Anti-Liquefaction Treatment by Compaction Grouting in Coastal Lagoon Deposits-Paper

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The paper describes anti-liquefaction ground improvement for a real-estate development in Saint-Barthélemy, a high-seismicity area with a design earthquake magnitude of 7.5. The coastal site contains water-saturated, potentially liquefiable clayey-sand lagoon deposits, approximately 5.6–7.2 m thick. Because the site was narrow and bordered by buildings, vibration-intensive methods and deep foundations were unsuitable.<br /><br />Menard treated the deposits using compaction grouting: low-slump cement mortar was injected under pressure to displace and densify surrounding soil. Columns were installed to the underlying weathered bedrock, with a 400 mm diameter and 1.4 m square spacing, giving a 6.4% replacement ratio. The technique can mitigate liquefaction through soil densification, reduced earthquake-induced shear stress, and changes in soil classification; the paper focuses on densification.<br /><br />Theoretical calculations predicted that treatment would increase relative density and raise cone resistance by a factor of two to three. Dynamic penetrometer tests conducted before and after construction confirmed the improvement. Average resistance increased from 1.9–2.9 MPa before treatment to 4.3–7 MPa afterward, corresponding to densification factors of 1.95–3.6 and an average of 2.6. Results also showed that the increase was evident soon after treatment.<br /><br />The authors conclude that compaction grouting effectively densified the lagoon deposits and that measured results broadly matched theoretical predictions. Treatment also supported upgrading the site classification from Eurocode soil class E to C, reducing the estimated maximum horizontal surface acceleration from 0.42g to 0.345g.

Keywords

anti-liquefaction

compaction grouting

soil densification

Saint-Barthélemy

liquefiable deposits

seismic ground improvement

cone resistance

dynamic penetrometer

Eurocode soil classification

earthquake mitigation