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Title: Construction of an unattended seismological observatory (USO) in permafrost
Authors: Sandia National Laboratories
Lange, G. Robert.
Keywords: Boring
Drilling rigs
Frozen ground
Seismological stations
Publisher: Cold Regions Research and Engineering Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: Special report (Cold Regions Research and Engineering Laboratory (U.S.)) ; 113.
Description: Special Report
Abstract: The construction of a large diameter cased borehole and surface instrument shelter for the installation of a high resolution, long term recording seismograph in marginal permafrost 15 miles west of Fairbanks, Alaska, is described. Permafrost extended to a depth of 123 ft and consisted of frozen silt, peat and sandy small gravel and was underlain by a thawed gravel aquifer. The first 48 ft of 16-in. hole was drilled with a truck-mounted auger. A Failing 1500 mounted on a tracked trailer was modified to accommodate a 4-in.-ID kelly, swivel and drill pipe so that compressed air in reverse circulation could be used for cuttings removal. Air was circulated by either pressurizing the annulus through a rotating seal or by an air eductor (injector). These systems were used to complete the hole to 92 ft. Although considerable difficulty was encountered, drilling rates of 10 ft/hr were measured when using compressed air chilled to below 20°F, shrouded bits to provide adequate bottom hole cleaning and either the eductor or the pressurized annulus. The latter is preferred since compressed air requirements are much less. Eleven and three quarter in. O.D. casing with flush, step-threaded joints was set using a soilwater-snow slurry as grout. Forty thermocouples were installed in the fill placed over the casing and in the ground beneath to monitor thermal behavior. Data from these are discussed. Five thermistors attached to the borehole package yielded data on the ground temperature at the 80 to 85-ft depth interval. Using these data, the permafrost thickness obtained by exploratory drilling, and the mean annual air temperature, the ground temperature profile at depth is estimated. This analysis yields a ground temperature of about -1.7°C for a depth of fifty feet (minimum depth of zero annual amplitude). It is concluded that rapid construction of similar installations in permafrost regions is feasible, but would present formidable logistical problems. Drilling "big holes with little rigs" in almost any frozen soil or rock also appears feasible. However, considerable development work will be required on this and other aspects of the problem before 100% success can be guaranteed for each hole started, considering the original limitations arbitrarily set on the problem; i.e., construction in unfriendly countries, in one week's time, with air transportable equipment.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Special Report

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