Compaction Grouting Intervention for the Mitigation of Soil Liquefaction Risk within the Earthquake-Stricken Area of Emilia in 2012-Paper

Paper

Pdf Summary

The paper describes compaction grouting to reduce liquefaction risk beneath a new school and kindergarten in earthquake-affected Emilia, Italy. Site investigations identified saturated silty sand from about 1.5–7 m depth. Liquefaction analyses found an average factor of safety of 0.75 and moderate-to-high risk.<br /><br />Designers developed a method to determine the minimum cone resistance needed to meet the required safety factor, then used this target to set column spacing and diameter. The initial design comprised 888 columns on a 1.75 m square grid. A trial field showed that ground heave reduced densification, particularly near column bases. The design was therefore revised: columns retained 1.75 m spacing, increased to 700 mm diameter in their lower section, and extended 0.5 m into the underlying clay.<br /><br />Post-treatment CPTU tests showed substantial increases in cone resistance. Shear-wave velocities also increased by approximately 100–200 m/s, generally reaching 200–350 m/s. Liquefaction analyses using measured shear-wave velocities confirmed the treatment’s effectiveness. Ground heave was generally 10–20 cm, with localized peaks up to 29 cm.<br /><br />Because treatment changes CPT-derived soil behavior indices, the authors recommend assessing improvement through the Soil Improvement Index (SII)—the ratio of post- to pre-treatment cone resistance—rather than repeating CPTU-based liquefaction analyses. Post-treatment assessments should instead use shear-wave velocities measured by seismic cone testing or tomography, not correlations based on cone resistance. The study also emphasizes trial-field validation and careful heave monitoring when designing and executing compaction grouting.

Keywords

compaction grouting

liquefaction mitigation

cone resistance

shear-wave velocity

CPTU

soil improvement index

ground heave

earthquake engineering

saturated silty sand

Emilia Italy