Relationships seemed clearer in 1960. There was a straight line between client and contractor with the ‘independent engineer’, responsible for detailed design and preparing the bills of quantity based contract, usually in the middle. The client and contractor rarely met, except for contract signing and the grand opening!
The ICE Conditions of Contract were introduced in the 1950’s, designed to provide a fair basis for sharing risk between the parties. Lump sum or cost plus was scarcely heard of. Clause 12, which placed the risk of ground conditions on the client, and the allowance for price fluctuation were most important for the tunnelling contractor in that time of rampant inflation.
With many more contractors there was less concern about monopoly. All were members of the Federation of Civil Engineering Contractors (FCEC). The important thing for a contractor was to be on client Select Lists (consisting of all UK based FCEC members). London Underground Limited’s list was the crème de la crème, cast in stone until someone dropped out through amalgamation or liquidation. While individual contractors had more limited powers than at present, the FCEC was extremely influential. They commonly issued instructions to their members to specifically modify.
Safety and compressed air
There have been bigger advances in safety than in any other area over the years. In the 1960s these would have been common:
- Work adjacent to live rail tracks with no barrier such as the Potters Bar Tunnel Contract (nominal 15 mph speed restriction)
- Helmets were worn only in rock tunnels, cloth caps elsewhere
- No hi-vis jackets, only donkey jackets
- No steel toe caps
- Access to shafts by long ladders
- Man-riding in skips was common
While risk assessment was not a phrase used, detailed method statements were used by contractors such as Charles Brand. It was considered normal for one fatality to occur in £1 million of construction work.
The normal solution to ground conditions problems was compressed air, mostly limited to 1 bar and occasionally used up to 3 bar. Cases of the bends were common amongst miners. The situation was improved by the introduction of a new set of decompression tables resulting from CIRIA Report No 44, commonly known as the Blackpool Tables. A wide variety of different air locks were used for decompression in the tunnel at the surface and in shafts.
Lining
Prior to World War II, cast iron was almost the only material used for tunnel lining. Normally only the cross joint surfaces were machined, with the circle joints packed with timber to ensure even contact without points of concentrated stress. Where greater accuracy was required all the joints were machined with much higher cost. The speakers noted that the effort in obtaining the accuracy specified was sometimes not justified. At the Portishead B Power Station shaft, great care was taken to ensure the accurate location of portals, but it transpired that the supposedly inflexible pipework could be adjusted by make-up pieces.
There were significant developments in use of concrete segments in this period:
- First use of concrete for linings occurred prior to WWII on the Circle Line extension
- An experimental section of smooth bore segments (Don-Segs) was used on the Thames Lee Tunnel just after the war
- Wedge Block segments followed on the Thames Water Main
- Sir William Halcrow designed a 26ft 6” diameter segmental lining for the Potters Bar Tunnel with 5t invert segment and 19 voussoir interlocking segments to complete the ring, without any bolts
- The first stage of the Victoria Line had two designs of smoothbore lining, by Halcrows and Motts
- Spun Concrete Ltd produced the Flexilok lining, grouted smoothbore lining in the early 1950’s
- Kineear Moodie Concrete Ltd designed a grouted boltless lining with interlocking joints KM Rapid in the early 1960’s
Primary support for rock tunnels was borrowed from the mines, in the shape of colliery arches, rolled steel columns formed into a “J” section and bolted together at the crown. Rock-bolts were not generally used.
Secondary lining for smaller tunnels designed to carry water had been engineering brick, laid to a high standard by members of an elite band of bricklayers. Larger diameter road tunnels and underground chambers had the panels filled in with concrete and then brick laid over the top, sometimes glazed as in the Blackwall Tunnel. In the 1960’s this changed with smaller tunnels lined with concrete; large diameter tunnels used such as the Clyde Road Tunnel with a lining of uPVC sheets supported on an aluminium alloy frame bolted to the cast iron lining.
Hand tunnelling and hand shields
Handwork has changed little over the years, but the work sites looked quite different from today. In the 1960’s there was less apparent regard for safe working practices and no formal risk assessment. Segments of 200kg or more were handled, much greater than today. Winch work with roller bolts and snatch blocks was used for larger cast iron work and required high levels of skill and supervision. Face timbering called for careful sequencing for support during the advance.
Good supervision was vital, particularly during grouting at the end of the night shift. On one occasion Buchan was barred from Metropolitan Water Board works on account of alleged bribery! The night boss paid the inspector a small retainer to stay at the face until the end of the shift to ensure the gang grouted up properly.
The principal tool for soft ground work was the Consolidated Pneumatic FL22 with clay spade and various hand-held picks for trimming rock. At that time there were no reported incidences of White Finger. The speaker wondered if problems now experienced could be due to the more effective tools and little attention to isolating the operator from vibration?
The shield developed in the 19th Century from Brunel to Greathead with little further development until after World War II. The Potters Bar tunnel shield was propelled by additive moderated water hydraulics, with motive power by reciprocating air-piston. The Taylor Woodrow set-up for the first Heathrow tunnel was very similar, except that it used modern hydraulics for propulsion, handling and erection. At the Clyde Tunnel, the hydraulics were oil and water, driven by fully protected electric motors, and with compact hydro-pneumatic accumulators. Oil-based hydraulics were not used because of the fire risk in compressed air. The hooded shield at the Clyde tunnel was built of welded steel by Westwoods and was sophisticated for its day. Every piece had to be small enough to fit through the air lock doors.
