A Simple Low-Cost Solution for Bridge Scour Monitoring Using Photoelectric Sensors

Majority of bridge failures across North America can be traced back to foundation instability due to hydraulic causes including scour. The inability to effectively inspect scour level at the foundations of bridges present a major risk to our ageing infrastructure. This has led to development of a number of scour monitoring devices such as SONAR, piezoelectric sensors, and tilt sensors among others. However, in addition to limited accuracy and low reliability, the high cost of technologies available today have restricted their widespread acceptance. In this laboratory study, the use of photoelectric sensors to monitor scour around a simulated bridge pier was evaluated. A sediment recess of depth 0.4 m and length 6 m filled with clean sand of D50 size 0.6 mm was centrally located in a flume of total height 1m and 15m length. The simulated bridge pier was mounted at the center of the sediment recess. Five photoelectric sensors were embedded at different depths on the simulated bridge. Two types of photoelectric sensors – throughbeam type, and diffusive type were investigated. To keep the costs low, the sensors were interfaced using the open-source Arduino platform for data acquisition. During the trials, the lowering of the sand level around the bridge pier exposed the sensors thus triggering a change in response. It was found that the sensor output was near zero when buried but jumped instantaneously to 3V (through-beam) and 5V (diffusive) when exposed. To mimic real-life conditions, the scour hole was manually refilled once scour progression ceased and equilibrium scour was reached. It was noticed that the burial of exposed sensors immediately changed the response of both types of sensors back to near zero. Thus, the laboratory tests confirmed that a series of photoelectric sensors embedded at different heights on the bridge pier/foundation can effectively and continuously monitor scour at bridge piers and abutments.