Laboratory investigation of sand and water inflow into a hole of under-waterway tunnels

The effects of a cracked tunnel underneath a canal bed on water and sand inflow through the tunnel hole and distortion of the canal bed were experimentally examined. A circular hole in the centre of the base plate of the flume was used to simulate the cracked tunnel. In total, 108 tests were conducted to investigate four factors that affect canal bed morphology (four water depths, three bed material sizes, four hole diameters and three bed material heights above the tunnel hole). The water and sand discharges into the tunnel hole were measured. The scour bed geometry due to the cracked tunnel, including the erosion volume and scour hole dimensions, was also measured and analysed. The results indicated that the sand height, tunnel hole diameter and bed material particle size were the important factors affecting the sand flux, while Froude number and canal water depth were the parameters governing the water flow rate. The tunnel hole became blocked when the particle size was larger than 0·2 times the tunnel hole diameter, indicating that this could be used to temporarily block a cracked tunnel. Relationships were developed to correlate the investigated parameters and to estimate the flow rate and the volumes of water and sand passing through the tunnel hole.