Southern region

Lawrence Hargrave Drive - northern amphitheatre embankment slip

RMS has undertaken a range of work to increase stability in the embankment in the northern amphitheatre on Lawrence Hargrave Drive since a land slip occurred in March 2012.

This work has focussed on construction of a sea wall to protect the embankment from erosion and drainage work and the installation of depressurisation wells to decrease water pressure in the slip.

RMS is continuing to monitor and review the impact of this work on the stability of the slope. This includes reviewing real time monitoring data and evaluating the movement within the embankment, and the water pressure level. See the management of instability page for further details.

This information is helping to guide the continued management of the embankment in the northern amphitheatre.

Next Steps

During the second half of 2013 RMS will continue with a range of minor work at the site, including installing access gates and asset protection work. This work will be completed with only minor impacts to road users. Lawrence Hargrave Drive may be reduced to one lane during some stages of some of the work, but through access will be maintained at all times. There will be no impact to pedestrian access.

Project Overview

Slippages are a characteristic of the northern amphitheatre on Lawrence Hargrave Drive because of its exposure to the ocean and the unstable geology. RMS has been monitoring and treating instability along Lawrence Hargrave Drive for many years.

In 2006 the embankment in the northern amphitheatre dropped approximately eight centimetres. In 2008 it dropped a further two metres. In July 2011 there was a storm event that caused a further 1.5 metre movement and a new slip area.

In December 2011 RMS undertook further investigation drilling and installed new monitoring equipment to better understand the extent of the slip, respond quickly to changing conditions, and help develop potential stabilisation measures for the embankment. RMS is now actively remotely monitoring this area.

This monitoring also provides real time measurements of rainfall, movement and water pressures.

During March 2012 movement of around two metres was detected. Monitoring during the slip indicated that the water level in the embankment was high, contributing to the movement.

RMS has worked to decrease the ground water pressure and help to increase stability in the embankment. This involved drainage work to divert surface water away from the embankment, and drilling wells to reduce ground water pressure in the embankment.

Seven wells have been drilled in the embankment on the western and eastern side of Lawrence Hargrave Drive.

Additional drainage pits have been installed on the eastern side of the road to divert water away from the slip area.

Further information

Please contact Peter Hawkins, Project Manager on phone (02) 4221 2582 or email southernprojects@rta.nsw.gov.au.

Embankment slip animation

Concreting the base of the catch ditch Concreting the base of the catch ditch Concreting the base of the catch ditch Increasing the height of the catch ditch Increasing the height of the catch ditch Increasing the height of the catch ditch Increasing the height of the catch ditch The access track and erosion protection The access track and erosion protection Delivering material to the site Contractors Coastwide Civil beginning construction of the sea wall Contractors Coastwide Civil meeting with RMS staff on site Construction of the sea wall Construction of the sea wall - the 4-6 tonne basalt blocks used in the construction of the sea wall Construction of the sea wall Construction of the sea wall Construction of the sea wall Construction of the sea wall Construction of the sea wall Construction of the sea wall - site meeting between RMS and Coastwide Civil discussing the progress of the works Construction of the sea wall Construction of the sea wall - nearing completion Construction of the sea wall - placement of 4-6 tonne basalt boulders Construction of the sea wall - placement of 4-6 tonne basalt boulders Completion of works and site decommissioning Completion of works from southern rock platform Rain gauge Drilling wells to decrease water pressure in the embankment Catch ditch: The catch ditch on the western side of Lawrence Hargrave Drive.  The catch ditch will be raised by around one metre New trench drain has been constructed to divert water away from the slip area. New trench drain has been constructed to divert water away from the slip area New concrete pit which connects into an existing culvert drain to divert water away from the slip area New concrete kerbing to divert water away from the slip area Three concrete pedestrian walkway slabs have been replaced at a steeper grade to divert water  away from the slip area A new concrete pit has been constructed which connects into an existing culvert drain Lawrence Hargrave Drive slip area
Locality map Before slip cross section After slip cross section