Ground-breaking innovation in rock drilling

01 February 2011

Atlas Copco’s new Elemex system minimises the escape of high pressure compressed air to surrounding

Atlas Copco’s new Elemex system minimises the escape of high pressure compressed air to surrounding ground. The state-of-the-art system is being used in work on Sweden’s new City Line railway expansio

Drilling equipment manufacturers have been busy over the last 12 months collaborating with contractors to find the best way round the physical and regulatory challenges that come with all new builds.

The cream of the crop has managed to break new ground in terms of productivity while reducing operating costs and downtime on even the most demanding builds.

For example, ground engineering expert Hercules Grundläggning and drilling contractor Terramek faced a series of challenges when reinforcement work began in preparation for Sweden's new City Line railway expansion (Citybanan) in Stockholm.

The contractors were tasked with strengthening a 250 m stretch of ground on the south side of the city at a point where the new Citybanan line will run on a 1.4 km bridge above an existing track.

Drilling in urban areas has always been a sensitive issue, and contractors are often under pressure to complete projects quickly and with minimal disturbance to the public.

Indeed, Swedish authorities had mandated that under no circumstances could the reinforcement work be allowed to disturb the stability of the sensitive ground surrounding the existing tracks, while drilling work could also only be undertaken in darkness when rail traffic was off-peak to minimise disruption.

Atlas Copco's state-of-the-art piling and ground engineering system, Elemex, and new Terranox down-the-hole (DTH) hammers were chosen to meet the challenge. The Elemex technology ensured that surrounding structures were not damaged by leakage from the compressed air used for piling, while the Terranox system can operate efficiently at lower air pressures to further minimise the rise of ground disturbance.

The Elemex design includes an extended ring bit which redirects the air flow across the bit face, resulting in an efficient flushing without air escaping to the surrounding ground.

And all of the cuttings and air are transported back up the pipe thanks to an innovative air channel design that features a freely rotating pilot bit inside the drill pipe sleeve which is fitted with a welded ring bit.

Site engineer Johan Blumfalk explained that the contractors had to work very fast and efficiently during night-time shifts lasting just four hours, but added that progress was good thanks to Atlas Copco's equipment.

"We have installed more than 480 piles on this stretch of only 200 m, and the new piling system works better than anything else in these difficult, urban conditions," Mr Blumfalk said.

Atlas Copco has also recently launched a new large tunnel rig, the Boomer XL3 D, which was designed with high productivity in mind as well.

Operators of the direct-controlled machine - which was first showcased in November last year at the Bauma China event - can drill precisely according to plan using the manufacturer's feed angle measurement system, resulting in less over- and under-break and longer rounds.

And the new rig can be fitted with a wide range of rock drills for different conditions, including the COP 1638, the COP 1838 and the powerful COP 2238, while work has been made less noisy thanks to an improved control system that has a reduced amount of high pressure hoses near the operator.

Indeed, drilling equipment manufacturers have continued to demonstrate throughout the last 12 months that difficult projects and working conditions present breeding grounds for innovation.

Maintaining the balance between high productivity and operator safety dominated Australian mining and construction contractor Macmohan's plans, for instance, when it recently won a contract for work on isolated hill sides for the Hong Kong West Drainage Tunnel scheme.

The project aims to alleviate the flooding problems in northern Hong Kong Island, and last year Macmohan was appointed to excavate 23 shafts for the scheme. The contractor selected Sandvik raise boring techniques for the job due the restricted weight loadings of the adjacent pathways, and it was considered to be the safest option since no people are required in the shaft during boring.

Raise boring was used to drill 2.4 m and 3.154 m diameter shafts to a variety of depths ranging from 40 m to181 m, while each shaft was started with a 350 mm pilot hole using Sandvik Pilot bits and 280 mm drill pipes. The pilot hole was then reamed to the final shaft diameter from the tunnel below using a Sandvik SR530 extendable reaming head.

The particular head used in the Hong Kong project is a CRH8E, which is designed to handle the region's hard, abrasive granites and volcanic tuffs and is extendable from 2.4 m to 3.5 m.

