Design and Optimization of Olivier Inclusions for Residential Towers on Soft Ground in Auckland: 3D Finite Element Analysis and Field Validation-Paper

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The study describes the design and validation of Olivier rigid inclusions beneath two residential towers on soft ground in Auckland, New Zealand. The eight- and eleven-storey buildings were expected to experience long-term settlements of up to 110 mm and 170 mm, respectively, without ground improvement.<br /><br />The solution used cast-in-place, full-displacement concrete inclusions beneath a 750 mm load transfer platform reinforced with geogrid. To account for complex soil and structural interactions, the authors used calibrated, fully coupled two- and three-dimensional finite element analyses in PLAXIS. Axisymmetric models were used to calibrate 3D embedded-beam elements, which were then applied to model both towers, nearby car parks, and interactions between structures and inclusions. Parametric analyses helped optimize inclusion lengths and spacing.<br /><br />Rather than extending all inclusions to bedrock—potentially requiring lengths over 30 m—the design embedded variable-length inclusions in a stiff to very stiff alluvial layer. Shorter inclusions were placed around foundation perimeters, with lengths increasing toward the centres. The final designs used 10–15 m inclusions beneath Building A and 16–20 m inclusions beneath Building B, with predicted total settlement of approximately 45 mm for each tower.<br /><br />Three full-scale compression load tests on inclusions of different lengths measured less than 5 mm displacement under serviceability loads. These results supported the design assumptions and showed that the predicted performance was conservative. The authors retained the selected lengths to provide a safety margin for variable site conditions. Overall, the study demonstrates how 3D modelling and field testing can support an efficient, cost-conscious alternative to deep foundations for adjacent buildings on soft ground.

Keywords

Olivier rigid inclusions

soft ground

Auckland New Zealand

residential towers

finite element analysis

PLAXIS

load transfer platform

geogrid reinforcement

settlement reduction

compression load tests