While most tunnellers are at least aware of ‘compressed air working’ in tunnelling, the related activity of diving seems to be outside the scope of the activities of most. This may be because diving teams are called in to perform a specific task, which they usually get on with in isolation, having minimal interaction with others in the tunnelling workforce.

However, diving has been associated with tunnelling ever since Marc Brunel lowered a diving bell into the River Thames in efforts to repair breeches in his Thames Tunnel at Rotherhithe; the world’s first tunnel under navigable water. Also in the Victorian era, lead diver Alexander Lambert working for contractor Thomas Walker entered the flooded Severn Tunnel in 1880 between Wales and England to help seal off the tunnel from persistent inflow from The Great Spring during construction. The work was completed in 1881, although flooding returned later and Lambert was called upon again. He used the newly developed Henry Fluess’ self-contained breathing apparatus instead of surface-fed air, the hoses of which became entangled as he entered through a shaft and walked 300m to close a watertight door and valves. A refined version of the self-contained underwater breathing apparatus (SCUBA) is still in use.

Divers are an elite, or should be, who have earned their position through intensive training, fitness, specialist knowledge and not a little courage. In fact, in many countries specific training to satisfy regulatory authorities. Divers also need to have regular and thorough medical examinations to check on fitness for their tasks, and in most cases to administer vaccinations against diseases such as hepatitis that may be acquired from contaminated water.

Although the uses for diving may have reduced in tunnelling over recent years, where they are needed they are essential, whether it is a planned activity in the project or to get the project out of difficulties. There are also roles to play in certain existing tunnels for inspection and maintenance.

Applications
One of the most common uses for divers in tunnelling was for work around the entry, and perhaps exit points for TBMs with shafts under groundwater. It is often more practical and safer to let a shaft flood and use divers to carry out steel cutting, welding and alignment work to clear the way for a TBM to pass through the lining.

In recent times such work has become less necessary both due to more accurate guidance and monitoring of TBMs, minimising cases of misalignment, and the advent of various designs of ‘soft-eye’ in tunnel linings that allow the TBM to cut its way into or from the shaft without allowing any major leakage of groundwater into the shaft. One exception was by Bekk Solutions (BSL) divers in Hunghom, Hong Kong, where they performed underwater welding, burning and grouting in the flooded reception shaft to recover a TBM. Bekk uses surface-supplied mixed gas diving procedures as well as more conventional approaches. Flooded TBMs have also been recovered using compressed air working in difficult ground conditions.

Immersed tube
Another situation in which water is a tool as well as a hindrance is in tunnel construction by immersed tube. The use of waterproof CCTV and digital imaging greatly simplifies the supervision of installation operations underwater, such as for dredging, lowering segments into position, and adjustments. However, there are many tasks requiring close inspection and handling duties such as checking seals and repositioning pumps.

One immersed tube operation that placed particular demands on diving was of the first tube segment of the new Amsterdam Nord-Zuid metro line including a crossing of the River Ij in immersed tube.

One of the divers on the intricate, and possibly unique operation by Strukton, Van Oord and Heijmans to place an immersed tube section under the Amsterdam Centraalstation is Martin Sitsen. He started commercial diving in harbour caisson work in 2006, and is also a hyperbaric lock attendant. His current underwater work, associated with placing the tube section in the Zinc slot, as it is known, includes high-pressure grout removal, cutting through old wooden piles with a chainsaw, and various metal cutting and welding jobs. He reports that visibility is fairly limited (about 16m), but he prefers the work near his home rather than the long periods away on previous North Sea oil and gas diving work.

Such has been the battle with the North Sea in Europe, particularly in the Netherlands, Belgium and west Germany that a great deal of expertise has been built up both for diving and other related hyperbaric activities. In the Netherlands in particular the invariable use of immersed tube tunnel technology until recently has involved diving and dredging work for placement and connection of segments.

