Permaculture Designers Manual
CHAPTER 9 –
EARTH WORKING AND EARTH RESOURCES IN PERMACULTURE
Section 9.2 –
Planning Earthworks in Permaculture
It is best to plan all aspects of the earth-moving process before the machines or laborers arrive on site.
1. Make an initial decision where you would like to place the road, dam, house site or drains, etc., using a contour map and plan if necessary.
2. Test the soil by auger holes, soil samples, and soil pits to determine if the soil is good enough to suit your plans (a good clay soil for dams is essential). Seek professional advice or do more research before deciding conclusively on placement.
3. Peg out the site, using a level (which can be simple or complex), a measuring tape and a good many stakes with red or white cloth attached (so that the earth moving machine can follow them).
4. Plan a place to store all the TOPSOIL removed during the excavations. Never allow topsoil to be mixed with subsoil, but carefully remove it, to be later returned to the site as a growing medium and to stabilize subsoil erosion.
To stabilize the site immediately, have on hand as much plant material as needed. These can be purchased from a nursery or grown in pots on the site several months before the planned earthworks (see Lesson 9.2 Planting after Earthworks).
When soil is moved, it becomes loose, so that soil air space and hence total volume may increase to 145% of the original. Even when compacted by machine, the fill may occupy a spare 10% larger than the cut it came from.
Although conscientiously compacted clay in dam walls may settle as little as 1% over time, loose fill will eventually settle to 75% or less of its un-compacted volume; this has great relevance to house foundations and wall stability.
When topsoil is replaced over fill, the area should not be over-compacted, or we risk water logging, but when it is replaced over deep or solid subsoil in a cut, we will probably need to first rip or loosen the base subsoil to allow root penetration, just as we need to rip old roads, quarries, parking areas, or heavily-trafficked fill before planting trees and meadows. (See Figure 9.1)
To prepare a house site (with drainage), we can proceed as follows:
Careful survey. Place pegs outside the site. Call in the bulldozer;
Strip off topsoil carefully and mound above and at either end of the site;
Cut house/garden level; use subsoil fill for access roads only;
Call in ditcher or backhoe to cut foundation and drainage trenches. Pour foundations and slab, paths; place drains and pipes;
Call in small blade and bucket machine (a Bobcat or wheel tractor) to replace topsoil and neaten the site where needed. Some soil can be mounded to the windward side for hedges;
Plant or seed all topsoil to prevent erosion;
Fine–tune with barrow, rakes check drainage.