Research On Deformation And Fracture Characteristics Of Fractured Rock Mass Under The Coupling Of Heavy Rainfall Infiltration And Mining Unloading

Under the long-term coupling of heavy rainfall infiltration and mining unloading,a series of slope disasters induced by the evolution,expansion and penetration of the original joint and fissure surface of rock mass pose a severe challenge to the safe mining of deep open pit and underground of metal mines in southern China.In this paper,based on the engineering background of the Dexing mine,Jiangxi province,which has been converted from open pit to underground mining,through geological investigation,field sampling and indoor physical and mechanical tests,the specimens with different water content,different fracture length and different fracture dip angle were preformed for uniaxial compression test,the PFC numerical simulation software is used to simulate the rock under different water-cut state,different buried depth,different fracture distribution,different loading and unloading methods and different pore water pressure,the mechanical characteristics and fracture propagation characteristics of fractured rock mass of high and steep rock slope under the coupling of heavy rainfall infiltration and mining unloading are analyzed,which provides necessary theoretical support for open pit slope mining and underground surrounding rock support,the main conclusions are as follows:(1)With the increase of water content,the compression stage increases,the elastic stage shortens,the brittleness weakens and the yield phenomenon is obvious.The failure mode begins with shear failure,followed by a combination of tensile and shear failure.The secondary fractures extend along both ends of the preformed fractures to the upper and lower ends of the specimen,and a small number of caving zones appear.The higher the water content,the more the number of cracks,the pattern of destruction is more complex.(2)The compressive strength of rock has negative linear relation with water content and length of fracture,and negative exponential relation with dip angle of fracture,and the elastic modulus of rock has negative exponential relation with water content and length of fracture,and positive exponential relation with dip angle of fracture.The influence of water content on the compressive strength and elastic modulus of rock is the greatest,the second is the length of fracture,and the influence of the dip angle of fracture on the compressive strength is the smallest.(3)The larger the initial in-situ stress is,the smaller the peak strain,the lower the ductility,the faster the drop rate after the peak,and the more obvious the brittleness is,the surrounding rock and overlying rock may be destroyed.After unloading,the failure of fractured rock mass is accelerated by the excavation of the open face.(4)In the process of loading and unloading,the axial displacement of the specimens with two parallel fractures is larger,and the compression of the fractures is more obvious.The rocks with two parallel fractures and two cross fractures have the phenomena of sudden displacement jump and sudden drop of stress,the crack propagation in the Rock is periodic and sudden,and the phenomenon of sudden jump and drop is different because of the different ways of crack propagation and Rock Bridge Connection.(5)Under the condition of different unloading rate,the faster the unloading rate is,the greater the influence on the rock mass strain is.The unloading is completed,the stress jump point appears,the rate of increase of the transverse strain increases,the specimen deforms violently in the unloading direction,and the dilatancy phenomenon is very obvious,the more brittle the failure occurs.(6)Under the condition of different pore water pressure,the pore water pressure increases,the compressive strength of the sample decreases,the peak strain decreases,the pore water pressure accelerates the failure of the rock,and the water softens the rock material,stress concentration and hydraulic fracturing are easily formed between micro-cracks and particles,which promotes the development of crack.(7)Under the coupling condition of pore water pressure and mining unloading,the process of rock failure is accelerated,and the failure form is more complex.The main failure mode is tensile failure,and the secondary failure mode is shear failure,the crack at the end near the excavation surface tends to penetrate with the crack at the middle of the preformed crack.Finally,the specimens are penetrated by the preformed cracks and the airfoil tension cracks produced at both ends.The specimens are completely destroyed and lose bearing capacity.