The site for a new two-story classroom building was underlain by a 4.57 mthick layer of natural marsh deposit consisting of very soft organic clay. The specialtycontractor provided a design-build solution of mass stabilization, a dry soil mixingtechnique, to increase the shear strength and decrease the compressibility of theorganic clay insitu. This method allowed the structure to be founded on shallowspread footings without soil replacement or deep foundations. Total settlement of thebuilding, on shallow foundations designed for an allowable bearing capacity of 192kPa, was limited to 25.4 mm, with differential settlement on the order of 12 mm. DryPortland cement was pneumatically pumped to a high-speed mixing tool mounted ontrack hoe arm. The clay and cement were systematically mixed insitu to proportionsdetermined by a pre-production laboratory mix design program. Post-treatmenttesting consisting of laboratory Unconfined Compressive Strength, ConePenetrometer and Column Penetration testing confirmed that the required strengthwas achieved. This paper presents the design, construction, and quality control testingof the mass stabilization program. A pre and post-treatment test data comparisonshows the extent of the improvement of the treated soil. No significant settlement wasmeasured during or after construction.
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