I was wondering if anyone had any feed back on this idea I have developed for a community garden my client wants me to create. First of all I am in Ottawa, Ontario, so my climate is cold temperate with a moderate amount of precipitation; I have designed for drainage and against erosion mostly, rather than water retention. The site I am working on is a beaten down embankment separating a parking lot from a storm water drainage swamp. The soil is really packed down, and likely salted from road salt. I have tried to dig into the ground, and its near impossible because it seems to be filled with rubble. This of course is not negotiable since it is the only site my client has access to. And they want the garden up and running by October.
The embankment is a three foot elevation, so my idea was to fast track the soil building time by terracing up. In the location I am working with there is an abundance of wood pallets and construction dirt, so I figured that I am going to try and build a wood pallet terrace on contour for one of the sides of the embankment in order to create a number of keyhole allotment plots.
I am not an engineer, I have a background in physical geography, so I know that I need to deal with some serious freeze-thaw heaving up here in Ice Planet Canada. My thoughts are to sink the pallets in one foot on contour and pin them in with five foot 4x4s. Then I am going to support the front end of the pallets with the dug-out earth and plant some deep taproot shrubs. This is going to be holding back about ten to twenty feet of soil back towards the peak of the embankment. I cannot tell if this is going to be enough support to hold back the earth, especially with the precipitation we receive; we get a lot of snow in the winter.
The pallets we have in abundance are softwood – and we are not sure about hardwood pallets being treated, we know that the softwood ones are untreated – which inevitably will last only a few seasons, but I was thinking of successionally building it up into a self-supporting berm held in place with shrubs.
I was just wondering if anyone has ever tried anything like this before, or if there are any civil engineers out there that could help me out. I am looking for feed back on how to make this terrace as strong as possible (how should I support it).
Thanks for reading, sorry for the long post.