking the underground reservoir formed in 31411 working face of Jinjie Coal Mine as the engineering background,the cyclic loading and unloading experiments of coal samples in different water-bearing states are carried out,and the acoustic emission equipment is used to monitor the damage status of coal samples in the experiment.NMR equipment is used to detect the pore development of coal samples after the experiment,and the cumulative damage law of coal samples under different water-bearing states and cyclic stress is analyzed.The numerical calculation model of groundwater reservoir is established to explore the damage characteristics of coal pillar dam during mining and reservoir water storage.The main results are as follows:(1)With the increase of cycle stages,the AE signals of coal samples in different water-bearing states gradually increase,and the degree of crack development increases gradually;in the single-stage cycle stage,the AE signals of coal samples mainly occur during the first cyclic loading and unloading period.the damage of coal samples under cyclic stress load mainly occurs in the first stress cycle.The peak value of AE signal of natural and saturated coal samples is lower than that of dry coal samples,but the signal mutation occurs during cyclic loading and unloading of stage Ⅲ.Water has a weakening effect on AE signals,and the damage degree of water-bearing coal samples increases during cyclic loading and unloading of stage Ⅲ.The strength of coal samples decreases with the increase of water cut and circulation stages.(2)After cyclic loading and unloading at levels I and II,the overall number of pores in coal samples with different water content states increases,mainly with microporous growth.After the third level cycle,the total number of pores in the dried coal sample increased slightly,while the total number of pores in the water containing coal sample decreased.Among them,the decrease in micropores in the water containing coal sample was significant.In the saturated state,micropores in the coal sample closed,and at the same time,mesopores cracked and penetrated to form a larger pore fracture structure.The porosity of each coal sample increases after the loading and unloading of Level I and II cycles,while the porosity of dry coal samples increases after Level III cycles,while the porosity of natural and saturated coal samples decreases.There are three main weakening effects of static load water on coal samples.(3)With the approach of the mining face,the damage and failure area of the coal pillar in the withdrawal channel gradually extends to the interior of the coal pillar,which is mainly shear failure,and the damage occurs in the middle of the coal pillar and the deformation is larger in the middle of the coal pillar.With the development of water leaching weakening cycle,the stress distribution gradually evolved from "saddle type" to "unimodal" distribution.The bearing capacity of the coal pillar on the side of the goaf decreases at first and then tends to be stable with the weakening cycle.(4)Combined with the experimental and simulation results,the cumulative damage mechanism of coal pillar dam in underground reservoir is analyzed.based on this,the stability control technology of coal pillar dam with coal pillar reinforcement and support,roof cutting and pressure relief of overlying rock,setting water curtain and intelligent monitoring scheme of coal pillar dam stability are put forward.There are 52 figures,12 tables and 72 references in this thesis.