Dolomite Stability Investigation | Thaba Tshwane War Cemetery

Geotechnical Report of Impala Platinum Mine

A dolomite stability investigation was carried out on the Thaba Tshwane War Cemetery Old 1, Gauteng Province to determine the stability conditions of the cemetery.

A number of sinkholes had occurred in the area and two sinkholes had been recorded on the site itself.

A geophysical survey was carried out to assess the gravity profile of the site. Eight rotary air flush percussion boreholes were drilled, the penetration times were recorded, borehole chips were logged and sample recoveries, as well as cavities, were noted. No water strikes were recorded.

The regional geology indicates that the site is underlain by chert-rich dolomite of the Eccles Formation of the Malmani Subgroup, Chuniespoort Group, Transvaal Sequence. The carbonate bedrock comprises compact and poorly bedded dolomite, limestone and chert layers. This site is located in an area characterised by surficial chert overlying dolomite bedrock at depth. No known fault zones are present on or in close proximity to the site.

The site is located in the A21D-03 Groundwater Management Unit, known as the Pretoria Fountains West Groundwater Compartment (PFWGC) which has a median groundwater level of 49,3m below surface.

The site was subdivided into three hazard zones. Cemeteries are considered as D3 up to IHC 4 whilst a D4 designation applies on sites classified as IHC 4 to IHC 8.  Zone 1 is therefore assigned a D3 rating whilst Zones 2 and 3 are both assigned a D4 rating.

Based on the outcome of the investigation, a large portion of the site presents a high hazard of sinkhole formation which implies that special precautionary measures will have to be implemented on the site. These include the upgrading of the stormwater management system to ensure that surface run-off is adequately drained away from the site and ponding is prevented as well as a  Dolomite Risk Management Program (DRMP) which will ensure constant monitoring and regular site inspections.