FOUNDATIONS TO PRECAST STRUCTURES

Grout bag systems reliably provide infill foundations to precast elements in the marine environment. The forms are normally prefixed to the precast foundation element before immersion or lowering and when pump filled can readily infill undulating bed voids. The system can be engineered to offer the following:-

grout bag systems• Reliable grouting compartments
• Protection against washout
• Control of compartment size
• Control of filling and uplift forces
• Risk management via multiple
compartments

Grout Bags are made from porous fabric which is grout tight yet water permeable and therefore avoids trapped water voids. They are often condensed with side break ties or diver release ties. Form compartments are zipped to one another whilst fixing for large bases. Once the element is lowered and positioned on jacks and/or temporary foundations, the compartments can be pump filled. Compartments are normally filled with neat cement grout or with sand cement grout/micro concrete. Filler sleeves sewn into the bottom enable filling in tremi fashion with grout travelling to the side vents. The side vents control and limit the compartment pressure which protects against failure of the grout bag and controls uplift pressures.

Grout Bag FoundationsThe system has been used for foundations on major marine projects for many years. It can typically cope with bed tolerances of ± 150 mm to ± 450 mm. The system can be diver worked or completely automated with prefixed hoses, and grout monitors to the vents.

The forms are made from polypropylene and polyester fabrics generally, with designed, tested and quality controlled seams. Fabrics of a 2 layer format are used for neat cement grouts and to give increased resilience where performance is critical. The system has been used for grout travel lengths up to 18 m with current proposals based upon 24m for 48m wide bases (Venice Barrage)

grout bag foundation systemsGrout bag foundation systems are normally developed using a risk management process (see Marine Construction Systems) where the mix, pumping and form systems are developed and where necessary tested.

For further details see “Foundations to Precast Marine Structures” Hawkswood M.G. & Allsop N.W.H. (2009)

Published Papers


“Foundations to Precast Marine Structures” Coasts, Marine Structures & Breakwaters, UK. (2009)

“Fabric Formwork Systems Used In Marine Construction, ICFF, Second International Conference on Flexible Formwork (2012)