Recent developments in tunneling have stimulated design practitioners to more effectively utilize the underground spaces.However,tunneling at shallow depth in soft grounds gives rise to concerns associated with tunnel...Recent developments in tunneling have stimulated design practitioners to more effectively utilize the underground spaces.However,tunneling at shallow depth in soft grounds gives rise to concerns associated with tunnel instability.Umbrella arch method(UAM),as a pre-reinforcement approach of tunnels in complex geological conditions,is widely used to maintain the tunnel stability.Quantitative assessment of the impacts of the entire approach and forepoling pipe features on tunnel stability remains challenging due to the complex nature of the UAM application.This study aimed to assess the effect of pipe design parameters on reinforcing the tunnels excavated in soft grounds.This practical investigation considered the actual field conditions attributed to the tunneling procedure and UAM deployment.Then,the tunneling process was modeled and the tunnel excavation-induced settlements were calculated.The post-processed results confirmed that deploying the UAM substantially reduced the tunnel crown and ground surface settlements by 76%and 42%,respectively.Investigation of various design parameters of pipes underscored the significance of incorporating the optimum value for each individual parameter into design schemes to more effectively control the settlements.Additionally,contrasting the settlement reduction rates(SRRs)for pipe design variables showed that the tunnel stability is more sensitive to the changes in the values of diameter and length,compared to values of the installation angle and center-tocenter distance of the pipes.展开更多
Due to advances in numerical modelling, it is possible to capture complex support-ground interaction intwo dimensions and three dimensions for mechanical analysis of complex tunnel support systems,although such analys...Due to advances in numerical modelling, it is possible to capture complex support-ground interaction intwo dimensions and three dimensions for mechanical analysis of complex tunnel support systems,although such analysis may still be too complex for routine design calculations. One such system is theforepole element, installed within the umbrella arch temporary support system for tunnels, whichwarrants such support measures. A review of engineering literature illustrates that a lack of designstandards exists regarding the use of forepole elements. Therefore, when designing such support, designersmust employ complex numerical models combined with engineering judgement. With referenceto past developments by others and new investigations conducted by the authors on the Driskos tunnelin Greece and the Istanbul metro, this paper illustrates how advanced numerical modelling tools canfacilitate understanding of the influences of design parameters associated with the use of forepole elements.In addition, this paper highlights the complexity of the ground-support interaction whensimulated with two-dimensional （2D） finite element software using a homogenous reinforced region,and three-dimensional （3D） finite difference software using structural elements. This paper further illustratessequential optimisation of two design parameters （spacing and overlap） using numericalmodelling. With regard to capturing system behaviour in the region between forepoles for the purpose ofdimensioning spacing, this paper employs three distinctive advanced numerical models： particle codes,continuous finite element models with joint set and Voronoi blocks. Finally, to capture the behaviour/failure ahead of the tunnel face （overlap parameter）, 2D axisymmetric models are employed. Finally,conclusions of 2D and 3D numerical assessment on the Driskos tunnel are drawn. The data enriched casestudy is examined to determine an optimum design, based on the proposed optimisation of designparameters, of forepole elements related to the site-specific considerations. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.展开更多
The Tunnel Oberau, with a length of 2.9 km, forms the core of the local bypass of Oberau. Between the two massifs Kirchbichl and Mühlberg, the tunnel is situated in the valley of the Gießenbach in alluvial g...The Tunnel Oberau, with a length of 2.9 km, forms the core of the local bypass of Oberau. Between the two massifs Kirchbichl and Mühlberg, the tunnel is situated in the valley of the Gießenbach in alluvial gravel with only a small overlap underneath settlement-sensitive buildings. In this paper, the measures in the tunnel to minimize the settlements of the buildings during the shotcrete excavations are described. Basis for this planning were extensive 3D-FE-calculations. Furthermore, under two buildings a compensation grouting measure was carried out, in order to compensate the occurring settlements. This paper describes how the required time and the amount of injection material (grout) could be reduced during the compensation grouting in highly permeable gravel.展开更多
