Effects of Pressure Fluctuations on Hydraulic Jacking in Pressurized Tunnels with Low Overburden

Document Type : Research Article

Authors

1 M.Sc. Student, Department of Civil Engineering, Isfahan University of Technology, Isfahan, Iran

2 Associate Professor, Department of Civil Engineering, Isfahan University of Technology, Isfahan, Iran

3 Associate Professor, Department of Mining Engineering, Isfahan University of Technology, Isfahan, Iran

Abstract

In the present study, fluid, structure and soil interactions in a pressurized water tunnel were modeled by a two-dimensional finite element method, using the “ABAQUS” software. The tunnel lining was considered as a roughening coverage to decrease the roughness coefficient and to increase the flow velocity. The mechanical parameters of surrounding rock were assumed as weak as possible compared to the tunnel concrete lining. Water flow inside the tunnel was modeled, using acoustic elements that are capable of simulating the hydrodynamic forces. Accordingly, the mechanism of crack development in the surrounding rock as the most probable place to prone this destructive phenomenon is studied applying both steady state and transient flow conditions, considering fluid-structure and rock interactions. Steady state and transient flow analyses were performed using the “HAMMER” software. The resulting loads obtained from the hydraulic analyses by HAMMER software were transmitted to the ABAQUS software for structural analyses. The stress analysis of cracked elements of the surrounding rock was carried out based on Mohr-Coulomb fracture criterion. The least values of the overburden to prevent failure due to the hydraulic jacking were evaluated by imposing the flow pressure in both steady and transient flow states. Finally, the effects of increasing height of the overburden on the hydraulic jacking phenomenon were investigated considering transient flow conditions. Results indicate that, with respect to the positions of surrounding rock elements, providing an extra overburden over the tunnel is not essentially a safe solution for the predication of hydraulic jacking phenomenon in rock around a tunnel.

Keywords


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  • Receive Date: 23 August 2017
  • Revise Date: 04 February 2018
  • Accept Date: 10 February 2018
  • First Publish Date: 22 June 2018