This paper describes a ground improvement case study where preloading and prefabricated vertical drains (PVDs) were used to accelerate foundation settlements. The case study is used in a classroom setting with the learning objective of introducing engineering students to methods for estimating settlement of shallow foundations on compressible soils. The project site was developed for a corporate retail chain planning to open a new facility in San Luis Obispo, California. Up to 2.5 meters of fill were needed across much of the site to raise foundations and improvements above the flood elevation. Loads from the fill and the structure were expected to cause total and differential settlements that exceeded the allowable values established by the retailer. To mitigate settlement, the geotechnical engineer developed a preloading plan. Although the soil conditions were complex (e.g., interlayering, dipping strata, variable compressibility), the preloading plan was successful in achieving the desired settlement within 3 months, and subsequent site performance has been exemplary. This case study has been used for several years within a quarter-long shallow foundation design course to teach settlement performance. Learning outcomes from the assignment are summarized in the paper. Students are given the subsurface information and test results originally acquired by the geotechnical engineer. The students, working in teams, try to estimate how much primary consolidation settlement will occur due to the fill plus the preload, and the PVD spacing needed to achieve 90% of that settlement in 3 months. The assignment and relevant data are included herein along with the grading policy. The project culminates with the geotechnical engineer of record presenting in class the results of site monitoring during preloading and consolidation. These results include settlements across the 16,908 m2 site, which were tracked up to three times a week at 20 locations. This project affords students a case study experience that is rich in the “messy” details of a complex and local (i.e. familiar) geotechnical project. Included is a discussion of lessons learned by the instructors who have taught several iterations of this case study.


Civil and Environmental Engineering

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URL: http://digitalcommons.calpoly.edu/cenv_fac/319