The Xingshandong tunnel of Yichang-Xingshan high-speed railway passes through carboniferous shale ground,where large deformation may occur."Strength-deformation-timing"integrated design method is used for the design of the support of the large deformation section of Xingshandong tunnel."Strength-deformation-timing"integrated design method for tunnel support is established on basis of the total safety factor method.The design method,suitable for the active and passive support patterns,achieves the coordinated load-undertaking of the multiple support layers subject to the deformation of the surrounding rock.Under the premise that the strength of the tunnel support meets the load-undertaking requirements and by adjusting the deformation capability and the installing time of the support components,the deformation capability of the tunnel support is greater than the necessary deformation of the surrounding rock under the designed supporting force(to prevent too-high support rigidity),and is less than the necessary deformation of the surrounding rock under the minimum supporting force(to prevent too-low support rigidity).Thus,the overall support structure"works"is in the most cost-effective way according to the design intention.Two support patterns,i.e.,support pattern consisting of double layers of primary support and yielding steel arches and active support pattern with prestressed anchor cables,are designed for the large deformation section of Xingshandong tunnel,and the installing time and safety control requirements of each support component are provided.The two support patterns are used in the trial sections of Xingshandong tunnel.The monitoring result shows that the supporting parameters of these two support patterns effectively realize the design intention and solve the problem of the large deformation in the carboniferous shale section of the tunnel.In the case of the support pattern consisting of double layers of primary support and yielding steel arches,the minimum safety factor of the primary support is 1.83 and the maximum horizontal convergence of the tunnel is 588 mm,which meets the design requirements;in the case of the active support pattern with prestressed anchor cables,the maximum horizontal convergence is 372 mm and the maximum axial force of the anchor cables is 310 kN,which meets the design requirements.
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