Experimental Study On Coupling Effect Between Bolt Tray And Concrete Shotcrete

Anchoring technology has been widely used in various fields of geotechnical engineering based on its unique advantages. Taking trays and concrete shotcrete as the research objects in this thesis, author carries on several bolt pullout tests under the different combination of flat tray, bowtie tray, pressure-yield tray with C15, C20, C25 plain concrete shotcrete and C20 concrete shotcrete in which the steel fiber contest are respectively 0.5%,1%,1.5%. While the bolt pullout test under different combination of C20 plain concrete shotcrete with eccentric tray in which the angle are respectively 3o, 7o and 11 o are also carried on. At the same time, author analyzes the stress state of bolt tail under eccentric load in theoretical method. The major research work and results are as follows:(1)According to the requirements of the subject, author designs a multifunctional bolt stress test system in the thesis, this system consists of the reaction frame and anchorage, loading device, measurement device, control system and data acquisition processing system. It can test the mechanics properties of conventional bolt, high strength bolt, large deformation bolt. The system can simulate the stress state of the scene bolt authentically, It can realize data real-time and diverse acquisition, dynamic demonstration, plotting graph and so on.(2)Curves of bolt elongation indicator and bolt drawing force under the coupling effect between tray and shotcrete is similar to steel tensile curve and it can be roughly divided into three stages which are elastic stage, yield stage, strengthening stage. The difference between the two curves is that the yield platform of the curves of bolt elongation indicator and bolt drawing force is obvious and its width is related to the test conditions.(3)Both yield strength and yield platform width of the bolt are the largest under the condition of bowtie tray and pressure-yield tray, when the shotcrete is C20 plain concrete. Both the bowtie tray and pressure-yield tray have the pressure function, and the latter can prevent the destruction of shotcrete.(4)Steel fiber concrete shotcrete can enhance the bolt’s yield strength under the coupling effect between shotcrete and tray. The yield strength increases with the increase of steel fiber under the condition of bowtie tray and pressure-yield tray, but the width of the yield platform is no affected.(5)The strain of the shotcrete increases with the increase of bolt drawing force, and the it yields at last. The strain of the steel fiber concrete shotcrete is much lower than the plain concrete, and its mechanical property is well. The steel fiber concrete shows the obvious characteristics of plastic damage, and the integrity of steel fiber concrete shotcrete is good when the test is over, the optimum adding quantity of steel fiber is 1%.(6)The stress of bolt tail under eccentric load is 5-7 times bigger than normal when the eccentric load is a concentrated load by theoretical derivation. The strain at the position of eccentric load is bigger than normal load according to the test, and the shotcrete damage start from the position of eccentric load surrounding the drilling, which matches the theoretical analysis.