Development of urban centers, residential areas, infrastructure, and industrial zones requires both land and earthen construction materials for fills, embankments, or other structures. In many areas, the development has outpaced the availability of land and materials. Ground improvement using additives is used to improve the strength, workability, and other engineering properties of unsuitable geomaterials. Laboratory treatability studies are typically used to determine a 28-day unconfined compressive strength (UCS) as a project-specific design strength. However, this presents limitations. Environmental conditions are not consistent between the field and the laboratory. Placement and sample creation methods in the laboratory often do not accurately mimic the field placement techniques which can vary drastically from project to project. UCS tests provided a limited understanding of soil behavior and do not account for the effects of confinement that soil would experience in the field. Long-term strength gains or losses can occur in stabilized geomaterials, changes that are not captured in a 28-day study. There is a limited understanding of the long-term strength and deformation characters of stabilized geomaterials. Relatively few studies have conducted oedometer tests on stabilized geomaterials, and long-term tests typically focus induced freeze-thaw or wet-dry cycles rather than tracking the compressibility evolution of the sediment over time. Even fewer studies utilized triaxial or direct simple shear (DSS) tests to gain a more complete understanding of material behavior, let alone long-term behavior.This thesis presents a mesocosm based approach for the in-situ evaluation of stabilized geomaterials. This approach was tested using a high-plasticity organic silt sourced from a back-bay dredging project in Wildwood, NJ, and stabilized using 4% Type 1L Portland cement by wet mass. Mesocosms were constructed as two sets of duplicates and placed in the fall and winter of 2024 under continuous environmental monitoring. Shelby tube samples were taken alongside duplicate dynamic cone penetrometer (DCP) and field molds at regular intervals over the course of 12 months. UCS, moisture content, and pH tests were conducted on all samples. DSS and oedometer tests were conducted on samples extracted from the mesocosms, as sample recovery allowed. Results showed that mesocosms were able to better capture the variability resulting from sediment variability, additive mixing, and placement of material which is more representative of large-scale placement projects. Field molds show initially higher strengths and densities than the mesocosm samples. After 12 months, however, mesocosm strengths equal or exceed the 28-day field mold strengths. DSS and oedometer tests show progressively increasing trends in peak shear strength and pre-consolidation pressure with increasing curing duration, indicating the sediment continuously develops shear resistance and reduces volumetric strain over the course of 12 months. Testing results also highlight several gaps in the literature regarding stabilized geomaterials. Future investigations are needed to develop procedures for testing stabilized material in DSS. Mesocosms should also be tested with a wider variety geomaterials and additives and against both traditional lab treatability samples and a real-world project to further validate the method. Overall, the mesocom method produced promising results and provided valuable insights in the current limitations in the understanding of stabilized geomaterial behavior and the direction for future work.
Kaleb M. Arnold (Thu,) studied this question.