Project reports
29 March 2014 |   ByP Yonatan, N Charue
Fugro Author
At a major tank farm in Antwerp, Belgium Fugro’s expertise produced technical specifications for foundation design, construction principles, quality control  and monitoring requirements for foundation repair. With over 150 vertical steel storage tanks, it was essential for the tank farm owner to minimise the time they were out of use and maximise their operational lifetime.
Thanks to Fugro’s specifications we are able to make the best possible foundation and had a suitable tool for inspection.
Evert Martens, QA/QC tank maintenance engineer, client representative

Optimising Foundation Capacity

Since the foundation is supporting the load from the tank and its contents, optimising its capacity and design will significantly influence its performance. This can be achieved by designing the foundation to account for all possible loading conditions. In the case of tank renovation, the challenge is to take into account subsoil conditions which have previously been loaded - long-term loading from a tank generally improves the subsoil. However, this improvement does not necessarily guarantee future tank stability due to changes in loading conditions, such as when large settlements occur and backfill materials are added to raise the foundation level. This often-neglected fact can reduce the operational life of the tank or even lead to foundation failure.

Controlling Future Settlements

Adverse stresses in the tank shell can result from differential settlements, causing significant structural problems. Settlement is observed by measuring shell elevation along its perimeter during hydrotest, repair phase and operational period. Industry standards normally provide detailed guidance on assessing various settlements to maintain tank integrity; however such guidance does not include the Percentage Allowable Settlement (PAS) that can be tolerated immediately after foundation repair. Specifying PAS after foundation repair or hydrotest allows control of foundation work, enforces quality construction work and provides sufficient margin for future deformation.

Foundation Quality Control

Another factor affecting the lifetime expectancy of tanks is the quality of the construction work. Enforcing foundation quality control during tank construction can maximise tank operational lifetime and such control should specify the methods, compliance testing quantity, acceptance criteria of the test methods and corrective action.

Project Facts

  • Storage Tank Diameter: 15m to 76m with maximum short-term foundation pressure of 175 kPa
  • Storage Tank Type: Cold tank - temperature < 70° C
  • Foundation Type: Annular stone-ring, inner sand pad
  • Software Tools: Plaxis 2D, LimitState:Geo, Fugro’s in-house software
 

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