| As the coal resource were exhausted in shallow mining area,the exploitation of resources continues to extend to the earth's deep interior,and more and more mines coal resources will be mined in thousand-meter scale deep mines.Due to typical "three high" environment of surrounding rock in deep mines,along with the influence of mining during mining,it is common phenomone in roadway,such as the frequent occurrence of roof fall accidents,large amount of extrusion in roadway sides,and serious floor heave and support failure,etc.,which makes the deformation of surrounding rock difficult to be effectively controlled,and directly restricts the safe and efficient mining of coal resources in shallow mining area.Therefore,it has important theoretical and engineering significance to study the control method and support technology for surrounding rock in deep roadway with high stress.Meanwhile,the research was supported by the Key project of Natural Science Foundation of China(51434006),as well as the National Natural Science Foundation of China(51374105).By means of the comprehensive research methods of theoretical analysis,numerical simulation,rock mechanics test and field engineering test,the mechanical mechanism of deformation and failure for surrounding rock in deep roadway was systematically studied,the influence of spatio-temporal evolution law and geometric distribution of plastic zone on the stability of surrounding rock was analyzed,and the supporting principle and method of stability control for surrounding rock in deep roadway with high stress was put forward.Finally,the following research results were obtained:According to the characteristics of strain hardening and strain softening on the strength of surrounding rock in deep roadway at the pre-peak and post-peak,and considering the internal friction and cohesion which could indicate the strength characteristic parameters of rock mass,the concepts of hardening coefficient and softening coefficient were introduced,and four line model of stress and strain of rock,inclinding elastic,plastic hardening,plastic softening and plastic flow,was adopted.On the basic of mohr coulomb yield criterion and non associated flow law,the mechanical model of surrounding rock in deep roadway was established,the analytical expressions for stress,displacement and radius,were obtained separately in the elastic zone,the plastic hardening zone,the plastic softening zone and the plastic flow zone.As for the plastic hardening zone,the radial and tangential stresses would increase with internal friction angle and cohesive hardening coefficient,and the radial and tangential strain also increased with the cohesive hardening coefficient;but,for the plastic softening zone,the opposite was true.Therefore,when the internal friction angle and cohesive hardening coefficient were increased in the plastic hardening zone and was decreased in the plastic softening zone,the bearing capacity of surrounding rock would be improved.As is known to all,the excavation process of deep roadway is the unloading process of urrounding rock,the rock mechanics experiment was carried out on common white sandstone during mining.The failure form of rock mass shows a "X" shape in under uniaxial compression,shear failure along a single slope under three axis compression and constant axial unloading confining pressure;When the unloading rate of confining pressure are the same,the greater the initial confining pressure,the longer the deformation and failure of rock mass will take,and Higher rock stress is the main cause for long-term deformation but not convergence of roadway surrounding rock.In addition,the peak strength and residual strength of rock mass,as well as the axial strain and circumferential strain at peak strength,would increase with the increase of confining pressure.Here if the support resistance was regarded as confining pressure,and the support resistance could be provided with the same strength as surrounding rock,increasing the supporting resistance would help to improve the peak strength,residual strength and allowable deformation capacity of surrounding rock,to enhance the ability to resist destruction.The geological environment surrounding rock in deep roadway is very complex,its stress state is also changing,and has experienced complicated the evolutionary process of loading and unloading stress path.Under the three axis loading-unloading confining pressure-uniaxial compression and the three axis loading-unloading axial pressure-uniaxial compression,there were many fracture surfaces and a considerable number of cracks along the axial direction of the specimen,and the macro and micro cracks increase gradually with the increase of the initial axial pressure,while the uniaxial compressive strength decreased gradually.The influence degree of mining on roadway surrounding rock is based on original rock stress,it is the ture nature of surrounding rock damage,mining is the additional attribute.Furthermore,the greater the original rock stress,the stronger the mining,the more serious the damage within surrounding rock,the greater the plastic zone range.The failure of surrounding rock in deep roadway with high stress,is essentially caused by the formation and expansion of plastic zone,and the geometrical distribution and range can determine the failure modes and extent of surrounding rock.The spatio-temporal evolution process of plastic zone in deep roadway with high stress would go through V stages under non isobaric conditions: I plastic point stage,II plastic ring stage,III plastic zone uniform expansion stage,IV plastic zone malignant expansion stage and V plastic zone uneven expansion stage.Based on the original rock stress,on the one hand,mining could change the principal stress of surrounding rock,increase the vertical stress of surrounding rock in mining roadway near working face,but reduce the horizontal stress,so that the surrounding rock is more likely to produce a butterfly shaped plastic zone,and the development size and plastic failure range are very large;on the other hand,mining could change the direction of principal stress,the geometric shape of butterfly shaped plastic zone would rotates accordingly.Besides,when the butterfly leaf was located above roof,the stability of roof is the worst,the deformation is the biggest,and there is a risk of falling off at this time.The prestressed anchor has no obvious influence on the stress field and plastic zone of surrounding rock and has limited control on the deformation of surrounding rock in deep roadway,but it can suppress the separation and sliding between the broken rock masses in anchorage zone and is very obvious to reduce the discontinuous deformation such as opening and sliding.At present,the supporting strength has limited effect on controlling the deformation of roadway surrounding rock,and there is always some deformation which cannot be controlled by the existing support level,where the uncontrollable deformation of surrounding rock is called "given deformation".For deep roadway,the "given deformation" is caused by high ground stress,and the amount increases with the original rock stress.In view of the fact that the existing support level can not control the large deformation of roadway surrounding rock,the stability control principle and method of surrounding rock was put forward.That is to say,under the condition of reserving the appropriate deformation space for roadway,the surrounding rock is allowed to have greater deformation,and the reasonable supporting method is adopted to reduce the discontinuous deformation,to enhance the integrity and stability of surrounding rock,to reduce the maintenance capacity and support cost.In this paper,based on the stability control principle and key supporting technology for surrounding rock in deep roadway with high stress,and combined with the site engineering geological condition,the main haulageway of I panel in Zhaogu No.2 mine was taked as the engineering example,and a certain deformation space should be reserved to accommodate the given deformation of surrounding rock during driving.Then the supporting scheme with " Anchor bolt capable of being lengthened+ Rigid and long thread bolt +Anchor net +W steel band + Concrete" as the corpus,and Anchor bolt capable of being lengthened for strengthening roof as the auxiliary,was proposed specifically.And the deformation of roadway surrounding rock could meet the safety production needs of mine during the service period,roadway has not been renovated.Moreover,the fracture of anchor rod,the failure of anchor,and roof fall and spalling of surrounding rock,were not found as well.Therefore,it can be said that the supporting scheme could reduce the maintenance cost of roadway and ensure its safety during the service period. |
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