Lateral Movements of Long-Driven Piles during Pile Driving

Large lateral movements of a pile during impact driving can cause yielding of the surrounding soil. When this happens, the effective stresses between the soil and the pile wall diminish, and the pile shaft resistance decreases. A piling project was carried out in a marble area in Hong Kong, where highly variable rockhead contours and deep depressions filled with weak soil deposits were found. Many steel H-piles were driven to depths of more than 100 m, and the verticality of such long piles was a concern. A pile test program consisting of four driven steel H-piles with pile lengths up to 164.5 m was conducted. Verticality monitoring and dynamic pile tests at several penetration depths were performed. This paper aims at interpreting the verticality of the four long piles, studying the relevance of pile verticality to the encountered geological features, and studying the effect of pile verticality on the pile capacity. The maximum lateral pile movement during driving was up to 8.7 m at a depth of 100 m, and the maximum local pile inclination reached 0.139. The lateral movements of the piles during driving well matched the rockhead inclination and soil conditions. Both one-way sway and two-way cyclic sway of the test piles were observed. Cyclic sway was shown to cause more severe reduction of the pile shaft resistance than one-way sway.