A Case Study of Passive Piles Failure in Open Excavation-Article

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The paper investigates pile failures during open excavation for pile-cap construction at a site in Malacca, Malaysia. The site had 5–7 m of very soft marine clay, with an average SPT N-value near zero and undrained shear strength of 16–20 kPa, overlying stiff to very stiff soils. After driven piles were installed to support the planned structure, uncontrolled excavation in the soft clay caused extensive damage to 300 mm diameter prestressed spun piles.<br /><br />The authors modelled 21 piles and the staged excavation using a three-dimensional finite-element program with the Hardening Soil model. The analysis represented excavation progressing from an initial 1.55 m depth to 4.5 m at a lift pit and 3.1 m near the affected pile groups. Predicted pile bending moments were compared with the piles’ 20.4 kNm cracking capacity.<br /><br />The model predicted that about 70% of the piles would reach or exceed the cracking threshold; most remaining piles were classified as critical, while only two were predicted to remain uncracked. Field observations showed that all 21 piles had failed. The cracks occurred near the boundary between the soft clay and the underlying stiff layer, consistent with the model’s predicted location of maximum bending.<br /><br />Although the simulation did not reproduce every observed failure, the authors considered its predictions satisfactory given uncertainties in the actual excavation sequence and geometry. They conclude that excavation-induced lateral soil movement in very soft clay can impose damaging bending loads on piles, especially when excavation follows pile installation. Three-dimensional finite-element analysis can help anticipate this risk and inform excavation planning and preventive measures. Key factors include the soft-layer thickness, soil stiffness, pile diameter, and excavation depth.

Keywords

pile failure

open excavation

soft marine clay

finite element analysis

Hardening Soil model

prestressed spun piles

lateral soil movement

bending moment

pile-cap construction

Malacca Malaysia