Visualizing air entry from footprints on the beach experiments using fine transparent soil

¹ BGC Engineering, Calgary, Alberta, Canada
² Geological Risk Prevention and Geotechnics Department, Geographical and Geological Survey of Catalonia (Institut Cartogràfic i Geológic de Catalunya), Barcelona, Spain.
³ GeoEngineering Centre at Queen’s-RMC, Department of Civil Engineering, Royal Military College of Canada, Kingston, Ontario, Canada.
⁴ GeoEngineering Centre at Queen’s-RMC, Department of Civil Q2 Engineering, Queen’s University, Kingston, Ontario, Canada.

^* Corresponding author: siemens@rmc.ca

Abstract

All beach goers have experienced the phenomenon of that walking on the edge of the swash zone is significantly easier and more comfortable relative to the submerged sand lake/ocean level or dry sand farther away from the beach. As each footstep descends into the sand temporary high bearing capacity is registered followed by a depression of the foot, a sand cone emerging around the depression, which is surrounded by a dilative fringe. From a geotechnical perspective, dilation-induced negative pore pressures provide temporary support during foot placement followed often by what appears to be a general shear failure. Footprints on the beach experiments using transparent soil are reported, which provide the benefit of visualizing air entry during the test. Results show that tests with phreatic surface placed at the ground surface recorded the highest bearing capacity, which is approximately 4.5 the pressure available for dry tests. Both tests with phreatic surface placed below and above the ground surface showed progressively decreasing bearing capacities. Results are compared and contrasted with traditional bearing capacity theory as well as literature reported unsaturated bearing capacity experiments.