Jet Grouted Columns-Ground Improvement for Liquefaction Resistance

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The case study describes jet-grout column ground improvement at a sewage treatment plant site in Tunasan, Muntinlupa City, Philippines, where loose sand and silt layers were vulnerable to liquefaction. The site is near the West Valley Fault, and the design earthquake was magnitude 7.2 with a peak ground acceleration of 0.71g.<br /><br />SPT-based liquefaction analyses using LiquefyPro identified potentially liquefiable soils mainly between 3 and 20 m depth. Because estimated settlement in the deeper layers was limited and some silts were considered non-liquefiable based on plasticity, treatment was focused on the critical layer from approximately 3 to 9 m.<br /><br />Stone columns, piles, and jet grouting were considered. Jet-grouted columns were selected because the silty soils were not suitable for vibration-based densification and the method suited site conditions and available equipment. Design followed Baez’s stress-concentration approach, treating the columns as stiffer inclusions that redistribute seismic stresses rather than densifying or draining the soil. Columns 0.8 m in diameter were installed on a 1.7 m square grid, with lengths of 8–15 m depending on soil profile and structural loading.<br /><br />Post-installation coring was used to check column diameter and unconfined compressive strength (UCS). Tested cores met the design UCS requirements, supporting the required column shear strength. The study concludes that the jet-grout system satisfied liquefaction mitigation, column strength, and settlement criteria, and demonstrates stress concentration as a viable ground-improvement strategy for the site.

Keywords

jet grouting

ground improvement

liquefaction mitigation

seismic design

silt soils

Tunasan Muntinlupa

West Valley Fault

stress concentration

unconfined compressive strength

sewage treatment plant