Interface Shear Testing of Glauconitic Sands for Pile Design

Abstract

With the continued growth of the offshore sector and plans for new wind farm developments, shallow marine environments are becoming key areas for the renewable energy projects. As a result, the likelihood of encountering glauconitic sands is growing, posing challenges to the offshore wind infrastructure. Glauconite, or glauconitic sand, also known as ‘greensand’, refers to a soil containing peloidal sand-sized grains primarily comprised of mineral glauconite, an iron- and potassium-rich 2:1 interlayer-deficient mica. The tendency of glauconite to transform from sand to fine-grained soil with shearing creates uncertainties in site characterization and negatively impacts pile drivability to targeted depths. This thesis examines shearing behavior of glauconitic sands at soil-pile interface using two samples of Belgian glauconitic sands. With the final goal being the derivation of reliable interface shear strength parameters, the study aims to develop test procedures capable of capturing the transition of glauconitic sands from their natural uncrushed state to a reworked degraded condition, simulating the effects of shear-induced particle breakage during pile installation. To achieve this, a systematic experimental program was completed in two phases. The first part focused on glauconitic sands in their natural state and the second aimed to assess the degraded soil. Comprehensive material characterization, including geotechnical index tests, mineralogical analyses, and soil-steel interface direct shear tests under various conditions, was carried out to support each phase. The findings link the interface shear behavior and strength of glauconitic sands to their intrinsic properties, identify limitations in current experimental procedures, and offer recommendations for future research. New insights are provided into the behavior of Belgian glauconitic sands with the relatively low glauconite content and varying crushability potential. Interface roughness, shear rate, and normal stress effects are considered.