For deep tunnel projects,selecting an appropriate initial support distance is critical to improving the self-supporting capacity of surrounding rock.In this work,an intuitive method for determining the tunnel’s initi...For deep tunnel projects,selecting an appropriate initial support distance is critical to improving the self-supporting capacity of surrounding rock.In this work,an intuitive method for determining the tunnel’s initial support distance was proposed.First,based on the convergence-confinement method,a three-dimensional analytical model was constructed by combining an analytical solution of a non-circular tunnel with the Tecplot software.Then,according to the integral failure criteria of rock,the failure tendency coefficients of hard surrounding rock were computed and the spatial distribution plots of that were constructed.On this basis,the tunnel’s key failure positions were identified,and the relationship between the failure tendency coefficient at key failure positions and their distances from the working face was established.Finally,the distance from the working face that corresponds to the critical failure tendency coefficient was taken as the optimal support distance.A practical project was used as an example,and a reasonable initial support distance was successfully determined by applying the developed method.Moreover,it is found that the stability of hard surrounding rock decreases rapidly within the range of 1.0D(D is the tunnel diameter)from the working face,and tends to be stable outside the range of 1.0D.展开更多
The convergence confinement methods are solutions employed to estimate convergence in circular tunnels. They are mostly based on constitutive equations governed by the Mohr-Coulomb and Hoek-Brown yield criteria. Howev...The convergence confinement methods are solutions employed to estimate convergence in circular tunnels. They are mostly based on constitutive equations governed by the Mohr-Coulomb and Hoek-Brown yield criteria. However, the solutions based on these criteria neglect the intermediate principal stress confining effect on the ground reaction estimation. Therefore, in this paper, a Drucker-Prager yield criterion governed solution integrated with the Lode angle parameter is employed. It considers the intermediate principal stress influence and the critical effect of the parameter on failure characterization.Subsequently, it is verified with results attained from numerical simulations which consider an elasticperfectly plastic constitutive law with a non-associative flow rule within FLAC3D. It was drawn from the results that the ground reaction and plastic evolution are influenced by the confining stress.Furthermore, considering a suitable yield criterion leads to realistic convergence and plastic evolution estimation. The circumscribed DP criterion governed solution with Lode angle parameter value(0.8) is considered appropriate for the realistic ground reaction estimation in the three-dimensional(3D) stress state rock mass. It estimates approximately 3.4% of tunnel convergence as compared to the classic solutions(5%) and plastic radius estimated to be approximately 2.45 m compared to 2.84 m.展开更多
According to the convergence confinement theory,it is an effective measure to control the large deformation of high ground stress in fractured soft rock tunnels by using yielding support.The yielding support can be cl...According to the convergence confinement theory,it is an effective measure to control the large deformation of high ground stress in fractured soft rock tunnels by using yielding support.The yielding support can be classified as either radial or circumferential yielding support.Circumferential yielding support is achieved by transforming radial displacement into circumferential tangential closure without compromising the support capacity of the primary lining support structure.Based on this,and inspired by the design principle of dampers,a yielding support structure system with spring damping elements as its core was developed,based on the connection characteristics of steel arches in highway tunnel,which can provide increasing support resistance in the yielding deformation section.Then the mechanical properties of spring damping elements were obtained through indoor axial pressure and flexural tests.In addition,according to these results with numerical calculations,the yielding support structure system with embedded spring damping elements can reduce the internal force of the support structure by approximately 10%and increase the area of the plastic zone of the surrounding rock by 11.23%,which can fully utilize the self-bearing capacity of surrounding rock and verify the effectiveness of circumferential yielding support.Finally,the spring damping support structure system was designed with reference to the construction process of the tunnel excavated by drilling and blasting method,and the transformation of the spring damping element to spring damping support structure was achieved.Based on field test results,surrounding ground pressure for the yielding support optimization scheme was reduced by 40%and more evenly distributed,resulting in the successful application and a reduction in the construction cost of large deformation tunnels in soft rock.展开更多
基金Project(2021JLM-49) supported by Natural Science Basic Research Program of Shaanxi-Joint Fund of Hanjiang to Weihe River Valley Water Diversion Project,ChinaProject(42077248) supported by the National Natural Science Foundation of China
文摘For deep tunnel projects,selecting an appropriate initial support distance is critical to improving the self-supporting capacity of surrounding rock.In this work,an intuitive method for determining the tunnel’s initial support distance was proposed.First,based on the convergence-confinement method,a three-dimensional analytical model was constructed by combining an analytical solution of a non-circular tunnel with the Tecplot software.Then,according to the integral failure criteria of rock,the failure tendency coefficients of hard surrounding rock were computed and the spatial distribution plots of that were constructed.On this basis,the tunnel’s key failure positions were identified,and the relationship between the failure tendency coefficient at key failure positions and their distances from the working face was established.Finally,the distance from the working face that corresponds to the critical failure tendency coefficient was taken as the optimal support distance.A practical project was used as an example,and a reasonable initial support distance was successfully determined by applying the developed method.Moreover,it is found that the stability of hard surrounding rock decreases rapidly within the range of 1.0D(D is the tunnel diameter)from the working face,and tends to be stable outside the range of 1.0D.
