The old Alveley Colliery bridge was given a temporary reprieve back in September, when engineers decided that it was too risky to work on its replacement over the winter. Thus it seems likely that it will survive until this August. There is perhaps some irony in the fact that back in 1936/7 it was built in under a year and work continued all winter with no serious mishaps. The key to this was the way in which it was built, as a “balanced cantilever”. Essentially, this means that it was designed as a see-saw. The bridge has three arches; a large one in the middle over the river and two smaller ones either side to connect with the access roads. These are the “land arches”. The bridge was designed so that all the weight rests on the two piers that are either side of the river. The land arches run from these to walls that support the access roads and hold back the approach embankments; the abutment walls. However, these were designed so that they did not carry any of the weight of the bridge, they simply supported the approach roads. The key part of the structure was the two parallel reinforced concrete beams that ran continuously over the piers from Highley to Alveley and which supported the deck (the surface of the bridge over which people walked). As long as the reinforcing held, the bridge was safe.
The bridge led an uneventful life until the 1960’s. However, the Severn Valley is a notoriously difficult area for buildings. The ground is unstable, frequently slipping towards the river. This had started to take its toll on the bridge; the pressure of the ground was forcing the piers into the river. In addition, the abutment walls had cracks and the deck of the bridge was worn and needed replacing. Thus in 1967 the Coal Board decided it needed major repairs.
The main work was to stabilise the base of the piers. Coffer dams were constructed and the ground was built up to help the piers resist the thrust from the side of the banks. This part of the work passed without incident. The abutment walls were demolished and work started on rebuilding them. Again, this went smoothly, although the bridge apparently flexed visibly when heavy machinery was working on it whilst the abutment walls were missing. The deck was removed with pneumatic picks. Unfortunately, over the Highley land arch, the picks went in too deep and exposed a joint between the reinforcing rods in the beams that supported the deck. The joints failed spectacularly, the concrete cracked and the beams fell several feet at their landward ends until they came to rest on the partially rebuilt abutment wall. It is believed this incident caused a certain amount of panic at Coal Board Area HQ. Ladders were rigged up to allow men to pass over the dropped beams; without this, an entire shift would have been trapped on the Alveley side of the river. The beams were lifted back into more or less their correct place by jacks and the abutment was hastily rebuilt to support them. There was still a difference of a few inches between the top of the beam and the level of the approach road from Highley but this was made up by increasing the deck thickness with concrete from 6" to around 9". The repaired crack was carefully monitored but there is no suggestion that it has moved.
The excitement with the deck replacement meant that the repairs were not finished until October 1968. They meant that the bridge was no longer a balanced cantilever. By the time they were complete, the colliery was in its death-throes, closing in January 1969. Thus ended one of the less cost-effective jobs undertaken by the Coal Board in the West Midlands. It may however be suspected that the Area Engineer’s office was pleased to be rid of the bridge with its now unorthodox structure.