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

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A large transportation project in the Middle East encountered soft silts and clays beneath loose sands, with substantial expected static settlement and liquefaction risk. Rammed Aggregate Pier (RAP) ground improvement was selected to support pavement and fill, control settlement, and improve ground performance.<br /><br />The study reports a full-scale zone load test of a 7.5 m square concrete footing supported by 600 mm diameter Impact piers, installed at 2.6 m spacing and extending approximately 10.5–12.5 m below the test platform. The footing was loaded to 150 kPa, the specified allowable bearing pressure, and monitored for 24 hours at full load. Post-installation cone penetration tests indicated significant densification in the upper sands, though little improvement in the fine-grained silts.<br /><br />At the design load, average settlement was approximately 30 mm, within the project’s 50 mm limit. The largest differential settlement was 10 mm over 10.4 m. Settlement developed rapidly during loading. The authors suggest that much of the load was carried by the densified upper sands and that the permeable piers provided drainage that accelerated consolidation of the silts.<br /><br />Back-calculations using a composite elastic modulus approach indicated that pier stiffness in the soft silts was higher than initially assumed, while estimates for the sands were broadly consistent with expectations. The test provides valuable large-area performance data for RAP systems, while the authors note that the contribution of rapid impact compaction to observed sand densification could not be separated from the effects of pier installation.

Keywords

Rammed Aggregate Pier

ground improvement

settlement control

liquefaction risk

soft silts

loose sands

zone load test

bearing capacity

cone penetration test

consolidation drainage