Breaking bad underground 27 Apr 2017

Roger Murrow for TunnelTalk
Hydraulic hammers and breakers have played a long, if unsung role in tunnelling. Generally mounted on excavators or specialist carriers, these increasingly sophisticated pieces of equipment are now essential tools. Technical journalist Roger Murrow explores the products of three major industry suppliers.

Breaking and trimming rock at tunnel faces is vital work. Varying tunnel conditions affected by water, rock strength and geological structures all affect the progress of excavation by hammers and breakers. As a result, equipment has had to be developed to meet the challenges presented. Recently there have been considerable developments in the field of equipment that has not been considered as tunnelling equipment traditionally but are nonetheless essential tools.

Rammer breakers at work in Hong Kong
Rammer breakers at work in Hong Kong

Some of the most interesting developments have been regarding hydraulic breakers and demolition robots. Two manufacturers, Brokk and Rammer, have updated their ranges recently, producing solutions that have proven to be ideal for tunnelling contractors excavating tunnels, or breaking material excavated by the drill+blast process.

Brokk, the Swedish manufacturer of demolition robots, is finding that its equipment is suited increasingly to the tunnelling industry. The robots are used mainly to excavate cross passages between twin tunnels; safety niches; TBM launch chambers and the enlarging of existing tunnels. The wide product range has proven to be suited particularly to working underground or in confined spaces. Their electric operation and small size provides users with manoeuvrability on site enabling access to the most confined of spaces.

Further enhancing its offering to tunnelling contractors, Brokk has added three models to its equipment range: B110, B120 (MKII), and the larger, more powerful B280. These new developments possess increased power and productivity to improve performance by approximately 50% over the last five years, without sacrificing any reach or versatility. This added power has enabled the equipment to contribute on tunnelling projects worldwide, where arduous operating conditions and tough materials are often encountered.

One of the latest models, the Brokk 280, has a reach of 6.2m, weighs 3,150kg, and possesses both a harder punch from each blow of the breaker and more blows per minute. The manufacturer states this is accomplished without sacrificing any of the compactness and flexibility of Brokk machines. The unit is also fitted with the company’s new Brokk SmartPowerTM electrical system.

The new intelligent system is particularly beneficial for tunnelling operations as it optimizes the performance of the machine based on factors such as the quality of the power supply and the environmental conditions in which it operates. In addition, the new system is designed specifically to deal with the harshest of working environments, which includes tunnelling projects.

A ready niche in Qatar

Some of Brokk’s newly developed units have used their recently added power on the Dohar Metro project for excavation of the cross passages. The B260 and B160 units were selected due to their high power to weight ratio and ability to take on a number of different tasks.

Brokk robots preparing to open a cross passage heading' style=
Brokk robots preparing to open a cross passage heading
Brokk breaker units working a rock tunnel face
Brokk breaker units working a rock tunnel face

In order to speed up the production rate on the excavation work in the tunnel, a Brokk machine was placed at either end of the cross passage, and then operated with the goal of meeting up in the middle. Progress averaged about 25 cubic metres per day, encountering mainly a relatively soft rock of a hardness of approximately 10-20 MPA. Nicolas Combe, Cross Passage Manager for Dohar Metro Red-Line South says: “This is the first time I have been working with Brokk machines. I am really impressed with their flexibility. They are good machines and powerful to work in confined space.”

Ultimately the project saw the use of six Brokk B160s, with four of them mounted with TEI-drilling rigs, breakers, scabblers and also shotcrete attachments. The procedure involved the Brokk robot equipped with a TEI-drill making approximately 40 x 75mm holes, with 9m depth to secure the cross passage. The estimated time to drill one hole was 15 minutes, with some of the rock encountered being as high as 120 MPA. Following this stage a breaker attachment was used for excavating through the rock or, in softer areas, a Brokk scabbler attachment. The Brokk machines were also used to trim the edges. A third step has been to shotcrete and secure the cross passages with the use of a bucket to remove the debris.

Breaking bad

Rammer, a name synonymous with quarrying and demolition breakers, has recently launched a series of breakers purpose designed for the requirements of tunnelling contractors. The two new hammers, the Rammer 2577 PRO and the Rammer 5011 PRO, have been designed specifically to work horizontally and purpose built to withstand high levels of dust when working in hard rock.