The project also required a series of shafts to be built using drill and blast techniques, and Sandvik supplied a compact drill rig for this task.

The DC300 Series drill rig weighs just 5000 kg, making it relatively easy to lift out of the shaft following drilling operations and prior to blasting (see image). The rig was fitted with RT300, 45 mm diameter bits and drills to excavate a lateral support chamber on the surface measuring 6.4 m x 9.4 m to a depth of 30 m.

With a total length of 5.6 m x 2.6 m high x 2.3 m width, the machine offered a very compact footprint making it ideally suited for drill and blast duties on the shaft project.

And Sandvik has also been focussing on the fuel efficiency of its drill rigs over the last year. Norwegian groundwork contractor Stangeland Maskin recently reported "exceptionally low" consumption rates on the Sandvik DP1500i rock drill - a machine which it selected to carry out pre-blast work in the Norstone quarry in Tau.

The top hammer rig has a 261 kW diesel engine and features load-sensing compressor pressure control, active diesel rpm control, an ambient oil cooler control fan and an advanced drilling control system.

"We are achieving a fuel consumption of approximately 1.7 l per drill metre in very challenging, extremely hard diorite," Stangeland Maskin drill rig operator Trond Horve explained, adding that the machine consumes an average of 37.5 l/hour, leaving more than enough fuel for a 10-hour day.

Drilling equipment manufacturers are constantly striving to include new features that can improve efficiency in this way, providing contractors with tangible changes to the way they operate.

Indeed, Vermeer recently saw an opportunity to improve productivity when replacing and expanding sewer and water infrastructure - traditionally time-consuming and labour-intensive tasks which require high precision.

The new AXIS GB812 guided boring system from Vermeer is a pit-launched, laser-guided system that can achieve pinpoint accuracy, and its versatile design allows for multiple applications in the installation of new sewer and water lines.

Designed to install 254 mm to 356 mm pipe at lengths up to 107 m, the system uses laser guidance to complete on-grade bores. Integrated into the drill head, a closed-circuit camera allows the operator to monitor and make adjustments to the process on a screen within the control console.

This new technology allows the Axis system to achieve the precision tolerances demanded by on-grade installation.

Project manager John Milligan explained that while some of the current, trenchless methods are designed to achieve the extreme accuracy needed for this kind of work, they "lack the productivity needed to compete with the open-cut method".

"We saw a void in the small-diameter, ground level installation solutions currently serving the water and sewer market," Mr Milligan added.

Meanwhile, Little Beaver has upgraded its range of mechanical earth drills to feature new, compact and lightweight designs.

The company's new MDL line can now access areas unreachable by skid steer loader-mounted augers.

Four models are available in the new line, featuring an operating speed of 360 rpm. Each model is also fitted with a centrifugal clutch which automatically slips if a buried object is encountered or the auger is overloaded, protecting the operator from serious injury and the drive cable and transmission gears from damage.

Little Beaver's new mechanical earth drills also feature a universal auger, allowing operators to change tips depending on surface type. A hard-faced tip suitable for soils is included as standard, while heavy-duty rock tips and carbide-blade tips are optional.

And the MDL drill can also be converted into a horizontal boring machine which can drill up to 1.2 m under pavements.

This type of versatility also looks set to become a firm feature of new drilling products, as does increased automation and the dual emphasis on productivity and safety.

Atlas Copco provided a first look at what the future may hold for the drilling equipment market when it presented a concept surface drill crawler at the Shanghai World Expo, which took place from May to October last year.

The futuristic model ROC X1 (see image) is said to offer a potential leap in productivity and mobility, as well as silenced operation.

Regional business manager at Atlas Copco Surface Drilling Equipment Mårthen Elgenklöw described the concept as, "In line with what modern societies will expect from pro-active suppliers in a not too distant future - the ability to be productive, at lengthy hours and in close proximity to urban areas".

iC will be keeping a keen eye on this an all other developments in the drilling equipment market for future updates.

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