| Concrete dams
Left: Figure 2. View of breach of shotcrete CFRD of upper reservoir of the Taum Sauk Pump Storage Plant caused by overtopping (ASDSO, 2005)
difficult and the damage that could occur in one dam may not occur in another one.
Failure or near-failure of CFRDs The performance of CFRDs have been discussed by
Marulando and Marulando (2008). They listed several high CFRDs, in which damage occurred in face slabs. Based on these observations, improvements were made in the design of face slabs and the water proofing system of the joints, which also account for larger joint movements as experienced, e.g. under seismic action. Up to now the following CFRDs have failed: (i) Gouhou CFRD in China due to seepage and internal erosion (Zhang and Chen, 2006) and (ii) Taum Sauk CFRD in the US due to overtopping (ASDSO, 2005). Gouhou Dam, a 71m high concrete-faced
rockfill dam with a crest length of 265m, which was completed in 1990 in Qinghai Province, China, stored a reservoir with a volume of 3.1Mm3
. Reservoir
impoundment started during the construction of the dam and when it was completed the reservoir level was 3.9m below the normal water level and seepage flow was observed in the downstream slope. When the reservoir level reached a maximum on August 27, 1993, seepage increased and caused failure of the dam. About 320 people were killed due to the catastrophic release of the reservoir water. The main reasons for this incident were the leakage through the
horizontal joint of the concrete face and the parapet wall structure on the dam crest, and rockfill materials that were susceptible to internal erosion. The embankment dam forming the upper reservoir
of the Taum Sauk Pump Storage Plant in Missouri, US, completed in 1962 and failed on December 14, 2005, due to pumping when the reservoir was full, causing overtopping of the dam and progressive erosion and dam failure (Figure 2). Fortunately, nobody was killed in the flood wave resulting from the dam`s failure, but the damage was estimated at US$1 billion. The embankment dam of the Upper Reservoir, was made of dumped, uncompacted rockfill. The inside of the reservoir was lined with shotcrete. In 2004, a geomembrane liner was installed to reduce the leakage through cracks in the shotcrete caused by differential settlements (ASDSO, 2005). Because this shotcrete liner was the water proofing element of this dam it is considered to be a type of CFRD, although this face slab has little in common with that of the CFRDs built today. The main reasons for this dam failure were deficient
water gauges, so that the operator was not aware that the reservoir was full and with the absence of any spillway. Although there was no inflow into the upper reservoir, a spillway with a minimum discharge capacity equal to the maximum pump capacity would be needed.
Left: Figure 3. Seepage through Tokwe Mukosi CFRD during a severe flood in 2014 in Zimbabwe, when the dam was still under construction and the concrete face was not yet in place (CC BY 4.0)
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