Assessment of Lower Bound Bearing Strength of Foreshore Sediments using Remote Sensing: The role of sediment saturation, beach slope & bearing failure type
Abstract
Beach trafficability is an issue for naval operations, as well as beach rescue operations. Beachmobility restrictions are governed"" by the sediment~s bearing and traction failure behavior, with bearing failure, or sinkage, representing the larger threat to mobili""ty. To-date mechanical testing of sediments allows an accurate assessment of bearing strength. However, many naval operations prohib""it the application of such tests, due to time or access constraints. Lower bound bearing strength of lunar soils was successfully as"sessed from images during the Apollo moon missions.The same approach was tested for dry sands at the upper foreshore with promising" results using digital images and panchromatic satellite images to derive friction angles, and from there, lower bound bearing stren""gth using bearing capacity theory. Here, we propose to advance this approach by investigating friction angles across the entire inte""rtidal zone and upper foreshore, and additionally, consider the role of sediment saturation, beach slope and bearing failure behavio""r. The goal is to include calibrated, and potentially, modified bearing capacity factors accounting for these effects. This follows"" the concepts of the bearing capacity equation for unsaturated sediments, the inclination factor, and the shape factor, being standa""rd approaches in geotechnical engineering. This goal will be achieved through correlation of remotely obtained digital, satellite, a""nd mobile X-band radar data to results of geotechnical laboratory testing of foreshore sediment samples, as well as to in-situ densi""ty, pore pressure, beach slope measurements, and bearing failure testing. Pore pressure and saturation will be determined using pore" pressure transducers installed in the beach sediment over a period of multiple days or weeks. Beach topography will be measured usi"ng real time kinematic satellite navigation. Bearing failure will be tested using a portable mini-loading frame, as well as concrete"" filled tires. Geotechnical laboratory testing will include determining sediment index properties, such as grain size and water cont""ent. Furthermore, soil water retention curves will be measured, as well direct and triaxial shear testing. Field test will be conduc""ted at two sandy beaches in Yakutat, AK, and in Duck, NC. Field testing in these locations builds onprevious collaboration with loc""al researchers and authorities. From the correlation of remotelyobtained data, in-situ measurements, and laboratory tests, a novel"" formulation of the lower boundbearing strength equation will be derived, and calibrated, which will enable a rapid assessment and" mapping of lower bound bearing strength from remotely obtained imagery in sandy beachenvironments. The second step of the proposed" project will aim for the application of the novelapproach to other coastal environments such as tidal flats, sandy shoals, and poc""ket beaches atrocky coastlines. Here, field measurements and the application of the novel approach will provide insight if this for""mulation of lower bound bearing strength is directly applicable to other coastal environments, if further modification and calibrati""on is required, and what may be potential limitations. In summary, the proposed study will advance current knowledge in geotechnical"" assessment of the foreshore from remote sensing, and demonstrate the applicability and limitations of the approach in different env"ironments. The findings are directly applicable to mobility issues during naval operations at the foreshore.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 05, 2017
- Source ID
- N000141712516
Entities
People
- Nina Stark
Organizations
- Office of Naval Research
- United States Navy
- Virginia Tech