Define Investigation Scour for Underwater Inspection of Bridge?
Investigation Scour is probably the most critical item to be aware of when performing an underwater inspection of pier/abutment or protection work of a bridge. The most important assessment of scour is how much of the pier or abutment or protection work is exposed when compared to plans and typical designs. Therefore, inspection for scour should be carried out near pier / abutment's base at bed level on the upstream side and adjacent to it.
Local scour is detectable by divers since this type of scour is characterised by holes near piers/protection works. Divers should routinely check for such scour holes. A typical approach is to take depth measurements around the substructure, both directly adjacent and at concentric intervals. Measurement should be taken at 10 cm increments from upstream to downstream end. Water depth and height of scoured level to normal mud line should be measured and recorded. It should be noted that divers operate in low current situations. Sediments often refill the scour holes during these periods. However, since this refilled sediment is usually soft, a diver using a probing rod can often detect soft areas indicating scour refilling.