ALMA-J Site Testing
＞ALMA-J Site Testing Archive
Last update 2005-01-24


Soil Resistivity

    Soil resistivity was measured with Yokogawa 324400 earth resistivity tester in 2000 June-July, 2000 September, and 2001 March. Significant point-by-point variation of the resistivity of upper weathered layer was found: ~4000 Ohm m at Llano de Chajnantor and ~1000 Ohm m at Pampa La Bola during austral winter. The bedrock in this area had a very large resistivity of ~2000 Ohm m. Better grounding may thus be achieved by digging wider than going deeper. The resistivity near the surface decreases down to ~1000 Ohm m at Llano de Chajnantor and ~300 Ohm m at Pampa La Bola in austral summer when lightning hazards are concerned.
    Ground resistance was measured in 2000 February with Yokogawa 323501 for the NRO containers, the CBI containers, the CBI power plant, and also for boreholes at Pampa La Bola and the Chascon-Chajnantor saddle point. The values were 47 Ohm for the NRO containers (two 20 ft containers + grounding rods), 26 Ohm for the CBI containers (~ten 20 ft containers + chemical ground), and 42 Ohm for the CBI power plant (~four 20 ft containers + chemical ground), respectively. A simple 70 cm copper stick resulted in very high ground resistance of 460 Ohm at Pampa La Bola and 950 Ohm at the saddle point, respectively.

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