SMALL DAMS PETITS BARRAGES

Fig. 7.7 – Dam overtopping protection with the ACB system and the downstream
concrete chute blocks. (Anderson and Henrich/2005)
(b) Roller Compacted Concrete – RCC
Roller-compacted concrete (RCC) has been used as a spillway or overtopping protection
on consolidated embankments for more than 130 dams in US as pointed out by Abdo and
Adaska (2007), over the past 27 years. Primary reasons for the popularity of RCC with
designers and owners are simplicity, speed of construction, strength and durability, and
economic advantages compared with alternative methods. The unit discharge is normally
limited to a maximum of 20 m 2 /s.
Comparative tests on soil-cement, RCC, and conventional concrete showed RCC to
have a greater resistance than conventional concrete of higher strength, primarily because of
a greater percentage of aggregate in the mixture and less paste. Several U.S. Army Corps of
Engineers research projects have confirmed the excellent abrasion resistance and durability of
RCC, as can be seen in the two following examples i.e. Lake Tholocco Dam and Red Rock
Detention Basin Inlet Spillway.
Lake Tholocco Dam (USA)
Constructed in the 1930’s, Lake Tholocco Dam is an earth embankment owned by the
US Army and located in Fort Rucker, Alabama, US. The dam is 732 m long with a maximum
height 13,7 m, in which the service spillway is 15,2 m long reinforced concrete structure with a
fixed ogee crest.
A 1979 Phase Inspection Report under the National Dam Safety regulations showed that
the dam did not meet current standards due to insufficient spillway capacity. Since its
construction the dam’s earthen emergency spillway was operated regularly, causing severe
erosion. Major storms in the 1990’s breached the emergency spillway twice. The emergency
spillway failed for the second time in July 1994 during tropical Storm Alberto. After that the
reservoir remained empty for six years.
The USACE Mobile District investigated several upgrade alternatives and concluded that
the most cost-effective solution would be to construct an RCC auxiliary spillway with a
collection channel in the embankment adjacent to the reinforced concrete service spillway.
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