The vehicle maintenance shop at the Jim River highway camp experienced severe total and differential settlement following original construction in 1977. Although the exact original grade could not be precisely determined, the lowest depth of building settlement was believed to be 3 to 4 feet (. 91 to 1.2 m) below the finish floor grade while slab diffential settlement of up to 2.5 feet (.76 m) occurred inside the building.

Previous exploratory work completed at the site indicated that settlement was most likely caused by thawing of ice-rich permafrost below the building. The original foundation design included 4 inches (101.6 mm) of insulation which was not adequate to counteract thermal degradation below the building. A sandy gravel material with cobbles extended beneath the floor slab to depths ranging from 10 to 14 feet (3 to 4.3 m). This coarse granular layer was underlain by a glaciofluvial deposit of frozen mixed fine and coarse-grained material having high ice content.

Rehabilitation of the building structure included short-term stabilization over a two to three month period that was accomplished using a mechanical refrigeration system. The "active" system was required because of the necessity for achieving shortterm stabilization of the building foundation. Following near total freezeback by the "active" system, it was planned to install permanent "passive" heat pipes to maintain the integrity of the frozen foundation soils on a long-term basis. Because of inadequate casing installation, the contractor was allowed to substitute a liquid-forced convection system.

The "active" mechanical refrigeration system began operating at the site on June 28, 1986, and was removed after 75 days of operation, when the degree of freezeback below the building was considered to be adequate. This paper presents design and construction considerations and provides information on the changing thermal regime beneath the building as revealed by thermistor readings versus the heat extraction calculated from temperature and flow measurement of the circulating coolant. Slab displacements are also described.

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