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

Author(s)
D. Marchetti
Abstract
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.
 
Keywords
Medusa Flat Dilatometer DMT Offshore Dilatometer Automated Dilatometer Cableless Dilatometer Offshore Shear Wave Velocity Offshore In Situ Testing Marine Soil Investigation Seafloor Dilatometer Geotechnical Engineering
 
Reference
Marchetti, D. (2018). Dilatometer and Seismic Dilatometer Testing Offshore: Available Experience and New Developments. Geotechnical Testing Journal, Vol. 41, No. 5, 2018, pp. 967–977, https://doi.org/10.1520/GTJ20170378. ISSN 0149-6115.
 
Related Equipment
The Flat Dilatometer (DMT) is an in situ test for the determination of various key soil parameters used for geotechnical design. The test is rapid, accurate, simple and cost-effective. The results are highly repeatable and independent from the operator. The blade may be advanced with most common field machines, including penetrometers and drill rigs. ... MoreDMT measurements are performed in situ, directly on the soil in its original position and state. This eliminates the disturbance caused by drilling, sampling and transport to laboratory. The profiles of the results are available real time during test execution. The direct measurement of soil deformation enables accurate estimations of the elastic modulus. The KD parameter provides stress history information of the soil, a very difficult property to estimate with other testing methods.

Main Applications

Main Applications

Soil stratigraphy

Stress history (OCR, K0)

Settlement prediction

Soil Improvement quantification

Slip surface detection in clayey slopes

P-y curves for laterally loaded piles

Liquefaction potential

Permeability in clay

FEM input parameters (e.g. Plaxis)

Subgrade modulus for pavements

Subgrade modulus for diaphragm walls
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