The existence of squeezing ground conditions can lead to significant challenges in designing an adequate support system for tunnels.Numerous empirical,observational and analytical methods have been suggested over the ...The existence of squeezing ground conditions can lead to significant challenges in designing an adequate support system for tunnels.Numerous empirical,observational and analytical methods have been suggested over the years to design support systems in squeezing ground conditions,but all of them have some limitations.In this study,a novel experimental setup having physical model for simulating the tunnel boring machine(TBM)excavation and support installation process in squeezing clay-rich rocks is developed.The observations are made to understand better the interaction between the support and the squeezing ground.The physical model included a large true-triaxial cell,a miniature TBM,laboratoryprepared synthetic test specimen with properties similar to natural mudstone,and an instrumented cylindrical aluminum support system.Experiments were conducted at realistic in situ stress levels to study the time-dependent three-dimensional tunnel support convergence.The tunnel was excavated using the miniature TBM in the cubical rock specimen loaded in the true-triaxial cell,after which the support was installed.The confining stress was then increased in stages to values greater than the rock’s unconfined compressive strength.A model for the time-dependent longitudinal displacement profile(LDP)for the supported tunnel was proposed using the tunnel convergence measurements at different times and stress levels.The LDP formulation was then compared with the unsupported model to calculate the squeezing amount carried by the support.The increase in thrust in the support was backcalculated from an analytical solution with the assumption of linear elastic support.Based on the test results and case studies,a recommendation to optimize the support requirement for tunnels in squeezing ground is proposed.展开更多
Squeezing ground conditions,which can lead to severe loads in tunnels,have historically been associated with the presence of clay minerals in the ground.Over the years,many methodologies have been proposed to predict ...Squeezing ground conditions,which can lead to severe loads in tunnels,have historically been associated with the presence of clay minerals in the ground.Over the years,many methodologies have been proposed to predict squeezing in tunnels based on tunnel depth,in situ stress,ground mineralogy,and ground strength and deformation behavior.This paper presents a comprehensive review of methodologies to predict tunnel squeezing in clay-rich rocks.A new methodology is proposed where ground conditions and squeezing potential are assessed based on the Stress History and Normalized Soil Engineering Properties(SHANSEP)approach adapted to clayrich rocks,Peck’s stability number and Hoek&Brown’s(1997)Geological Strength Index(GSI).A squeezing number S is suggested to classify ground conditions based on the level of squeezing that the ground may experience in response to tunneling.Finally,it is demonstrated that by combining the proposed classification system and an existing classification system for ground squeezing condition,an accurate estimate of tunnel strain can also be obtained.The proposed method is applied to four case studies of tunnels in squeezing ground in shale and mudstone.展开更多
基金financial support of the University Transportation Center for Underground Transportation Infrastructure(UTC-UTI)at the Colorado School of Mines under Grant No.69A3551747118 from the US Department of Transportation(DOT)。
文摘The existence of squeezing ground conditions can lead to significant challenges in designing an adequate support system for tunnels.Numerous empirical,observational and analytical methods have been suggested over the years to design support systems in squeezing ground conditions,but all of them have some limitations.In this study,a novel experimental setup having physical model for simulating the tunnel boring machine(TBM)excavation and support installation process in squeezing clay-rich rocks is developed.The observations are made to understand better the interaction between the support and the squeezing ground.The physical model included a large true-triaxial cell,a miniature TBM,laboratoryprepared synthetic test specimen with properties similar to natural mudstone,and an instrumented cylindrical aluminum support system.Experiments were conducted at realistic in situ stress levels to study the time-dependent three-dimensional tunnel support convergence.The tunnel was excavated using the miniature TBM in the cubical rock specimen loaded in the true-triaxial cell,after which the support was installed.The confining stress was then increased in stages to values greater than the rock’s unconfined compressive strength.A model for the time-dependent longitudinal displacement profile(LDP)for the supported tunnel was proposed using the tunnel convergence measurements at different times and stress levels.The LDP formulation was then compared with the unsupported model to calculate the squeezing amount carried by the support.The increase in thrust in the support was backcalculated from an analytical solution with the assumption of linear elastic support.Based on the test results and case studies,a recommendation to optimize the support requirement for tunnels in squeezing ground is proposed.
基金the University Transportation Center for Underground Transportation Infrastructure(UTC-UTI)at the Colorado School of Mines for funding this research under Grant No.69A3551747118 from the U.S.Department of Transportation(DOT).
文摘Squeezing ground conditions,which can lead to severe loads in tunnels,have historically been associated with the presence of clay minerals in the ground.Over the years,many methodologies have been proposed to predict squeezing in tunnels based on tunnel depth,in situ stress,ground mineralogy,and ground strength and deformation behavior.This paper presents a comprehensive review of methodologies to predict tunnel squeezing in clay-rich rocks.A new methodology is proposed where ground conditions and squeezing potential are assessed based on the Stress History and Normalized Soil Engineering Properties(SHANSEP)approach adapted to clayrich rocks,Peck’s stability number and Hoek&Brown’s(1997)Geological Strength Index(GSI).A squeezing number S is suggested to classify ground conditions based on the level of squeezing that the ground may experience in response to tunneling.Finally,it is demonstrated that by combining the proposed classification system and an existing classification system for ground squeezing condition,an accurate estimate of tunnel strain can also be obtained.The proposed method is applied to four case studies of tunnels in squeezing ground in shale and mudstone.
