Study On The Mechanical Properties Of Wholly Grouted Anchor In Thermal Damage Tunnel

With the construction of more and more deep buried tunnels with extremely large length, it is inevitable to go through rock masses with complex geological conditions, and will encounter a series of special geological problems, such as high geothermal etc. With the general application of bolting technology in tunnel constructions, a series of physical and chemical changes exists in anchoring materials, which caused by high geothermal, leading to bonding performance deterioration and structural damage of anchorage body. Research on the bond behavior of anchorage body under high temperature will help to provide the theory foundation for the promotion and improvement of anchorage technology.In this paper, considerable research on the force transmission mechanism and the interface mechanical property of anchorage system was summarized, to get the bonding stress distribution of anchorage body under stress condition and sum up theory calculating formulas according to specific failure modes. The ultimate bearing capacity was put forward. Three experiments were carried out on the basis of integrated study.(1) Increasing the additional angle to analyze the influence of temperature on the mechanical properties of the anchor solid material, the effect of curing conditions, such as different temperatures (20℃,35℃,50℃),on the elastic modulus, the compressive strength and the drying shrinkage of cement mortar was studied and compared. The results show that the compressive strength and elastic modulus of the grouting material decrease with the rise of temperature, and the shrinkage of the grouting material increases with increasing of temperature, and the establishment of contraction produce equivalent radial pressure relation between force and temperature. This paper derives the relational equation that the radial compressive stress caused by shrinkage of the grouting material,varies with temperature。(2) Based on pullout tests of anchor solid specimens, lengths of which were 100mm, 300mm respectively anchor solid specimens, the following results were obtained:For 100mm long anchor, the ultimate bearing capacity and ultimate bond stress decrease with the increase of temperature, and compared with the effect of 20 ℃, the ultimate bearing capacity and ultimate bond stress of the specimens under the action of 35℃ and 50℃ are reduced by about 3.6% and 8.5%. The relational equation between the ultimate bond stress under high temperature and the strength of the mortar under room temperature is obtained. For the 300mm long anchor rod, with the temperature increasing, the ultimate bearing capacity and the average bond stress decrease,and compared with the effect of 20 ℃, the ultimate bearing capacity and the average bond stress of the specimens under the action of 35 ℃ and 50℃ are reduced by about 2.3% and 0.5%. With the applied load increasing, the ultimate bearing capacity increases.(3)Study on distribution of interfacial bond stress of 1000mm anchor solid experimental specimens, which is basic condition to analyze the effect of high temperature on distributions of the axial force and the shear stress of anchor bolt under different load. It is proved that with the temperature increasing, the elastic modulus and the maximum shear stress on the interface of anchor bolt decreases. With the increase of temperature, the maximum shear stress is smaller and the distribution of shear stress along anchorage section is well distributed, and the attenuation trend of the axial force along anchorage length is speeding up. With the increase of pulling force, the maximum shear stress and the axial force increase accordingly.According to the combination of experimental and theoretical knowledge, overall, high temperature has a negative effect on the bond performance of anchor. Measures are taken to improve the performance of anchor system caused by high temperature in the construction of anchor bolt support, such as the way of ventilation cooling, or the addition of additives to improve the strength of grouting. The conclusions in this paper provide some theoretical support for the promotion of the technology of anchor bolts.