Effect of degradation on geotechnical behavior of glauconite sands from the U.S. Mid-Atlantic Coastal Plain

Abstract

Glauconite sand is a challenging sediment that can pose risks to foundation installation and performance due to its tendency to transform from coarse-grained material into fine-grained material due to particle crushing. Glauconite is characteristically green iron potassium mica and smectite often found in sand-sized peloidal form. It forms under reducing conditions within marine depositional environments below wave base and has been found in coastal plain and offshore regions of the U.S. This paper presents an overview of the geological basis for glauconite sand formation, describes its depositional environment and maturation process, and summarizes the state of knowledge of geotechnical challenges in glauconite sands. Laboratory test results are presented for glauconite sands collected from the U.S. Atlantic coastal plain, showing that initial sample conditions, drying methods, and degradation methods affect the initial, temporary, and long-term geochemical and mechanical characteristics of glauconite sands. The degree to which particles crush or degrade from their natural peloidal form to clay-size particles is linked to maturity and depositional method. Intentionally degraded specimens used in laboratory testing can simulate the effect of pile driving through creation of a shear zone of degraded soil along the pile shaft, and quantify its impact on soil-structure interface strength.