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Second Mersey Road Tunnel

Tunnels

This was the most challenging job of my tunnelling career. The Second Mersey Road Tunnel comprised twin highway tunnels 9.6m in diameter and 2.29km in length, to link Liverpool with Wallasey. I was project manager, employed by the same contractor - Edmund Nuttall - which had built the original Mersey tunnel opened in 1934, which still represents a major feat of engineering.

Several innovative design features and construction methods were adopted for the second road crossing. Not least was the flexible cross-jointed 300mm thick steel faced segmental lining. The 1.2m long segments weighed 4.5t and were the largest ever cast.

The Second Mersey Tunnel pushed the frontiers of knowledge and was completed to budget and on time, but its execution represented a huge ordeal in terms of water, construction and labour problems.

Heavily fissured, the Bunter sandstone permitted more than 14M litres/day to enter each pilot tunnel. The soft rock, reduced to 75% sand by the Robbins unshielded tunnel boring machine (the largest ever built at the time) combined with the water to produce a thick, abrasive slurry.

The overspill from the cutter head played havoc with all the hydraulic and electrical systems. Eventually, the punishing conditions proved too extreme for the labyrinth seals to the thrust bearing which became unserviceable and had to be replaced in each drive.

This was the first time such a tricky operation had been attempted underground. The bearing was 4.5m in diameter and weighed over 6t. The work involved separating the 90t cutter head from the main body and opening a large cavity close to the riverbed in pouring water to provide access.

A major geological fault encountered in each drive had to be bridged, above and ahead of the TBM. The operation was carried out in the same arduous conditions and delayed the drive by seven weeks.

The contract was among the largest in the country at that time and was conducted at the height of industrial unrest in the UK. Merseyside was a notoriously difficult area in which to work. The job attracted the worst and most disruptive Trotskyist elements to three of the unions on site, and managing the works became a nightmare of constant strikes, endless union meetings, broken agreements and serious plant sabotage.

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