Hydraulic tunnels

• 15.1.

  Introduction

• 15.2.

  Geomembrane systems

• 15.3.

  The exposed liner system

• 15.4.

  The covered liner system

• 15.5.

  Summary of main points

• 15.6.

  Some common questions and their answers

• Acknowledgement

• References

The main function of hydraulic tunnels is to convey water, under pressure or in free flow, for power and/or water supply works. Hydraulic tunnels are usually lined with steel, cast in situ concrete or sprayed concrete. The most common concrete linings are rarely free from defects such as voids and cracks. During operation, when the concrete linings are exposed to the dynamic action of water, they suffer from deterioration, resulting in the formation of fissures/cracks, increased permeability through body and joints, and increased roughness. The use of geomembranes allows the combination of continuous watertightness and improved friction properties with the strength of the concrete lining at a much lower cost. Geomembrane systems have reached a high degree of refinement and reliability, and, when adequately designed and installed, they are durable and reliable under high water heads and demanding environments. This chapter provides a complete description of the engineering aspects of geosynthetic-based lining systems for new and old hydraulic tunnels.