Armour Unit Stabilisation

Armour Displacement

Rock or concrete armour units can suffer a degree of movement or localised failure after installation on revetments. Mobilising plant to repair with similar replacement armour can be impractical and uneconomical once construction is complete due to the cost of marine plant for small quantities.

Grout Bag Infill

In situ concrete can infill gaps and lost areas in the top armour layer. The system can adapt to rock revetments and other common forms of concrete armour units. The formwork is placed and then pump filled with concrete ensuring stability and impeding further failure.

The bottom of the infill block forms an intimate shape to adjacent units. Neighbouring repairs need to be spaced or shaped, to maintain revetment porosity. Repair blocks can be shaped to provide matching upstand legs for interlock.

Initially the infill units produce a more intimate and stabilised arrangement, although this changes if movement is progressive. For stability comparisons, the coefficient of friction between in situ fabric formwork units and smooth concrete armour units have been determined by testing to be 0.48. If required, degradable hessian forms can be used to match frictional properties between concrete units, or repair armour weight can be increased accordingly.

Installation

The void or damaged area needs to be surveyed to allow the infill forms to be sized to achieve a weight comparable with the armour units for future long-term stability. The repairs can be performed in the dry with suitable safety arrangements, or underwater. In the wave zone, forms can typically be filled in wave heights up to 0.5 m before initial hardening.

The forms can be suspended by crane or temporary scaffold pole top support then pump filled via 50mm Ø hose which is readily handled by divers.

Advantages

Repairs involving modest quantities can be undertaken quickly and cost effectively before more extensive damage occurs.

Contact The Expert

Contact The Expert

Martin Hawkswood

Director & Principal Engineer

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