Sealing gaps
Close the gap between caissons, behind sheet piles, or under a structure so flow and fines cannot pass.
Technology
Sealing · foundations · connections
Grout bags & sock seals.
Fabric forms filled with grout in place, used to seal gaps, form foundations and connect marine structures. Most are small, routine jobs, sock seals and cofferdam seals fitted in a day; the same technique also founded the caissons of Venice’s MOSE barrier.
What they are
A form, filled exactly where it’s needed.
A grout bag or sock is an envelope of grout-tight, water-permeable woven fabric, pre-fixed to the structure or positioned by divers, then pump-filled from the surface. The fabric holds the mix and takes the shape of the void it sits in, closing a gap, bearing a load, or wrapping a connection, then cures into a solid, permanent element.
Because the form conforms to the surfaces around it, the seal or foundation follows the real geometry on site, not the geometry on a drawing, which is what makes it work underwater, around obstructions, and against uneven ground.
Grouted to full contact beneath the structure, filled and monitored from the surface.
What they solve
The jobs rigid formwork can’t reach.
No dewatering
Filled in place, underwater
No rigid shutters
Form conforms to the void
Surface-monitored
Vent sensors confirm the fill
Forming foundations
Create bearing pads and hard points on an uneven or submerged bed where shuttering cannot be set.
Connecting structures
Wrap and bond pile sleeves, repairs and connections that have to be made in place, underwater.
The three forms
One method, three jobs.
The same fabric-and-fill technique, configured for sealing, for bearings and connections, or for foundations. Most of what we supply is the first two: small, routine and fitted quickly. We specify the right form for the condition on site.
Grout Sock Seals
Everyday · Seals, Bearings & Shear KeysTubular fabric socks for filling and sealing gaps that are variable and difficult to access, in air or water. Lowered or pushed into position and filled from the top only, with the filling rate controlled so the fluid concrete contacts every structural element without over-pressurising the sock. Purpose-designed for each project, for gaps from 0 mm to 1.2 m and lengths over 15 m.
Remote Grout Seals
Everyday · Surface-operated sealingCompartmentalised bags pre-fixed to the structure before it is placed, then pump-filled through prefixed filler sleeves with vent sensors confirming the fill from the surface. Routine on cofferdam and fender seals; the same system sealed beneath the caissons of the MOSE barrier with no diver involvement.
Foundation Grout Bag System
Major works · Bearing foundationsCompartmented bags fixed beneath precast units and grouted to full-contact bearing, accommodating up to 900 mm of bed variation without underwater levelling. Proven beneath the 20,000-tonne caissons of the MOSE barrier and the 48 pier bases of the NRL viaduct, La Réunion.
Beyond the three forms
Engineered to the condition.
Every formwork solution is engineered to the project. These are some of the conditions the same technique has been configured for.
Armour unit repairs
Grout bags pump-filled between displaced armour units to re-establish interlock and stability, as on the Xbloc revetment at Sumburgh Airport, Shetland, installed with conventional plant in overnight working windows.
Tunnelling seals
Pre-fixed grout bag seals filled by controlled remote grouting, producing seals up to 10 m in diameter for the tunnelling industry as well as the marine environment.
Marine pile seals
Expanding grout socks sealing and transferring load between structural elements in tidal conditions, as at Dover Western Docks: seals, bearings and shear keys in one operation.
A gap, void or connection that isn’t listed? Describe it to our engineers →
In service
Proven on landmark marine structures.
The same forms, at work on some of the most demanding foundation and sealing projects in marine construction.
MOSE Barrier, Venice
719 compartmented grout bags seated the 20,000-tonne caissons of Venice's flood barrier, filled and monitored entirely from the surface, with no diver intervention.
Nouvelle Route du Littoral
48 offshore pier bases founded on the grout bag system: over 17,000 m² of bearing area and some 3,500 m³ of grout, placed from the surface in cyclone-exposed waters.
Second Severn Crossing
An early landmark for the foundation grout bag system, and the precedent cited when the MOSE Barrier and the NRL viaduct selected it.
How it installs
Position the form
The bag or sock is pre-fixed to the structure in the casting yard, or placed by divers into the void, around the pile, or on the bed.
Pump-fill from the surface
Grout or micro-concrete is pumped through prefixed filler sleeves. The grout-tight, water-permeable fabric retains the mix and conforms to the geometry.
Confirmed, then cured
Vent sensors confirm full contact before pumping stops, and the fill cures into a solid, permanent seal, foundation or connection.
FAQs
Frequently asked questions
What are foundation grout bags?
Foundation grout bags are fabric formwork bags pump-filled with grout to fill the gap between a precast structural element and the seabed, forming an engineered load-bearing foundation.
They replace compacted stone bedding layers and take up natural seabed variation. Proserve grout bags found caissons, bridge piers, tunnel units and other heavy marine structures.
How are grout bag foundations installed?
The bags and their fill pipes are fixed to the underside of the precast element before it is lowered. Once the element is set on jacks on the seabed, the bags are pump-filled with grout in a designed sequence.
Filling is controlled from a barge or the surface, with vents managing pressure and uplift, so the element ends up fully and evenly supported.
Why use grout bags instead of a stone bedding layer?
Stone bedding is hard to level accurately underwater, and can settle, wash out or scour. Grout bags conform to the seabed, taking up variation of up to 900 mm, and set into a tight-tolerance foundation with full contact.
Proserve grout bag foundations have three decades of proven performance on major marine structures, including the MOSE flood barrier in Venice and the Second Severn Crossing.
Can grout bags be filled without divers?
Yes, grout bags can be filled entirely by remote surface control, with no divers in the water. On the La Réunion coastal highway, 48 bridge-pier bases of 20 to 23 m diameter were grouted this way in fast-flowing sea conditions.
Each grouting operation took around 12 to 16 hours. Surface-controlled filling suits deep, high-flow or otherwise hazardous locations.
Can grout bags underpin an existing structure?
Yes, grout bags are used to underpin marine structures whose foundations have been undermined by scour or settlement, restoring full bearing without major demolition.
Bags are introduced beneath the caisson, quay wall or foundation and pump-filled to fill the void. The same method serves both repair and new-build foundations.
Tell us the condition
Describe the gap, the pile, the bed.
Send us the situation and the loads. Our engineers will tell you which form fits and how it would be installed.
or call Martin Hawkswood, Director & Principal Engineer · +44 (0)1926 512 222 · [email protected]