Author: R.P. Greyling, C. Zhang
Conference: AFRICA 2017
Date: March 14-16, 2017
The Neckartal Dam Project is currently under construction on the Fish River near Keetmanshoop in Namibia. The main purpose of the dam is to form an impoundment of 857 million m3 that will supply irrigation water to 5000 ha of agricultural development in the Karas Region. The outlet works at the dam is also equipped with a mini hydropower facility (3MW), which generates from the ecological releases made.
The dam wall is a 78,5m high mass gravity structure, aligned on a curved upstream axis and constructed using a zoned roller compacted concrete (RCC) mix. The crest length measures approximately 520m from abutment to abutment. The dam is equipped with a 395m long uncontrolled ogee spillway crest, which is divided into two segments. The main spillway defining full supply level (FSL) at 787,5 mASL is 290m long, and caters for flood peaks between the 5 to 10-year AEP (Annual Exceedance Probability) flood event. The raised spillway segment at 789,9 mASL is 105m long, positioned on the right flank for passage up to the SED (Safety Evaluation Discharge) and was specifically designed to reduce flow down the abutment that caused circulating flow downstream of the apron.
The dams structural section is a conventional gravity profile with sloped upstream face, 1:0,2 (V:H) and a stepped downstream face, defined on a slope of 1:0,75 (V:H). The dam is presently under construction by Salini Impregilo and will contain some 900 000 m3 of RCC upon construction completion.
The project site is located in a semi-arid region, known for its hot desert climate with long, very hot summers and moderate to warm winters. Average monthly temperatures vary over approximately 14ºC throughout the year between winter and summer. Considering this temperature variation and owing to the size and significance of the structure, strict temperature controls are being enforced, achieved by restricting the allowable RCC placement temperature to 28ºC by means of a dedicated aggregate chilling plant.
In this paper, the authors present a summary of the related thermal analyses applied for the design of Neckartal Dam, undertaken to determine the magnitude of the anticipated thermal stresses that will develop and ultimately, to evaluate the potential for cracking within the RCC dam. In this manner, the typical approach and techniques required for a transient thermal and stress analysis of a major RCC dam is demonstrated.
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