Tunnel inspection
Ideally water tunnels should be inspected and maintained while dry, but for operational reasons this is not always practical and diving has to be adopted. The New York water supply system has had a long history of difficulties, frequently needing underwater inspection and maintenance. One such campaign started in 2008 when Global Diving & Salvage of Seattle was called in to repair a valve for the Roundout Contractors JV on the 73km-long Roundout-West Branch tunnel from the Catskill Mountains reservoirs. This necessitated diving saturation techniques, similar to those in extreme hyperbaric tunnelling, using a breathing mixture of around 97.5 per cent helium and 2.5 per cent oxygen to work in over 200m of water. Prior to the work it was necessary for Global to demonstrate to the client that its divers could carry out the necessary tasks within an immersed mock-up layout in Seattle. The equipment required nondestructive testing, including underwater cutting welding and drilling equipment. Various tasks meant that the diving team have been engaged there until this year.

The team of six divers required a total global team of 32 to support them with life-support control, food and drink, and special reading material. Various necessary goods were passed through a materials airlock into the saturation living chamber that also included showers, a television and a basketball hoop. The diving teams live in the chamber for a month at a time leaving only to enter the diving bell for work, or to leave after decompression at the end of their stint. For work the diving bell was lowered with three divers to the work site for a 12-hour shift with each man taking a four-hour turn to work, including partial demolition to gain access to replace valves.

Equipment
Due to the complexity of many diving requirements and the need to ensure safety, any assembly of diving equipment is likely to contain many parts that will need to work together. Functions will include a portable or mobile air compressor with filtered air discharge, air tanks and back up system, full instrumentation for pressures and air/gas supply, communications to all parties, video systems, testing equipment, sufficient tubes and cables, diving suits to cope with the expected conditions, diving helmets, weights, gloves to suit the work to be performed, and the tools required such as underwater cutting and welding equipment, hydraulic power saw.

There are well-known suppliers of such equipment. Draeger, well known in tunnelling for gas detection and rescue equipment, supplies a full range of diving equipment including compressors and diving helmets. Another well-known make of diving helmet is Kirby Morgan.

The unusual
Diving teams have to be prepared to tackle the unusual, and this may not even mean going under or into water. They are just deemed the best people for the job. In the aftermath of the New York World Trade Center (WTC) attack divers were sent to wade through water in a 1,500ft (460m) tunnel to reach the PATH station below the WTC where siphon pipes were installed to remove the flooding. Among the hazards that might be expected were excess carbon monoxide and high temperatures.

Another unusual task that ended
tragically was when five men were sent into the new 9.5-mile (15.2km) long sea outfall tunnel from Boston’s Deer Island sewage treatment plant in 1999 to remove safety plugs to allow connection to the sea and let the tunnel become ‘live’. Although the tunnel was relatively dry, diving techniques still had to be employed, as there was no ventilation in the tunnel and minimal oxygen. Equipment was carried in using two Humvee rough-terrain vehicles and a trailer. As the tunnel got narrower the team split, three advancing on foot and two remaining with the Humvee as back-up. The two back-up divers suffocated due to faulty prototype breathing equipment.

While this incident is now old it still holds many lessons, including the importance of thoroughly testing all equipment and procedures before use, the dangers of long distances without proper communications, and the need to resist the pressures from project delays and finance when such difficult procedures and unusual procedures are being undertaken. No similar work has been attempted since, but use of double or triple breathing supplies is now common.

Unmanned inspection
One approach to increase safety is to remove divers altogether from the necessary task, if this is possible. The equipment was originally developed for deep-sea work without exposing divers, but some flooded tunnel inspections lend themselves to this work. A leading supplier, Seaview Systems of Michigan, subcontracting to ROV Downunder, completed Australia’s longest tunnel penetration at 2.2km for the sea intake. The work was for as-built investigations of the intake and outlet tunnel for the Gold Coast desalination plant, which the Gold Coast Desalination Alliance, a JV of John Holland, Veolia Water, Sinclair Knight Mertz and Cardno, constructed for the WaterSecure authority of Queensland’s government.


Seaview Systems control centre used in the inspection of the GCDA desalination plant intake tunnel, Australia