Case Studies of Ground Improvement Using Rammed Aggregate Piers in Problematic Soils Allowing for Conventional Foundation-Paper

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The paper presents two British Columbia projects demonstrating the use of rammed aggregate piers (APs) to improve weak soils and enable conventional foundations instead of deep piles or large raft foundations. APs are 600 mm-diameter compacted aggregate columns installed beneath building footings to increase soil stiffness and bearing capacity.<br /><br />At the four-storey Fine Arts University building in Vancouver, loose fills overlay soft glaciomarine silt. The design installed 2,158 APs, extending 4–14 m through the weak deposits to dense till or sandstone. This replaced the originally proposed pile foundations and shortened the construction schedule.<br /><br />At the four-storey Kelowna police services building, fills and loose-to-compact sandy soils overlay clayey silt. A total of 673 APs, designed to improve the upper 8 m of soil, replaced a proposed preload and raft foundation.<br /><br />Full-scale load tests at both sites showed acceptable performance. At the 200 kN service load, measured creep displacements were below 1 mm over the test holding period. The projects increased design bearing capacity from 150 kPa to 300 kPa, allowing pad and strip footings while meeting the required settlement limit of less than 25 mm.<br /><br />The case studies show that AP ground improvement can provide a cost- and schedule-effective alternative to deep or raft foundations in challenging urban soil conditions.

Keywords

rammed aggregate piers

ground improvement

weak soils

British Columbia

foundation design

bearing capacity

settlement control

load tests

soil stiffness

urban construction