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Farooq, Mohammed

University of British Columbia

This thesis evaluates industrially-available sensors for their effectiveness in real-time monitoring of foundation soil level and bridge scour. Two types of photoelectric sensors, namely diffusive-reflective and through-beam, and two types of dielectric (capacitance) sensors, namely low frequency printer-circuit board type, and higher frequency stainless steel type, were independently investigated. Laboratory investigations carried out in a hydraulic flume used a simulated bridge pier comprising of an array of sensors mounted vertically and interfaced via Arduino. The state of “burial” in foundation soil or the state of “exposure” to water was determined from the sensor output. On scouring, the sensors provided an instantaneous shift in signal from the state of “buried” to “exposed”, and vice versa. The results indicate that all the four sensors could be monitor sediment level, scour, scour-hole refill, and scouring rate. The dielectric sensors were susceptible to misinterpretation at high concentrations of NaCl in water. Improvements on isolating the effects of NaCl were made using lab-made steel electrodes excited using an external electrical waveform ranging from 1 Hz to 70 MHz. The results indicate that low frequencies were influenced by NaCl content, whereas at high frequencies (35-50 MHz), the sensors performed well. Although a single signal frequency worked well for the range of NaCl content from 0% to 3.5%, the use of two or more frequencies is recommended for higher reliability. Passive thermometry using a vertical array of DS18B20 digital temperature sensors buried at different depths in sediment and water studied the diurnal thermal variations in the media. Although the technique required historic data (few diurnal cycles), a clear distinction could be noticed in the buried and the exposed temperature waveforms. A field prototype using photoelectric sensors was installed in a small creek in UBC, and a second prototype using dielectric and temperature sensors was installed at a scour-susceptible over-water platform on Guichon Creek, Burnaby. Both the field prototypes validated laboratory results, were able to notify the onset and progression of scour around the pier over long periods of time. The detected scour events and subsequent re-deposition could be correlated to reference water level and rainfall data.

Text

2022-08-26

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/82542

Civil Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/