Study On Relationship Between Bolt Pre-stresses And Supporting Effect Of Roadway

With the improvement of pre-stressed bolting support technology, the development of anchor theory as well as the appearance of some new bolt materials with high-strength, the pre-stressed bolt has been widely used in many underground projects reinforcement such as the water conservancy, mining, traffic, civil engineering and so on. In last few years, with the fast development of coal industry, gradual enlargement of coal production and the increasement of mining depth, the problems of roadway support emerge frequently. The traditional bolting support technology can't meet the need of modern mining development with high-production and high-efficiency. The pre-stressed bolting support technology offers the modern bolting support system with high-strength, high-rigidity, high- reliability and low-supporting density.The modern bolting support system can improve the development speed and safety of roadway, and provide an effective solution method for roadway support difficulties.Due to the complexity of interaction between bolts and surrounding rock, the study on pre-stressed bolt is still in the exploring stage and does not form a perfectly theory system. The pre-stressed bolting design mainly depends on the engineering analogy and the design theory seriously falls behind the engineering practice.This paper further studied the mechanism of interaction between pre-stressed bolts and the surrounding rock mass.A special experiment equipment has been developed and some M-T experiments have been made in the laboratory in order to find the relationship between bolt pretension torsional moments and its axial pre-stresses. Some numerical models have been established by using FLAC3D to simulate the pre-stresses distribution in surrounding rock and in order to find the relationship between bolt pre-stresses and roadway support effect. At last, this paper further researched the relationship between bolt pre-stresses and roadway support effect by analyzing the underground stress monitoring results of some experimental roadways with different bolt's pre-stresses.Some main conclusions of this paper are as follows:(1) The main function of pre-stressed bolt support is to provide higher pre-stresses early and effectively in the surrounding rock mass, which can limit the further distortion of surrounding rock. Pre-stressed bolt can integrate the surrounding rock in the broken and plastic state, and then form the structure with high bearing capacity. At the same time, the pre-stressed bolt can enhance the mechanics parameters, modify the stress-state and improve the anti-distortion capability of surrounding rock.(2) The roof pre-stressed bearing structure is formed to prevent horizontal stress destroying the surrounding rock of the roof and to ease or mitigate the roof delamination, stress-centralization and the breakage of surrounding rock mass. At the same time, the roof pre-stressed bearing structure can promote the load distribution evenly of anchorage zone and enhance the stability of roadway surrounding rock mass.(3) Relationship between pretension torsional moment and axial pre-stress is linear and can be simplified as M = k?T?d(or T = M ( k ? d)).Under the same condition, the axial pre-stress can be increased by a range of 15.67%～110.47%, 26.57%～77.76% on average when useing the different antifriction materials. It is discovered that the nylon No.1010 is the best antifriction material.(4) In view of the difference between roadway surrounding rock and rigid contact in laboratory, the correction coefficientαshould be determined according to the condition of surrounding rock mass.(5) After applying the axial pre-stress on the bolt, an additional pre-stressed field is generated in a range of surrounding rock. It makes the stress-state of surrounding rock return to 3-dimension stress state from 2-dimension before surrounding rock distorted. At the same time, an arch structure was built to enhance the bearing ability and to reduce the broken range of the roadway surrounding rock. (6) The deformation and delamination of roadway roof is decreased by increasing the pre-stresses of the bolt. It can increase the rigidity and keep the rock strata integral by installing pre-stressed bolt timely. The successful application of pre-stressed bolt provides an effective way to solve the supporting questions of the deep mine.