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Slope Management

The national Slope Management System (SMS) has become fully operational in the northern, southern and western regions during the past year, whereas in the eastern region the first two stages of the system is still under development.

 

 

Extra-ordinary heavy rains encountered along the southern Cape coastal region,

during August and September 2006, caused a number of unexpected failures in the Kaaimans River Pass – Wilderness area on the N2 route in the western region, also westwards at Glentana / Groot Brak River and eastwards as far as Grahamstown in the southern region. These events once again highlighted the hazards and costs involved, as well as the high level of inconvenience caused to road users during the remedial work period when alternative routes are not available.

The management of the degree of risk allocated to individual slopes

\\to individual slopes across the country has thus far rendered a satisfactory degree of confidence (even for those areas and sites with a record of previous instability), despite the shortcomings of not being able to timeously avoid, predict or pinpoint slope failures caused by inordinate rains. The various slope failures that occurred in the Kaaimans Pass to Groot Brak area and at the Grahamstown cutting are typical examples.

Other high risk sites pointed out by the SMS surveys have in the interim also been earmarked for particular remedial or precautionary measure works during the 2006/2007 and 2007/2008 financial years, and include the following:

Southern Region
  • Olifantskop Pass cutting * (N10/1)
  • Barberskrans Pass * (N10/3)
  • Grahamstown High Embankment * (N2/13)
  • Jamestown fill (N6/5)
  • Queenstown – Confimvaba, 2 cuttings (R61/5)
  • Witkrans Nek Cutting (N10/4)

Note: *: Remedial work currently in process or already completed

Northern Region
  • Loskop Dam Cutting (N11/10)
Western Region
  • Groot Brak embankment (N2/7)
  • Various small cutting / embankment failures between George and Mossel Bay (N2/6 & 7)

In the southern region alone, the SMS surveys have furthermore identified another 37 sites with significant risk (medium to high risk) requiring precautionary remedial work during the next two financial years (say), in order to avoid failures or partial failures before they occur.

Two more sites in the western region have been added to the list requiring more detailed investigation and monitoring, viz the Van Rhyn’s dorp Pass embankment/cutting (route R27) and an embankment at Groot Brak (km 5.0 N2/7)

As far as the long-term asset maintenance to permanently anchored slopes, walls and foundations are concerned, another SANRAL contract has been let during the past year to do the necessary lift-off tests and permanent anchor head inspections at the Plettenberg Bay Heights laterally supported pile walls (N2), also at the Dolphin’s Point cutting (N2) and at the Florence – Worcester cutting (N2), all in the western region. The N3TC Concessionaire also let a similar contract at SANRAL’s insistence, to verify the permanent anchor loads of the laterally supported pile walls at Van Reenen’s Pass.