The company states that the PRO Range is as innovative as it is tough, being designed for carriers in the 21-32 and 43-80 tonne weight range respectively. Both the new Rammer models possess such well-known Rammer features as an idle blow protector that works regardless of working mode to provide greater levels of protection. Additionally they are equipped with long-life, high-tension VIDAT tie rods for improved reliability and are said to deliver extended service periods and lower operating costs.

Breaking power of the Rammer breaker
Breaking power of the Rammer breaker

A selection of Pro Range breakers have been working successfully on the Hong Kong Link Road, specifically the section between Scenic Hill and the Hong Kong Boundary Crossing Facilities. The breakers were used by the company VSL Intrafor, which specialises in technically challenging ground engineering and foundation construction works.

This section of the project involved excavation of an 80m tunnel beneath the tracks of the Airport Express rail line using boxjacking construction and without disrupting services on the rail link above.

A single Rammer 2577 PRO unit has been achieving excavation rates of 250m3 on the rock fill, whilst two 4099 PRO breakers have been achieving an average daily production rate of 170m3 of Grade II and III granite. The breakers are mounted on Doosan DX480SC and Doosan DX420 SC excavators respectively, and both are equipped with a tunnel tilting boom.

Revolutionary drilling system

Finnish company Robit has developed a drilling system for top hammer drilling that uses fibreglass grout-injection tubes instead of steel tubes. This works by constructing a temporary structure reinforced by fibreglass tubes with injected grout. The original idea behind the method was to reinforce a tunnel face when it was being excavated in soft ground conditions. Actual drilling may be accomplished by tunnelling jumbos. Grout injection of the tubes if required is with normal injection equipment using cement or polyurethane grout.

Showing the effectiveness of the development, the drilling system has been successfully utilised on a railway tunnel in Switzerland, where serious risk of tunnel face collapse was causing project delays. To overcome the issues, the tunnel crown was reinforced with forepoling comprising 15m long x 159mm diameter injected steel tubes and the face also stabilised with 76mm fibre glass tubes.

Fibre glass rods being fitted using a jumbo drill rig
Fibre glass rods being fitted using a jumbo drill rig

The fibreglass tubes had to provide support for at least a further 8m of tunnel advance and were drilled a total length of 20-21m. Using a Sandvik and Atlas Copco drilling jumbos, and drilling small 76mm drill bits, presented a real challenge to the drilling equipment. The new method was used to replace conventional self-drilling anchors, which proved to be unreliable, and did not comply with the project‘s requirements for hole straightness (50cm in 20m). The new solution met this requirement, with the contractor, ATS Infratunnel, reporting that the project, the first with this fibreglass bolting method in Europe, is now back on schedule and maintaining an excellent safety record.

Rocksplitting - high production without blasting

An award-winning project in Hong Kong has required particular engineering and excavation expertise to complete a mined hard rock trinocular highway tunnel without using drill+blast. The 50m wide highway tunnel span passes under the portal structure of the existing Cross Harbour highway tunnel, and was undertaken by China State Construction Engineering (CSCE). To begin excavation, CSCE equipped itself with drill jumbos from Atlas Copco and and hydraulic splitter units from Yamamoto Rock Splitter of Japan, mounted on Hitachi EX120 chaises, and hydraulic breakers Sandvik (Rammer), Montabert and Soosan.

Rocksplitting provides an alternative to drill+blast for the highway bypass in Hong Kong

The rock splitting method involved the drilling of a continuous row of interconnected drill holes around the tunnel profile to provide the necessary free face slot or cut holes, and a pattern of holes in the face for inserting a hydraulic splitter tool for forcing the rock to break back and be removed. The core of each round was then excavated and the profile trimmed with the breakers.

These advances in solutions based equipment show how manufacturers are working with tunnelling companies to produce equipment which is needed to deal with arduous operating conditions. Productivity, user friendliness and increasingly environmental concerns all have a bearing on how equipment is being developed. It is through close relationships between tunnelling contractors at the sharp end of the business, and the equipment manufacturers that will see more advanced equipment being developed that truly reflect the full range of excavation requirements.


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