Theoretical Calculations And Influence Factors Of The Broken Rock Zone In Tunnels With Large-span And Flat Section

In tunnel engineering, the thickness of the first spray layer or the second lining intunnels depending on the surrounding rock when tunnels were excavated, during theactual construction, this tend to be conservative. It is obviously that resource can besave more, the construction time can be reduce, the construction progress can bespeed up if the thickness of tunnel lining how to determine more accurate was known.In the broken rock zone theory, the parameters supporting for the tunnel can bedetermine by the thickness of the broken rock zone. In recent years, experienceformula or approximate formula of the broken rock zone was got by scholars, thefactors that were considered in the process of research were the in-situ stress, burieddepth and rock mass strength of the tunnel, etc. while the weathering of the rockmass, joint spacing and blasting damage of changes before and after the tunnels wereexcavated were not taken into account.Based on Hoek Brown’s strength criterion, the thickness of the broken rock zone wasderived. However, there is no clear resources selected for geological strength indexin the selection of GSI and disturbed parameter D from Hoek Brown criterion, theengineering practice was fuzzy. A variety of means such as field testing, theoreticalanalysis and so on were combined to do research, the constructing disturbance by theinfluence of rock mass and how it should be considered in the practical engineeringwere discussed. Based on extension theory, how to get the value of disturbedparameter D method is proposed, and the improved disturbed parameter was appliedin theoretical calculation of the broken rock zone. The main research content are asfollows:(i) Based on quadratic orthogonal test method, influence factors of the broken rockzone were analyzed. The essence of the broken rock zone is the formation of thehulking deformation of surrounding rock, while the hulking deformation ofsurrounding rock was produced by loosening or damaging after the unloading oftunnels, the influence factors not only the groundwater and the ground stress, butalso the other geological mechanic indicators, such as Hoek-Brown parameters wereincluded. The quadratic orthogonal combination experiment4factors5level schemewere used in this paper, and connecting with the geological radar,17times of thefield tests have been carried out in accordance with the combination of design table.After calculation and analysis of influencing factors of significance from high to loware: the Hoek-Brown parameter S, the Hoek-Brown parameter M, interacting of theHoek-Brown parameter S and M, buried depth of tunnels.(ii) In order to reflect the real disturbance degree of rock mass, not only the disturbed influence by level of surrounding rock and blasting factors in engineering rock massin the broken rock zone were taken into account, but also with the engineering rockmass classification standard of rock mass integrity index Kvand ultrasonic detectiontechnique to determine the parameters for the disturbance D were combined as well.According to the actual disturbance characteristics of surrounding rock, based on thetheory of extenics, matter-element model of the rule to value Hoek Brown disturbedparameter D was established, at the same time, the entropy method was introduce toanalysis the index weights.(iii) The reference values of disturbed parameter D in Hoek-Brown criterion wasfuzzy and full of discreteness. On the basis of the matter-element model theory fromthe principle of extension theory, with the blasting damage, unloading situation, thedeveloping degree of structural plane and rock classification combined. Thereference range value of disturbed parameter D was determined, as an effectivereference provide for rock mass disturbance level.(iv) Improved rock disturbed parameter D was applied, with other parameters ofsurrounding rock in tunnels were combined. The theoretical thickness of the brokenrock zone in tunnels was calculated, and with the application of acoustic testing onbroken zone of in tunnels, the thickness values were tested, and this were comparedwith the theoretical values. Results indicate that the theoretical thickness of thebroken rock zone improved by matter-element model was basically the samecompared with the measured value, the reliable theoretical solution was verified.