Project Purpose
The Olmsted Dam project on the Ohio River required the installation of massive precast caissons in fast-flowing water (approx. 2 m/s or 6 ft/s) as part of the replacement of the river control structure and locks. These caissons were installed using a float-in and sink procedure, with tight positional tolerances and the need for immediate and reliable temporary and permanent support upon placement.
Concrete Mattress Technology: Expanding Grout Socks
To stabilise and interlock the caissons in these high-flow conditions, Proserve’s Expanding Grout Socks were employed to form engineered bearings and watertight seals. These formed key structural interfaces by adapting to voids beneath and between caissons, supporting controlled tremie concrete pours and ensuring structural continuity across the dam’s modular assembly.
Design and Fabrication
Grout Socks were pre-manufactured in custom shapes and dimensions using high-strength woven fabric formwork. Each sock was supplied in a condensed form and pre-fitted to the caisson structure during prefabrication. This ensured they remained compact and protected during handling and float-in, yet ready to expand on command. The ability of fabric formwork to accommodate complex geometries and tight access tolerances was central to the success of this approach—principles also explored in Fabric Formwork Systems Used in Marine Construction (Hawkswood).
Installation and Activation Two systems of Grout Socks were employed:
Perimeter Bearings: Installed around the caisson base to provide immediate bearing capacity upon touchdown on the riverbed. Once grouted, these socks expanded to fill local voids and establish intimate contact between the caisson and foundation, ensuring stability in dynamic hydraulic conditions.
Inter-Caisson Seals: Installed along the vertical faces of the caissons to seal against adjacent caissons already in position. Once filled, these created watertight compartments between units to enable controlled in situ tremie concrete pours that locked the modular structures together.
Operational Resilience
Given the velocity of the river and the critical nature of the installation, site trials were conducted in flow velocities up to 4.5 m/s (15 ft/s) to confirm that the socks would remain stable and in position during extreme hydraulic events. Their robust stitching and protective sleeves ensured they could endure significant hydrodynamic loads prior to inflation.
Control and Monitoring
To enable rapid activation from the surface, all socks were equipped with pre-fixed grout filler hoses. Grout sensors were integrated to monitor the expansion and confirm full inflation, allowing operators to halt pumping precisely and avoid overfill or grout release into the river. This precision reduced environmental risk and improved quality assurance during placement.
Technical Advantages
- Immediate Bearing and Sealing: Enabled rapid stabilisation of floated-in caissons without delay for secondary operations.
- Adaptability to Tolerances: Fabric formwork naturally accommodated installation variability without needing precise matching of rigid interfaces.
- Controlled Concrete Pours: Allowed secure compartments to be formed for tremie concrete work between caissons.
- High Flow Resistance: Demonstrated stable performance in demanding river conditions due to robust design and pre-installation validation.
- Environmental Safeguards: Integration of sensors and closed system filling reduced risk of grout escape into the aquatic environment.
Project Outcome
The use of Expanding Grout Socks contributed significantly to the safe and precise placement of the Olmsted Dam caissons under extreme flow conditions. The system delivered structural stability, seal integrity, and construction efficiency—reinforcing the broader value of flexible formwork systems in complex marine infrastructure.
