The webinar presents the Finite Element Analysis of the Southern portion of the Olifantspoort Dam. The dam comprises an Off-channel Storage Facility to be constructed near the Olifanstpoort water abstraction works on the Olifants River in Polokwane, South Africa.
The dam has been designed as a ring structure incorporating five enclosure walls to enclose a valley to the west of the abstraction weir. The southern portion of the dam structure is the highest of the ring components and it comprises a 22 m high Rubble Masonry Concrete (RMC) multiple-arch buttress dam with a crest length of 230 m.
The southern portion is made up of arches with varying radius size. The varying arch sizes were implemented to account for changing foundation conditions under the dam footprint. The buttress portion of the dam transfers most of the load to the foundation, so it was deemed suitable to found the buttresses on the most competent portions of the foundation footprint. To achieve this a customized span and radius size was adopted for arches between buttresses placed accordingly.
The arch and buttress components of the dam configuration were initially designed and analysed for sliding and overturning stability assuming rigid body motion of the dam. Cylindrical arch and elementary beam theory were assumed to determine the required thickness of the arches and buttresses.
These assumptions do not consider the flexibility of the structure resulting in rib-shortening and other geometrical changes from deflection of the structure under loading.
Rigid body motion assumptions do not consider the flexibility of the structure resulting in rib-shortening and other geometrical changes from deflection of the structure under loading. The FE analysis performed in Midas FEA NX duly models the flexible elastic behaviour not addressed in a rigid body motion analysis.
ARQ Consulting Engineers / South Africa
ARQ is an award-winning consulting engineering firm specialising in dams and geotechecnical engineering. ARQ was established at the beginning of 1993 on the platform of the specialist capabilities of its founders in bridge, dam, and geotechnical engineering. Over the years, the company has consolidated a local and international reputation as a leading dam and hydropower engineering consultancy.
ARQ has been active in dam engineering since 1993. ARQ has been involved in over 150 projects involving dams, hydropower, and river engineering in 33 countries; with 43 new dams completed or currently under construction (the highest being 275 m), 14 completed projects involving major rehabilitation or raising, 25 projects at pre-feasibility and feasibility level (highest dam of 275 m) as well as dam safety/asset evaluation studies. ARQ has furthermore contributed staff as specialists on local and international projects as members of expert panels and/or reviewers, and have undertaken various hydropower projects.
ARQ has worked on all dam types, including Roller Compacted Concrete(RCC), Rubble Masonry Concrete (RMC), hardfill, concrete (arch and gravity types), Concrete Faced Rockfill Dam (CFRD), earthfill, rockfill, and composite dams. Our teams have worked across most continents and are well versed in international best practice, routinely applying state-of-the-art technology and systems to support a more efficient project process.
- Ryan professional profile
- ARQ Location
- Company background and dam legacy
- RMC multiple-arch buttress dam, near Polokwane, South Africa
- Foundation conditions
- Dam type choice based on foundation conditions and material availability
- Adoption of a RMC multiple-arch buttress Dam with different arch configurations according to lineation in foundation
- Selection of RMC material
- 3D solid geometry of Dam (arches, buttresses and foundation)
- Dam body loaded to account for various loading combinations including pseudo-static seismic and thermal temperature drop
- RMC design strength criteria
- Develop and implement suitable meshing strategy for dam and foundation using 3D solid elements
- Interface elements at the joints between dam and foundation with non-linear stiffness
- Verify analysis results by checking sum of forces against a hand calculation
- Evaluate displacement results of dam for suitability
- Extract plots of arching and vertical stresses to understand load transfer
- Extract plots of P3 stress vectors to review efficiency of load transfer of in dam body
- Probe vertical stress contours on underside of dam
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