Shaft sinking design is typically driven by what has been successfully utilised in the past and the availability of sinking plant and equipment. This study considers a case study where the sinking design and methodology is unconstrained by conventional thinking and removed from the commonly held belief that a sinking methodology should be developed based on the available winding plant. Schedule was a key driver for the Project and led to an alternative sinking design that aimed to optimise sinking advance rates by specifying new winders that compliment known sinking plant while providing improved safety, redundancy and flexibility within each part of the sinking cycle. The project is remotely located in the South Gobi region of Mongolia and the scope of work included the blind sink and concrete lining of two (2) ventilation shafts to an approximate depth of 1,150 m to a finished diameter of 10 m and 11m respectively. All sinking and lining operations to be completed as in-line activities. The design centred on the mucking cycle given that this is the most significant part of the sinking cycle and typically accounts for a third of the overall cycle. Vertical Shaft Muckers (VSM’s) are tried and true sinking plant and typically operated in pairs, however existing VSM models would not have the extension to cover a 10m or 11m diameter shaft if only two (2) units were in operation. Thus, the sinking stage design was optimised to allow for four (4) stage mounted or “nested” VSM’s in favour of an excavator/s. In order to accommodate the VSM’s the sinking design required a reduction in the size of the kibble well and ultimately the kibble payload. To counter the smaller kibble payload, two (2) kibble winders were introduced to allow four (4) kibbles to be utilised. This also doubled as the secondary egress, negating the requirement for an otherwise redundant “Mary-Ann” winder and provided the opportunity to sustain 50% hoisting capacity during planned and unplanned maintenance activities. It also provides a greater flexibility to segment the cycle further and reduce waiting times for equipment being lowered to the shaft floor. The use of four (4) vertical shaft muckers also provides for a mucking efficiency of greater than 85% if a single mucker was out of service for an extended period of time, while maintaining approximately 93% coverage of the shaft bottom. Far superior to the what may be achieved with a single or even two excavators. The use of VSM’s provides other benefits by removing the operator from the floor when compared to an excavator, most significantly; No personnel required on the shaft floor during the mucking cycle and therefore mitigates one of the highest risk activities from the sinking cycle and allows on the job training of employees without additional exposure to sinking personnel, (this requires the kibbles to remain attached during loading, ie no changing bale) The ability to excavate the full shaft round (4.5m) without installation of temporary support, (support installed from the stage) The same four (4) kibble wells provide the same flexibility and redundancy during the delivery of concrete via concrete kibbles during the pouring of the concrete shaft lining. The design also catered for the delivery of concrete via two (2) slicklines, in the event that concurrent shaft lining, (pouring of the barrel plates) is approved during mucking due to no personnel being at the shaft bottom when mucking. The objective of the design was to provide a safer and more flexible sinking system that has redundancy within every part of the sinking cycle. That could thereafter achieve instantaneous sinking advance rates superior to current large diameter blind shaft sinking advance rates.
