Trial trenching is the process of digging into the ground a sample area of the site. Local Planning Authorities usually require that trenching takes place to between 1% to 5% of the site area if it is suspected that there is the potential for archaeological remains.
The dimensions of a trial trench are usually 50m x 1.84 or 30m x 1.84, the width of 1.84 being commensurate with width of the bucket on a mechanical excavator. The depth that a trial trench extends to depends upon the depth at which the archaeological horizon is located.
In a greenfield development this could be as little as 0.30m below ground surface whilst in an urban context the trench could exceed 2m or 3m in depth and so for health and safety reasons require shoring or stepping.
A geophysical survey can sometimes lower the requirement for trial trenching and in some circumstances it would be more cost effective not to undertake the geophysical survey, but go ahead with trial trenching.
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