Bedford Dam

Type: Rock-Fill, Face Slab Dam
Construction Date: April 2008 - August 2011
Location: Ladysmith KwaZulu Natal, South Africa
S 28.237992° E 29.585277°
Bedford Dam, situated on the mountains above Ladysmith, Kwa-Zulu Natal, South Africa is a 49m high Concrete Face Rock-Fill Dam (CFRD) with an 810m crest length. This dam structure forms the upper reservoir of the Ingula Pumped Storage Scheme. During construction the river diversion works consisted of channels, a cofferdam and a training wall where the Main Contractor Bedford/Bramhoek Dams Joint Venture (BDJV) trained their personnel and honed their dam building skills.

The Main Embankment (480m) has a 170m Long clay core extension and 42m dry well single-level intake tower.

The Dam capacity is 22.4 million m³ with an active water storage volume of 19.2-million m³.

Bedford Dam Instrumentation consists of the following:
  • Convergence points in the Outlet-Tunnel measuring expansion/contraction.
  • Vibrating Wire Strain Gauges in and around the Outlet-Tunnel, measuring concrete and re-enforcing strain.
  • Vibrating Wire Load Cells and Vibrating Wire Pressure cells around and on top of the Outlet-Tunnel, measuring total load and pressure.
  • Vibrating Wire Piezometers in the Clay Core of the coffer wall/embankment, measuring pore pressure.
  • Five sets of Vibrating Wire Perimetric Joint Meters are installed on crucial structural points on the plinth and the concrete face slab, measuring three-dimensional movement between the plinth and the starter slab.
  • Eighteen Vibrating Wire Embedment Jointmeters are installed in the top parts of the various vertical joints of the concrete face slab measuring movement between the joints.
  • Two Horizontal Inclinometer casings on the face slab measuring deflection of the face slab as such.
  • Vibrating Wire Settlement Cells in the rock-fill for measuring settlement.
  • Standpipe Piezometers for measuring water table.
  • Vibrating Wire Transducer measuring seepage.

Instruments installed in and around the Dam Embankment are intended to monitor:
  • Settlement of the Embankment;
  • Opening of the concrete face slab joints;
  • Stresses and deflection in the face slab concrete;
  • Stresses, strains and convergence of the Conduit;
  • Pore pressure build-up around the Conduit and Main Embankment.

Installed Instruments Specification:
Seepage (Dam, Conduit and Spillway)
Geokon Vibrating Wire Transducers Vented Model 4580
Piezometers (Clay Core against Retaining Wall)
Geokon Vibrating Wire Model 4500S
Joint Meter (Concrete face and plinth)
Geokon Vibrating Wire Model 4400
Strain Gages (Face and Conduit)
Geokon Vibrating Wire Model 4210/4200/4202
Pressure Cells (Conduit and Main Embankment)
Geokon Vibrating Wire Model 4800
Settlement Cells (Fill)
Geokon Vibrating Wire Model 4650
Convergence Meters (Conduit)
Geokon Model 1610 Tape Extensometer
Data Acquisition System CR800/1000 (Valve House)
Geokon Micro-1000 Data logger Model 8021
Geokon Multiplexer (MUX) Model 8032

Designers: Steward Scott Incorporated (SSI), Arcus Gibb and Knight Piésold

Consulting Engineers: Braamhoek Consultants Joint Venture (BCJV) comprises three of the country's mayor consulting firms namely Steward Scott Incorporated (SSI), Arcus Gibb and Knight Piésold

Contractors: Concor Roads & Earthworks, Wilson Bayly Holmes-Ovcon (WBHO), Edwin Construction and Silver Rock (BDJV)

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