Evaluation of Seepage, Internal Erosion, and Remedial Alternatives for East Branch Dam, Elk County, Pennsylvania

Abstract

East Branch Dam is a Pittsburgh District U.S. Army Corps of Engineers (COE) dam that nearly failed in 1957, several years after construction. The dam is a zoned embankment that is 56 m (184 ft) high and 526 m (1,725 ft) long. Its primary purpose is flood control. Following the observation of muddy water flowing from a rock drain at the downstream toe of the dam, soon after construction, emergency drilling through the embankment exposed a void that demanded lowering the pool and subsequent grouting. Localized grouting was accomplished to treat the void but did not involve a comprehensive repair of the dam. The 1957 near failure of East Branch Dam represents an excellent case history that provides dam designers and operators today insight into the mechanisms of internal erosion within an embankment dam, and it underscores the need to quickly take all necessary actions to protect the public. Since the 1957 emergency, the project has performed satisfactorily and has been closely monitored with a network of piezometers, weirs, and alignmentsettlement pins. Even though evidence of further internal erosion has not reappeared, the fundamental conditions that caused the original problem were not corrected by the 1957 emergency repairs. Recently, the dam was evaluated under the COE Screening Portfolio Risk Assessment (SPRA) program.

Factors Affecting Failure by Internal Erosion of Geosynthetic Clay Liners Used in Freshwater Reservoirs

“…During internal erosion, the repulsive forces between soil particles become greater than the attractive forces, leading to deflocculation and dispersion of the soil (Burns and Ghataora, 2007). The seepage forces caused by high hydraulic gradients initiate the detachment of soil particles (Greene et al, 2010;Muresan et al, 2011;Benahmed and Bonelli, 2012;and Baena and Toledo, 2014). During the initiation phase, fine particles erode slowly within the matrix of coarser particles (Chang and Zhang, 2013).…”