Test And Mechanical Properties Of Tunnel Anchorage System Under High Ground Temperature

In recent years,with the development of tunnel engineering toward the trend of deep burial and long length,high geothermal hazard tunnels have appeared in different degrees in the construction process of tunnels in various countries.In high temperature ground tunnel,as the basic structure of rock and soil reinforcement,anchor rod was in high-temperature environment once it was applied,and grouting material was condensed and hardened in high temperature environment,which would inevitably lead to changes in mechanical properties of anchorage system.In this paper,the mechanical characteristics of bolt anchorage system in high temperature environment were studied by experimental method and theoretical analysis.The work and main conclusions of this paper are as follows:(1)The tunnel model was simplified to a circular one,and then the theoretical calculation model of air-lining-surrounding rock was established.The discrete equation of node physical quantity should be deduced for the discretization of time-space region,and the theoretical prediction method of temperature field in high ground temperature tunnel was established.Under different initial temperatures,the surrounding rocks are rapidly cooled within 5 days,then slowly cooled and tended to stable temperature.On this basis,the curing method of high temperature and variable temperature in laboratory test was established.(2)The compressive stress-strain curves of cement mortar under different curing conditions were obtained through compressive strength tests of grouting material.High geothermal environment makes grouting material shows obvious early strength effect and late strength degradation effect.The higher the initial curing temperature and the lower the curing humidity,the more serious the degradation of peak strength,residual strength and deformation resistance.At the same time,the compressive constitutive equation of grouting material suitable for high ground temperature environment was proposed.(3)Through pull-out test of anchorage system specimens,the change rules of failure mode of the anchorage system in high ground temperature environment were obtained and the failure mechanism was analyzed.The test results show that the failure modes of F1,F2and F3 occur successively with the increase of age under standard curing conditions,and all the failure modes are F2 under high temperature and low humidity curing conditions.On the28~thh day,only F3 damage occurred in high humidity condition and only F2 damage occurred in low humidity condition.(4)The effects of curing conditions on the ultimate pull-out force,bond strength,bond slip and constitutive properties of the anchorage system were analyzed.The ultimate pull-out force and ultimate bond strength are negatively correlated with the initial curing temperature and positively correlated with the curing humidity,and show the early strength effect and the later strength degradation effect.The constitutive equations of the anchorage system under different failure modes were established.