Comparing seismic piezocone and seismic dilatometer test results for the characterization of a coastal silt deposit from Finland

This paper focused on the performance comparison of in situ testing methods for geotechnical characterization of a silt deposit at Haistila, in western Finland, in the vicinity of the coastal city of Pori. Soil conditions comprise a homogeneous, up to 9 m thick, slightly overconsolidated silt deposit. The Haistila test site is part of the ongoing FINCONE II research project funded by the Finnish Transport Infrastructure Agency (FTIA, Vaylavirasto) and carried out by Tampere University. Testing included piezocone along with in situ measurements of shear wave velocity (SCPTU), in addition to laboratory testing, including index and consolidation tests, among others. Furthermore, seismic dilatometer testing (SDMT), using the novel Medusa SDMT equipment and technology, was carried out at Haistila. This work documents the first known application of the flat dilatometer test (DMT) in geotechnical investigations carried out in Finland. The paper critically compares the SCPTU and Medusa SDMT outcomes and their applicability in the determination of site-specific engineering properties of Haistila silt. SCPTU and Medusa SDMT provide a similar interpretation in terms of soil stratigraphy, drainage, constrained modulus, and hydraulic properties of the soil deposits, while some discrepancies can be noted for stress history and strength, probably in relation to the availability of site-specific correlations only for SCPTU. Finally, remarkable differences are notable for shear wave velocity data due to the use of the 1-receiver configuration for SCPTU and the 2-receiver configuration for Medusa SDMT.