Static Plate Load Test in Local Foundation Code – A Case Study
DOI:
https://doi.org/10.21467/proceedings.7.7.30Abstract
Footings and raft foundations remain widely used in many countries. Local designs often rely on empirical formulae derived over fifty years ago. Prior to construction, a plate load test is required to verify the allowable bearing capacity of the supporting stratum, as stipulated in the Code of Practice for Foundations by the Buildings Department, first issued in 2004 and revised in 2017. Using a large raft foundation from a project as an example, the author proposes a more practical approach: reverting the test load to three times the working pressure, as specified in the 2004 Code, while increasing the allowable settlement by 2.5 mm to account for elasto-viscous deformation under higher loads. For very large raft foundations, the allowable bearing capacity should be capped, and the test may be eliminated entirely. Additionally, soil stiffness is not a material constant as the secant modulus varies with mean stress levels. As soil modulus degrades with increasing strain, the elastic modulus derived from load-settlement data tends to be stiffer than the design value used for settlement calculations at higher strains. The current approach to deducing operational soil stiffness for design purposes requires reconsideration.
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