Challenges and experiences of executing DSM columns in stiff clayey soils: A field validation results

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4. Challenges and experiences of executing DSM columns in stiff clayey soils: A field validation results

The stratigraphy of soils in offshore constructions may necessitate the implementation of soil improvement methods such as deep soil mixing (DSM) to ensure the required design parameters. The DSM method includes incorporating chemical admixtures such as cement into the existing soils. However, executing DSM in offshore regions poses a significant challenge due to the presence of soft fine-graded soils, and stiff cohesive soil layers beneath them. These stiff cohesive soils tend to adhere to the auger blades, resulting in the formation of soil-cement bulbs around the blades (i.e., entrained mixing phenomena). This issue can prevent the proper functioning of mixing blades. The current study demonstrates various challenges and experiences regarding implementing DSM in stiff cohesive clayey soils using results of a comprehensive field validation program conducted by Baspar Pey Iranian (BPI) company in Iran. The subgrade soils consisted of medium stiff lean clay (CL) soils, underlayered by a stiff CL layer. The field validation included seven mix designs with and without water predrilling phases, along with 14 DSM columns. The results demonstrate that the inclusion of a water predrilling phase significantly enhances the uniformity of DSM columns in stiff clayey soils, albeit with a considerable increase in execution time. However, the predrilling phase and additional water in the soil-cement grout may result in less unconfined compression strength (UCS) values when compared to mix designs without the predrilling phase. The experiences gained in this study can serve as a valuable benchmark for practitioners and engineers involved in DSM soil improvement projects.

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

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