RELIEF DRAIN HOLE CLEANING and DAM SAFTEY

摘要

Though often neglected, Drain Hole Cleaning is a necessary maintenance item for thernprevention of hydrostatic uplift and pore pressure build-up within gravity block dams. Based onrnpublished information on dam safety, uplift in the form of hydrostatic forces, acting within arndam and its foundation, is a potential source of dam failure. In most gravity block dams, porernpressure dissipation is accomplished by a curtain of cored, vertical holes that extend into thernbedrock along the central core of the dam. However, where dams are constructed withinrncarbonate bedrock, the carbonates tend to precipitate sediment that can fill the drain hole, orrncrystallize, completely bridging the drain hole within generally high flow zones. If notrnaddressed, the resulting reduction in the effectiveness of the drain holes can permit anrnincrease in the hydrostatic pressures beneath the dam, thereby increasing the possibility ofrnuplift of the concrete structure. In many cases, the high costs associated with the cleaningrnprocess, and the lack of a quantitative method for evaluating the effectiveness of the cleaningrnprocesses, has caused many dam owners to put off the process year after year, until therneffectiveness of the drains may be impaired. Since the year 2000, several methods have beenrnquantitatively evaluated in an effort to provide a viable drain hole cleaning system. Therneffectiveness of the cleaning processes has been determined through a program of pre- andrnpost-testing that has been customized for each dam and its unique drainage system. Throughrnthe evaluation process, improved techniques for drain hole cleaning have been developed.rnThe pre- and post-cleaning evaluation process can be further utilized as a baseline to conductrnannual or bi-annual reevaluations. Those drain holes showing a marked reduction in flowrnduring annual pre-cleaning testing can then be scheduled for cleaning. Instead of 100% of therndrain holes requiring cleaning, only 5% to 10% of the drain holes may require attention in anyrngiven year, resulting in substantial cost savings.