Hydraulic structures with defective sheet pile walls

Abstract

A sheet pile wall driven to form a barrier wall below the floor of a hydraulic structure is frequently assumed to be watertight. Although the leakage through the interlocks of the sheet piles is usually small, damage and other factors can result in significant leakage. Consequently, this assumption is rarely, if ever, satisfied in reality. The present study used a finite-element model to investigate the effect of leaks through sheet piles driven under the floor of a hydraulic structure on seepage losses, on the uplift force and on the exit hydraulic gradient. Flow through the channel banks was considered to obtain accurate and robust calculations. The study indicated that when the leak existed in a sheet pile wall, driven centrally below the floor of the hydraulic structure, it has a small impact on seepage losses, the exit hydraulic gradients and the uplift force. However, when the leak existed at a sheet pile wall driven at the downstream end of the floor, its impact was significant, particularly on the exit hydraulic gradient with consequent risk to the stability against piping and undercutting of the structure. A combination of both cut-off walls did not provide a significant benefit, should leakage occur.