A preliminary study has been made of the effects of test duration, power quality, and borehole retesting on in situ thermal conductivity testing. A series of controlled experiments was conducted to investigate these issues. This paper first demonstrates the need for accurate thermal property values and then briefly describes the experimental test apparatus and test site. The results indicate that test duration does significantly affect conductivity test values and that test durations of at least 48 hours are necessary. Also, low heat rates do significantly affect the test results, and heat rates representing the expected peak loads on the U-tubes are recommended. The best technique for measuring initial ground temperature is to measure the lowest return temperature of the water upon test start-up. Finally, if a full-length test has been previously performed on a borehole, a minimum delay of ten days is recommended before another thermal test can be conducted.

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