During tunneling in loose grounds, the ground deformation caused by drillings around the tunnel, leads to land subsidence and the adjacent tunnel which would affect tunnel structure and surrounding structures. In such...During tunneling in loose grounds, the ground deformation caused by drillings around the tunnel, leads to land subsidence and the adjacent tunnel which would affect tunnel structure and surrounding structures. In such situations it is necessary to improve the properties of the ground prior to drilling operations. In order to acquire tunnel face stability during excavation operations in areas with loose soil fault or areas with lack of adhesion, there are various methods such as split cross drilling, frame holder or auxiliary pre-holding methods such as umbrella arch method;pre-holding methods must provide safety when drilling and must be affordable, economically. In this study, we assessed the previous studies on methods and behaviors of umbrella arch strategy in reinforcing the concrete tunnels, reached the purpose with experimental and numerical methods and offered the latest design achievements, implementation progresses and analysis in relation with this method.展开更多
The stability of shallow tunnels excavated in full face has been a major challenge to the scientific community for a long time. In recent years, new techniques based on the installation of a pre-reinforcement system a...The stability of shallow tunnels excavated in full face has been a major challenge to the scientific community for a long time. In recent years, new techniques based on the installation of a pre-reinforcement system ahead of the tunnel face were developed to control the deformations and surface settlements induced by the excavation and to ensure the sustainability of the tunnel in the long term. In this paper, a finite difference numerical simulation was conducted to study the behaviors and effects of two pre-reinforcement systems, i.e. the face bolting and the umbrella arch system installed in a section of southern Toulon tunnel in France. For this purpose, two approaches were taken and compared： a two-dimensional （2D） approach based on the convergence–confinement method, and a three-dimensional （3D） approach taking into account the complete modeling of the tunnel. A 2D numerical back-analysis was performed to identify the geomechanical parameters that offer satisfactory agreement with the measurement results. The limit of this method lies in the exact choice of the stress relaxation ratio λ. To overcome this uncertainty, a 3D model was developed, which permitted to study the influence of different pre-support systems on the reaction of ground mass. Both 2D and 3D numerical approaches have been fitted to measurements recorded in a section of the Toulon tunnel and the very satisfactory correspondence has allowed validating the simulations. The results show that the 3D numerical analysis with a full discretization of the inclusions seems unquestionably the most reliable approach.展开更多
文摘Recent developments in tunneling have stimulated design practitioners to more effectively utilize the underground spaces.However,tunneling at shallow depth in soft grounds gives rise to concerns associated with tunnel instability.Umbrella arch method(UAM),as a pre-reinforcement approach of tunnels in complex geological conditions,is widely used to maintain the tunnel stability.Quantitative assessment of the impacts of the entire approach and forepoling pipe features on tunnel stability remains challenging due to the complex nature of the UAM application.This study aimed to assess the effect of pipe design parameters on reinforcing the tunnels excavated in soft grounds.This practical investigation considered the actual field conditions attributed to the tunneling procedure and UAM deployment.Then,the tunneling process was modeled and the tunnel excavation-induced settlements were calculated.The post-processed results confirmed that deploying the UAM substantially reduced the tunnel crown and ground surface settlements by 76%and 42%,respectively.Investigation of various design parameters of pipes underscored the significance of incorporating the optimum value for each individual parameter into design schemes to more effectively control the settlements.Additionally,contrasting the settlement reduction rates(SRRs)for pipe design variables showed that the tunnel stability is more sensitive to the changes in the values of diameter and length,compared to values of the installation angle and center-tocenter distance of the pipes.
