A new method for determining the incremental cohesion △Cm of surrounding rock due to prestressed cable anchor is presented, and the formulas for △Cm are deduced and △Cm distributions also are discussed, based on th...A new method for determining the incremental cohesion △Cm of surrounding rock due to prestressed cable anchor is presented, and the formulas for △Cm are deduced and △Cm distributions also are discussed, based on the two anchorage effects, one is the effect with the prestressed vaIue △σ3 of cable anchor improving the stress state of surrounding rock and increasing the surrounding rock strength, the other is the fully encapsulated effect. The determined incremental cohesion △Cm is subiected to the model test and field measurement in the references, and coincides well with those tested results. The formulas for △Cm can be used in designing supoport parameters and related numerical analyses of prestressed cable anchor.展开更多
The evaluation of the seismic stability of high rock slopes is of vital importance to ensure the safe operation of the hydropower stations.In this paper,an equivalent pseudo-static force analysis based on the finite e...The evaluation of the seismic stability of high rock slopes is of vital importance to ensure the safe operation of the hydropower stations.In this paper,an equivalent pseudo-static force analysis based on the finite element method is developed to evaluate the seismic stability of reinforced rock slopes where the prestressed cables are modeled by the bar elements applied with nodal forces and bounded only at the anchored parts.The method is applied to analyze a high rock slope in south-west China and the optimization of cables.The stabilization effects of prestressed cables on the seismic stability of the slope are studied,the simulations of the concrete heading are discussed and the potential failure modes of the shear concrete plug are compared.Based on this,the optimization of cables is studied including the anchor spacing and inclined angles.展开更多
The Haidong Tunnel is one of the four soft rock tunnels of the Central Yunnan Water Diversion Project(CYWDP),where large deformation hazards of soft rock occur frequently,which seriously affect construction safety.The...The Haidong Tunnel is one of the four soft rock tunnels of the Central Yunnan Water Diversion Project(CYWDP),where large deformation hazards of soft rock occur frequently,which seriously affect construction safety.The effect of highly prestressed anchor cable support was studied based on the active support test in the No.3 branch tunnel of Haidong Tunnel.Firstly,the geological conditions and failure causes were analyzed on the basis of the results of geological survey,in-situ test,and rock laboratory test.Then,the Mohr circle form of the highly prestressed anchor cable active support theory for the support of bedded rock mass was given in combination with the excavation compensation method.It is considered that the prestress active compensation value required for the bedded rock mass is larger than that for the homogeneous rock mass.The deformations of rock mass under both passive and active supports were analyzed by numerical simulations.Furthermore,the'pressure bubble'mechanical model for anchor cable support of bedded rock mass in Haidong Tunnel is given.Field monitoring results show that the highly prestressed anchor cable support can control rock mass deformation well,with a maximum deformation of about 200 mm.The prestressed anchor cable is effective in the bedded stratum,which makes the stress of rock mass uniform and reduces the risk of failure of steel arches due to local bias.Meanwhile,the expansion of plastic zone was efficiently controlled,which is of positive significance for the overall stability of rock mass.展开更多
Excavating super-large-span tunnels in soft rock masses presents significant challenges.To ensure safety,the sequential excavation method is commonly adopted.It utilizes internal temporary supports to spatially partit...Excavating super-large-span tunnels in soft rock masses presents significant challenges.To ensure safety,the sequential excavation method is commonly adopted.It utilizes internal temporary supports to spatially partition the tunnel face and divide the excavation into multiple stages.However,these internal supports generally impose spatial constraints,limiting the use of large-scale excavation equipment and reducing construction efficiency.To address this constraint,this study adopts the“Shed-frame”principle to explore the feasibility of an innovative support system,which aims to replace internal supports with prestressed anchor cables and thus provide a more spacious working space with fewer internal obstructions.To evaluate its effectiveness,a field case involving the excavation of a 24-m span tunnel in soft rock is presented,and an analysis of extensive field data is conducted to study the deformation characteristics of the surrounding rock and the mechanical behavior of the support system.The results revealed that prestressed anchor cables integrated the initial support with the shed,creating an effective“shed-frame”system,which successively maintained tunnel deformation and frame stress levels within safe regulatory bounds.Moreover,the prestressed anchor cables bolstered the surrounding rock effectively and reduced the excavation-induced disturbance zone significantly.In summary,the proposed support system balances construction efficiency and safety.These field experiences may offer valuable insights into the popularization and further development of prestressed anchor cable support systems.展开更多
