Characterization of young sediments using CPTu and Medusa SDMT

Piezocone penetration tests (CPTu) and seismic flat dilatometer tests (SDMT) present costand time-efficient insitu investigation techniques for onshore as well as offshore projects. Since soil sampling is often related to a strong soil disturbance in fine-grained sediments, parameter identification is frequently based on insitu measurements in combination with correlations. As shown in previous studies, correlations are more difficult to develop in silt-dominated sediments. To overcome this problem, the research project PITS (parameter
identification using insitu tests in silts), was launched by Graz University of Technology in cooperation with the Federal Chamber of Architects and Chartered Engineering Consultants. To investigate the influence of time effects (age) and microstructure on the load-settlement behaviour of normallyto slightly underconsolidated sediments, deposits younger than 50 years have been investigated at the water storage reservoir Raggal (Austria) using CPTu as well as Medusa SDMT. Both probes were pushed first through the water and subsequently into the sediments by means of a stand-alone pushing device, where the testing setup was installed on a floating pontoon. In order to prevent buckling of the penetration rods, additional casing tubes (along the water) were used. In
a last step, soil sampling was executed using the CPT-Ranger system by Geomil. To characterize and quantify the sediments microstructure, shear wave velocities determined insitu by means of SDMT (VS,SDMT) are compared with measurements on reconstituted soil samples using bender elements (VS,BE). Ratios S,BE/VS,SDMT ≈ 1 indicate the presence of no or moderate soil microstructure. On the other hand, postglacial deposits of similar grain size distribution are characterized by smaller VS,BE/VS,SDMT ratios, indicating a higher microstructure.