Settlement of test fills for Chek Lap Kok Airport

Embankments were constructed about 200 m offshore from Chek Lap Kok to examine the feasibility of using vertical drains to allow successful airport reclamation over the very soft marine clay forming the seabed. Settlement and pore water pressure observations are available over a period of about 600 days. ILLICON methodology was used to evaluate oedometer data, to obtain information on compressibility and permeability of seabed, and to predict and interpret pore water pressure and settlement profiles under the embankments. At Chek Lap Kok, the mobilized discharge capacity, q_w(mob) of Alidrains was less than the initial minimum discharge capacity, q_w(min) required for negligible well resistance; however, as horizontal permeability of marine clay decreased during consolidation, the required q_w(min) decreased and Alidrains functioned quite adequately. The sand drains which were installed after significant undrained loading of the soft seabed, were intruded by the soft clay. The mobilized permeability of contaminated sand drain, k_w(mob) was significantly less than the permeability of clean sand. However, as k_w(min) required for negligible well resistance decreased substantially during consolidation, the sand drains did enhance consolidation rate of the soft marine clay.