The successful construction of a four-pump grout plant at Anglo Platinum Ltd’s RPM Union Section by Murray & Roberts Cementation will meet the ongoing support needs for production on the mine’s decline section.
Murray & Roberts Cementation was awarded the contract in January 2006, and the plant was commissioned in May 2006, well within budget and on schedule. This was accomplished through teamwork, coupled with the necessary expertise and available resources. Johan van Zyl, engineering foreman – mining services for Murray & Roberts Cementation had a strong team and completed the work with no lost time accidents.
Designed to pump 100m3 in a single eight-hour shift, the custom-designed grout plant comprises two 100t silos for fly ash and cement, a slimes sand bay for classified tailings, a 600L high-shear mixer, a 6,000L storage tank and a fully automated batch weighing system. The silos are equipped with dust filtration units.
In some instances the automatically batched grout is pumped a distance of up to 4,000m to the requisite working areas, where it is being used in pack filling for underground support.
Prior to construction of the new grout plant, packed grout requirements were met using the existing grout plants, with additional ranges feeding the decline section by operating the system with additional labour.
While construction was taking place, Murray & Roberts Cementation concurrently designed and erected a fully automated two pump pilot plant to provide the interim grout requirements while the main plant was being built. This pilot plant was operational by mid March and took over the remote pumping from existing plants. Now that the new grout plant is operational, the pilot plant will be decommissioned and relocated to a new site at Union Section for ongoing grout production.
It is Murray & Roberts Cementation’s intention to grow the grout plant outsourcing portion of its business. Grout plants first became popular when this support technology was introduced into the market in the late 1970s when the significant logistical benefits were realised. There is a growing trend for mines to outsource the design, installation and operation of grout plants because of the expertise and knowledge required for this type of plant.
Outsourcing grout plants
Outsourcing appears to be the buzzword of the moment. However, one activity which has long been outsourced by mines in South Africa is the design, construction and operation of cementitious grout plants.
Murray & Roberts Cementation has provided this service for many years. As part of this offering, the company not only designs, erects and manages grout plants, but offers a full service that includes installation of grout support packs underground, and where required the placing of grout for wetcreting and general construction, including physical application activities.
Freddie Geldenhuys, general manager – mining services at Murray & Roberts Cementation, says the major advantage of surface grout plants to customers is the significant reduction in shaft hoisting time taken for conveying materials such as aggregates and cement underground. By pumping ready mixed grout to practically any underground destination, this equates to a direct increase in productivity and many reduced logistics related labour costs.
Murray & Roberts Cementation is in a position to offer single-pump pilot plant-type installations at very short notice, giving customers the flexibility to do whatever “up-front” tests are necessary and also facilitating an early start to production.
“Within 48 hours of arriving on site, Murray & Roberts Cementation can be pumping grout, making this service ideal for emergency as well as start-up situations,” Geldenhuys says.
Murray & Roberts Cementation has designed, erected and operated numerous grout plants over the past 30 years. It currently operates 15 plants featuring sophisticated, programmable batch controllers with an overall accuracy of 98.5%, highly efficient electro-hydraulically driven pumps, and pneumatically driven pumps installed as a backup to clear pipe ranges in the event of a power failure.
Murray & Roberts Cementation has developed and refined the design of its grout plants over many years and offers its knowledge, experience and a guaranteed commitment to all its valued clients. The current activity level on various projects include high pressure injection at a rate of 75m3/month and grout production at a rate of 13,600m3/month.
A typical cementitious grout plant comprises a high shear mixer and storage tank, pumps and power packs. Cementitious grout is pumped to the underground workings through a selected series of 25mm nominal bore ‘grout ranges’ and an electro-hydraulically driven pumping system.
A pneumatic pump is supplied as a back-up in case of a power failure as it is important to be able to clear the ranges to prevent them from blocking up and being lost. All pumps are double-acting high-pressure positive displacement types with one pump generally able to provide cementitious grouting to one or two levels on a shaft.
A grout plant installed on a surface site has the following advantages:
Major saving in labour and shaft time
Conventional support such as timber needs to be transported, occupying cage and winder time; grout is pumped down a grout range, which is independent of any other shaft hoisting activity, freeing up shaft time. Grout can be mixed underground, but materials such as sand and stone would again need to be transported to the level where the grout is being mixed. Maximum efficiencies are achieved with the grout plant located on the surface.
Mix is designed for each application
There are various mix designs, depending on the type of grout required. Each plant is designed, configured and controlled to produce a particular mix design. This ensures that the specified cementitious grout solution is applied to a particular task. The ratio and quantities of raw materials are automatically selected to achieve the specified strength.
Automated batch controller
The accuracy and consistency of each mix is controlled by an automated batch controller, reducing human error. The controller provides a physical printout, supplying accurate data for management reporting and verifying the actual mix. This is crucial for presenting indisputable technical information and is also utilised for invoicing purposes.
A scraper winch is used to move sand up into the sand hopper. From here it is drawn down using a belt conveyor and then introduced into the high shear mixer, which is suspended on load cells. Once the pre-determined mass has been reached, the batch controller switches off the conveyor belt and sequentially proceeds to switch on each successive unit in the process.
Prior to the sand being sent to the high shear mixer, water flows in at a rate of approximately 30L per second until the requisite mass has been reached. A screw conveyor is then used to transfer cement and fly ash, being the final ingredients, from the individual silos to the high-shear mixer.
The entire process is managed by the batch controller and at the end of the mixing cycle, the cementitious grout is pumped across to a storage tank where inter alia, quality control tests are undertaken. Random samples are drawn to confirm the specific gravity, which is a critical measure, as it ensures pump-ability. Random cube test samples are also taken to verify specified day strengths.
From the storage tank, the cementitious grout is distributed to a pump and ultimately to the workings on a particular level.
The cementitious grout plant supplies grout for:
Grout support packs
Murray & Roberts Cementation offers a comprehensive service for grout pack support including grout provision, pumping and installation of underground packs. The installation activity of the cementitious grout support pack is considered safer than that of conventional timber packs. Grout is pumped to the level where it is required, the support pack is filled to the correct level, topped up and then pressurised.
Wetcreting grout plant
The grout is pumped to a storage tank underground. From there it is transferred to the mixer and the remaining shotcrete additives and ingredients such as fibres are introduced. Once mixed to the required consistency, the shotcrete is sprayed onto the hanging wall or side walls and applied to the specified thickness. If required, test panels are produced, where test samples are taken and checked for consistency and quality. These are also crushed to test strength.
Cementitious grout is used for different types of construction. An example is footwall construction, where the floor or foot wall is covered with grout or in some cases a coarse aggregate is first put in place to provide the bulk, and then the grout filters through to consolidate the mix.