Investigating the effects of an NPK fertilizer on the strength characteristics of soil

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4. Investigating the effects of an NPK fertilizer on the strength characteristics of soil

Various agricultural practices, including the use of fertilizers, have been shown to impact the physical structure of soil. However, the effects of these practices on the geomechanical properties of soil have not been fully explored. Additionally, conflicting results from different agricultural studies present challenges for geotechnical engineers while assessing the response of soils treated with fertilizer. This study aims to measure the impact of a commonly used NPK fertilizer (Yara Mila 15-15-15) on a natural sandy soil from California's Central Valley, a region with predominantly agricultural land use. Direct shear and consolidation tests were conducted on soils treated with varying fertilizer concentrations (ranging from 0.5% to 5%) and were compared with baseline measurements of the untreated soils. Companion permeability tests were also conducted to measure changes in the hydraulic conductivity of the soil. Results of this study showed that while the cohesion of the soil increased with increasing fertilizer content, the angle of friction decreased. Compression and recompression indices did not show a specific trend, but the coefficient of consolidation decreased with increasing fertilizer concentration, indicating faster consolidation rates in fertilizer-treated soils than in untreated soils. The hydraulic conductivity measurements also provide supporting evidence as the permeability of the tested soil was found to increase with increasing fertilizer concentrations. These findings suggest that fertilizer amendments may weaken soil’s strength and increase the rate of settlements, which has significant implications for the performance and sustainability of geotechnical systems such as foundations for buildings and other infrastructure projects.

4th Asia-Pacific Conference on Physical Modelling in Geotechnics (ACPMG2024)

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