Quarrying In Cider Country
WCD Sleeman & Sons choose Atlas Copco drill rigs
From their base in Frome in the West Country, WCD Sleeman & Sons Ltd supply drilling and blasting services to a total of 18 quarries in Somerset and Herefordshire, counties that have extensive cider apple orchards, abundant limestone and good rail connections with London. Output from most of these quarries is crushed and screened and then transported by rail to London on purpose-built trains.
Founded some 27 years ago by William ‘Dixie’ Sleeman, with a single Atlas Copco pneumatic drill rig, the company now operates a fleet of eight Atlas Copco down-the-hole (DTH) machines, comprising two ROC L8s, one ROC L6 and five ROC 460s. All of these machines are moved frequently between sites because their individual productivity outstrips the capacity of any single client quarry. However, the combination of fast drill rigs and ease of movement makes good economic sense and is becoming increasingly popular among contractors working small and medium-sized quarries. The ROC series of drill rigs is designed with easy transportation in mind, and the dimensions of all of the Sleeman machines are well within the European guidelines for movement by low-loader, so no permits are required.
Company history
Sleeman originated in Roche, Cornwall, near to the largest china clay operations in the world. Here, William ‘Dixie’ Sleeman was, for many years, operations manager for Mid Cornwall Contractors, a drilling contractor with a fleet of Atlas Copco drill rigs. The fledgling Sleeman company was originally engaged by English China Clays (ECC) in drilling and blasting the granite dykes that were inhibiting hydraulic extraction of the clay.
Since their inception, Sleeman have offered a full drilling and blasting service to their clients. The company provides the drill rigs and site personnel, and undertakes the design and layout of the blasting grid, surveys the holes, carries out laser profiling of the face and specifies the blast design. Most drilling and blasting contracts are ‘rock-on-ground’ packages, which are priced on a per tonne or per cubic metre basis.
Sleeman’s first venture outside Cornwall was in 1983 when they were awarded a contract by John Wainwright & Co. Ltd at Moons Hill Quarry, Somerset, which has been in operation for over 100 years. This site’s long-term success lies in the fact that it is the only local source of basalt and, despite a regular output of around 1 million tonnes per year, still has 80 years of accessible reserves under development in a westerly extension of the main pit.
Today, nearly 20 years later, Sleeman are still the drilling and blasting contractors at Moons Hill, employing one of their new ROC L8 drill rigs at the site.
Moons Hill Quarry
Wainwright’s Moons Hill Quarry is a typical Sleeman drilling and blasting contract. In an extension of the main pit, the ROC L8, equipped with a Secoroc COP 44 hammer, is employed drilling 115mm holes on a 4.0m x 4.0m grid pattern. The bench height is 10m and the basalt itself is hard and loose jointed, a situation in which DTH drilling excels. The face angle is currently 15°, but this may be reduced to 10° in certain areas.
Explosives are delivered on an ‘as-needed’ basis to avoid the potential problems associated with site magazine location and security. The lower 6m of each prepared hole is loaded with 13kg/m of Orica bulk emulsion and a 16L Pentolite booster primed using a Sureline non-electric detonator. The top 4m of each hole is stemmed using 14mm chippings.
Following blasting, Wainwright use an excavator and 40-tonne dumptrucks to deliver the rock to the primary crusher at the main pit, some 1.2km distant. Here, the material is crushed and screened to form up to 12 different roadstone products, some of which are consumed on site in Wainwright’s own coating plant. The remainder is stocked ‰ in the open for sale and is shipped out by the company’s own fleet of trucks or by customers or contract haulage.Every month Sleeman bring in a 20-tonne excavator equipped with a hydraulic breaker to deal with any build-up of oversize boulders.
Atlas Copco ROC L8
The ROC L8 from Atlas Copco is a high-production crawler rig, mounted on heavy-duty tracks, with ample power to deliver high penetration rates and deep holes. It has a rod-handling capacity for hole depths of 54m and can be used for both pre-splitting and production, making it a complete solution for drilling in quarries and open-pit mines.
The ROC L8 cab provides good all-round visibility and a user-friendly instrument layout, and meets all international safety requirements. The machine is equipped with a high-performance DTH rock drill for fast and straight drilling, and features a hydraulic break-out table and double drill-steel support, which helps the operator to thread and unthread the drill steels. The rock drill assembly is mounted on a flexible single-section boom with a wide feed swing to the left and right, as well as backwards and forwards.
The rig is powered by a 317kW (431hp) Caterpillar diesel engine, while an on-board Atlas Copco screw compressor delivers 405 litres/s (858ft³/min) of air at 25 bar (363psi).
The unit is capable of drilling holes as large as 165mm (6.5in) down to depths of 54m (176ft), and flushing them clean for charging. The ROC L8 can be fitted with a range of Atlas Copco Secoroc DTH rock drills such as the COP 44, COP 54 and COP 64 (4in, 5in and 6in, respectively), which are among the fastest on the market.
An electronic system for hole inclination and depth control ensures that the blast holes are accurately aligned.
Contracts elsewhere
Sleeman’s second ROC L8 joins its sister machine in providing drilling services to seven or eight other quarries in and around the Mendip Hills — the Somerset geological structure that hosts large limestone reserves. Among the sites being worked are Hanson Aggregates’ Battscombe and Tytherington quarries. Sleeman are also carrying out development work for Hanson at Chipping Sodbury, where some 500,000 tonnes of rock is being drilled and blasted. The ROC L8s also work at Foster Yeoman’s Torr Works and Dulcote Quarry.
Three of Sleeman’s Atlas Copco ROC 460 drill rigs are also engaged in small jobs around the Mendips, while the fourth is based at Tarmac Western’s Bayston Hill Quarry, near Shrewsbury, and the fifth covers Tarmac Western’s Strinds, Dolyhir and Gore quarries.
Each of the ROC 460 drill rigs is powered by an Atlas Copco XR compressor rated at 12–20 bar pressure.
Sleeman’s ROC L6 rotates between three drilling and blasting contracts located at Tarmac Southern’s Halecombe, Stancombe and Durnford quarries.
Bench heights at all these operations are in the order of 14–15m, which is close to the maximum height allowable in the UK without a full geological survey. Hole size is normally 115mm, but around 20% are drilled at 127mm diameter. In the limestone rock that characterizes most of these sites, a 4.5m x 4.5m grid pattern is employed in order to reduce fly-rock and concentrate the rock pile.
The Secoroc Magnum premium-quality drill bits being used last a minimum of 1,000 drilled metres and are treated as consumables, so re-grinding is not carried out.
Planned performance for the ROC L6 and ROC L8 machines is 1.5m/min, and 600mm/min for the smaller ROC 460s.
Sleeman have eight operational staff and two working directors, the latter comprising Steve Sleeman and his brother. There are four blasting licence holders to handle the 5.5 million tonnes per year extracted under the various drilling and blasting contracts.
