ABSTRACT:

The technique of using explosives to achieve compaction of a soil mass has been tested in connection to a road construction project in the central part of Sweden. The natural soil, 2 to 5 meters of organic soil (peat), was excavated and replaced with a fine grained till. The test site was instrumented with pore pressure gauges, inclinometers and a device for settlement measuring. The fill was subjected to compaction by blasting on three occasions, each blasting separated by, at least, 2 to 3 weeks. To obtain the fill stiffness determination of Raleigh wave travelling velocities were carried through using the SASW (Spectral Analysis of Surface Waves) technique. These measurements were carried through on three occasions with the aim of detecting changes in stiffness due to the "compaction by blasting" activities.

BACKGROUND

In a large part of northern Sweden the road construction projects are associated with cutting through hills of till and the excavation of organic soil when the road goes over bog- and mire-soil. By substituting the excavated organic soil with fine grained tills instead of the traditional rock masses substantial economic savings can be made. In terms of money, savings about 100 SEK per cubic meter will be possible, or in the magnitude of SEK 10 000 to 20 000 (that is $1300 to 2500) per meter of road. At least as important are the environmental savings. The transportation of rock masses to the building sites and the removal of natural till masses can almost be eliminated. The damage in the nature due to rock pits will be reduced as well. The use of a fine grained till as fill under water-table is associated with some difficulties. In this project the "compaction by blasting" method was chosen.

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