Aggregate Pier Group Load Test Results For Large Infrastructure Project In The Middle East-PPT Presentation

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A transportation project in the Middle East required a 2.1 m grade raise and foundations capable of supporting an allowable raft pressure of 150 kPa. Because the site was highly susceptible to liquefaction during a design Mw 7.5 earthquake, the project also specified static settlements below 50 mm and post-liquefaction settlements below 25 mm.<br /><br />The proposed ground improvement used 600 mm-diameter Impact rammed aggregate piers, spaced 2.6 m apart and extending approximately 9–12 m to reach medium-dense sands. A zone load test evaluated the treatment. A concrete footing centered over nine piers was loaded in 25% increments to the full design pressure of 150 kPa. The target load was reached 16 hours after loading began, and settlement was monitored throughout the test.<br /><br />The test showed that the pier system controlled settlement within the project’s specifications. A composite-modulus back-calculation estimated total settlement at 30.9 mm. The analysis indicated that Impact pier stiffness in the soft silts was greater than initially assumed, while stiffness in the sands was close to the original estimate.<br /><br />Settlement developed relatively quickly, likely because much of the load was carried by the densified upper sands and the permeable piers provided drainage paths that accelerated consolidation in the soft silts. Post-installation CPTs indicated good densification in the upper sands, which contained few fines, but little to no improvement in the fine-rich silts. The load test verified static performance; the stated post-liquefaction settlement criterion was a design requirement.

Keywords

ground improvement

Impact rammed aggregate piers

liquefaction mitigation

zone load test

settlement control

raft pressure

post-liquefaction settlement

Middle East transportation project

CPT densification

earthquake design