Detection of Local Wall Stiffness Drop in Steel-Lined Pressure Tunnels and Shafts of Hydroelectric Power Plants Using Steep Pressure Wave Excitation and Wavelet Decomposition

• Published in: Journal of hydraulic engineering (New York, N.Y.) Vol. 138; no. 1; pp. 35 - 45
• Main Authors: Hachem, F. E, Schleiss, A. J
• Format: Journal Article
• Language: English
• Published: Reston, VA American Society of Civil Engineers 01.01.2012
• Subjects: Applied sciences; Buildings. Public works; Computation methods. Tables. Charts; Dams and subsidiary installations; Decomposition; Exact sciences and technology; Hydraulic constructions; Measurements. Technique of testing; Monitoring; Pressure waves; Shafts (power); Stiffness; Structural analysis. Stresses; TECHNICAL PAPERS; Tunnels (transportation); Tunnels, galleries; Walls; Wavelet; Experimental device; Modeling; Wavelet decomposition; Wavelet; Pressure wave; Transient pressure signals; Wavelet base; Steel-lined pressure tunnels; Stiffness; Excitation; Localization; Monitoring; Tunnels; Power plants; Hydroelectric power plant; Speed; Hydro power; Wave reflections; Theoretical study; Pipe; Front wave speed; Wave reflection; Wave velocity; Detection; Pipes; Comparative study
• ISSN: 0733-9429; 1943-7900
• DOI: 10.1061/(ASCE)HY.1943-7900.0000478

A new monitoring approach for detecting, locating, and quantifying structurally weak reaches of steel-lined pressure tunnels and shafts is presented. These reaches arise from local deterioration of the backfill concrete and the rock mass surrounding the liner. The change of wave speed generated by the weakening of the radial-liner supports creates reflection boundaries for the incident pressure waves. The monitoring approach is based on the generation of transient pressure with a steep wave front and the analysis of the reflected pressure signals using the fast Fourier transform and wavelet decomposition methods. Laboratory experiments have been carried out to validate the monitoring technique. The multilayer system (steel-concrete-rock) of the pressurized shafts and tunnels is modeled by a one-layer system of the test pipe. This latter was divided into several reaches having different wall stiffnesses. Different longitudinal placements of a steel, aluminum, and PVC pipe reach were tested to validate the identification method of the weak section.