The disagreements, to say the least, over whether hand-arm vibration syndrome (HAVS) is a real hazard in tunnelling activities started with the virtually continuous use of pneumatic spaders in hand-excavating pipejack work and some other types of tunnelling. Both the levels of vibration determined to be experienced by miners, and the periods of time over which the tools have been used are deemed in excess of the limits now imposed through safety legislation.

Spaders, by their nature, are used invariably in soft ground, chiefly clay and fill, to dig into and lift away the ground to be excavated. Even though, as it is claimed by contractors and miners, that no case of HAVS (or ‘white finger’) has been caused by powered hand mining in clay, it is logical that there should be efforts to minimise the total amount of vibration to which miners are exposed, and these are required in some law. Similar manually operated rock drills (hand-held and air-leg) and peckers can also be used in tunnelling, with an associated higher level of potentially harmful vibration, to which the same must apply.

Vibration exposure can be minimized through either using tools generating lower vibration levels or limiting the periods that power tools are used, or a combinations of the two.

Lower vibration
Prompted, it appears, mainly by the do-it-yourself and general construction and demolition markets, there have been efforts to reduce the levels of vibration in manually operated power tools. Manufacturers such as Hilti, Kango and Makita have all been advertising lower-vibration tools in recent years, but these are mainly powered by electric or hydraulic feeds and are not often used underground despite being arguably more efficient than compressed air. It should be possible to provide an electrical supply of suitable voltage or hydraulics from a power pack or take-off from other plant that may be available in the tunnel. A drawback, however, is that it is undesirable to operate standard hydraulic hammers at the sort of angles traditional pneumatic tools are used. Specially designed larger hammers such as scalers used in drill-and-blast and some demolition hammers are tolerant of this.

Manufacturers and safety enforcers often claim that miners do not understand the operation of more modern, lower vibration, equipment and say that they insist on being able to feel the vibration to believe that the device is working properly. There is clearly a need for education when trying to introduce new equipment and make it more acceptable. In this hand miners should be no different to other tunnel workers to be trained in the use of new equipment.

It appears that convincing the traditional miner will still be an uphill struggle. “The problem with this one is that really complicated and short sections are actually better done with a gang of hand miners with the old FL22s or ‘Germans’”, states Dickie Dexter, construction director of tunnelling with Joseph Gallagher. “Oddly these two are still, by a country mile, the best two hand tools manufactured even with all the new vibration-damped machines, the miners will always try and grab the old machines before the new ones.”

Traditional skills
Hand miners are very proud of their traditional skills and rightly so. Just because their efforts are chiefly manual does not mean that they do not require in-depth skills built up through years of experience. And, many contractors value these skills even though, due to diverse circumstances it is difficult to keep them readily available.

Contractors value traditional skills because there are still many circumstances in which hand mining is seen as the most practical or most economic way to progress an excavation. Bill Clowes, construction manager at the MTR Corp in London, and formerly with Bechtel offers the opinion, “The key to successful hand mining is to utilise specialist gangs and not try to and use the TBM crew or ‘local labour’ in these conditions. In Singapore we bought in an Irish handworks gang to complete cross passage construction, and this was money well spent. Other projects that tried to use local labour with ‘main tunnel’ supervision struggled both with safety and production. There will always be elements of hand mining in tunnels, and it is important that we maintain the specialist crews and supervision for these works.”

Economy is, of course, no excuse for an unsafe practice, but safety considerations might halt a particular means of tunnelling. There are, however, usually alternatives, albeit at higher costs of equipment investment or operational costs.

Patrick Hudd, manager of estimating with Cementation Canada formerly worked in some hand-mining operations in the UK said, “There are not that many, miners nor engineers, who can supervise and safely do timber headings, breakups, etc, which is a shame.”

Ronnie Christer, tunnelling manager of contractor Fineturret in Preston, UK, reports, “Fineturret were involved three years ago in repair work to a Victorian tunnel in Somerset. The tunnel carried water from several reservoirs in the Mendips (Hills) to a holding reservoir near Bristol. When the holding reservoir was completely full it allowed the tunnel to be drained and repairs carried out it during a limited period of six weeks.”

“The access shaft where the repairs were done was only 2m in diameter and 60m deep. Due to these limitations (maximum size of equipment etc) all the work was done manually, and there were 10 miners on each shift to comply with HAVS regulations. Only two FL22s were used on a rotation system, but the repairs were completed on time. We had an agreed daywork rate with a completion bonus”

Hand mining can also produce a better job in terms of tunnel construction, if the crew is sufficiently skilled. Dexter points out that the Dorchester Link Tunnel was at first proposed as a hand tunnel but was changed to a larger sprayed concrete lined (SCL) drive, resulting in more settlement. Gallagher didn’t think it would be accepted as a hand tunnel because of concerns over HAVs. Small excavators were tried instead.

