Posted by: Marc Hendrickx | April 2, 2015

NSW RMS Geotechnical Conference 2015

We were asked to present at the 2015 NSW RMS Geotechnical Conference held at the Power house Museum in March. Subject of our talk was on the geotechnical aspects of the recently completed slope works at Clyde Mtn on the Kings Highway.

Abstract is outlined below:
Clyde Mountain, Kings Highway: Slip sliding away…Not

Kings Highway is the main link between Canberra and the NSW coast at Bateman’s Bay. The section of the highway across the top of Clyde Mountain, east of Braidwood follows a route laid out by Sir Thomas Mitchell in the 1850s and cuts through very steep, densely forested terrane. The road in this section has a long history of instability and is affected by landslides from above and embankment failures below.

The main landslides above the road have their origin in construction works in the late 1950s and early 1960s, where widening the road to a modern standard undercut unfavourably inclined meta-sedimentary rock strata. This provided the potential for large scale planar failures on bedding to occur. The first landslide event involved about 30,000m3 and occurred on December 15, 1959 while widening works were in progress. Another landslide of about 5000m3 occurred on October 28, 1993. At this time workers installing concrete drains at below the slope reported the mountain groaning and observed small rock falls. A subsequent engineering inspection found an open tension crack above the slope. The road was closed and the slide occurred an hour or so later. On April 20, 2012 a smaller slide of about 930m3 occurred following heavy rain and damaged rock fall fences. On Tuesday June 25, 2013 a section of the crest of the 1993 failure slipped following a >200mm rainfall event resulting in about 600m3 coming to rest against the existing rock fall fence which burst in a number of sections but prevented most of the landslide debris reaching the road. In addition to these larger failures smaller rock falls and slips are common but generally go unreported. The area has also been affected by embankment failures below the road with repairs undertaken in 1975.

Prior to the early 2000’s the only preventative measures in place were a series of light weight rock fall fences. These were replaced in the early 2000’s by a series of RMS Type 3 rigid rock fall fences with an estimated capacity of about 350kJ. At the same time a series of draped mesh installations, shotcrete and rock bolts were installed to reduce landslide risk.

Following the 2012 event RMS engaged Marchgeo to undertake an investigation to better understand the geology, history of failures and to develop remedial measures to reduce the likelihood of failures affecting the road over the short to medium term.

The large landslides are planar failures on bedding planes best developed where the road and bedding are parallel. Where there is a slight difference in orientation, potential wedge style failures dominate. Rainfall is a major factor in triggering some of the slide events, but lack of an onsite rain gauge (until recently) has made it difficult to match historical events to precise rainfall figures. The study highlighted the importance of keeping accurate records of past failures, with the dates of previous slides being obtained from third party sources.

Remediation focused on reducing the likelihood of further large slides. This was done in two stages in 2013 and 2014. Initial work involved extensive de-vegetation, hazard mapping, and extensive scaling with blasting, machine and hand tools. The 2013 landslide occurred during this period of works. The second phase involved further development of the scope with the main construction phase of long term measures occurring between April-September, 2014. Works included installation of a series of reinforced shotcrete toe buttresses pinned back into the slope with long rock anchors that cross cut potential failure surfaces, along with additional scaling, spot bolting and shotcrete. Draped mesh (Geobrugg – Deltax) was used to control small rock falls across the slope. In addition to reducing the likelihood of small rock falls reaching the road the mesh is intended to reduce the rock fall risk to workers involved in clearing debris from behind the fences. Prior to the mesh being installed the fences were subject to puncture damage from high velocity impacts from small rock falls that contributed to a loss of capacity over time. The mesh now prevents these high velocity impacts and helps extend the life of the fences that were also extensively repaired.

Repair of a fill embankment downhill from Pooh Bear corner by soil nailing was also undertaken as part of the remedial works.


One of the figures used:

Clyde geotech model

Clyde Mountain: simplified geotechnical model for 2012 failure zone.


Posted by: Marc Hendrickx | February 28, 2015

New Landslide maps for US state…where are ours?

The US State of Oregon has developed a new series of landslide maps showing susceptibility of their highway network to a large scale earthquake.  see

In NSW we don’t have an up to date Engineering Geological map of our State’s capital. It is long overdue for a series of detailed Engineering Geology maps to be produced for the states larger population centres!


