ABSTRACT
The city of Launceston is situated at the confluence of two major rivers, where they enter a drowned river valley. It is traversed by major fault lines (thought to be inactive), and encompasses both swamp plains and steep slopes of more than 40°. It has grown to a city of 60,000 inhabitants in less than 200 years since it was founded, and currently faces an unusually wide range of major engineering problems which were not recognised at the time of settlement.
These problems include: highly expansive soils, major and extensive landslip, flooding and river sedimentation, deep soft soils (nearly quicksilt), variable layered and lensed alluvials, and the largely unknown risks associated with seismic action. Almost no part of the city is exempted from one or more of these problems requiring engineering solution.
Not all the problems are natural hazards. Landslip and sedimentation, for example, are substantially influenced by development practices. Thus the geomorphology of the Tamar river basin has greatly accelerated since first settlement. This report draws on historical records as well as recent investigations to show the importance of recognising how dynamic landform change influences the choice of engineering solutions for the various soil stability problems. In effect, there is a need to work with nature rather than against it.