Other considerations
In reviewing the tunnelling system to reduce vibration exposure, other hazards in small-sections must also be addressed, all of which are the subjects of, mainly recently introduced, safety legislation. These include:

• Manual handling – of, as examples, steel supports, lining segments, equipment, and large sacks of construction materials such as cement. Problems include the transfer of loads by twisting the body as well as direct lifting. Where the loads exceed the maximum manual handling limits set down in regulations, and even as good practice in any case, the miners should be provided with lifting devices such as hoists, Tirfors or hydraulic manipulators, whether manual or powered.

• Ventilation – small sections leave little room for standard ventilation ducts so those of smaller diameter have to be used. Compressed air supply has also been used, but this can create another hazard unless treated properly with additional equipment. Gas monitors, including for oxygen levels, must be provided, and possible noxious emissions from, for example, repair materials solvents, must be considered.

• Confined spaces – should a hazardous incident occur, such as a build-up of toxic or suffocating gas, an inrush, fire or collapse, the miners should be able to reach a safe egress point. This is a function of the tunnel section, the distance from the exit, any obstructions in the tunnel such machinery and muck skips, ventilation supply, use of self-rescuer devices and the number of people working in the tunnel.

Hudd claims, “True hand excavation, timber heading, hand-built rings and ‘jiggers’ are difficult. Certainly in the UK, hand excavation is difficult due to all the exposure monitoring that is required for ‘white finger’. The damped jiggers and electric models are not nearly as good as an FL22 or Hausherr/Flotman.”

Pipe jacking
Being aware of the difficulties of hand mining within small-diameter pipejacking, timbered headings, etc the ‘Guidance on the design of hand excavated pipejacks’ produced by the UK Pipe Jacking Association together with the British Tunnelling Association and Health & Safety Executive presents a table of dimensions for the use of designers stating acceptable limits. No hand operation below the surface is acceptable below 1200m diameter. Recognising the additional possible hazards of powered equipment in small diameters, the minimum diameter is raised to 1.35m if mechanical excavation or a mechanical erector is used. The only operations not to be avoided in small diameter pipejacks are operator controlled pipejacking of 1.2m diameter, or, if machine erectors are used, above 1.8m diameter.

This guidance places the bias firmly in favour of mechanical excavation, either operated remotely from the surface (i.e. microtunnelling), or within the shield machine at larger diameters. The former places a primary requirement on the reliability of microtunnelling equipment in avoiding breakdowns that require access to the shield machine or cutterhead, and a limit to the length of drives so that, depending on the hardness and abrasivity of the ground, cutting elements do not wear out before the end.

The difficulties of safe egress in small diameters is also recognised in the guidance. Man entry, for whatever purpose, has to be avoided or is not acceptable below 1200mm diameter. Above this diameter the maximum distance to the nearest exist point is set down in stages increasing from 25m at 1200mm diameter.

If they can be made to work in the circumstances of the tunnel, and in particular the dimensions, small excavators can eliminate many of the problems associated with hand mining. They can provide a means of excavation, a carrier and/or power source for other equipment such as hydraulic breakers, and a means of lifting support materials into place. However, they have to be ‘up to the job’ chiefly in terms of power availability, as this is a drawback for many contractors. The standard diesel drives may not be acceptable for ventilation reasons.

Andrew Smith, also of Joseph Gallagher Ltd, says the contractor used a ‘Celtic Miner’ made by Metal Innovations of Wales when working on the Hampton Pump-out Shaft in southwest London, subcontracting to Costain, but not very successfully. “But I understand it has been upgraded as regards power since then and we are probably about to use it on Costain’s National Grid tunnel work at Willesden to drive launch adits in SCL for the Cat TBM. We are currently using a Schaeff 112 at Eade Road to drive launch adits for the Herrenknecht TBM, which are larger. The Schaeff is too big for the Willesden adits.”

Following its use at Hampton, main contractor Costain also hired a unit for work on Southern Water’s Brighton project.

In a project to create extra visitor exhibition galleries underground at the England National Mining Museum contractor Amoco (Amalgamated Construction) chose a Celtic Miner 4500 because it can be easily dismantled to be transported in the small mine shaft and reassembled underground.

