Once a Cattle Grid is no longer required a conscious decision should be made about its future. Left to rot is can present a serious danger to track users. Corroded bars can twist upwards when vehicles pass over it damaging this or any further vehicles which may pass.
Many are left to silt up.
The most satisfactory (safest) way is to remove the steel grid an fill the pit with suitable material.
Ensure the base has the capacity to carry the load now imposed through the fill when before this may have been carried by the enclosing walls
This excellent example installed on an INEOS site is to fill in with mass concrete allowing almost any vehicle safe passage
The life of a cattle grid will depend on 3 factors. Firstly has it been designed and made correctly. Secondly has it been adequately protected from corrosion and thirdly is it maintained. There are 3 or 4 firms which make units to an agreed standard – even based on British Standard occasionally!
There are any number of small fabricators who will have a go at making a unit with varying degrees of success. Using a local supplier is good for the local economy. It will save on significant delivery charges and is easy to do. If however it is incorrectly designed and/or made and it fails (and they do) the costs will outstrip any saving on purchase cost.
There are really only 2 options to protect a cattle grid from corrosion. The right way and the wrong way.
The right way is to galvanize it. The galvanizing process strips off the Mill Scale and metallurgically bonds the zinc to the steel. This is not a coating it becomes part of the grid.
The wrong way is to paint it. Painting, no matter how well applied will wear off and corrosion will begin. Galvanising gets inside and protects the tubes from the inside. Paining does not.
Generally properly designed and constructed Cattle Grids will successfully contain stock. They can rarely get stuck if they try to cross the grid. If the bars are made from materials and in sections permitted by the BS their legs will not be injured. If the pit is the correct depth their chests will not come into contact with the bars.
Smaller wild animals (Mice, hedge hogs and amphibians) are more at risk.
Sad experience has taught lessons which need to be learned.
Firstly the pit needs proper drainage. Without this they may fall into standing water and drown or die of cold. Drains can be a mixed blessing. The pit is lower than the local ground level and if there is no active drainage and the drain is not sealed water can come INTO the pit!
Wild animals need to have provisions made for them if they fall through the bars into the pit. Larger mammals will usually cope with or be deterred by the Cattle Grid.
Secondly they need a ramp to escape from the pit. Thirdly there needs to be a duct or pipe which allows them to get past any sleeper walls to access the ramp.
It is not clear where or when Cattle Grids emerged as an effective solution to confining stock while allowing wheeled traffic unimpeded access through fences. There are indications that it emerged separately in regions hemispheres apart.
In the UK there were units in place in Victorian and perhaps Georgian times as Country Estates grew in popularity. Tricky to open a gate wearing a crinoline while up to knees in poo! Ask Ian Harvey!
The intervention of an Engineering Genius in the form of Geof Freedman, Chief Civil Engineer of the Forestry Commission was a game changer. The FC used huge numbers of Cattle Grids and he needed to standardise them and reduce the cost for installation. His design is now the Industry Standard. It is modified to deal with different loads. The beauty of this elegant design is its speed of installation – road closed for hours rather than days.
There has been an attempt to offer a “Standard Unit” by IAE but these rely completely on the quality of the concrete works with often dire results. Grids banging as they are crossed are irritating and in time the repeated flexing can made welds fail or members to fail. It is impossible to hold down a grid which does not fit properly onto the concrete.
A novel, (novelty?)approach by Ian Harvey Fabrications is to supply a pre cast concrete base for the units. Laugh – I thought my trousers would never dry!!
You may gather that your guru prefers the Pitless/Drop-in units as they usually work instantly and for a very long time. There are occasions when a conventional unit is the best solution and it can be the cheapest.
The Conventional Cattle Grid rests on has a concrete slab placed below ground level. Cast onto this as a series of concrete sleeper walls and a surround which usually includes a shelf along the sides of the pit for the ends of the steel cattle grid to rest on. The grid itself is a large fabricated grating which rests on the shelves and the sleeper walls. Its performance depends on : Precisely cast base & Properly designed and fabricated grid
The Pitless or Drop-in Unit can be installed onto either a flat concrete slab at a particular level or a bed of compacted DoT Type1 or similar, to spread the load and not crumble over time. The delivery vehicle arrives and the unit is placed into the excavation and back filled. It is ready to use.
Although there is more steel, labour and galvanising costs in a Pitless or Drop in unit this has to be set off against the cost to provide the concrete base and sleeper walls and the disruption of the track/road being closed for days.
The fact that the surface is broken generates noise but this can be more or less depending on other factors.
The shape and spacing of the bars is a crucial issue. The BS defines the permitted size and ranges of spaces for bars. This is to ensure effectiveness and to protect animals who become stuck in a grid.
Circular Bars with maximum permitted spaces are the noisiest.
Square or rectangular bars with minimum, permitted, spacing are the quietest solution to this particular aspect.
but there are further relevant factors….
The steel unit needs to be a good fit with the concrete sleeper walls or base. Steel banging on concrete does not aid sleep! This is best dealt with by ensuring high quality concrete forming to ensure a snug fit with the flat steel structure.
It is increasingly difficult to secure the services of Contractors with the necessary skills. This is a driver for the switch to the Pitless Units also known as Drop-in Units . These units if correctly fitted are very quiet.
These Pitless or Drop-in units avoid sleeper walls by providing a steel base for the grids to sit on. It is vital that these are well made so the removable grids do not bang against the base creating another source of noise.