Prestressed anchor cables are widely used for slope reinforcement,but the loss of prestress makes it difficult to guarantee the reinforcement effect.Anchor cable prestress degradation was considered as a stochastic pr...Prestressed anchor cables are widely used for slope reinforcement,but the loss of prestress makes it difficult to guarantee the reinforcement effect.Anchor cable prestress degradation was considered as a stochastic process,and the probability density function of this process was established using gamma theory and impact theory respectively.Combined with the failure threshold,the probability density was integrated to find the time-dependent reliability of the anchor cable.Based on the monitoring data of the prestress degradation of the anchor cable,parameters in the probability density function were solved by the maximum likelihood method,and the time-varying reliability and service life of the anchor cable were obtained analytically.The applicability of two degradation theories,gamma stochastic process and impact theory,was compared.The results showed that the probability density curves of both degradation models were normally distributed and the error of reliability results did not exceed 0.06.The life prediction results of the gamma stochastic process were closer to the actual life of 400 h than the 500 h of the impact theory,and the probability curves of the anchor cable life also indicated that the impact theory overestimated the service life probability of the anchor cable.Taking the anchor cable reinforcement within the slope of the Dagushan open-pit mine as an example,and the results verify the feasibility of using gamma theory to predict the degradation of anchor cables and provides theoretical support for prevention of the degradation of anchor cables in the slope of an open-pit mine under the action of external forces.展开更多
Corrosion can significantly impact the safety and stability of the entire structure by reducing the service life and load-bearing capacity of anchors.This study provides an in-depth examination of the effects of corro...Corrosion can significantly impact the safety and stability of the entire structure by reducing the service life and load-bearing capacity of anchors.This study provides an in-depth examination of the effects of corrosion on prestressed anchor cables,covering the effects on the anchor cables themselves and the bond interface.The force characteristics and load transfer mechanisms within the anchorage structure were explored through a detailed analysis of the three key components:the anchor cable,the grout,and the surrounding rock.The distribution functions of axial force and interfacial shear stress considering the debonding of the anchor-grout interface were derived,and the prestressed corrosion damage model was further developed.Taking the anchoring project on the slopes in Nagasaki as an example,the stress distribution of anchor cables under different surrounding rock conditions was analyzed in depth.The results showed that the relative deformation of the grout and the surrounding rock decreases when the elasticity modulus of the surrounding rock increases,resulting in a reduced axial force in anchor cables and an increased interface shear stress.Thresholds exist for the effect of the total anchor length and radius on prestressing stability.When designing anchor structures in corrosive environments,there is no need to choose excessive anchor length or anchor radius to achieve better cost-effectiveness.In practical underground engineering,the force in anchor cables is transferred to the surrounding rock through the anchoring section,where the length of the anchorage section has a more direct impact on prestress transfer and stability.展开更多
The Haidong Water Conveyance Tunnel(HWCT),a notable engineering feat located within Dali City,Yunnan Province,China,represents an ultra-long water conveyance tunnel situated in a region characterized by medium in-situ...The Haidong Water Conveyance Tunnel(HWCT),a notable engineering feat located within Dali City,Yunnan Province,China,represents an ultra-long water conveyance tunnel situated in a region characterized by medium in-situ stress conditions.As part of the Central Yunnan Water Diversion Project,this tunnel was specifically engineered for soft-rock environments.The excavation of such tunnels presents significant challenges due to rock mass deformation,commonly referred to as squeezing ground behavior.These challenges are exacerbated when navigating through diverse geological and geomorphological units,particularly in areas with complex geological conditions.To address these issues,an innovative active support system utilizing prestressed anchor cables was developed for the HWCT.This study provides a comprehensive analysis and comparison of rock mass behavior between two support systems:a conventional passive system employing steel arches and the proposed active system using prestressed anchor cables.The numerical modeling was performed using FLAC3D software to simulate various scenarios,while an extensive monitoring program was implemented in several representative tunnel sections to measure key parameters including rock mass stresses,displacements,internal forces in steel arches,and axial forces in anchor cables.The results from both the numerical simulations and field observations were systematically compared.The analyses demonstrated the superior performance of the active support system using prestressed anchor cables in the HWCT,significantly enhancing overall rock mass stability and effectively mitigating large deformation issues throughout the tunnel.展开更多
文摘A new method for determining the incremental cohesion △Cm of surrounding rock due to prestressed cable anchor is presented, and the formulas for △Cm are deduced and △Cm distributions also are discussed, based on the two anchorage effects, one is the effect with the prestressed vaIue △σ3 of cable anchor improving the stress state of surrounding rock and increasing the surrounding rock strength, the other is the fully encapsulated effect. The determined incremental cohesion △Cm is subiected to the model test and field measurement in the references, and coincides well with those tested results. The formulas for △Cm can be used in designing supoport parameters and related numerical analyses of prestressed cable anchor.
