21no. 800mm diameter piles to 13.5m depth were required for the foundation of a new water filtration structure at the existing NWSC plant at Ggaba.

During an extended tender period EAP worked with Sogea Satom to develop a concept design since the access was limited and the soil parameters unknown. An additional geotechnical investigation was completed and from the results the main contractor’s engineers designed piles to suit EA Piling’s recommended parameters.

The concrete was provided by the main contractor. It was batched elsewhere on the Ggaba Water Intake plot and delivered by truck mixer. The reinforcement cages were tied at site by the main contractor. Lifting services were provided by a tower crane installed by the main contractor at the site.

EA Piling mobilised a Soilmec R620 to site to complete the works along with the required 800mm drilling tools and temporary casings. The R620 in rotary mode with the 4-section interlocking Kelly bar is capable of piles up to 1.5m diameter and 40m deep and so was more than sufficient for the work. Casings were installed using the casing driver on the rotary head.

The site chosen for the structure was immediately adjacent an existing part of the plant and multiple obstructions in the form of old construction materials were discovered in the first 2m of drilling. The soils in the upper strata were extremely wet and prone to collapse, necessitating the use of temporary casings down to 6m.

Despite these difficult conditions the installation period for the 21 piles was 2 weeks.

The pile heads were cut down to cut off level using pneumatic jack hammers.

Once the piles were installed, they were tested for integrity by EA Piling using the TDR2 machine by Test Consult, which employs the transient dynamic response method. The data collected at the site was analysed by ND Technology, an independent specialist engineer, who confirmed that the test results did not indicate anomalies in any of the piles.