The Celtic Miner, or CM4500, is only 1.6m wide, 1.5-1.8m high, and 2.7m long. Its hydraulic power comes from a source that can be up to 350m away. Possible functions include a cutterhead, hydraulic hammer, and support lifting. The maximum dimensions that can be excavated are 5m width by 4.5m height and down to 2.5m. The carrier can turn in a 2.7m radius and climb at 1 in 4 grade.

Dexter says that Gallagher tried a Butor electric excavator for the Dorchester Link Tunnel. The contractor bought one and had it converted into even more compact dimensions as it wouldn’t fit into the 3.5m wide excavated, and 3.2m wide spray-lined tunnel, without banging into the tunnel walls but it was still too big. “We ended up with a (Takeuchi) diesel 1.5-t mini-digger which, oddly enough, worked very well, if a little cramped. …. The industry is crying out for something small, heavy, powerful that can spray shotcrete, and dig and shift ‘muck at a rate of knots’.”

Small-diameter shields can also be equipped with hydraulic backhoes. These have the additional advantages over manual excavation in that the operator is better protected by the shield, especially when digging out the invert.

Another useful device in replacing hand excavation are rotary cutterheads of the types used on roadheaders, but at a smaller scale. These can be attached to small hydraulic excavators, usually on tracked carriers for more stability, or within small shields similar to backhoes. Provided there is a suitable hydraulic supply, the main consideration is a suitably small but powerful carrier.

Hydraulic hammers
Depending on the working space available, a hydraulic hammer can also be attached to an excavator of suitable size.

For efficient excavation the hammer tool should always be held perpendicular to the rock or ground to be broken and excavated, and ideally with the boom of the carrier held in a position to provide a constant feed force. Failure to do this will lead to increased vibrations through the carrier, perhaps affecting the operator. Zero feed and contact between the hammer tool (‘idle’ operation) and the ground shield should be avoided at all costs to prevent rapid wear of the tool mechanism. Care of the equipment also avoids excessive use for levering the ground out unless, as with a scaler, the equipment is designed for it.

Excessive reach between the tool carrier and the ground can result in the carrier’s hydraulic cylinders working at their maximum extent, which will also increase wearing vibration.

In harder rocks, drill-and-blast may be an alternative, but, again, with hand-operated tools there is a danger of excessive vibration. Single-boom hydraulic, and sometimes compressed air, drill-rigs are available, of the type used in mining to follow metalliferous mineral veins.

Tony Morris, now senior project engineer with Agrium in Canada, and formerly with Cementation, reports driving a 12ft x 12ft (3.66m x 3.66m) starting with an 8ft x 8ft (2.44m x 2.44m) pilot drive to assist in preventing overbreak. Throughout handheld drills were used in ‘moderately hard’ rock. “There were no problems with the regulatory authorities,” he reports. “Mechanised techniques would not have been cost effective.”

Hudd reports, “I was on a job in Somerset (UK) for drill and blast, but blasting restrictions became so limiting we went to hand excavation in mudstone, and made good progress. Jacklegs continue to have a place for small headings, miscellaneous utility work and initial off-shaft developments for sure.”

Mucking out
As is well known in tunnelling, it is of no use excavating efficiently if the spoil cannot be removed and transported in an equally efficient manner. This can also present problems in small sections, but, many practical ways of spoil removal have been developed over the years in conjunction with hand mining including rope-hauled pans on tyres or tracks (see separate Tenbusch article in this issue), armoured conveyors fed by gathering-arm or rotary loaders. If the whole length of the tunnel being worked is of small section, the equipment may cause an obstruction .

ITC-Schaeff models are available with a loading apron and a chain conveyor running through the centre of excavator that can be adjusted to suit the means of main muck transport.

On the Hampton project mentioned earlier, more efficient clearance of spoil was required so Metal Innovations delivered a Celtic Miner conveyor system and tracked materials transporter to the site, custom-made to work with the CM4500 excavator.

Cutaway diagram of an Atlas Copco light hydraulic breaker for manual use Small roadheaders may be applied to restricted working space such as this Sandvik set-up in a Swiss tunnel enlargement This Bobcat 324 compact miniexcavator has a retractable undercarriage and a reach of 4.27m Atlas Copco’s SB52 hydraulic breaker, here on a miniexcavator, is the smallest in the range at 55kg weight Hand excavation in pipe jacking can be avoided by complete microtunnelling mechanisations, but it has to be reliable, such as with this Herrenknecht slurry system