Bi-Directional Pile Load Test - Case Studies-Paper

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The paper presents a bi-directional static load test (BDSLT) on a 1.2 m × 2.8 m barrette pile at Singapore’s Great World Station project. Because the excavation and deep foundations required very high test loads, a conventional kentledge test was considered risky. BDSLT instead used six embedded hydraulic jacks, positioned 2.6 m above the pile toe, to apply load upward and downward. The total applied load reached 10,800 tonnes, with 13 levels of embedded strain gauges measuring load transfer along the pile.<br /><br />The test focused on the capacity of the deep G(III) rock layer. It mobilized an ultimate unit shaft friction of 188.4 tonnes/m² in this layer and an end-bearing resistance of 734.5 tonnes/m². The equivalent top-loaded pile settlement was 4.6 mm at the proposed working load and 7.8 mm at 150% of working load—below the respective allowable limits of 7 mm and 14 mm.<br /><br />By applying load directly within the pile and near the layer of interest, BDSLT successfully mobilized deep, stiff strata and confirmed a higher G(III) rock shaft-friction capacity than the initially assumed design value of 90 tonnes/m². The findings enabled consultants to optimize the design and consider shorter working piles.<br /><br />The authors conclude that BDSLT is a useful alternative to conventional static testing when very large loads or deep-layer capacities must be assessed. Successful testing depends on careful jack placement to balance the capacities of the upper and lower pile segments, as well as precise planning and sound pile construction.

Keywords

bi-directional static load test

barrette pile

hydraulic jacks

shaft friction

end-bearing resistance

G(III) rock layer

pile settlement

load transfer

deep foundations

Singapore Great World Station