Dilatometer and Seismic Dilatometer Testing Offshore: Available Experience and New Developments

The flat dilatometer (DMT) was first used in offshore site investigations in the late 80s. Since then, the DMT and also the seismic dilatometer (SDMT) have been increasingly used worldwide in over-water projects, mainly nearshore with limited water depth (maximum 50 m). The limitation for deep DMT testing is due to the need of a pneumatic cable, which is necessary to supply the pressure from a gas tank at the surface down to the blade at depth., The first part of this article presents the available experience of DMT and SDMT testing nearshore using the traditional pneumatic equipment. In the second part of this article, the recently developed Medusa DMT is described. This device is a self-contained cableless probe that is able to autonomously perform dilatometer tests up to a maximum pressure of 25 MPa. Hydraulic pressurization is achieved with a motorized syringe, enabling volumetric control during membrane expansion. Initially conceived only for offshore testing, the Medusa DMT also provides higher quality dilatometer data onshore, with the possibility of additional measurements not feasible with the traditional pneumatic equipment.