Research On The Mechanical Behavior And Anchoring Mechanism Of Rock-like Material With Discrete Fracture Network

Coal remains crucial to China’s economic and social development during the progress of achieving carbon emission targets.China’s shallow coal resources is going to be exhausted after a long time,high-intensity,large-scale coal mining.Deep coal resources mining is of great significance to national economic development.The deep rock mass contains complex discontinuities of different scales,and secondary fractures will occur in roadway surrounding rock under the action of disturbance stress,Surrounding rock structure controls the stability of roadway surrounding rock.This dissertation focus on the serious deformation and instability of surrounding rock of kilometer-deep roadway,mechanical behavior and progressively failure of rock mass with complex discrete fracture network was studied,and the fracture mechanism and anchoring mechanism of rock mass with discrete fracture network was demonstated.Main research contents and conclusions are as follows.（1）Cement-based similar materials were used to develop sandstone-like specimens,and the laboratory test results showed that the deformation index and brittleness index of the rock-like materials were similar to those of natural sandstone.According to the inherent statistical law of fracture distribution of natural rock mass,the probability distribution function method was employed to describe the fracture geometric parameters of the rock mass.Fracture network models with different fracture dips and different fracture densities were generated,Rock mass like material with discrete fracture network was developed by using 3D printing technology.（2）Laboratory tests on the mechanical properties and fracture evolution law of rock mass containing fracture network were carried out by acoustic emission and digital image correlation techniques,and the test results showed that:①With the increase of fracture density,the strength of the rock mass does not decrease monotonically,but increases first and then decreases,and tthere was more complex mechanism of the fracture network on the strength of rock mass.②The varaiation of crack initiation stress and crack and damage stress of rock mass is consistent with the varaiation of peak stress,and the ratio of crack initiation stress to its strength is in the range of 0.53～0.63,which is larger than the ratio of 0.3～0.5 times of intact rock.The fracture density has little effect on the magnitude of the ratio of crack initiation to uniaxial compressive strength of rock masses,while the ratio of crack damage stress to uniaxial compressive strength decreases with increasing fracture density.③The strength and elastic modulus of the rock mass shown significant anisotropic characteristics,with the increase of fracture dip angle,the strength of fracture-containing network rock mass has"V"type distribution,the elastic modulus of rock mass has"U"type distribution,and the post-peak ductility of rock mass is enhanced.④The fracture evolution of the fracture-containing network rock body shows the characteristics of progressive damage.The cracks first emerge at the tip of the prefabricated fracture near the end face of the specimen and expand along the loading direction,and as the cracks expand through many places inside the rock mass and further expand to the free surface,the bearing structure of the rock mass is destabilized,causing the overall damage of the specimen,and finally a macroscopic crack is formed through the whole rock mass in the post-peak stage.⑤The damage modes of rock masses containing fracture networks are divided into three categories:tensile splitting damage along the prefabricated fractures,tensile damage of prefabricated fractures before the peak front+slip damage of the block after the peak,and rotational damage of the nascent block.（3）The strength influence mechanism of the fracture network-containing rock masses was further investigated,and the relationship between the fracture network-containing rock masses and the fracture density was modeled.The strength influence mechanism of fracture network-containing rock masses is obtained as follows:when the fracture density is low,the fracture network-containing rock masses have different fracture expansion penetration paths inside the specimens due to different fracture location distribution,resulting in differences in the macroscopic damage patterns of the rock masses.When the fracture-containing network rock mass macroscopically shows the"X"shape conjugate shear damage,the central bearing structure of the rock mass remains relatively intact,and the strength of the rock mass is higher at this time.When the fracture-containing network rock body macroscopically exhibits shear damage,the core bearing structure of the rock mass is destroyed,the bearing performance of the rock body is significantly reduced,and the strength of the rock body is lower.With the increase of fracture density,the rock strength is weakened by the fracture distribution.When the fracture density is high,the strength of the rock mass containing fracture network has a negative power function with the fracture density,and the relationship is y=99.78x^-0.675.（4）Acoustic emission monitoring technology,digital image correlation technology（DIC）and bolt axial force monitoring technology were used to carry out laboratory tests on the influence mechanism of bolt on macroscopic mechanical properties and fracture mechanism of rock mass with fracture network.The test results showed that:①Anchoring could inhibit the rock masses from producing violent damage,and the stress fluctuation phenomenon before the peak of anchored rock masses was moderated,and the brittle fall phenomenon after the peak was all significantly improved.②With no preload end anchoring,the strength of the anchored rock mass increased slightly compared with the unanchored rock mass,and with the increase of preload,the strength and elastic modulus of the anchored rock mass increased exponentially as a function.And with the increase of fracture density,the strengthening effect of anchor on rock mass is enhanced.③The type of rock fracture sprouting under anchoring action changes from wing-type fracture to secondary fracture,and the shear micro-rupture of anchored rock mass is suppressed under anchoring action,and the percentage of tensile fracture of anchored rock mass increases further with the increase of preload force.④Under the condition of full-length anchorage,the anchor rod strengthens the rock body strength more than the end anchorage without preload,the anchor rod inhibits the rock body peak front microfracture more,and the anchor rod axial force increases more timely with the rock body deformation.（5）Deformation and instability mechanism of the fractured surrounding rock of the kilometer deep mine mining roadway is studied by using the synthetic rock mass numerical simulation method.It was pointed out that due to the propagation and coalescence of the deep shear crack of the surrounding rock in the side wall of 13501working face,large slip deformation were occur in the rib along the shear failure surface.which resulting in the shear fracture of the anchor bolt,and finally the structural instability of the surrounding rock.Combined with the anchoring mechanism of rock mass with fracture network and the deformation and instability mechanism of surrounding rock along the track of 13501 working face in Zhujixi mine,the control principle of fractured surrounding rock and bolt mesh support technology of mining roadway in kilometer deep mine are put forward,which are verified by numerical simulation and field industrial test.The field industrial test shows that the optimized support scheme can effectively control the deformation of surrounding rock along the track of 13501 working face.There are 128 figures,21 tables and 217 references in this dissertation.