Engineering geology of north Lantau; discussion and reply

M. D. Howat writes: The authors' review is admirably complete yet makes no mention of the sensitivity of the marine clays, especially in relation to the problems posed by the so-called "lower marine deposits" which could be attributed either to the base of the Hang Hau or the top of the Chek Lap Kok Formations. The sensitivity of the marine soils of Hong Kong, first reported by Holt (1962), was noted in North Lantau boreholes by Fung et al. (1984) and observed in situ by Howat (1985, 1987) in excavations and tunnels for the Island Line of the Hong Kong Mass Transit Railway. The sensitivity can be gauged on Fig. 1 which compares the Chek Lap Kok liquidities with those of the sensitive clays analysed by Skempton & Northey (1952). There was at the time of publication some discussion on its engineering significance (Endicott 1984; Howat 1984). While this sensitivity may not pose a particular problem for the very weak upper marine deposits, whose yield stresses are exceeded during large-scale reclamation allowing consolidation to occur (Koutsoftas & Cheung 1985), it could be vital for the stiffer lower marine deposits whose higher yield stresses are approached, but not exceeded, and can therefore find themselves in a rather delicate metastable condition after a considerable thickness of fill has been placed. The gradual breakdown of the resulting highly stressed soil structure with time can explain the 'stagnation of pore pressure dissipation' (continuous regeneration of excess pore pressures?) to which the authors allude. The ... This 250-word extract was created in the absence of an abstract.