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Tue, Sep 01, 2015

Sinkholes and Subsidences

Peer review Service

The lack of access to geotechnical expertise makes assessment of these reports difficult for many government authorities.  Being an expert body with more than 60 years institutional memory, and with no vested interest, the CGS is able to provide an independent review service to local and national authorities of the quality of dolomite development reports.

The history of this service to government authorities is detailed in the following paper which can be downloaded by clicking HERE .


The CGS has developed guidelines for development to guide:

a)    Consultants on the requirements for dolomite stability investigations.

b)    Developers, planners, authorities on the risks associated with development on dolomitic land 

The  Council for Geoscience (CGS) have produced guidelines for consultants entitled “Approach to sites on dolomite land, November 2007”. These guidelines are to be read in conjunction with the “G


uidelines for engineering geological characterisation and development of dolomite land” produced in conjunction with the South African Institute of Engineering Geologists (SAIEG) in 2003 (‘little yellow book’). The more recent document does not replace the earlier one rather it adds to it and provides functional information on how the CGS entertains submissions made to it in terms of local and provincial authorities and NHBRC requirements.  These guidelines were initially published by the CGS in conjunction with SAIEG in 2004 and are known as the ‘little yellow book’, which can still be purchased from the CGS bookstore. This set has now been replaced by an updated version, which can be downloaded by clicking HERE .

Ever increasing demands for more intense use of dolomitic land, which unfortunately is susceptible to sinkhole formation, results in more people inhabiting and infra structure being erected on such land. The purpose of these guidelines from the CGS is to provide a  standard for a) dolomite stability risk investigations and assessment and b) recognition of appropriate development of this type of risk surface.

What it’s about

The CGS Guideline is divided into a number of sections:

  • The initial sections give a brief overview of legal responsibilities and obligations for practicioners, local authorities and the role of the CGS in development on land underlain by dolomite.
  • The middle chapters cover minimum investigative and reporting requirements for dolomite stability investigations.
  • The later chapters cover appropriate development types including development densities and specific matters relating to types of development. The information service provided by the Council’s Dolomite Databank which supplies positions of existing boreholes and reports is also described.
  • Also described is the process of enrolment with the National Homebuilders Registration Council (NHBRC) who require that the CGS review the proposed development and co-sign their B4 form.

Who it’s for

The CGS Guideline is aimed at engineering geologists, geotechnical engineers, planners, municipal authorities etc. As this is a developing science new techniques and approaches, are continually developing and this latest guideline attempts to provide the latest approaches to these matters.

How to use it

The 2007 Guideline is around 32 pages long, is a handy guide, also available in digital form from the CGS. Different users may need different types of information from the Guide such as the number of drill holes per hectare for an investigation or the development densities supported by the CGS.

The 2004 Guideline describes:

  • the geological nature of dolomite rock in South Africa,
  • the process of sinkhole formation and their size classification
  • the NHBRC enrolment process
  • the necessary requirements for typical dolomite stability investigations
  • risk assessment
  • the selection of appropriate development types
  • suitable foundation types appropriate to the expected sinkhole size
  • the importance of preparing well thought out, tailor made risk management plans for each individual site.

This guideline is available to be purchased from the CGS shop.

Further information

Information about the Guideline and about the CGS policies on stability investigations and approach to development can be found on this website. The CGS can be contacted at: +27 12 841 1165 (Greg Heath) for specific information on developing on dolomite.

It should be noted that these Guidelines will more than likely be surpassed by proposed guidelines of the South African National Bureau of Standards (SANS) during mid-2009. These standards will be known as:

  • SANS 10400-B    The Application of the National Building Regulations, Structural Design
  • SANS 1936 -1:    General Principles and Requirements
  • SANS 1936-2:    Geotechnical Investigations and Determinations
  • SANS 1936-3:    Design and construction of buildings, structures and infrastructure
  • SANS 1936-4    Risk Management
  • SANS 633    Profiling, percussion borehole and core logging in Southern Africa
  • SANS 644    Geotechnical investigations for township development