Field instruments for in situ measurement of geotechnical properties of sediments
Abstract
Marine sediments cover ~70% of Earth???s surface, and understanding their geotechnical andacoustic properties is critical for operations such as seafloor mapping, target recognition usingacoustics, and construction and transport operations that depend on sediment stability. Thesesediments are also inhabited by diverse communities of animals that can occur in highabundances and can alter sediment properties by burrowing, constructing tubes and burrows, andsynthesizing hard materials such as calcium carbonate shells. Recent work has shown that muddysediments are elastic solids through which bubbles grow and animals burrow by fracture. Theseprocesses depend on the geotechnical properties of muds, stiffness and fracture toughness, whichare poorly studied in sediments but important in altering animal behaviors, bubble growth, andthus likely affect acoustic properties. We propose to build submersible instruments to measuresediment stiffness and fracture toughness in situ in shallow water sediments (limited to ~33m,for diver deployment). These instruments will be modified from existing designs to measurethese properties in intertidal sediments. Each involves lowering a probe into sedimentsincrementally to measure depth profiles. The probe for the stiffness instrument has an inflatablemembrane and measures the pressure required to inflate the membrane against the stiff sedimentinterface, and this pressure is converted to elastic modulus, or stiffness. The probe for thefracture toughness instrument is shaped like a corkscrew and is rotated into the sediment andpulled upwards to fracture a plug of sediment. The force required to pull the corkscrew up andextend the crack inward to fracture the sediment is converted to critical stress intensity factor, ameasure of fracture toughness. Instruments will be deployed in conjunction with measurementsof acoustic properties and animal abundances and community composition to link animalactivities with changes in sediment properties.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 04, 2018
- Source ID
- N000141812806
Entities
People
- Kelly M. Dorgan
Organizations
- Office of Naval Research
- United States Navy