VERTICAL PIT DESIGN Sample Clauses

VERTICAL PIT DESIGN. The Koidu vertical pit mining project was characterized by a unique set of circumstances comprising political, social, geographical and administrative challenges. A highly detailed design process with large numbers of boreholes and multiple sets of laboratory tests, followed by of the required design work was not financially feasible, nor practically possible. The decision was made to base the design on the information already collected during the earlier open pit feasibility study, with an additional site visit to audit the core logs and give the designers a better feel for the geology of the country rock surrounding the pit. The design of the vertical pit excavation was carried out using various calculation approaches to ensure design integrity. The material parameters were obtained by back analysis of the existing highwall at the No. 1 Pipe, excavated during previous mining attempts, and using the ▇▇▇▇-▇▇▇▇▇ failure criteria based on the laboratory tests and core logs. The design calculations comprised limit equilibrium, 2-dimensional and 3-dimensional numerical modeling. The results obtained from each of these methods were ranked according to stability and a final design decision made. 3.1 ROCK MASS STRENGTHS – The design rock mass strengths were selected based on the back analysis of the existing highwall and the ▇▇▇▇-▇▇▇▇▇ failure criteria (▇▇▇▇ et al., 2002). In addition to the normal factors incorporated by the ▇▇▇▇-▇▇▇▇▇ failure criteria, the following factors were considered subjectively: • Additional confinement provided by the constrained geometry of the vertical pit sidewalls; • The small scale of the vertical pit in terms of cross-sectional area and height; and • Time related degradation of the rock mass strength through creep and strain softening. The final design parameters based on the above evaluation were: Material Cohesion (kPa) Friction Angle (°) Tensile Strength (kPa) Granite Rock Mass 800 41 70 Granite Joints 0 41 0 As these parameters included many subjective components that may have changed with time once mining commenced, these parameters were based on the following design assumptions: • Effective pit limit blasting; • Effective dewatering of the pit sidewalls; • Ongoing monitoring of the pit sidewalls to give warning of unacceptable sidewall displacement and possible sidewall collapse; • A maximum mining life of 3 years from start to completion to limit the time dependant changes in rock strength; • Vertical sidewalls or flatter,...