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Investigation of Bovills landslip, near Devonport, Tasmania

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Moon, Alan Thomas 1984 , 'Investigation of Bovills landslip, near Devonport, Tasmania', Unspecified thesis, University of Tasmania.

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Abstract

Bovills Slip occurs in weathered basalt colluvium at the base
of a coastal scarp about 2 km east of Devonport on the north coast of
Tasmania. The colluvium consists of red-brown fissured silty clay with
rock fragments. Many landslips occur in colluvial soils on the coastal
scarp and also in basalt-derived soils elsewhere. Thus a detailed
investigation and stability analysis of Bovills Slip is relevant to the
general slope failure problem in Tasmania.
Pore water pressures measured with open standpipe piezometers show
a correlation with rainfall, with peak pressures occurring during wet
winter months.
Effective shear strength parameters were determined by both multi
stage direct shear tests and consolidated undrained triaxial tests with
pore pressure measurements. Different residual shearing mechanisms were
recognised in the shear box tests. Significantly different values of
residual strength were associated with these different mechanisms. The
fully softened strength parameters appropriate for the analysis of
first-time landslips were investigated by both triaxial and shear box
tests. For the soil tested both the residual and fully softened
effective friction angles showed a pattern of dependence on the plasticity.
Surface movements have been monitored by repeated surveys, and
subsurface movements have been monitored by regularly checking piezometer
tubes for deformation. After heavy rain, in August 1981, the landslip
moved by 20 to 30 mm.
A two dimensional model of the August 1981 failure has been
analysed by limit equilibrium methods. The factor of safety is most
sensitive to variations in piezometric head and cohesion. Analysis has been
used to assess the relative change in factor of safety (stability)
caused by changes in the slope and by remedial measures. The stability
was reduced when the slope was undercut by roadworks in 1973, and the
first movements caused a decrease in shear strength of the soil.
Downslope movements have produced shape changes which have tended to
increase the factor of safety. Toe drainage, toe surcharge, 'and re
grading have already resulted in increased stability. Subsurface
drainage, although effective, would be relatively expensive. Lime
stabilisation and tree planting were also considered. In the long term
well established trees may increase the factor of safety by as much as
50%.
Possible future research on landslips in Tasmania is discussed in
order to demonstrate how the results of this detailed investigation may
be used as a starting point for regional studies.

Item Type: Thesis - Unspecified
Authors/Creators:Moon, Alan Thomas
Keywords: Slopes (Physical geography), Slopes (Soil mechanics), Landslides
Copyright Holders: The Author
Copyright Information:

Copyright 1984 the author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (M.Sc.)--University of Tasmania, 1984. Includes bibliography

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