Modern hand shields are very similar in principle to earlier ones, although most are fully open and designed to accommodate mechanical aids to excavation and progress. They are of much lighter, welded construction, enabled by computer-aided analysis and better welding technology.
Tunnelling machines
Early tunnelling machines tended to be designed for specific conditions and unable to cope with wide variations in ground conditions. The very first machines in the UK were Colonel Beaumont’s Machine in the 1880’s on a pilot bore for the Channel Tunnel and the Price rotary excavator for London Underground in the 1930’s.
There were significant changes in the 50’s and 60’s. The development of compact hydraulic motors for military use and mining machinery together with enclosed electric motors enabled more flexible and efficient machines. The Kinnear-Moodie drum digger was used on the 100” Metropolitan Water Board tunnels, and an enlarged version on the Victoria Line Experimental Length running tunnels. The Drum Digger consisted of an inner “drum” supported by peripheral bearings and driven by hydraulic motors. Modifications were made to the digger in a later version by McAlpine, but the machines tended to clog when moisture content of the clay was high.
Subsequently, Nuttall-Priestley developed a very successful shaft mounted TBM used on the Ely Ouse water transfer scheme and Priestley went on to produce a range of successful rock and soft ground machines including the British Bentonite machine, based on John Bartlett’s patent.
It is regrettable that the British Tunnelling Industry has always been pitifully under-capitalised and, apart from Howden’s Channel Tunnel TBMs and Markhams, the development initiative has passed to elsewhere in Europe, Japan and North America.
Survey and setting out
In the 1960’s the first Microptic instruments with a stable accurate etched glass circle were just appearing. The typical six inch railway micrometer theodolites were difficult to read and heavy. A series of readings on different faces and averaged, was required to measure one angle. In the absence of optical distance measurements accurate distance measurement was by steel band, averaged and corrected for temperature and catenary. The tapes were carefully rolled and oiled after each use. With no lasers setting out utilised string line, boning rods and an ingenious arrangements of light beams with cross hairs.
Tunnelling in rock
The equipment at the face on the Clyde Tunnel comprised air-driven rotary percussive drills mounted on air-legs, plastic explosive cartridges with half-second delay detonators. It was a time of great transition. Air legs had not long been introduced, the tungsten carbide tipped drill steel was just coming in and there was much argument over cost benefit when the expensive Coromant steels were compared with other types. The intervening years have seen a revolution in hard rock tunnelling, largely resulting from use of the tungsten carbide drill tip.
The Clyde Tunnel which passed through coal measures, sandstones as well as soft ground encountered a variety of challenges including two compressed air blow outs, timber piles in the face, and collapses in the weak rock face. Use of explosives in urban areas was more relaxed and straightforward than today, nevertheless issues of vibration and noise needed to be addressed by innovative design of drilling patterns.
The Potters Bar Rail Tunnel The Clyde Tunnel Lining Clyde Tunnel construction Clyde Tunnel ground treatment Manual handling of linings The Kinnear Moody Drum Digger (model) Questions & Answers
James Thompson recalled the progress in pipejacking over the last 50 years. Techniques have developed from 1958 when casings were jacked under railways; in the 60’s concrete pipes were jacked, but limited to 2m diameter; in the 70’s the Japanese developed soft ground tunnelling EPBM and slurry techniques combining with pipejacking to make remote operation and small diameter jacking feasible.
Sir Alan Muir Wood the project engineer for both the Clyde Tunnel and the Potters Bar Tunnel commented on his re-design of the Potters Bar Tunnel with segmental lining at Horace Morgan’s insistence. This was the first big tunnel with segmental linings pushed directly against the ground, an interesting project which went well.
The Clyde tunnel had three clients demanding use of their own form of contract. The ICE Conditions were used in a way which removed risk the contractor was unable to control, from Brand’s contract. He did however accept partial responsibility for the blow which occurred on meeting the timber piles, which turned out to be deeper than stated in the details from 1882 construction.
The Clyde Tunnel was a similar magnitude to the Forth Road Bridge constructed at the same time. Unlike the Forth Road Bridge this exciting project was completed on time and within budget with relatively little publicity, an advert for a partnering approach.
Anthony Umney related how Charles Haswell told of the contractor’s claim for £0.5M on the Clyde Tunnel, how Charles Brand needed to be reminded that they should get the claim in before the end of the maintenance period otherwise there would be no claim.
Tommy Talbot recalled working on a 3 mile long 2 yard diameter tunnel in Sidcup in the early 60’s with London miners controlled strongly by foremen like Charlie Durrell and Tom Gibbs. They achieved 6 rings a shift and paid £78 per week. There was a big change with the influx of Irish miners. In the 60’s there were many more miners than there are today.
Rapporteur – Michael Francis
The speakers expressed their appreciation of all the friendships through the years in tunnelling as well as those who assisted them with pictures and preparing the presentation.
