The application of Rubble Masonry Concrete (RMC) construction for African dams and small hydropower projects

Authors

R. Greyling, Pr.Eng.

Knight Piésold (South Africa), Lead: Dams and Hydro, Pretoria, South Africa

E. Scherman, P.Eng.

Knight Piésold (Canada), Specialist Engineer: Design Manager, Vancouver, Canada

S. Mottram, P.Eng.

Knight Piésold (Canada), Managing Principal, Vancouver, Canada

The use of Rubble Masonry Concrete (RMC) for the construction of small to medium-sized dams are becoming increasingly attractive within the African context. Through recent successful developments in South Africa and the Democratic Republic of the Congo (DRC), RMC designs and construction techniques have been advanced. For projects where labour-intensive construction approaches are preferred, RMC application provides the necessary skills training and job creation to regions that are desperately underemployed. From water supply projects in rural areas to remote run of river hydropower schemes, RMC offers a cost-effective, low-maintenance, unskilled labour-based, simple dam construction technology, resulting in a very robust lifelong asset that meets international dam safety standards. This paper and presentation will cover the design methods and standards applied to recent projects that have incorporated RMC weirs and the construction techniques that were successfully implemented. Case studies of RMC Dams constructed for water supply reservoirs and a remote (11 MW) hydroelectric power project will be presented and discussed.

Introduction and brief history

Stemming from an ancient beginning, the earliest account of major dam engineering work has been linked to the use of Rubble Masonry Concrete (RMC) as a durable dam construction material. Masonry structures proved to be far superior to the simple embankment dams that had been attempted before, with embankments often failing due to uninformed flood hydrology, materials strength and behaviour and limited manual compaction methods available at that time.

RMC origins date back to 4500 B.C., as seen in the remains of the abutments of Sadd el-Kafara Dam in Egypt, an 11m high gravity wall formed by rubble masonry, and regarded as one of the oldest dams constructed in the world (Jansen, 1980).

The oldest operational masonry dam is believed to be Quatinah Barrage (or Lake Homs Dam) in Syria. This 2 km long and 7 m high masonry gravity dam is presumed to have been constructed by the Romans during the reign of the Egyptian Pharaoh Sethi in around 1310 B.C.

Several examples of masonry dams have been recorded in history across the world, many of which still remain today. These early RMC dams were relatively low structures constructed using a mortar and cut stone-block facing, configured as massive gravity walls.

Construction techniques and experimental understanding developed and higher masonry gravity dams were progressively attempted.

An example is the 41m high Alicante Dam constructed using rubble masonry in Spain. The dam construction started in around 1580 but was suspended sometime afterwards before resuming construction several years later. The unfinished structure had survived multiple seasons before being completed in around 1594. The dam became the highest operating dam in the world for well over 300 years.

The industrial revolution and commensurate development of heavy mechanical plant and equipment changed the course of the RMC dam.

With specialized excavating plant, compacting equipment, blast quarrying and aggregate crushing facilities becoming readily available in developed countries, high embankment dams and mass concrete equivalent dam types could be built faster than the hand-built method. While RMC dam development was stinted, it remained attractive in countries with high availability of low-cost labour. Today, the basic utilization of low-cost labour still applies to the competitiveness of RMC dam construction.

More challenging arch and multiple arch-buttress dam designs have since been successfully completed, particularly in Zimbabwe and South Africa.

The most ambitious of these is Lucilia Poort Dam, a 42 m high arch dam constructed in a narrow gorge on the Dwimbika River in Zimbabwe. The structure was constructed using granitic stone plums, founded on a banded ironstone foundation. The dam wall volume comprises approximately 22,000 m3 and is potentially the tallest RMC arch dam under operation in the world.

Read the full technical paper presented at the International Commission on Large Dams (ICOLD) Annual Meeting: The application of Rubble Masonry Concrete (RMC) construction for African dams and small hydropower projects

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