Landslip 1
The landslip is located along Wattamolla Road, 130 m west of Mountain Road and Wattamolla Road intersection.
Geotechnical engineers have completed investigation work, design work will be completed end of October. Tenders called early November, closing mid-December and construction to commence early 2023.
The site is comprised of a fill formation constructed on a north facing hill and is located above an undulating gully to the north where slope movement has occurred in the past.
The area is located on a large relict landslide which extends 100 m to the west. A significant rotational slide has occurred on the crest of this slide.
Short-term recommendations include:
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Road kept out of service. Given the movement on the slide, it is likely to continue to creep downslope over time, with ongoing repairs required to the road. Remedial works will require support to the edge of the road. The other option is possible water wells to manage the water, but given the location, having this run of solar power etc may be difficult.
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Monitor for ongoing movements.
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Short term reinstatement for drill rig access could be undertaken to allow geotechnical investigation and establish ground conditions. This may facilitate one lane access for local residents - with it noted that such works is likely to be subject to on going creep movements and will not provide a long term solution.
Landslip 2
The landslip is located along Wattamolla Road, about 2.5km west of Mountain Road and Wattamolla Road intersection. Work has been completed.
The site is comprised of a cut and fill formation constructed on a north facing hill and is located above a wide alluvial gully to the north.
The up hill side (cut) is comprised of colluvial soils underlain by rock. The down hill side (fill) is comprised of an very steep embankment retained in part with a concrete retaining wall (which we understand has bored piles supporting it).
Tension cracks are observed through the centreline of the road behind the retaining wall and continue to the east where a notable slip has occurred associated with a gully to the north.
Short-term recommendations include:
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Keep east bound lane out of service. The west bound lane can be opened for local residential access in the short term.
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Monitor for ongoing movements behind the retaining wall.
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Sandbag behind the tension cracks to divert water around the slippage.
Landslip 3
The landslip is located along Wattamolla Road, about 3.5km west of Mountain Road and Wattamolla Road intersection.
Geotechnical engineers have completed investigation work and design work will be completed by end of October with Tenders being called early November, closing mid-December and construction early 2023.