Stability Analysis Of Single And Closely-Spaced Double Tunnels Based On Load-Unload Response Ratio Theory

Regard the underground cavern as a nonlinear system,The paper introduces the LURR(load-unload response ratio)to judge the stability of Single and Closely-Spaced double Tunnels through the method of laboratory experiments after load-unload response model be established.Major achievements have been made in the following aspects.(1)Through the marble load/unload experiments under three types of paths,conclusions can be drawn as follows: LURR of axial strain vs.axial stress shows little change with low load,whereas,presents sharp increase and drops before the rock specimens break,which can be used to predict macroscopic damage of the rock.(2)The paper apply the hierarchical loop load/unload way to model experiments,Juge out tunnel instability ultimate load by LURR theory in single and double hole tests.The load/unload response characters is studied.Combining with the acoustic emission,the paper discuss the damage evolution law and damage characteristics of roadway.(3)By comparison with single and double hole model test,The paper analysis the influence of the characteristics of new tunnel on adjacent tunnel when be excavated in stages.Central force of middle rock pillars significantly increased and rock pillars appear tensilestress,compressive stress which mainly lead lead to the destruction.Through the acoustic emission experiments we can directly observe internal cracks' s location,direction,and the formed space curved surface shape and better reflect the dynamic evolution process of roadway crack.(4)Using RFPA software the paper make a numerical simulation about single and closed spaced hole.Compared with experimental data the response characteristics parameters and acoustic emission location results are consistent.Meanwhile the small spacing tunnels' main damage form is sidewall damage near the middle rock pillars.