A Deep Soil Mixing Application for a Road Slip Fast Repair-Paper

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The paper presents a rapid repair of an unstable section of Italy’s SR2 Cassia Road near Siena, where movement of weathered slope soils had caused pavement depressions, extensive cracking, and up to 50–80 cm of displacement. The affected downstream lane was closed, while traffic was diverted to the upstream lane.<br /><br />To improve road stability with limited traffic disruption, the project used deep soil mixing from the road surface. Cement-treated columns, 600 mm in diameter and 3.5–6.2 m deep, were installed in three patterns: isolated columns beneath the upstream lane, a triangular column arrangement beneath the inner downstream lane, and reinforced, overlapping columns forming shear walls along the outer downstream lane. Finite-element analyses indicated that the treatment would transfer road loads to stronger ground and substantially reduce roadway movement. They also showed that movement beyond the treated area would continue, so the work was an urgent, localized repair—not a solution to the entire slope instability.<br /><br />Construction was monitored in real time. The authors developed a wet-sampling procedure to obtain representative specimens from fresh soil-cement columns for laboratory testing. Tests produced an average unconfined compressive strength of about 7.6 MPa and a characteristic strength of about 6.16 MPa, exceeding the design requirement.<br /><br />The case demonstrates that deep soil mixing can provide a relatively fast, economical road repair with only partial and short-term traffic restrictions. Comprehensive stabilization of the broader slope would require further investigation and more extensive investment.

Keywords

deep soil mixing

road repair

slope instability

Italy SR2 Cassia Road

soil-cement columns

finite-element analysis

traffic diversion

unconfined compressive strength

roadway stabilization

weathered slope soils