Twin-span tunnel destroyed by snow

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Joined: Friday, 27 July, 2012 - 14:26
Twin-span tunnel destroyed by snow

Came back to the farm after a brief Xmas break to find our 25m twin-span tunnel totally destroyed under the "weight" of snow. The centre poles of both spans were now lying on the floor; nearly every hoop had buckled so were now forming a 'M' shaped instead of an 'n' (hopefully you can picture it!) 

The mystery is... it only snowed about 15mm on the night of the 26th when (i assume) it happened (the damage was discovered on the 27th). The tunnel showed no visible signs of problems after a far, far heavier snowfall in the second week of december when we got more like 150mm. (I have wondered if the snow might be a red herring and the damage might have been done by the strong winds on christmas day, although the tunnel has survived far, far worse storms than we had that day).

The tunnel didn't have any crop bars or bracing, so let this be a lesson!

We are hoping to have a replacement sorted relatively soon (we are a CSA and fortunately have some cash reserves for this kind of disaster) but I'm trying to work out what we could do better. Obviously bracing. The old tunnel also had 2.5m between hoops - i'm wondering if this might have been a contributing factor when most tunnels seem to have more like 1.8m, so you get more hoops sharing the weight. The ground tubes weren't concreted in and had no anchor plates, they were just pushed in to the ground - perhaps this made it more vulnerable too, if the uprights could easily be pushed outwards by the weight?

I'd appreciate any comments anyone might have...

thanks v much, Dom in Warwickshire