Research On Slipping Mechanism Of Bolt In Non Full Length Anchorage Unit And Engineering Application

Support technology with resin bolt is widely used in the control of surrounding rock of coal mine roadway in China,and it is the most economical and effective active support method at present.In order to improve the prestressing effect and improve the digging speed,non-full-length anchorage method is adopted.Influenced by the occurrence characteristics of surrounding rock,stress environment,bonding characteristics of capsule resin and construction technology,slipping failure of bolt often occurs,which leads to serious deformation of surrounding rock and even support accidents.It restricts the development and application of anchorage support technology,and seriously threatens the safety of coal mine production.In this paper,a variety of methods are used,including theoretical analysis,laboratory tests,numerical calculation and engineering practice.The failure type of anchor support,the load transfer law of anchor section,the design of support scheme and the optimization of parameters are studied systematically in coal mine roadway.The main research results are as follows.(1)The concept of anchorage element is put forward.In this paper,the "three body and two sides" structure of anchorage element is analyzed from a mesoscopic point of view and the load transfer mechanism of anchorage element under axial load of anchor is discussed;Based on the numerical calculation of PFC,the development and propagation of cracks in the anchorage unit under axial load are studied.It is found that the smaller the anchorage length,the smaller anchorage agent thickness,the greater the surrounding rock strength and stress,the lower the crack development and expansion in the anchorage unit,and the smaller the potential failure risk of bolt slipping.(2)Through similar simulation test,the bearing characteristics of bolt with different anchorage length were studied.It was found that axial force and interfacial shear stress of elastic deformation stage presented a decreasing distribution along the direction of anchorage length;Numerical calculation shows that the distribution law of bolt axial force and interfacial shear stress is basically consistent with the test under different anchorage length and different load grade,The first and the second interface shear stress maximum value respectively at 2cm and port in the end from the anchorage,and the second interface shear stress maximum value is greater than the first interface,verify the coal rock anchoring agent interface more prone to slippage debonding.(3)Based on three-stage linear function proposed by Benmokrane B,the equilibrium equation of the coal-anchorage agent interface at the full elastic stage is established,and the formulas for calculating the elastic ultimate bearing capacity and the interfacial shear stress distribution of the bolt under tension load are derived in this paper.Combining with the calculation formula of elastic ultimate bearing capacity,the calculation formula of critical anchorage length of bolt is deduced,and the main influencing factors of determining reasonable anchorage length are discussed.(4)Based on the analysis of the whole process of failure evolution of bolt slippage,combined with theoretical research,tension test and acoustic emission monitoring research results,three conditions for failure of coal-rock-anchorage agent interface in non-full-length anchorage unit are proposed,and the failure mechanism of bolt slippage is revealed.(5)In this paper,the design principle and working process of anchorage support are put forward,which can not only satisfy the safety and economy,but also give full play to the anchorability of surrounding rock and the properties of bolt material.The calculation formula of interface strength parameters of short anchor tension test is deduced.Based on the initial determination of main parameters of anchorage support by conventional design method,an optimization method of support parameters based on interface slip debonding prevention and control is established.Industrial test shows that the support scheme of roadway surrounding rock is safe and reliable,and the control effect of surrounding rock is good.Its economy,material properties of support materials and anchorability of surrounding rock are well developed,which provides theoretical and technical guidance for optimization design and safety evaluation of roadway anchorage support parameters.