In deep ground engineering,the use of high-strength and high-toughness steels for rock bolt can significantly improve its energy absorption capacity.However,the mechanisms and effects of rock loading conditions on thi...In deep ground engineering,the use of high-strength and high-toughness steels for rock bolt can significantly improve its energy absorption capacity.However,the mechanisms and effects of rock loading conditions on this kind of high energy-absorbing steel for rock bolt remain immature.In this study,taking Muzhailing highway tunnel as the background,physically based crystal plasticity simulations were performed to understand the effect of rock loading rate and pretension on the deformation behaviors of twinning induced plasticity(TWIP)steel used for rock bolt.The material physical connecting to the underlying microscopic mechanisms of dislocation glide and deformation twinning were incorporated in numerical modeling.The rock loading conditions were mimicked by the real-time field monitoring data of the NPR bolt/cable equipment installed on the tunnel surrounding rock surface.The results indicate that the bolt rod exhibits pronounced deformation-softening behavior with decrease of the loading rate.There is also a sound deformation-relaxation phenomenon induced by the dramatic decrease of loading rate after pre-tensioning.The high pretension(>600 MPa or 224 k N)can help bolt rod steel resist deformation-softening behavior,especially at low loading rate(<10~(-1)MPa/s or 10~(-2)kN/s).The loading rate was found to be a significant factor affecting deformation-softening behavior while the pretension was found to be the major parameter accounting for the deformation-relaxation scenario.The results provide the theoretical basis and technical support for practical applications.展开更多
In recent years,there is a scenario in urban tunnel constructions to build super-large-span tunnels for traffic diversion and route optimization purposes.However,the increased size makes tunnel support more difficult....In recent years,there is a scenario in urban tunnel constructions to build super-large-span tunnels for traffic diversion and route optimization purposes.However,the increased size makes tunnel support more difficult.Unfortunately,there are few studies on the failure and support mechanism of the surrounding rocks in the excavation of supported tunnel,while most model tests of super-large-span tunnels focus on the failure characteristics of surrounding rocks in tunnel excavation without supports.Based on excavation compensation method(ECM),model tests of a super-large-span tunnel excavation by different anchor cable support methods in the initial support stage were carried out.The results indicate that during excavation of super-large-span tunnel,the stress and displacement of the shallow surrounding rocks decrease,following a step-shape pattern,and the tunnel failure is mainly concentrated on the vault and spandrel areas.Compared with conventional anchor cable supports,the NPR(negative Poisson’s ratio)anchor cable support is more suitable for the initial support stage of the super-large-span tunnels.The tunnel support theory,model test materials,methods,and the results obtained in this study could provide references for study of similar super-large-span tunnels。展开更多
With the reduction of shallow resources,the degree of damage and the frequency of dynamic hazards,such as deep rock bursts and impact ground pressure,are increasing dramatically.However,the existing support materials ...With the reduction of shallow resources,the degree of damage and the frequency of dynamic hazards,such as deep rock bursts and impact ground pressure,are increasing dramatically.However,the existing support materials are incapable of meeting the safety require-ments of the refuges and roadways under a strong impact force.To effectively solve these problems,a novel negative Poisson’s ratio(NPR)anchor cable with excellent properties,such as impact resistance and the ability to withstand large deformation,is proposed.In the present study,a series of field tests and numerical simulations are conducted to investigate the mechanical and support charac-teristics of NPR anchor cables under blast impact.Laboratory mechanical tests show that NPR anchor cables can maintain constant resistance and produce large deformation under the action of multiple drop hammer impacts.According to the results of field tests,the roadway supported by conventional anchor cables was unable to endure the blast impact,while the roadway supported by NPR anchor cables was able to withstand the severe impact equivalent to a Class 3 mine earthquake.The dynamic response of the NPR anchor cable that supports the roadway under explosion is investigated using the innovative coupled modeling approach that combines the finite element method and the discrete element method,and the support effect of the NPR anchor cable is verified.The study shows that the NPR anchor cable has a superior impact and blast resistance performance,and a broad application prospect in the support of chambers and roadways that are at high risk of rock bursts and impact ground pressure.展开更多
Although super-large-span tunnels ensure convenient transportation,they face many support challenges.The lack of normative construction guidance and the limited number of reference engineering cases pose a significant...Although super-large-span tunnels ensure convenient transportation,they face many support challenges.The lack of normative construction guidance and the limited number of reference engineering cases pose a significant challenge to the stability control of superlarge-span tunnels.Based on the geological conditions of a super-large-span tunnel(span=32.17 m)at the bifurcation section of the Shenzhen interchange,this study determined support parameters via theoretical calculation,numerical simulation,and engineering analogy.The support effects of negative Poisson’s ratio(NPR)anchor cables and ordinary anchor cables on super-long-span tunnels were simulated and studied.Further,based on FLAC3D simulations,the surrounding rock stress field of NPR anchor cables was analyzed under different prestressing conditions,and the mechanism of a long-short combination,high-prestress compensation NPR anchor cable support was revealed.On the basis of numerical simulations,to our knowledge,the three-dimensional(3D)geomechanical model test of the NPR anchor cable and ordinary anchor cable support for super-large-span tunnel excavation is conducted for the first time,revealing the stress evolution law of super-large-span tunnels,deformation and failure characteristics of the surrounding rock,and the changing trend of the anchor cable’s axial force,and verifies that NPR anchor cables with high preloads are suitable for super-large-span tunnel support and have advantages over ordinary anchor cables.This study can provide a reliable theoretical reference for the support design and stability control of the surrounding rock of similar shallow-buried super-large-span tunnels.展开更多
基金the National Natural Science Foundation of China(Grant No.41941018)the Science and Technology Major Project of Gansu Province(Grant No.19ZD2GA005)the Research Institute for Deep Underground Science and Engineering Foundation(Grant No.XD2021023)。
文摘In deep ground engineering,the use of high-strength and high-toughness steels for rock bolt can significantly improve its energy absorption capacity.However,the mechanisms and effects of rock loading conditions on this kind of high energy-absorbing steel for rock bolt remain immature.In this study,taking Muzhailing highway tunnel as the background,physically based crystal plasticity simulations were performed to understand the effect of rock loading rate and pretension on the deformation behaviors of twinning induced plasticity(TWIP)steel used for rock bolt.The material physical connecting to the underlying microscopic mechanisms of dislocation glide and deformation twinning were incorporated in numerical modeling.The rock loading conditions were mimicked by the real-time field monitoring data of the NPR bolt/cable equipment installed on the tunnel surrounding rock surface.The results indicate that the bolt rod exhibits pronounced deformation-softening behavior with decrease of the loading rate.There is also a sound deformation-relaxation phenomenon induced by the dramatic decrease of loading rate after pre-tensioning.The high pretension(>600 MPa or 224 k N)can help bolt rod steel resist deformation-softening behavior,especially at low loading rate(<10~(-1)MPa/s or 10~(-2)kN/s).The loading rate was found to be a significant factor affecting deformation-softening behavior while the pretension was found to be the major parameter accounting for the deformation-relaxation scenario.The results provide the theoretical basis and technical support for practical applications.
