Rocla Polokwane was recently contracted by a mining operation in Limpopo to manufacture a precast solution for a surface stockpile tunnel that was no longer structurally stable without temporary additional supports. This led to the loss of full operational functionality of the stockpile impacting on the mines daily operations.

The surface stockpile area continuously faced downtime due the tunnel being damaged from machinery and vehicles, commented Rocla Technical Executive, Muhammad Bodhania.

“The tunnel structure supports the stockpile and hoppers feeding a conveyor in the tunnel that supplied the metallurgical beneficiation plant on the mine.

The client required the structural integrity of the tunnel to be restored to allow full operational functionality of the stockpile and the conveyor. The repairs had to be done during the limited period of the shutdown which did not allow traditional in-situ construction. The process of shuttering, fixing, casting and curing – even if rapid strengthening concrete was specified – would have exceeded the timeframe to carry out the required rehabilitation works,” said Bodhania.

The preferred solution therefore was segmented steel-clad precast concrete sections assembled on site during the short time period available. This entailed the manufacture of foundations blocks placed on either side of the existing tunnel supporting a 4.6m slab spanning over the existing tunnel with a 100mm clearance over the existing tunnel.

This ensured that no load is transferred to the existing tunnel whose structural integrity was compromised. With a 7m high stockpile at a bulk density of 30kN/m3, the slab was designed to support a 210kPa load. The cladding was to ensure that the structure is not damaged from the day to day hammering of the heavy machinery and vehicles operating in the stockpile area. This solution required detailed planning and co-ordination of the various parties to ensure a successful execution of the project.

A total of 45 products were manufactured, with some product having a mass of 15 tonnes. Due to the shape of the products, the products were cast upside down and had to be rotated prior to delivery. Rocla together with its handling equipment supplier ensured that the rotation of these product was carried out safely. Bodhania said; “Rotating 15 tonnes comes with a lot of challenges and risks that have to addressed to ensure a safe operation.”

Prior to the placement of the sections, the stockpile was cleared and the ground preparations were complete. After the necessary compaction, self-levelling, quick drying screed was used to create a level surface for the foundation sections. This process was verified by the survey team to ensure that the levels were accurate prior to the placement of the precast tunnel.

In total over 750 tonnes of precast concrete segments were assembled safely one week ahead of schedule creating a tunnel of over 40m long, ensuring that the stockpile area operations returned to be functional at maximum capacity.

“This project has showcased the team’s ability to meet all challenges through innovative design, expertise and capability while keeping to a tight schedule. This is a reflection of our commitment to our customers’ requirements,” commented Bodhania

Rocla is a member of the Concrete Manufacturers Association of South Africa.