Hydraulic Transients in Rock‐Bored Tunnels

Abstract

The nature of hydraulic transients in rock‐bored tunnels is expected to be frequency‐dependent. Three issues related to the frequency dependence are addressed in this paper. A complex‐valued and frequency‐dependent wave speed in a rock‐bored tunnel filled with water is formulated with consideration of the dynamic effect of the rock mass surrounding the tunnel, and its physical meaning is defined. The theory of hydraulic resonance in pipelines is extended to tunnels with frequency‐dependent wave speeds. Results show significant changes in resonant conditions, illustrate dramatic reductions in response at practical frequencies, and confirm the low probability of the occurrence of high‐frequency resonances in long tunnels. A variation in the impulse response method is applied for transient analysis. It is found that pressure waves propagating in tunnels are subject to dispersion and attenuation, and the complex wave speed may alter a transient to some extent, depending on the frequency spectrum of the transient.