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Client

Grinaker-LTA

Location

KwaZulu Natal

Project Description

Imvutshane Dam Access Road, KwaZulu Natal, SOUTH AFRICA (2021-23) – Permanent lateral support for the new, 1.9km long access road that connects Main Road 711 (P711) to the Maphumulo Raw Water Pump Station located at Imvutshane Dam, northern Kwa-Zula Natal. Support was designed for cuttings up to 18m deep and reinforced fill structures up to 10m high. The lateral support structures comprise a shotcrete and nail soil system in combination with mechanically stabilized fill systems using gabion baskets, geocomposite reinforcement, and engineered backfill.

Project Tasks

  • Detailed slope stability analysis and design.
  • Limit equilibrium methods were used for the analysis using Rocscience software Slide2 together with detailed design calculations from relevant codes and standards.
  • Permanent and temporary construction oversight was provided for assessing the geological
    conditions of the exposed soil/rock face after every excavation lift and to ensure compliance with the design requirements.

Project Results

  • On-site rock mapping revealed critical sections where bedding planes were dipping unfavorably into the excavation. This required adjustment to the affected slope stability models using anisotropic material properties.
  • Changes to the road alignment during construction posed numerous design challenges as the affected sections required re-evaluation and design.
  • In-situ slope stability, on a small section of the site, showed factors of safety between 1.3 and 1.4. A factor of 1.5 was generally required to satisfy permanent stability and would have required extensive measures to stabilize such a large slope to achieve a factor of safety equal to 1.5. Therefore, a reduced factor of safety was considered for this section of the site with reference to TRH18, 1993 (Technical Recommendations for Highways).
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