Prediction, Testing, and Analysis of a 50 m Long Pile in Soft Marine Clay-Article

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The study reports a static load test of a 50 m long, instrumented precast concrete pile driven into soft, normally consolidated marine clay in Göteborg, Sweden. The clay extended to roughly 90 m depth, with undrained shear strength increasing from about 20 kPa at 10 m to 80 kPa at 55 m. The test was conducted 210 days after installation.<br /><br />The pile reached a peak load of approximately 1,800 kN at 22 mm of head movement, while the toe moved only 3 mm; most displacement resulted from pile compression. Strain-gage measurements indicated an axial stiffness of 3.25 GN and an estimated concrete modulus of 34.3 GPa. Analysis showed that shaft resistance dominated and was consistent with an effective-stress beta coefficient of about 0.19. Toe resistance was small. The results also indicated residual force in the pile, attributed to clay reconsolidation after driving, which affected interpretation of the measured load distribution.<br /><br />Before the test, 22 engineers from 10 countries submitted predictions of the pile’s load–movement response. Predictions varied substantially: estimated peak loads ranged from 65% to 200% of the measured peak, and predicted loads at 22 mm movement ranged from 35% to 300% of the actual value. The study also found considerable variation in predicted stiffness and displacement, and differing interpretations of “capacity.”<br /><br />The authors conclude that the test provides useful evidence on the behavior of long, floating piles in soft clay and highlights the variability in current engineering prediction methods and capacity definitions.

Keywords

static load test

precast concrete pile

soft marine clay

Göteborg Sweden

shaft resistance

toe resistance

effective-stress beta coefficient

pile compression

residual force

pile capacity prediction