基金The authors gratefully acknowledge the supports from National Natural Science Foundation of China(Grant No.51109162)China National Twelfth Five-Year Science and Technology Supporting Programme(2011BAB08B01)Research Programme for Western China Communication(2011ZB04)and the Fundamental Research Funds for the Central Universities.
文摘The evaluation of the seismic stability of high rock slopes is of vital importance to ensure the safe operation of the hydropower stations.In this paper,an equivalent pseudo-static force analysis based on the finite element method is developed to evaluate the seismic stability of reinforced rock slopes where the prestressed cables are modeled by the bar elements applied with nodal forces and bounded only at the anchored parts.The method is applied to analyze a high rock slope in south-west China and the optimization of cables.The stabilization effects of prestressed cables on the seismic stability of the slope are studied,the simulations of the concrete heading are discussed and the potential failure modes of the shear concrete plug are compared.Based on this,the optimization of cables is studied including the anchor spacing and inclined angles.
基金supported by the China Yunnan Province Major Science and Technology Special Plan Foundation Project (Grant No. 202002AF080003)the China Railway No.5 Engineering Group Co., Ltd.
文摘The Haidong Tunnel is one of the four soft rock tunnels of the Central Yunnan Water Diversion Project(CYWDP),where large deformation hazards of soft rock occur frequently,which seriously affect construction safety.The effect of highly prestressed anchor cable support was studied based on the active support test in the No.3 branch tunnel of Haidong Tunnel.Firstly,the geological conditions and failure causes were analyzed on the basis of the results of geological survey,in-situ test,and rock laboratory test.Then,the Mohr circle form of the highly prestressed anchor cable active support theory for the support of bedded rock mass was given in combination with the excavation compensation method.It is considered that the prestress active compensation value required for the bedded rock mass is larger than that for the homogeneous rock mass.The deformations of rock mass under both passive and active supports were analyzed by numerical simulations.Furthermore,the'pressure bubble'mechanical model for anchor cable support of bedded rock mass in Haidong Tunnel is given.Field monitoring results show that the highly prestressed anchor cable support can control rock mass deformation well,with a maximum deformation of about 200 mm.The prestressed anchor cable is effective in the bedded stratum,which makes the stress of rock mass uniform and reduces the risk of failure of steel arches due to local bias.Meanwhile,the expansion of plastic zone was efficiently controlled,which is of positive significance for the overall stability of rock mass.
基金supported by the National Natural Science Foundation of China through Grant No.51978523.
文摘Excavating super-large-span tunnels in soft rock masses presents significant challenges.To ensure safety,the sequential excavation method is commonly adopted.It utilizes internal temporary supports to spatially partition the tunnel face and divide the excavation into multiple stages.However,these internal supports generally impose spatial constraints,limiting the use of large-scale excavation equipment and reducing construction efficiency.To address this constraint,this study adopts the“Shed-frame”principle to explore the feasibility of an innovative support system,which aims to replace internal supports with prestressed anchor cables and thus provide a more spacious working space with fewer internal obstructions.To evaluate its effectiveness,a field case involving the excavation of a 24-m span tunnel in soft rock is presented,and an analysis of extensive field data is conducted to study the deformation characteristics of the surrounding rock and the mechanical behavior of the support system.The results revealed that prestressed anchor cables integrated the initial support with the shed,creating an effective“shed-frame”system,which successively maintained tunnel deformation and frame stress levels within safe regulatory bounds.Moreover,the prestressed anchor cables bolstered the surrounding rock effectively and reduced the excavation-induced disturbance zone significantly.In summary,the proposed support system balances construction efficiency and safety.These field experiences may offer valuable insights into the popularization and further development of prestressed anchor cable support systems.
