ABSTRACT
LIGHT PERCUSSION DRILLING Mobile A-frame is easily towed on its own wheels by a small 4WD, simply erected, and fitted with power winch. Steel shell is driven into the ground by a weight that is repeatedly dropped 1-2 m and then lifted by cable over the A-frame (hence ‘cable and tool’ rig). Only suitable for shallow exploration of soils and soft clay rocks, though a chisel head may be fitted for some limited penetration into rock. In cohesive clay soils, the smooth shell is driven into the ground by the weight dropped onto it, and the soil simply adheres to the inside for recovery. In non-cohesive sand soils, the whole weighted shell may be surged and dropped, and the soil has to be retained inside by a hinged clack valve. Can add light rotary drive for auger drill in clays (hence ‘shell and auger’ rig) but less suitable for most site investigations as sample is disturbed. Widely used, as all sites require soils investigation; usually with 100 mm sampler inside 150 mm casing, capable of reaching depths of 15-40 m. Window sampler is a small track-mounted percussion drill, which is very mobile and economical but can reach only 6-8 m deep in soils.
