Sensitivity analysis and seepage/leakage monitoring using point heat source

Abstract

Seepage monitoring is an important issue in the health monitoring and performance evaluation of geotechnical engineering, and one of the effective ways to monitor seepage is the thermal method. Based on the coupling effects between the seepage field and the temperature field, a point heat source (PHS) method is presented in this paper. The PHS seepage monitoring system was composed of a monitoring tube, multiple sensing–heating elements, a regulated power supply and a demodulator. The sensing element, a fibre Bragg grating (FBG) sensor, is integrated with the heating element (a ceramic heating tube). To optimise the monitoring scheme of this system, the influence of sensitivity-related factors on the identification effects of seepage is studied. The implementation pattern of the sensing–heating element, dimensions of the monitoring tube, heating voltage and heating period were used as factors for calibration experiments at different seepage velocities. The results reveal the following: (a) both implementation patterns, with heat conduction glue or a copper tube filled in the gap between the FBG sensor and the ceramic heating tube, obtained good monitoring results; (b) the dimensions of the monitoring tube significantly influenced the effects of seepage identification, where the larger the gap was between the monitoring tube and the sensing–heating element, the worse were the results of monitoring; (c) within the relevant ranges, the heating voltage and period had nearly no effect on the monitoring results. Based on these conclusions, a monitoring scheme that combines the sensing–heating element with heat conduction glue filled in the gap and monitoring tube of 20 mm dia. was chosen for a leakage monitoring experiment. Three patterns of the leakage passage were tested in the experiment, and each was tested with three values of leakage intensity. The results show that leakage was accurately determined by the PHS seepage monitoring system, and its estimates of flow flux agreed well with empirical values.