28 March 1997



A traditional silage clamp provides a cost-effective method of storing farm-produced feed. Peter Hill looks at the construction options, while

Jonathan Riley gives some pre-season clamp maintenance tips

SILAGE clamps have come a long way from the pit dug into the ground or the heaped pile in the field. Modern construction methods provide a long working life of 20 years or more, help produce high quality feed and control effluents to avoid contamination of water courses.

A concrete floor is standard fare, but there is more choice when it comes to wall construction – stand-alone pre-cast concrete panels, concrete beams or panels, ex-railway sleepers or new timber supported by steel stanchions.

With the floor and apron area generally accounting for around two-thirds of the total cost of a silage clamp, the choice of wall construction makes little difference to the final bill of, typically, £30-£40/t of material stored. Panelling may be more expensive in itself, for example, but is usually easier and therefore cheaper to install than alternatives.

Savings can be made by using on-farm labour. But as ADAS Anglia building design consultant, David Ellis, warns: "Installing a new silage clamp comes under the scope of the Construction (Design & Management) Regulations 1994 (CDM), as do all new structures and buildings.

"This places responsibility on the farmer to ensure he appoints competent persons in all areas of the work, and applies equally where contractors are employed," says Mr Ellis.

Effluent is a key consideration in silage clamp design and construction, he emphasises. It is vital to prevent the corrosive liquid attacking the concrete; to prevent it passing into the sub-base where it can cause instability; and to prevent polluting by allowing it to run into drainage systems or directly into a ditch or water course.

"To guard against pollution, there must be a drainage gully right around the outside of the clamp with effluent piped into a sealed storage tank," Mr Ellis explains. "It can later be spread in diluted form on to land as long as there is no pollution risk from doing so. Or it can be used as a feed supplement."

The principle specification requirement is that when the clamp is full, the drain across the apron area should be at least 1m (3ft 3in) away from the face. But it is also worth weighing up drain designs that will either not clog too readily or are easily cleaned out.

Drain requirements

Internal drains must be within 500mm (20in) of the face of the wall at floor level, but some clamp designs allow effluent to escape beneath the outer walls to be collected by the perimeter drain.

The other main specification requirement, apart from those relating to wall strength, are that a guide rail must be fitted between 1.0m and 1.2m (3ft and 4ft) above the top of the wall to provide some measure of protection against people walking on the silage going over the edge.

Concrete walling systems include free-standing "L" panels for outer walls and "L" or "T"-shaped internal dividing walls. Ideally, these are set in concrete for a fixed installation that enables complete sealing of joints to prevent effluent seepage and corrosion of concrete. For short term use, these panels can simply be bolted down or positioned against a kerb – though this would be a false economy for long term applications.

Other concrete options are flat panels set vertically in concrete to leave an unobstructed internal area or horizontal panels positioned against stub stanchions or the stanchions of an existing building. Panels intended for dividing walls are thicker with a higher load capacity. Both types usually include tongue and groove joints to spread loading and aid joint sealing.

Protecting the first metre of floor and wall concrete from the point where they meet against corrosion is essential if the clamp is to have a long, useful and safe life. Gaps between wall panels and gaps in floor sections must be fully sealed using appropriate materials and the surfaces treated with a special designed coating. Maintenance must be carried out every year to repair damaged areas.

Railway sleepers

Ex-railway sleepers supported by RSJs have been a popular means of building silage clamp walls but, with the switch to concrete sleepers, supplies are dwindling. Purpose-made wooden panels are therefore the most common alternative to concrete construction, usually comprising a timber frame faced with 127mm (0.5in) plywood supported by 20cm x 5cm (8in x 2in) bearers.

Wooden panels are arguably more susceptible to loader damage but, equally, the plywood and/or bearers can be easily replaced.

The decision to self-build a clamp should not be taken lightly. It is time consuming, requires considerable labour and equipment, and particular care in complying with the specifications laid down by the manufacturer in order to meet British Standard requirements.

"Correct design of the total installation, including compliance with the Control of Pollution Regulations 1991, will help avoid serious problems that can show up within three or four years," says David Ellis. "Farmers should seek professional advice, ensure safety requirements are fully met and carry out any maintenance regularly to achieve the normal 20 year life expectancy and consistent silage quality," he adds.

A new silage clamp (this one by Whites) soon loses its pristine looks. But, if built from sound materials, properly installed, and regularly maintained, it should give long service.


&#8226 Stand-alone, pre-cast concrete panels

&#8226 Concrete beams

&#8226 Timber panels

&#8226 Railway sleepers