基金funded by the Natural Sciences and Engineering Research Council of Canadathe Department of National Defence (Canada) as well as graduate funding obtained at Queen’s University and the Royal Military College of Canada
文摘Due to advances in numerical modelling, it is possible to capture complex support-ground interaction intwo dimensions and three dimensions for mechanical analysis of complex tunnel support systems,although such analysis may still be too complex for routine design calculations. One such system is theforepole element, installed within the umbrella arch temporary support system for tunnels, whichwarrants such support measures. A review of engineering literature illustrates that a lack of designstandards exists regarding the use of forepole elements. Therefore, when designing such support, designersmust employ complex numerical models combined with engineering judgement. With referenceto past developments by others and new investigations conducted by the authors on the Driskos tunnelin Greece and the Istanbul metro, this paper illustrates how advanced numerical modelling tools canfacilitate understanding of the influences of design parameters associated with the use of forepole elements.In addition, this paper highlights the complexity of the ground-support interaction whensimulated with two-dimensional （2D） finite element software using a homogenous reinforced region,and three-dimensional （3D） finite difference software using structural elements. This paper further illustratessequential optimisation of two design parameters （spacing and overlap） using numericalmodelling. With regard to capturing system behaviour in the region between forepoles for the purpose ofdimensioning spacing, this paper employs three distinctive advanced numerical models： particle codes,continuous finite element models with joint set and Voronoi blocks. Finally, to capture the behaviour/failure ahead of the tunnel face （overlap parameter）, 2D axisymmetric models are employed. Finally,conclusions of 2D and 3D numerical assessment on the Driskos tunnel are drawn. The data enriched casestudy is examined to determine an optimum design, based on the proposed optimisation of designparameters, of forepole elements related to the site-specific considerations. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.
文摘The Tunnel Oberau, with a length of 2.9 km, forms the core of the local bypass of Oberau. Between the two massifs Kirchbichl and Mühlberg, the tunnel is situated in the valley of the Gießenbach in alluvial gravel with only a small overlap underneath settlement-sensitive buildings. In this paper, the measures in the tunnel to minimize the settlements of the buildings during the shotcrete excavations are described. Basis for this planning were extensive 3D-FE-calculations. Furthermore, under two buildings a compensation grouting measure was carried out, in order to compensate the occurring settlements. This paper describes how the required time and the amount of injection material (grout) could be reduced during the compensation grouting in highly permeable gravel.
文摘During tunneling in loose grounds, the ground deformation caused by drillings around the tunnel, leads to land subsidence and the adjacent tunnel which would affect tunnel structure and surrounding structures. In such situations it is necessary to improve the properties of the ground prior to drilling operations. In order to acquire tunnel face stability during excavation operations in areas with loose soil fault or areas with lack of adhesion, there are various methods such as split cross drilling, frame holder or auxiliary pre-holding methods such as umbrella arch method;pre-holding methods must provide safety when drilling and must be affordable, economically. In this study, we assessed the previous studies on methods and behaviors of umbrella arch strategy in reinforcing the concrete tunnels, reached the purpose with experimental and numerical methods and offered the latest design achievements, implementation progresses and analysis in relation with this method.
文摘The stability of shallow tunnels excavated in full face has been a major challenge to the scientific community for a long time. In recent years, new techniques based on the installation of a pre-reinforcement system ahead of the tunnel face were developed to control the deformations and surface settlements induced by the excavation and to ensure the sustainability of the tunnel in the long term. In this paper, a finite difference numerical simulation was conducted to study the behaviors and effects of two pre-reinforcement systems, i.e. the face bolting and the umbrella arch system installed in a section of southern Toulon tunnel in France. For this purpose, two approaches were taken and compared： a two-dimensional （2D） approach based on the convergence–confinement method, and a three-dimensional （3D） approach taking into account the complete modeling of the tunnel. A 2D numerical back-analysis was performed to identify the geomechanical parameters that offer satisfactory agreement with the measurement results. The limit of this method lies in the exact choice of the stress relaxation ratio λ. To overcome this uncertainty, a 3D model was developed, which permitted to study the influence of different pre-support systems on the reaction of ground mass. Both 2D and 3D numerical approaches have been fitted to measurements recorded in a section of the Toulon tunnel and the very satisfactory correspondence has allowed validating the simulations. The results show that the 3D numerical analysis with a full discretization of the inclusions seems unquestionably the most reliable approach.
