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Highlights
- Detailed geological and hydrogeological mapping and
interpretation
- Integration of geotechnical data and broad concepts
- Assessment of subsidence vulnerability.
Background
Planning and design for the proposed M5 East Motorway highlighted
the need for further assessment of geological and groundwater
conditions in the vicinity of stretches of the motorway
development where cuttings and tunnels were proposed.
C. M. Jewell & Associates Pty Ltd was engaged by Evans
& Peck Management to make the assessment of conditions,
and to report on the geology, hydrogeology and risk of subsidence
resulting from drainage of the shallow groundwater.
Hydrogeological Environment
The motorway alignment crosses areas of mixed surficial,
deeper alluvial and basement sediments of the Hawkesbury
group. The western section cuts through shale and residual
shale soils. The central section crosses areas of Hawkesbury
Sandstone and alluvial sands and clays. Alluvium, in places,
occupies incised channels in the underlying sandstone. The
eastern section crosses clay-rich estuarine sediments. All
sediments mapped were saturated to some extent. Perched
water tables are encountered in sandstone ridges and rises.
Scope
The investigation comprised compilation of geological and
water level data, and the drawing of cross-sections across
the motorway alignment. Review of previous geotechnical
determinations also formed part of the assessment. Conditions
were assessed in this manner over sections of the proposed
motorway alignment totalling approximately 10 kilometres.
The assessment included consideration of structures potentially
affected by vulnerable sediment, such as the South Western
Ocean Outfall Sewer. 
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Projects