Ground Improvement and Construction Challenges of Massive Fine-Grained Fill Embankments to Support Settlement Sensitive Structures

Design and construction of massive thick fills over compressible clayey soils due to the highly variant topography is a challenge in itself. Additionally, when the use of on-site fine-grained soils (that would typically be discarded) is needed, the geotechnical challenges increase. This paper presents the soil investigations, geotechnical design evaluations, ground improvement recommendations, quality assurance program and post-construction settlements measurements for several large warehouses within a 300-acre logistic complex in Costa Rica. This site required thick fills between 15 to 25 feet (5 to 8 meters) to be constructed in order to create large building pads, roads and parking areas. Due to the large warehouse areas between 86,000 to 215,000 (8,000 to over 20,000 meter2), the necessary earthwork operations had to be performed utilizing majority of onsite soils to make the project economically feasible. A comprehensive QA/QC program was developed/executed during the filling process to minimize the risk associated with fine-grained fill materials (volcanic clays/silts). Additionally, post-fill confirmatory field tests (e.g. CPT, plate load test) were performed to validate the strength and modulus values of the compacted fill. The subsurface conditions consisted of soft clayey soil layers, with thicknesses ranging from 8 to 18 feet (2.5 to 5.5 meters). Given the large footprints of the warehouses and relatively high structural loads at the columns and floors; a combination of several cost-effective ground improvement techniques were recommended to minimize settlements. Preload heights between 6.5 to 10 feet (2 to 3 meters) were utilized to simulate future floor loads. A detailed stress distribution model/analysis was performed to minimize the soft native soil replacement depth and area beneath the footings. Settlement plates were installed prior to fill placement to monitor the required fill and the different recommended preload heights. These plates provided real-time settlements during the filling process and beyond, providing data to back-calculate the soil’s geotechnical parameters. This information was used to refine our design calculations and estimate future settlements more accurately. Post-shell construction settlement measurements confirmed our settlement predictions and models during design.