Construction World December 2018

Consulting Engineers

T he Neckartal Dam will be the largest dam in Namibia, with a full supply volume of 853 m³, exceeding the volume of the existing largest dam, Hardap Dam by a factor of three. Projects of this magnitude need innovative construction technology in order to be executed successfully, Neckartal more so due to its desolate location in the arid climate of the southern Namibia. Making use of a continuous uniform double curved shape (the ogee spillway) for the dam spillway inherently posed some difficulties for construction. Innovation was required to decrease construction time while maintaining the accuracy of the profile, avoiding honeycombing and blowhole formation of the finished ogee structure. For the main dam, conventional construction methods (using sliding formwork or guide rails) needed a re-think in order to reduce the duration time to construct the ogee crest. The construction of the crest was executed using controlled permeability formwork. This technique reduced the construction duration by a factor of more than two when compared to conventional construction techniques. Furthermore, to aid the site engineers’ supervision (developing, monitoring and quantifying different construction activities), unmanned aerial vehicles (UAVs) were introduced. UAVs were utilised a 9 km-long, 1,1 m diameter pipeline; and an HDPE-lined embankment balancing dam to hold 90 000 m 2 . The project consists of a 76,5 m-high roller compacted concrete (RCC) gravity arch main dam; a 10 m-high RCC abstraction weir (both with an uncontrolled ogee crests); a 2,1 m/s pump station; CONSTRUCTION OF NECKARTAL DAM PHASE 1

HIGHLY COMMENDED

for photographic surveys to develop accurate three-dimensional models used for construction progress monitoring of the project. In addition, accurate surveys, project monitoring, material quantity measurements, Building Information Modelling integration and the sharing of insights around the construction site, were carried out with the aid of UAVs. The project is one of the first dam construction projects in the SADC region to apply this technology. Contributing to a decrease in construction time, an improved productivity in the site laboratory was achieved by concentrating testing on the final RCC product rather than the individual constituents. The RCC mix design sieve analysis envelopes were based on the required upper and lower limits of the specification for each particular material ingredient. As a production and quality control measure, this new material sieve analysis and moisture content test procedure was developed in the laboratory to correlate between designed RCC and produced RCC. This new laboratory technique drastically reduced the testing time when compared to testing all the different aggregates, sieve analyses and moisture contents. In the future, flakiness and elongation test methods may be incorporated into this testing procedure during RCC construction. This innovative procedure allowed a quick assessment of the final RCC product.  PROJECT INFORMATION

• Company entering: Knight Piésold Consulting • Client: Ministry of Water, Agriculture & Forestry (Namibia) • Project value: N$4-billion • Start date: September 2013 • End date: February 2019 • Main Contractor: Salini Impregilo • Principal Agent: Knight Piésold Consulting • Project Manager: Knight Piésold Consulting • Consulting Engineer: Knight Piésold Consulting

2 18 BEST PR O JECTS

Construction WORLD

52