Posted by: Marc Hendrickx | February 26, 2015

New NOA research from the US

Interesting results on new sources of NOA from Nevada. It would be worth looking at similar igneous systems in Australia.

Mesothelioma in southern Nevada likely result of asbestos in environment
February 10, 2015
International Association for the Study of Lung Cancer
Malignant mesothelioma has been found at higher than expected levels in women and in individuals younger than 55 years old in the southern Nevada counties of Clark and Nye, likewise in the same region carcinogenic mineral fibers including actinolite asbestos, erionite, winchite, magnesioriebeckite and richterite were discovered. These data suggest that these elevated numbers of malignant mesothelioma cases are linked to environmental exposure of carcinogenic mineral fibers.


Posted by: Marc Hendrickx | December 30, 2014

Happy New Year

The stats helper monkeys prepared a 2014 annual report for this blog.

Here’s an excerpt:

A San Francisco cable car holds 60 people. This blog was viewed about 1,500 times in 2014. If it were a cable car, it would take about 25 trips to carry that many people.

Click here to see the complete report.

Posted by: Marc Hendrickx | November 9, 2014

RMS Slope Risk Analysis Training

We have been acting as the lead trainers for RMS Guide to Slope Risk Analysis Ver. 4 training since 2012 (Marc has been involved with the slopes program since the early 2000s). Accreditation for completion of training is through courses conducted by NSW Roads and Maritime Services.

Contact Marc to discuss your training needs.

Posted by: Marc Hendrickx | August 25, 2014

Slope remedial works Summerland Way

Marchgeo provided design and supervison for cutting rehab works on the Summerland Way north of Kyogle in August. The video below just one of a number of large rocks removed. Risk now down to ARL4!

Posted by: Marc Hendrickx | June 4, 2014

International Rockfall Protection Conference 2014

Marc attended the International Rockfall Protection Conference 2014 hosted by Geobrugg in Switzerland and Austria over May 21 to 28, 2014. The conference included a field test of Geobrugg’s 500kJ flexible rockfall protection canopy at their testing facility in Wallenstadt. Following technical talks a tour was held of remedial sites in Switzerland, Austria and Southern Germany. Among the numerous installations visited was the large rock fall canopy along the spectacular Route des Pontes, in the Canton of Valais:Image

The tour provided invaluable information about state of the art slope remedial works.

Posted by: Marc Hendrickx | April 9, 2014

Clyde Mountain works continue

Marc is involved in the second stage works at Clyde Mountain. an interesting and challenging site. RMS providing updates via the following website:

Marking up works in the 1993 slide area

Marking up works in the 1993 slide area

Posted by: Marc Hendrickx | September 26, 2013

Slope Stability 2013

Slope Stability 2013 will provide a forum for open pit mining and civil engineering practitioners, consultants, researchers and suppliers worldwide to exchange views on best practice and state-of-the-art slope technologies. Best practice with respect to pit slope investigations, design, implementation and performance monitoring will be discussed during the symposium.

The ACG is delighted to host this symposium in Brisbane for the first time. Past symposia have been held in Vancouver, Canada, 2011; Santiago, Chile, 2009; Perth, Australia, 2007; and Cape Town, South Africa, 2006.


We are attending this Friday

Posted by: Marc Hendrickx | June 14, 2013

Clyde Mountain Stabilisation works

We are currently assisting RMS with slope stabilisation works at Clyde Mountain on the Kings Highway. The area has a long history of landslides driven by a coincidence of road geometry and bedding. Widening works in the late 1950s undercut bedding dipping steeply into the road way leading to the current problems. Failures occurred during widening (1959-about 30,000m3), in 1993 (about 5,000m3) and last year (April 2012-about 1000m3).

1993 slide BW

Kings Highway, Clyde Mountain. Landslide of 28/10/1993. From front page of The Canberra TImes 30/10/1993



Marc Hendrickx assessing potential planar rock slide west flank of 1993 landslide. This material was successfully removed by machine scaling.


More information about the project available through the RMS website.


« Newer Posts - Older Posts »