There is an interactive relationship between the spatially varying Geological parameters and the changing stress conditions imposed by tectonics and mining activities for any particular area. These combination of factors influence the sitting and support requirements of shafts and their service excavations. The evaluation of a typical case history could benefit similar projects in future.
Il existe entre les paramètres geologiques à espace variable et les conditions de fatique changeantes rapport un rèciproque isposè par tectoniques et activitès de aines pour untel domaine. Ces considerations ci-dessus influencent le choix d'emplacement et les exigences de soutènement des puits et des excavations de service. L'evaluation d'une telle ètude des cas typique peut ainsi être avantageuse aux projets seablables a l'avenir.
Es bestehen gewisse Verhaltnisse zwischen geologischen Kennziffern, und tektonischen und abbau induzierten Spannungs veranderungen fuer bestimmte Gebiete. Die kombination dieser Faktoren beeinflusst die Position und Ausbau von Schachten und anderen Öffnungen. Eine typisher Fall wird hier besprochen und konnte vπn nutzen sein fuer andere zukuenftige Projekte.
The stability of excavations, and the resulting support requirement, is a function of the geological environment and the acting stress levels. The geological parameters varying in three dimensions are a function of the geological history of the area. The stress field is a function of the tectonic history, and the stresses induced by mining activity in the vicinity. Thus stability and support requirements can differ significantly over short distances. The effect of the abovementioned factors was clearly illustrated when large service excavations were cut in a shaft pillar on a Witwatersrand Gold Mine at 2000 metres below surface. Excessive movements occured in a cooling plant excavation, and additional support was installed in order to contain these. An additional shaft was also planned for this area to increase the hoisting capacity in that part of the mine. With the experience of deformations on the service excavations, and deformations of the existing shaft it was possible to predict the support requirements in the new shaft, and sinking was completed according to schedule. This paper deals with a detailed account of the deformation of important service excavations, and the support installed to stabilise these. Also, a detailed account is given of the support requirements of the new shaft in the light of variation of geological parameters, as well as the change in the stress field past, present and future.
Hartebeestfonein Gold Mine is situated in the Western Transvaal in the Republic of South Africa and is one of four mines exploiting the tabular Vaal reef of the Witwatersrand super group in the Klerksdorp area. No 6 Shaft serves the western part of the mine and was sunk in 1972 when the area was still unmined. Mining commenced in earnest during 1973 with a-resultant increase in the stress level in the vicinity of no 6 Shaft. During 1980 it was decided to increase the cooling capacity and an underground cooling plant was designed for 71 level. Excavation started in 1981 and was completed in 1982, when the plant was commissioned. It was during the development stage in 1981 that a sudden increase in shaft deformation, and tunnels in its immediate vicinity, was noticed. This increase in deformation was generally attributed to the increase in the number of excavations in close proximity to each other as well as the increase in the overall stress level due to mining on the western side of the shaft pillar. It was clear that a detailed analysis was required since at that stage planning of 6N Shaft was nearing finality, and it was obvious that problems could possibly be expected during sinking. Also, the effect of the increase in the overall stress level due to increased mining, to the end of life of the mine, had to be determined. The investigation consisted of three parts. 1 Determination of the primitive stresses. 2 Calculation of induced and total stresses past, present and future. 3 Evaluation in rock properties for the various geological horizons.
Fig 2 is a plan giving details of all excavations on 71 level. Attention is drawn to the fridge plant room and the pump chamber. During excavation of the fridge plant room abnormal amounts of sidewall/hangingwall/ footwall movements were observed and measuring stations were installed. The trend of measured displacements is shown in Fig 4. The displacements appeared to carryon unabated and the decision was made to increase the support density as given in Fig 3. The displacements reduced after the support had been installed, and the trend of displacement has settled to a rate of 0,015 mm/day. The amount of failure around the pump chamber has also been investigated by borescope and extensometers and Fig 5 is a summary of all data to date.
