INTERVIEW | ALASTAIR BIGGART
had used for the cutterhead bearing seals
just the same very small seals that they had for all their other small machines and had not taken into account the fact that when you put on the pressure at the face of an earth pressure balance machine it will flex the bulkhead and flex the cutterhead a bit where it engages with the face. And, mistakenly, they had put the seals on the radial face rather than axial face. If they are on the axial face, if the front bit moves against the rear piece the seals can just
move slightly on the surface that they are engaging on. But if you put them on the radial face the seals would get crushed. That’s exactly what was happening. It was only discovered when bits of seal were squeezing out through inspection holes. “Between us we gave them advice to
change the whole sealing system, which they did just before they started driving under the river. It worked well, so that was good.” Biggart had been involved with seals
since his earliest days at Priestleys. “As I said, we were designing and making tunnel boring machines there. Main bearings in those days weren’t so big – around four or five metres – and the seals that we used went right round them and were made in a giant mould, in one piece. It was very difficult to get the diameter absolutely spot on.” Today there is a solution that is for sale in every high street: “Now you can make those seals just in long strips, and you can calculate the length that you need. You make a scarf joint at each end, and you join the two ends with superglue. Superglue is amazing stuff. It takes the stress and strain of going round and round about ten thousand times. So this was a big advance in the design of seals. “Of course that is just one of the advances
that I have seen during my career. I think one of the most significant was the gradual or rapid change from cast iron to concrete linings. It was all cast iron when I started in 1958. The Post Office tunnel that I first started my career on, for example, was cast iron and the joints were caulked, believe it or not, with asbestos rope impregnated with cement. At least one colleague of mine died of asbestosis, and I am sure that a lot of those caulkers must have died from it as well. “The art of designing segments now
is well developed. In the early days each segment had a sort of well in it to make a space for the bolts to go in. That has completely changed. Now you have an arrangement where the bolts go in at an angle just from a small tapered hole, and the sealing system is now fantastic. You expect to have a dry tunnel, which in itself is a huge advance. “For the future, I think we are getting
Above: A landmark project in Alastair’s career was the Channel Tunnel 46 | February 2025
towards the limits of size for TBMs. There is no doubt that machines may be slightly bigger in diameter than the EPBM for Alaskan Way in Seattle at 17.43m or the slurry machine used at Tuen Mun to Chek Lap Kok in Hong Kong at 17.6m, but, in the
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