Comparison of Cement Injection Options for Deep Mixing-Paper

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The study compares two cement-injection methods for deep-mixing (DM) columns used to stabilize an earth bund and limit seepage: injection during tool penetration and injection during tool withdrawal. A field trial installed 18 blocks with varying cement contents (120, 140, and 160 kg/m³) in marine clay, silt, sand, and residual soils. Cores collected after 28 and 91 days were tested for unconfined compressive strength (UCS) and permeability.<br /><br />Penetration injection generally produced more uniform strength and lower permeability than withdrawal injection, likely because the soil receives additional mixing during tool retrieval. However, both methods yielded substantial variation in strength with depth, reflecting changes in soil type and properties. Withdrawal-injection columns showed somewhat greater strength variability. Permeability also depended on soil type; treated sand tended to be more permeable. Some results met the proposed permeability limits, but not all.<br /><br />The trial columns generally exceeded the intended strength range, with samples above the proposed 450 kPa upper limit. The authors recommend reducing cement content to achieve adequate—not excessive—strength, improve ductility, lower costs, and reduce the risk of cracking that could compromise seepage control. Cement content and mixing procedures may also need adjustment for different soil layers.<br /><br />The proposed quality-control programme combines digital monitoring of installation parameters (including mixing time, grout flow, rotation speed, and mixing energy) with continuous coring and strength and permeability testing. It sets indicative acceptance criteria for both properties and calls for site trials to establish operating curves and refine procedures before full construction. The authors emphasize that further trials are needed to achieve consistent columns meeting both stability and seepage-control requirements.

Keywords

deep-mixing columns

cement injection

penetration injection

withdrawal injection

marine clay

unconfined compressive strength

permeability

quality control

seepage control

cement content