The concept of using atmospheric pressure to apply a precompression load for accelerating the consolidation of foundations for embankments constructed on soft clay soils was first described by Kjellman in 1952. The method, although theoretically sound, was impractical then because the plastic sheets that covered the sand filter deteriorated rapidly in field use, and consequentlythe vacuum could not be easily maintained. Recently, new plastic and fabric materials have been developed tliat promise to make the Kjellip. an vacuum preloading method practical. The materials are cheap, strong, and resistant to deterioration by SWllight and weather. Practical applications and several specific advantages of the vacuum method are described, and factors affecting the costs of highway and other preloading construction are given. Depending on the relative costs of the fill materials and the plastic membranes, the vacuum method can be significantly cheaper than conventional preloading using sand or gravel surcharge fills.

• IN 1952, Walter Kjellman (1), then director of the Swedish Geotechnical Institute, described a new method for using atmospheric pressure to apply temporary surcharge loadings for precompressing clays under highways and buildings. In the method, a plastic or rubber membrane is placed over a sand or gravel fllter layer and sealed to the clay below the ground water table. Then a vacuum pump is connected, and the air