Prestressed Concrete-Lined Pressure Tunnels

Hydropower can be a source of sustainable energy, provided environmental considerations are taken into account and economic aspects of hydropower design are appropriately addressed. Using concrete-lined pressure tunnels instead of steel pipes may be economically attractive but may also have limitations due to the low tensile strength of concrete. Cracking in concrete tunnel linings can lead to loss of energy production, extensive repairs, and even accidents. One of the techniques available to improve the bearing capacity of pressure tunnels is through prestressing the concrete lining by grouting the circumferential gap between the concrete lining and the rock mass at high pressure. A classical approach to determine the bearing capacity of such tunnels is based on the theory of elasticity, assuming impervious concrete. In this research, a new concept is introduced to assess the effect of seepage on the bearing capacity of pressure tunnels. Also, an innovative approach is proposed to explore the effects of the in-situ stress ratio on the lining performance. Distinction is made based on whether the rock mass behaves as an elasto-plastic isotropic, or elastic anisotropic material. Furthermore, a simplified method is introduced to quantify seepage associated with cracks around the tunnel, which is useful for assessing tunnel stability.