Unconfined Compression Tests of Cement-Treated Soil Containing Unmixed Soil-Paper

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The study examined how small amounts of unmixed soil affect the strength and stiffness of cement-treated clay used in deep-mixing ground improvement. Laboratory specimens were made with Fujinomori clay, water, and Portland cement. Consolidated, untreated clay pieces (approximately 5 mm cubes) were randomly placed in the cement-treated slurry at volumetric contents of 0%, 1%, or 2%. Six specimens per condition were cured for seven days and tested in unconfined compression.<br /><br />Mean unconfined compressive strength (UCS) decreased from 1.74 MPa with no untreated clay to 1.59 MPa at 1% content and 1.52 MPa at 2% content—reductions of approximately 9% and 13%, respectively. The modulus of deformation also declined, from 970 MPa to 940 MPa and 850 MPa, corresponding to reductions of about 3% and 12%. Stress–strain behavior remained broadly similar across conditions, and observed failure patterns showed no significant differences. The variability in strength did not consistently increase with untreated-clay content.<br /><br />The results show that even a small proportion of unmixed soil can meaningfully reduce the strength and stiffness of cement-treated ground. Its presence should therefore be considered in design and quality-assurance procedures. The study used a fixed inclusion size and a limited number of specimens; further testing is needed to assess how unmixed-soil size affects overall performance.

Keywords

cement-treated clay

deep mixing

unconfined compressive strength

modulus of deformation

unmixed soil

untreated clay

ground improvement

Fujinomori clay

stress-strain behavior

quality assurance