RSV has successfully completed the construction of a UG 2 reef storage silo at the Dishaba Shaft at Amandelbult East. Work started on this portion of the project in April 2007 with site establishment, earthworks and civils work. At peak the project employed 60 people, and over 220 000 manhours were worked without any lost time injuries being recorded.
The mine previously extracted Merensky ore and the existing silos house Merensky and waste product. This new project provides an infrastructure for UG 2 mining and the new silo, which will house the UG 2 ore. The project also provided a third ore pass system to hoist the UG 2 at the Dishaba Shaft.

“An impressive aspect of this project is the high level of survey accuracy,” Pierre Lombard, project principal at RSV, says. “The silo set out was done within 50 mm of the specified survey coordinates. This was possible as a result of the skilled and experienced personnel on site as well as the use of advanced survey technology including GPS.

“As this was an addition to an existing operational part of the mine, it was necessary to dovetail all aspects of the construction and installation work so as not to interfere with or disrupt production,” Lombard says. “We accordingly planned for the civils and earthworks to take place during the winter months to avoid having to work in what is often a high rainfall season.”

One of the major challenges on this project was to ensure the accurate transfer of both the UG 2 to the new silo and the waste to the existing silo even though the new silo is slightly offset from the centre line of the existing silos. “The reason for it being offset was to accommodate the radius of the new railway line which now runs under the UG 2 silo,” Lombard says.

The use of innovative design work was applied to achieve the optimum solution. The existing waste chute was utilised and now incorporates a flopper gate and the new transfer chute. “An interesting aspect of the transfer point itself is that the chute was designed with a twisted configuration to accommodate two different angles,” Ettienne de Beer, lead mechanical engineer at RSV, says.

“Design work was critical for the success of this transfer point as it had to be configured in a manner that would allow transfer to take place while simultaneously maintaining the correct angle of repose and allowing the material to move freely through the chute into the silo,” de Beer adds.

“In achieving the correct angle, another challenge had to be overcome in controlling the speed of the material in order to eliminate spillage. This was achieved by making use of appropriate technology. It goes without saying that detailing of the design was imperative to ensure matching of the two structures,” de Beer explains.

Another interesting element of this project was the design and installation of spilmanator chutes. “Traditionally these chutes are used to control mud rushes and were selected for this silo application to enhance safety. Attention was given to the design work to ensure easy and safe access to the chutes for maintenance and repair work and to ensure the structural integrity of the spilmanator chutes,” de Beer says. The spilmanator chutes were structurally designed by RSV for and on behalf of CAN Mining, who was responsible for the manufacture of the chutes.

“With safety being of primary concern on all structures today, the silo has been equipped with a second escape route,” de Beer says. “In addition anti-rollback idlers were installed on the conveyor system.”

Winches have been installed to facilitate the lifting of large components for repair and maintenance to the silo penthouse. In addition to this, the winches were used for the installation of the 90 metre long conveyor belt and, as a permanent installation, will fulfil this role in the future.

“In the actual construction phase, a solid base foundation, founded on Norite was used instead of piling as this was determined to be a more cost effective method and would not compromise the integrity of the structure. In addition pumped grout was used as backfill material instead of compacted rock, as there was some additional cost savings,” JJ de Klerk, mechanical project engineer at RSV, says.

The silo was slid over a period of nine days using 3357 tons of concrete and thereafter the installation of the structural and mechanical portions of the project began. Prior to the structure of the new conveyor and transfer points being installed, modifications were made to the existing waste chute. “An important aspect of this is that it was planned and scheduled over a required timeframe,” Piet Roets, senior project planner at RSV, says.

An access platform was attached to the existing silos by means of chemical anchor resin bolts. “We took a decision to use this manner of fastening so that there would be no disruption to the existing production,” de Beer says. “Traditionally a hole would have been bored through the silo and the platform attached with fasteners on both sides. The method we chose called for a blind hole, which allowed normal production to continue while the installation was being done.”

Following this, the 42 metre long conveyor gantry was preassembled on the ground and then lifted into position as a single unit using mobile cranes. The silo penthouse was also preassembled and lifted into position.

Using an unconventional design methodology, the silo is fitted with rail liners to eliminate wear on its interior surface. The 12.7 metre diameter, 31 metre high silo with a 3 500 ton live storage capacity, was completed at the end of February 2009 on schedule and within budget. “This is due to the coordinated efforts of an experienced and skilled team,” Lombard concludes.