Mechanism Analysis Of Relief Effect Of Parallel Pilot To High Geostress Soft Rock Tunnel

Many geological disasters in today’s tunnel projects，not only result in significantfinancial losses，but also bring great harm to construction workers. To improve the economicefficiency and provide safe operating environment for tunnel projects， it is essential to studythe high geostress relief technology in-depth. This article summarizes the current status ofhigh geostress relief research at home and abroad，discusses the pressure relief mechanismand presents the algorithm to excavate parallel pilot to help high geostress release in advance.Using numerical analysis method，this article studies appropriate parallel pilot size andreasonable space between parallel pilot and main tunnel in V surrounding rock conditions.The article also analyzes the influence factors of large deformation of surrounding rocks andsuggests a series of prevention and control measures. Main conclusions of this article includeas followings：1. In high geostress zones of tunnels，soft rocks are more likely to generate largedeformation and hard rocks are more likely to rock burst. In order to prevent such disastersfrom happening，most feasible measure is to excavate parallel pilot in high geo-stress zones tomake pilot tunnel deformation to help releasing geostress.2. Circular section is the best form of pilot cross sections in the circumstance of highgeostress zones of V surrounding rocks. It leads to best stress release results for the cases thatthe area of the pilot section is43㎡and the clear distance with the main tunnel is8m. That isevidenced by the cases that main tunnels are better excavated with pilot excavations thanwithout pilot excavations. At the same time，the excavation of main tunnels also lowersstress field of pilots. The parallel pilot and main tunnel excavations ultimately result in arelatively low stress field circumstance.3. The factors that affect deformation of weak surrounding rock in high geostress zonesinclude：geological structure characteristics of the surrounding rock，mechanical properties ofrock masses，depth of tunnels，initial ground stresses，subterranean water，constructionmethods and technology，tunnel cross section shape，supporting mode and supportingparameters，size effect etc. 4. To prevent deformation of surrounding rocks，the following measures should betaken：to make main line of tunnel with the same direction to the major principal stress in thechannel selection；to release surrounding rock’s geostress ahead of time in order to reducegroundwater around tunnel surrounding rocks；to choose the reasonable cross section of theform and adopt the right construction methods and technology.