基金supported by the National Natural Science Foundation of China(No.52074292)National Key Research and Development Program(No.2017YFC1503103)。
文摘Prestressed anchor cables are widely used for slope reinforcement,but the loss of prestress makes it difficult to guarantee the reinforcement effect.Anchor cable prestress degradation was considered as a stochastic process,and the probability density function of this process was established using gamma theory and impact theory respectively.Combined with the failure threshold,the probability density was integrated to find the time-dependent reliability of the anchor cable.Based on the monitoring data of the prestress degradation of the anchor cable,parameters in the probability density function were solved by the maximum likelihood method,and the time-varying reliability and service life of the anchor cable were obtained analytically.The applicability of two degradation theories,gamma stochastic process and impact theory,was compared.The results showed that the probability density curves of both degradation models were normally distributed and the error of reliability results did not exceed 0.06.The life prediction results of the gamma stochastic process were closer to the actual life of 400 h than the 500 h of the impact theory,and the probability curves of the anchor cable life also indicated that the impact theory overestimated the service life probability of the anchor cable.Taking the anchor cable reinforcement within the slope of the Dagushan open-pit mine as an example,and the results verify the feasibility of using gamma theory to predict the degradation of anchor cables and provides theoretical support for prevention of the degradation of anchor cables in the slope of an open-pit mine under the action of external forces.
基金funded by the National Key Research and Development Program Young Scientist Project(2024YFC2911000)State Scholarship Fund of China(No.202306650001).
文摘Corrosion can significantly impact the safety and stability of the entire structure by reducing the service life and load-bearing capacity of anchors.This study provides an in-depth examination of the effects of corrosion on prestressed anchor cables,covering the effects on the anchor cables themselves and the bond interface.The force characteristics and load transfer mechanisms within the anchorage structure were explored through a detailed analysis of the three key components:the anchor cable,the grout,and the surrounding rock.The distribution functions of axial force and interfacial shear stress considering the debonding of the anchor-grout interface were derived,and the prestressed corrosion damage model was further developed.Taking the anchoring project on the slopes in Nagasaki as an example,the stress distribution of anchor cables under different surrounding rock conditions was analyzed in depth.The results showed that the relative deformation of the grout and the surrounding rock decreases when the elasticity modulus of the surrounding rock increases,resulting in a reduced axial force in anchor cables and an increased interface shear stress.Thresholds exist for the effect of the total anchor length and radius on prestressing stability.When designing anchor structures in corrosive environments,there is no need to choose excessive anchor length or anchor radius to achieve better cost-effectiveness.In practical underground engineering,the force in anchor cables is transferred to the surrounding rock through the anchoring section,where the length of the anchorage section has a more direct impact on prestress transfer and stability.
基金support provided by the Technology Development Service Project Funds of China,Railway 5th Bureau Group Fifth Engineering Co.,Ltd and Yunnan Institute of Water&Hydropower Engineering Investigation,Design and Research(Grant No.20230525)the Major Science and Technology Special Plan of Yunnan Province Science and Technology Department(Grant No.202002AF080003)the Fundamental Research Funds for the Central Universities(Grant No.2022YJSSB04).
文摘The Haidong Water Conveyance Tunnel(HWCT),a notable engineering feat located within Dali City,Yunnan Province,China,represents an ultra-long water conveyance tunnel situated in a region characterized by medium in-situ stress conditions.As part of the Central Yunnan Water Diversion Project,this tunnel was specifically engineered for soft-rock environments.The excavation of such tunnels presents significant challenges due to rock mass deformation,commonly referred to as squeezing ground behavior.These challenges are exacerbated when navigating through diverse geological and geomorphological units,particularly in areas with complex geological conditions.To address these issues,an innovative active support system utilizing prestressed anchor cables was developed for the HWCT.This study provides a comprehensive analysis and comparison of rock mass behavior between two support systems:a conventional passive system employing steel arches and the proposed active system using prestressed anchor cables.The numerical modeling was performed using FLAC3D software to simulate various scenarios,while an extensive monitoring program was implemented in several representative tunnel sections to measure key parameters including rock mass stresses,displacements,internal forces in steel arches,and axial forces in anchor cables.The results from both the numerical simulations and field observations were systematically compared.The analyses demonstrated the superior performance of the active support system using prestressed anchor cables in the HWCT,significantly enhancing overall rock mass stability and effectively mitigating large deformation issues throughout the tunnel.
