Centurion, Tshwane, South Africa, 15 to 17 November 2017 © SANCOLD, ISBN 978-0-620-76981-5 439 STABILITY ANALYSIS OF A CONCRETE GRAVITY DAM TONGUE WALL RO Cassells 1 , GD Roberts 2 1. ARQ Consulting Engineers, Pretoria, South Africa 2. ARQ Consulting Engineers, Pretoria, South Africa PRESENTER: RYAN CASSELLS ABSTRACT A concrete gravity dam tongue wall comprises a concrete structure that transitions from the concrete gravity spillway section of a dam, to the non-overflow earthen embankment section. The stability analysis of a concrete gravity dam tongue wall is affected by lateral earth loads imposed on it due to the embankment fill, and a specific analysis methodology is not generally defined. The magnitude of the active and passive lateral earth load acting on the tongue wall is directly related to the deflection of the structure under such loading. This paper discusses how active and passive lateral earth loads were applied by progressive mobilisation of wedge forces in the fill, and proposes a defined methodology for the stability evaluation of tongue walls. 1. BACKGROUND The Nwamitwa Dam is being developed by the DWS to increase the assurance of yield and enhance the water resources of the Groot Letaba River in the Limpopo Province. ARQ was subcontracted by LTE Consulting to prepare the tender design for the dam. The dam is designed as a concrete gravity dam with zoned earthfill embankments as indicated in Figure 1 . The central concrete section is 350 m in length with a maximum height above foundation of 43.5 m. The concrete section comprises a 54 m long tongue wall on the right flank, a 190 m long RCC gravity spillway and a 96 m long tongue wall on the left flank. The zoned earthfill embankments are 1900 m in length on the right flank and 1200 m in length on the left flank. Figure 1. Nwamitwa Dam Layout