Effects of Confining Stress During Curing and Shearing on Shear Strength of Lime-Cement Improved Clays-Paper

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The study examines how confining stress during curing and shearing affects the strength of lime-cement-treated clays, using laboratory tests on clay from Klett and direct simple shear (DSS) tests on columns from Drammen.<br /><br />At Klett, samples cured for 28 days under effective stresses of 0, 200, or 400 kPa were tested in unconfined compression and triaxial compression. Higher curing stress produced a modest strength increase: raising it from 0 to 400 kPa increased average compressive strength by about 1.2–1.5 times. Higher confining stress during shearing had a much larger effect, increasing strength by an average factor of about 1.9 per 100 kPa increase in stress. It also changed failure behaviour from brittle to more ductile.<br /><br />DSS tests on high-strength Drammen columns showed increasing shear stiffness with greater consolidation stress, but no clear increase in peak shear strength over the tested range. The authors suggest that stress effects may be less evident in already strong treated soils.<br /><br />Field strengths estimated from reversed column penetration tests were generally 40–250% higher than laboratory strengths, averaging roughly twice as high. This comparison is uncertain because the methods measure different failure conditions, and penetration-test strength estimates are themselves uncertain.<br /><br />The findings are relevant to design, particularly for deep excavations: excavation reduces confining stress in treated soil and may therefore reduce its available shear strength. Designers should consider stress conditions during both curing and shearing, while accounting for soil variability, test-method differences, and the strain compatibility needed between treated and untreated soil.

Keywords

lime-cement-treated clays

confining stress

curing stress

shearing stress

direct simple shear

compressive strength

shear stiffness

field strength

deep excavations

soil treatment design