| In China,underground mining accounted for more than 90%of total coal output.The roadway must be excavated for all purposes of underground mining At present,more than 80%of modern mine roadway layout is coal roadway.The main body of underground engineering such as coal roadway is coal and rock mass.In the engineering rock mass,the most common are the primary or secondary micro joints and fractures.The existence of these structural planes plays a decisive role in the mechanical properties and behaviors of rock mass.In the coal roadway engineering,the unloading disturbance due to roadway excavation and dynamic pressure due to coal mining caused the instability accidents such as gradual large deformation due to static pressure and instantaneous large deformation due to dynamic pressure in surrounding rock.The prestressing provided by ordinary anchor or cable failed to form enough confining force to prevent the development of fractures caused by excavation unloading and dynamic pressure emerge of surrounding rock,the elongation of bolt or cable body was too low to the control discontinuous and uncoordinated large swelling deformation of surrounding rock,and the strength of bolt or cable body was too low to resist the shear sliding and opening separation of surrounding rock along the structural face.In view of the above scientific problems in roadway drivage and coal mining,the following aspects of research are carried out specifically in this paper:(1)The engineering geomechanical background for experiment is introduced,the deformation and failure characteristics of roadway surrounding rock and the failure situation of supporting body were analyzed,and the numerical experimental model of slowly inclined jointed rock mass coal roadway is established by using discrete element software UDEC.The evolution and transfer process of the maximum principal stress and tensile stress in surrounding rock during the gradual stress release process during excavation was reproduced,as well as the initiation,development,incorporation process of new microscopic tensile cracks,shear cracks and macroscopic fractures,and the large deformation failure process was also revealed.The space-time evolution law of maximum principal stress,fracture and asymmetric large deformation during excavation unloading was revealed.The asymmetric large deformation failure mechanism in coal roadway has been revealed.(2)The mechanical and structural properties of high constant resistance and large deformation cable developed for coal mine,which is composed of constant resistance device and cable body,were tested by the methods of indoor static tensile test and instantaneous dynamic pressure impact test.The results of laboratory tests show that the extension deformation can reach 300?950 mm and constant support resistance of 350 kN can be supplied and maintained by the cable during the extension deformation.Under the impact of instantaneous dynamic pressure load,the impact resistance was basically stable at 280?375 kN.(3)By using the discrete element simulation method,the mechanical properties of anchored ordinary cable and constant resistance cable were studied and compared,which showed that both two types of cable can provide higher support resistance,but the elongation of ordinary cable too small,which undergoing rupture failure with even small deformation in surrounding rock;while the elongation of constant resistance cable was large,which can maintain high support resistance during the large deformation in surrounding rock.(4)Using discrete element simulation method,the supporting under the condition of deformation characteristics of slowly inclined jointed rock mass during gradual release due to excavation unloading are studied,the results showed that confining stress was spread on the surface and the internal of surrounding rock by the constant resistance cable through its own large elongation,high tensile bearing capacity and cooperating with W steel belt,which effectively improved the stress state of surrounding rock during the process of excavation unloading,and significantly reduce the fragmented,swelling and release degree and zone of surrounding rock due to excavation unloading.Generation degree of tensile stresses significantly reduced,relevant generation degree and zone of shear and tensile cracks decreased,thus significantly inhibiting the generation,propogation and incorporation of macroscopic fractures.(5)The physical model experiment system of YDM-C type employed for deep soft rock roadway failure process test is adopted to carry out the physical model experiment for roadway stability controlling excavated in slowly inclined jointed rock mass.Gypsum and water were determined to be rock mass similar materials for physical model experiment.Through strength mechanics experiment,the composition proportion of water and gypsum for simulating coal rock,mudstone and tuff were finally determined.The physical finite element slabs with different specifications are used to simulate coal,mudstone and tuff.Considering the geometrical and mechanical properties,breaking load and elongation of metal materials,the material of simulating constant resistance cable body is determined.The similar materials and assembly mode of the simulated constant resistance device were determined.High-precision tension and pressure sensor was selected to monitor the axial force of cable in real time during the experiment.The monitoring technologies used in the physical model experiment are infrared thermal imaging technology,two-dimensional digital image correlation technology and static stress and strain data acquisition technology.(6)The results of the physical model experiment for roadway stability excavated in slowly inclined jointed rock mass under supporting condition were analyzed.The displacement evolution law of physical model was obtained by analyzing the horizontal displacement field,vertical displacement field and key points displacement evolution characters in surrounding rock during the process of boundary loading and unloading.The stress evolution law of physical model was obtained by analyzing the key points strain evolution characters in surrounding rock during the process of boundary loading and unloading.The infrared radiation temperature evolution law of physical model was obtained by analyzing the infrared radiation temperature evolution characters of key points during the process of boundary loading and unloading.Finally,by analyzing the monitoring results of cable axial force,the difference of supporting resistance and elongation between ordinary cable and constant resistance cable in the process of large deformation in surrounding rock is obtained,which verifies the feasibility of using constant resistance cable to control large deformation of surrounding rock in slowly inclined roadway.The deformation law of supporting physical model during boundary loading was revealed.According to the thin shell theory,the instability mechanics model of physical model floor was established.The minimum buckling load mechanical expression of deflection instability failure in floor physical finite element slab was obtained.The influence degree of the element slab length,width,thickness,dip Angle and gravity on the stability of the element slab was quantitatively analyzed.(7)In the gob-side roadway excavated in slowly inclined bedding joint rock mass of Kong'zhuang coal mine,the field experiment was conducted to study the roadway surrounding rock large deformation control effect with constant resistance cable supporting system and the common cable supporting system under the instantaneous dynamic pressure impact in contrast.The relative displacement of roof and axial force of constant resistance cable and ordinary cable were monitored by using real-time roof displacement sensor and axial force real-time monitoring sensor.The stretching damage situation of constant resistance cable and ordinary cable was investigated in the underground field.Monitoring results show that constant resistance cable provided a high pretightening force and a longer duration constant slip deformation resistance by itself and W steel belt to balance and release the impact roof dynamic pressure,eliminating the dynamic pressure source which caused the roof abscission layer and crack opening,which effectively inhibiting the roof abscission layer and crack opening.The slip value did not exceed limit slip value of constant resistance device and constant resistance cable and tray did not appear failure phenomenon;Although ordinary cable can also provide higher support resistance,but the duration high support resistance is shorter,because the abscission layer value and crack opening value of roof surrounding rock exceeded their ultimate elongation value,The failure pattern can be characterised as tray dropped,cable snapped off and retreat into the anchor hole. |
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