Study On Failure And Disaster Mechanism Of Water-Resisting Coal Mass Under Influence Of Roadway Excavation

Goaf water disaster is one of the important factors affecting the safety of mine production.And the water inrush accident in the old empty area at the same layer accounts for a large proportion of the water disaster accident in the old empty area.It is of great significance to study the mechanism of water inrush disasters at the same layer and improve the foundation of prevention and control for the management of water hazards in the old empty area.Based on the background of water inrush in the old empty area at the same layer induced by roadway excavation,this paper selects the water-resistant coal mass between the goaf and the heading of the excavation roadway as the research object,and the means of theoretical analysis,experimental research,numerical simulation and similar simulation are comprehensively adopted to conduct a comprehensive study on failure and disaster mechanism of water-resistant coal mass in goaf under the influence of roadway excavation.The main research results are as follows:(1)Through the analysis of the typical accident cases of water inrush in the same layer of the old gob in Shanxi Province,according to the difference of the water accumulation space in the old gob,the water inrush caused by the roadway excavation in the old gob of the same layer is divided into two types: the water in the goaf and the water in the abandoned roadway.The water-resistant coal mass between the heading of the roadway and the accumulated water in the gob is divided into the roadway excavation disturbed plastic zone,the elastic core zone,and the old gob excavation disturbed plastic zone.Using the rock mass limit equilibrium theory and the catastrophe theory,the theoretical analysis of the size of the two water-retained coal mass are carried out,and the corresponding calculation methods are put forward.Combined with the characteristics of stress environment and stagnant water environment of water-resistant coal mass in different regions,the main influencing factors of damage and deterioration of water-resistant coal are analyzed.(2)The water-resistant coal mass close to the side of the water-filled goaf is approximately in a one-dimensional stress state of axial compression.According to the difference of the height of water accumulation in the goaf,from the perspective of basic research,the different immersion heights(0%,25%,50%,75%,100%)uniaxial of coal mass under compression test are carried out to explore the influence of non-uniform distribution of moisture on the damage of coal mass.The study shows that in the partially flooded coal mass(the soaking height of is 25%,50%,and 75% of the height of the coal mass),with the increase of the soaking height,the strength of the partially soaking coal mass shows a gradually increasing trend,and the coal with the height of 25% water soaked has the lowest strength.In the process of damage and failure,the local water-soaked coal mass has obvious non-uniform deformation characteristics.By introducing the non-uniform deformation coefficient,the degree of non-uniform deformation of the coal mass soaked in water is quantitatively analyzed.The analysis shows that the degree of non-uniform deformation of the coal mass soaked in water at 25% height is the largest,and the nonuniform deformation aggravates the damage of the coal mass.(3)In order to explore the influence of water content and crack angle on the damage of the water-resistant coal mass,the uniaxial compression damage test of the prefabricated cracked coal mass with different water content was carried out.The results show that with the increase of water content,the peak strength and elastic modulus of coal mass gradually decrease.As the angle increases,the elastic modulus increases gradually,while the peak strength decreases first and then increases.When the angle is 30°,the strength is the lowest.Compared with water content,the effect of fracture angle on coal crack propagation is more significant.Based on digital image correlation technology and acoustic emission monitoring technology,the multi-parameter response characteristics of prefabricated fractured coal with different water contents in the deformation process were studied,and the coevolution of acoustic emission b value and surface strain field during the failure process of prefabricated fractured coal was found,and he influence mechanism of water content and fracture angle on the damage of fractured coal mass is discussed.(4)The coal mass located in the elastic core area in the middle is restricted by the coal bodies on both sides,and is approximately in a stress state of triaxial compression.Aiming at the multi-source stress situation that this part of the coal mass may be subjected to water pressure,static load and disturbance load,triaxial compression failure tests of fractured coal mass under the action of different water pressure and disturbance load were carried out.And the damage and deterioration mechanism of water pressure and disturbance load on fractured coal mass was explored.The research shows that with the increase of water pressure,the strength of fractured coal mass decreases gradually.Under the same hydraulic pressure,the triaxial compressive strength of the coal mass first decreases and then increases with the increase of the angle,and the triaxial compressive strength of the coal mass with the prefabricated fracture angle of 30° is the smallest.The damage degree of the coal mass caused by the disturbance load has obvious correlation with the prefabricated crack angle.With the increase of the prefabricated crack angle,the damage degree first increases and then decreases.The disturbance load further induces the initiation and expansion of micro-cracks inside the coal mass,making the overall failure form of the coal mass more broken.(5)The roadway excavation under the threat of water accumulation in the same layer of goaf is selected as the specific engineering background,the geological model of roadway excavation under the influence of goaf water in the same layer is generalized,and the threedimensional fluid-solid coupling numerical model and physical similarity Model are constructed,the evolution process of the instability and failure of the water-resistant coal mass during the excavation process is simulated and analyzed from the engineering scale.The results show that the development of the plastic zone,the expansion of the seepage field,and the evolution of the concentrated stress are highly correlated in the process of gradually reducing the size of the water-resistant coal mass with the tunnel excavation.Finally,the technical idea of monitoring and early warning for the stability of waterresistant coal mass is put forward based on the comprehensive research results,which provides a certain useful reference for the prevention of water inrush disasters in goafs.