DMT Testing for Site Characterization and QA/QC on a Deep Dynamic Compaction Project

This paper describes the use of the Marchetti flat dilatometer (DMT) on a major highway relocation project in Carver, Massachusetts (USA). Parts of the new highway span former cranberry bogs. Sheet piling was installed along both sides of the new highway alignment, and organic material was dredged from between the sheet pile walls. The area was then backfilled with sands. Since most of the sand was placed in a fairly loose state under water, liquefaction was a potential problem. Therefore, deep dynamic compaction (DDC) was used to density the fill. An extensive in situ testing program was instituted to characterize site conditions prior to densification, and to assess the sufficiency of the DDC after treatment. The results of this study suggest that the DMT can be used to provide accurate and cost-effective stratigraphic profiles. The DMT was particularly helpful in identifying pockets of organic soils (i.e., peat) that were not completely removed during the initial dredging operations. In terms of compaction QA/QC, the modulus values determined from the DMT appear to be very sensitive indicators of densification effects.