基金supported by the Innovation Fund Research Project of State Key Laboratory for Geomechanics and Deep Underground Engineering,China University of Mining and Technology(Grant No.SKLGDUEK202201)the Foundation for the Opening of State Key Laboratory for Geomechanics and Deep Underground Engineering,China University of Mining and Technology(Grant No.SKLGDUEK2129)the Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences(Grant No.Z020007)。
文摘In recent years,there is a scenario in urban tunnel constructions to build super-large-span tunnels for traffic diversion and route optimization purposes.However,the increased size makes tunnel support more difficult.Unfortunately,there are few studies on the failure and support mechanism of the surrounding rocks in the excavation of supported tunnel,while most model tests of super-large-span tunnels focus on the failure characteristics of surrounding rocks in tunnel excavation without supports.Based on excavation compensation method(ECM),model tests of a super-large-span tunnel excavation by different anchor cable support methods in the initial support stage were carried out.The results indicate that during excavation of super-large-span tunnel,the stress and displacement of the shallow surrounding rocks decrease,following a step-shape pattern,and the tunnel failure is mainly concentrated on the vault and spandrel areas.Compared with conventional anchor cable supports,the NPR(negative Poisson’s ratio)anchor cable support is more suitable for the initial support stage of the super-large-span tunnels.The tunnel support theory,model test materials,methods,and the results obtained in this study could provide references for study of similar super-large-span tunnels。
基金supported by the National Natural Science Foundation of China(Grant No.41941018).
文摘With the reduction of shallow resources,the degree of damage and the frequency of dynamic hazards,such as deep rock bursts and impact ground pressure,are increasing dramatically.However,the existing support materials are incapable of meeting the safety require-ments of the refuges and roadways under a strong impact force.To effectively solve these problems,a novel negative Poisson’s ratio(NPR)anchor cable with excellent properties,such as impact resistance and the ability to withstand large deformation,is proposed.In the present study,a series of field tests and numerical simulations are conducted to investigate the mechanical and support charac-teristics of NPR anchor cables under blast impact.Laboratory mechanical tests show that NPR anchor cables can maintain constant resistance and produce large deformation under the action of multiple drop hammer impacts.According to the results of field tests,the roadway supported by conventional anchor cables was unable to endure the blast impact,while the roadway supported by NPR anchor cables was able to withstand the severe impact equivalent to a Class 3 mine earthquake.The dynamic response of the NPR anchor cable that supports the roadway under explosion is investigated using the innovative coupled modeling approach that combines the finite element method and the discrete element method,and the support effect of the NPR anchor cable is verified.The study shows that the NPR anchor cable has a superior impact and blast resistance performance,and a broad application prospect in the support of chambers and roadways that are at high risk of rock bursts and impact ground pressure.
基金supported by the Foundation for the Opening of State Key Laboratory for GeoMechanics&Deep Underground Engineering(Grant No.SKLGDUEK2129).
文摘Although super-large-span tunnels ensure convenient transportation,they face many support challenges.The lack of normative construction guidance and the limited number of reference engineering cases pose a significant challenge to the stability control of superlarge-span tunnels.Based on the geological conditions of a super-large-span tunnel(span=32.17 m)at the bifurcation section of the Shenzhen interchange,this study determined support parameters via theoretical calculation,numerical simulation,and engineering analogy.The support effects of negative Poisson’s ratio(NPR)anchor cables and ordinary anchor cables on super-long-span tunnels were simulated and studied.Further,based on FLAC3D simulations,the surrounding rock stress field of NPR anchor cables was analyzed under different prestressing conditions,and the mechanism of a long-short combination,high-prestress compensation NPR anchor cable support was revealed.On the basis of numerical simulations,to our knowledge,the three-dimensional(3D)geomechanical model test of the NPR anchor cable and ordinary anchor cable support for super-large-span tunnel excavation is conducted for the first time,revealing the stress evolution law of super-large-span tunnels,deformation and failure characteristics of the surrounding rock,and the changing trend of the anchor cable’s axial force,and verifies that NPR anchor cables with high preloads are suitable for super-large-span tunnel support and have advantages over ordinary anchor cables.This study can provide a reliable theoretical reference for the support design and stability control of the surrounding rock of similar shallow-buried super-large-span tunnels.
