| Based on theoretical analysis,this paper carries out the test of bolt mechanical properties in the laboratory,combined with numerical simulation calculation method.The force changes during the shearing process of the bolts under different influencing factors,such as different type of bolts,different pre-tightening force,different surrounding rock strength,different anchoring methods and different Drilling diameter are studied.The influence of various factors on the shear performance of the bolt is obtained.The main results are as follows:(1)It reveals the mechanism of the bolt playing a shearing effect in the jointed rock mass.The deformation region of the bolt in the jointed rock mass is divided into the elastic deformation section and the extrusion failure section,and the force analysis is performed.It is believed that the contribution of the bolt to the shear strength of the joint surface is mainly composed of two parts: The “dowel” effect of the bolt itself and the restraining effect of the axial force of the bolt.(2)The double shear test model of the bolt was designed,and the corresponding shear test frame was fabricated to form the test device for the shear mechanical properties of the bolt.At the same time,two different strength concrete blocks were simulated to simulate two kinds of surrounding rock with different hardness.The experimental study on the shear mechanical properties of bolts under different influencing factors was carried out.(3)The shear force change during the shearing process of jointed rock mass is mainly divided into four stages: elastic stage,yield stage,plastic stage and failure stage;The axial force change of the bolt also undergoes four stages: a stationary stage,a slow rising stage,a uniform rising stage,and a slow falling stage.The shear stiffness of the system changes continuously during the shearing process,and the initial shear stiffness is greater than the later shear stiffness,which reflects the enhanced toughness.The shearing force is different in the initial variation between the full-length anchoring and the end anchoring,but the later trends are consistent.(4)During the shearing process,the bolt is subjected to pull-shear or pull-bend composite action in the vicinity of the joint surface,resulting in a “Z”-shaped shear deformation of the rod at the joint surface.According to the failure mode of the bolt,it can be divided into two modes: tensile shear failure and tensile bending failure;Thebolt rod forms a “pull stress zone” and a “compression stress zone” on the upper and lower surfaces of the joint surface,and crushes the orifice to form a fan-shaped damage zone,and the concrete test blocks all have different degrees of cracking.(5)The experimental and numerical simulation results show that: After the pre-tightening force is increased,the initial shear performance of the bolt can be effectively improved,and the initial shear stiffness of the system is also improved.After the strength of the surrounding rock is increased,the yield load during the shearing process of the bolt is obviously improved,and the shear displacement at the time of breaking is obviously reduced,indicating that the bolt is more susceptible to shear performance in the jointed rock mass with higher strength;When the full-length anchoring is adopted,the bolt is sensitive to the deformation and sliding of the surrounding rock,At the initial stage of shear deformation,the bolt can exert the shearing effect,and the initial shear stiffness of the system is about twice that of the end anchoring. |
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