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Fred McKenzie wrote:
In article , Dave Lemper wrote: The soil in central Texas is called Caliche with a lot of clay, CaCO3 & shale. Attempting to drive in a ground rod yielded only a mushroom on top & blisters on me. Local tool rental place has concrete bits, but maximum length of 18 inches. Possibly longer bits are available in a larger city. Dave- Last year there was a discussion here about sinking a ground rod using an "SDS Plus" Hammer Drill set to hammer-only. I think it was Ian White, GM3SEK, who proposed that method. The other point was that SDS+ bits are available up to 1.0 metres long, so by using both rotary and hammer action you can drill a pilot hole through most kinds of rock down to that depth. There is also an article at http://www.n4lcd.com/groundrod/ that proposes a slightly different method of coupling the hammer drill to the ground rod. The question is whether Caliche can be penetrated by such a method. Has anyone tried it? We don't have caliche here, by that name, but from accounts on the web I'd doubt if it could be penetrated by hammer action alone. However, it seems more likely that an SDS+ bit could drill through it. Another consideration is whether or not there is moisture in the soil below the Caliche. If not, then it might not provide a low-impedance ground even if you could penetrate it! That is certainly the problem at this QTH, where an earth rod drilled and hammered into the very rocky subsoil produced a resistance of 500ohms! Long horizontal electrodes are the only kind that work at this QTH. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
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