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Abstract

This paper describes the first tests of a free fall penetrator and acoustic Doppler-shift instrumentation system, designed to profile the properties of soft marine sediments to depths of 50 metres below the seafloor. The experiments were performed in October 1986 from the MV Tyro at three sites within the Great Meteor East study area on the Madeira Abyssal Plain, where the water depth is 5400 metres. These trials provided the opportunity to study the influence of surface finish and density on penetration depth, and to test two more-versatile acoustic instrumentation systems. The new Doppler-penetrator system surpassed expectations by successfully measuring penetrations of up to 58 metres. Using the BREPEN soil model, similar profiles of strength and depth were derived from tests at the same site with penetrators of different density and surface finish. The two abyssal plain test sites had similar strength profiles, but the sediments were some 2.5 times stronger at the abyssal hill site. Terminal velocity was found to be highly dependent on surface finish, the measured drag factor varying from 0.113 for a glossy finish to 0.207 for a rough finish. The variation of final penetration depth with density agreed well with that predicted by BREPEN and the motion in the sediment appears to be independent of surface finish.

Additional information

Authors: FREEMAN T J BUILDING RESEARCH ESTABLISHMENT, GARSTON, UK MURRAY C N JRC-ISPRA, I SCHUTTENHELM R T E RIJKS GEOLOGISCHE DIENST, NL , BUILDING RESEARCH ESTABLISHMENT, GARSTON, UK;JRC-ISPRA, I;RIJKS GEOLOGISCHE DIENST, NL
Bibliographic Reference: OCEANOLOGY INTERNATIONAL '88, BRIGHTON/UK, MARCH, 8-11, 1988, AVAILABILITY: CEC-LUXEMBOURG, DG-XIII/A2, BP 1907, MENTIONING PAPER ORA 33849 E
Availability: Can be ordered online
Record Number: 1989126090200 / Last updated on: 1989-05-01
Category: PUBLICATION
Available languages: en