The floor of your silage clamp is probably the most important part of the whole structure. It’s the hardest working, the most abused, often overlooked bit of the clamp and yet when it does its job well it keeps you out of the sh!t, both practically and legally. The SSAFO regulations require your silage clamp to have a floor formed from either concrete or tarmac and the choices have been covered elsewhere in this series, but here I am going to look at the profile of the floor, regardless of what it’s made from.

Why don’t silage clamps have flat floors?

Ask a builder and a flat floor is the easiest to produce; setting out is easy, the concrete or tarmac is semi-liquid and has a tendency to want to level itself, So why do most silage clamps have floors that are not level? The reason often quoted is “so the effluent can run out” but this is not really the whole story.

Back in the “bad old days” of low dry matter silage there might have been some truth in this and looking back to some of that direct cut silage we made in the wet years anything that could help with getting the effluent away would have been a help. Today most producers are making much higher dry matter silage with much lower effluent production. Also as clamps have got bigger and, more importantly, higher, the floor has less of an impact on the progress of effluent out of the clamp. If you consider a 5m high clamp compacted by a 15t loading shovel, a 1 degree slope on the floor is having little impact on the effluent transit through the clamp. So do we really need a clamp floor to slope?

For effluent drainage, perhaps the floor slope is not that important, but it’s far more important for rainwater drainage. One of the very best ways to ruin silage is a good soaking, in the field or in the clamp, rainwater – or worse still dirty water – is to be avoided at all costs. So a clamp floor needs to be designed to make sure that any rainwater runs away from the exposed silage face and can’t pool into the clamp.

Does the floor need to fall so the water runs off?

Well that’s the thinking, but not really the practice. For clean water to run off a power floated (smooth) clean concrete surface the concrete needs to be on a slope of about 1 in 6. For a 50m long clamp the back would need to be over 8m higher than the front for the water to “run off”. That sounds crazy but if you think about it a bit more, water actually clings to the windows of the tractor cab so it’s almost impossible to make a surface that water will actually “run off” and that’s on clean, low friction surfaces. Once you start looking at a tamped concrete, or textured asphalt floor, along with a scattering of residue silage it’s clear that this is not going to run off dry.

So what is a realistic silage clamp floor fall? 

For most clamps, 1 in 80 or 1 in 100 seems to be a practical target fall. For indoor clamps protected from the rain it’s safe to look to even flatter floors if desired. Again for the 50m long clamp at 1:80 that’s 625mm or for 1:100 its 500mm of fall from the back to the front. These figures are more practical on site and will give reasonable face protection from rainwater pooling.

This is assuming a clamp that’s 3 sided but for clamps open at both ends you need to consider what happens when the clamp is “reversed” and you start taking silage out of the other end. There isn’t any simple solution to this but it’s usual to fall the clamp from the middle of its length, dropping each way. In a 50m long clamp you would get 25m falling to one end, and 25m falling the other way.

Should the clamp floor slope towards the centre?

It used to be common for the clamp floor to have a main slope from back to front and then a cross fall either to the centre or towards the walls. With higher dry matter silage, this doesn’t offer much benefit and has a couple of issues that make it less attractive than a simple, single slope floor.

Firstly it’s much more complex to form a fall of multiple fall, secondly there is a greater risk of pooling. For a clamp with cross-falls to the centre, any blockage or obstruction in the centre of the clamp will quickly cause a pool of rainwater in the centre of the clamp. In contrast, run off will make its way around obstructions on a simple sloping floor avoiding the problem.

Finally, floors with cross-falls are not very machinery friendly. Forks and buckrakes can easily damage a cross fall and tipping trailers are more unstable on a cross fall. So in conclusion a uniform, simple, sloping floor is usually a desirable solution.

Now we have an ideal floor profile, how do we deal with the walls meeting the floor and its fall? Unfortunately that’s a big enough topic for its own section in this series so I will come to that one at a later date.

If you want to discuss how to design the falls in your next clamp or to discuss any of the other aspects of silage making covered in this series – contact Jeremy Nash @ jeremy@silageconsultant.co.uk

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