Using willow spiles to retain a soil riverbank 1

[fernley]

I've put forward a proposal to the Environmental Agency to retain my riverbank using 900mm high 75mm dia live willow spiles angled into the bank at 20 deg. Backfilled to the top with soil which will repose away from the edge upwards at an angle of 20 deg. below the soil is a foundation of igneous rock. They would like see a calcultaion to demonstrate how deep the spiles need to be sunk into the river bed to remain stable. I have no idea how to calcultae this, does anyone out there have a formula I could apply?

 

[naturalengineer]

Normally we like to have one 1/3rd above the bed level and 2/3rd below. you need to use longer posts, say 2.4m in length.

You will also need to place a woven geotextile behind the spiling to prevent the soil fines from washing through the face of the willow.

James Hector
Willowbank Services

http://www.willowbankservices.co.uk

 

[fernley]

Many thanks for that advice, could you also tell me if it's possible to split larger diameter willow longditudinally in half and still make it strike? I'm only asking as there is some larger dia material currently available for harvesting

 

[naturalengineer]

It would probably kill the willow. We often install willow stakes 100mm to 200mm

 

[rockchip]

fernley. If you haven't already located or used it, an excellent discussion of the means/methods, and analyses pertaining to protecting a slope with natural materials can be found in Donald Gray's books on biotechnical slope stability. One is published in 1982 and the newer version can be found on Amazon at:

http://www.amazon.com/Biotechnical-...9786/ref=sr_1_2?ie=UTF8&qid=1294088207&sr=8-2

rockchip