Burgan Cape Terminals (Pty) Ltd (BCT) is an independent storage company constituted by VTTI B.V. (Holland), JICARO (RSA) and Thebe Investment Corporation (RSA) to develop a much needed fuel storage facility in the port of Cape Town. In 2015 BCT signed a 20-year lease agreement with the Port of Cape Town for the use of the site on the Eastern Mole.
Chemie-Tech SA (Pty) Ltd, a Dubai-based company specialising the construction of storage facilities, was awarded the project in late 2015, and they in turn appointed Franki Africa as their specialist geotechnical contractor to design and construct the foundations.
The site is a reclaimed area made up of demolition rubble in a variable soils matrix overlying weak soil horizons to depths of 20 m and more. This presented an engineering challenge to achieve acceptable settlement limits for the proposed large storage tanks. Furthermore, the close proximity of existing storage tanks with unknown foundations and vibration tolerances posed another challenge.
Due to a shortage of oil refinery facilities in Cape Town, long haul distances and congested loading at existing facilities, BCT proposed the construction of ten large tanks with 118 million litre storage capacity within the port of cape Town. The storage facility consists of:
- 6 x 26 m Ø x 19 m high diesel and ULP Tanks
- 4 x 31 m Ø x 19 m high diesel tanks
- 2 x 12 m Ø x 18 m high ethanol tanks
- 1 x 15 m Ø x 17 m high fire water tank
All have allowable differential settlement criteria between the tank centres and edges i.e. value of angular distortion, to be less than 1:300.
Due to the presence of rubble and the like in the made up ground, normal piling techniques could not be used in an economical way, so Franki used the dynamic compaction technique to compact the in-situ materials to a design depth of 10 m below ground working level.
Dynamic compaction involves ground compaction by falling weight, thereby generating ground vibrations which, if uncontrolled, may result in structural damage to neighbouring structures. The challenge on this project was to achieve the required ground compaction without excessive vibrations, which might have led to excessive settlement to the existing operational tanks as close as 30 m.
Vibration levels were first reduced by excavating a vibration cut-off trench located between the existing tanks and the site to be compacted. State-of-the-art monitoring systems were then positioned on critical tanks to measure movement, as well as peak particle velocity (vibration intensity). The monitoring systems provided real-time deflection and vibration data which allowed adjustment of the dynamic compaction works with minimum disruptions. The system was also set up with alert, alarm and action values to ensure that vibration limits were not exceeded.
Obstructions also precluded the normal post-testing procedure (Cone Penetration Testing) and therefore the Continuous Surface Wave technique was used together with plate load and rotary core drilling with SPT’s.
Franki employed the services of GETEC, a Keller company, which specialises in vibration and movement/settlement monitoring and recording. A system was installed on existing tanks to allow remote monitoring and reporting, as mentioned above. Targets and a total survey station were fixed to the existing tanks, and a predetermined reading timetable was set. Readings were taken automatically and transmitted to GETEC in the UK for analysis and reporting. This, together with the 3 m deep isolation trench, allowed operations to proceed without incident or stress to the existing nearby storage tanks.
Impact on the Economy
The new terminal will strengthen and secure energy supplies, as well as bring important economic benefits to Cape Town and the region. These include:
- A major injection into the local economy of a projected R650 million
- High quality employment for up to 130 contract workers during the construction, for a period of 18 – 22 months.
- Once in operation, annual local expenditure of R35 million
- Around 21 full-time operational jobs with salaries totalling around R7 million each year.
The Western Cape region is dependent on a single local refinery, and one which is unable to produce environmentally friendly products such as low-sulphur diesel. The new terminal will bring a vital new source of secure next-generation energy to drivers, homes, businesses, and also for the country’s gas turbine power generation.
Source: Civil Engineering Magazine, SAICE
Date: November 2016
Reference: Vol 24 No 10 p38-39