基金The author gratefully acknowledges the financial support and affiliation from the University of Adelaide.
文摘The convergence confinement methods are solutions employed to estimate convergence in circular tunnels. They are mostly based on constitutive equations governed by the Mohr-Coulomb and Hoek-Brown yield criteria. However, the solutions based on these criteria neglect the intermediate principal stress confining effect on the ground reaction estimation. Therefore, in this paper, a Drucker-Prager yield criterion governed solution integrated with the Lode angle parameter is employed. It considers the intermediate principal stress influence and the critical effect of the parameter on failure characterization.Subsequently, it is verified with results attained from numerical simulations which consider an elasticperfectly plastic constitutive law with a non-associative flow rule within FLAC3D. It was drawn from the results that the ground reaction and plastic evolution are influenced by the confining stress.Furthermore, considering a suitable yield criterion leads to realistic convergence and plastic evolution estimation. The circumscribed DP criterion governed solution with Lode angle parameter value(0.8) is considered appropriate for the realistic ground reaction estimation in the three-dimensional(3D) stress state rock mass. It estimates approximately 3.4% of tunnel convergence as compared to the classic solutions(5%) and plastic radius estimated to be approximately 2.45 m compared to 2.84 m.
基金supported by the National Nature Science Funds of China(Grant Nos.52038008,and 42207176)the Science and Technology Project of the Department of Transport of Yunnan Province China(Yunnan Transportation Science and Education[2021]No.7)Ningbo Natural Science Funds(Grant No.2022J116).The authors gratefully acknowledge their financial support.
文摘According to the convergence confinement theory,it is an effective measure to control the large deformation of high ground stress in fractured soft rock tunnels by using yielding support.The yielding support can be classified as either radial or circumferential yielding support.Circumferential yielding support is achieved by transforming radial displacement into circumferential tangential closure without compromising the support capacity of the primary lining support structure.Based on this,and inspired by the design principle of dampers,a yielding support structure system with spring damping elements as its core was developed,based on the connection characteristics of steel arches in highway tunnel,which can provide increasing support resistance in the yielding deformation section.Then the mechanical properties of spring damping elements were obtained through indoor axial pressure and flexural tests.In addition,according to these results with numerical calculations,the yielding support structure system with embedded spring damping elements can reduce the internal force of the support structure by approximately 10%and increase the area of the plastic zone of the surrounding rock by 11.23%,which can fully utilize the self-bearing capacity of surrounding rock and verify the effectiveness of circumferential yielding support.Finally,the spring damping support structure system was designed with reference to the construction process of the tunnel excavated by drilling and blasting method,and the transformation of the spring damping element to spring damping support structure was achieved.Based on field test results,surrounding ground pressure for the yielding support optimization scheme was reduced by 40%and more evenly distributed,resulting in the successful application and a reduction in the construction cost of large deformation tunnels in soft rock.
