| GEOTECHNICAL DIVISION
Confined Groundwater
Zone and Slope Instability in Hillsides of Weathered Igneous Rock in Hong Kong
Date, Time & Venue
10 January 2001 (Wednesday); 5:30pm, refreshments for 6:00 pm; HKIE
Program Highlights
It is customary in Hong Kong to assume that the
hydraulic conductivity of weathered igneous rock decreases with depth or as the rock mass
becomes less decomposed. Generally, groundwater flow studies for slope stability purposes
treat the saprolite as an aquifer and the ‘rockhead’, notionally the upper
surface of a zone dominated by Grade III or less weathered material, as an impermeable
boundary. This talk will examine published hydraulic conductivity data and groundwater
observations and show that such a model may be inappropriate. Evidence is cited to
demonstrate that, at least in some places, a more permeable zone may exist at depth,
either in the lower saprolite or at rockhead. The groundwater flow regime in such a high
hydraulic conductivity zone may be confined, resulting in higher water pressure rise in
response to rainfall than might otherwise be expected. These high pressures may be
responsible for a significant reduction in slope stability. The talk will demonstrate that
misinterpretation of the hydraulic conductivity profile will lead to incorrect groundwater
flow and slope failure models. In addition to slope stability study, the presence of a confined groundwater zone in the weathering profile may
have implications for tunnelling, bored pile construction and deep excavations.
Speaker
Dr Jimmy Jiao obtained his PhD
in the Department of Civil Engineering at the University of Birmingham, UK in 1993. From
1994-1996, he worked as a post-doctoral research fellow in the Department of Geosciences
at the University of Alabama, USA. He joined the Department of Earth Sciences at the
University of Hong Kong as an Assistant Professor in 1997. Much of Dr Jiao's research
involves groundwater-related geotechnical and environmental problems. Currently, his
research interest includes impact of groundwater flow on slope stability, modification of
groundwater regimes by land reclamation, and groundwater contamination due to urban
development in the Pearl Delta River region.
Book Prizes
Up to two Book Prizes will be awarded to young members who submit reports on the meeting
to Ir Dr J-H Yin and judged by the Geotechnical Division Committee to be of sufficient
merits.
Registration & Enquiries
No prior registration is required. For enquiry, please contact Ir Dr P L R Pang, Tel: 2762
5362 or Ir Patrick A Chao, Tel: 2378 4488.
Photos (taken
by Dr HC Chan)
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