Engineering London Bridge: an interview with Michael Leeming
Interview with Michael Leeming, Lead Engineer of London Bridge's superstructure
In January 2019, the Illuminated River Foundation met with engineer Michael Leeming on the banks of the Thames to discuss his experience of completing the superstructure for London Bridge. After years of working on the bridge, and sending off its predecessor to Lake Havasu City in Arizona, today’s London Bridge was finally opened on 16th March, 1973. Fifty years later, Michael Leeming recalls a fascinating time spent on one of London’s engineering feats.
What challenges were involved in building the busiest bridge in London?
Particularly challenging was a requirement that vehicular, pedestrian and river traffic was at no time to be interrupted. Thankfully, we achieved this. Pedestrian traffic was especially important, with hordes of commuters crossing the bridge daily on their way from London Bridge station to the City. This is why we made the pavement on the eastern side of the bridge wider than on the western.
The space for construction was extremely limited because of the bridge’s historical location. This meant that units of bridge were cast off-site at derelict Surrey Docks, then barged upriver and lifted into place. To facilitate this, a huge steel truss was erected at high level across the river, which not only supported the units as they were joined together, it could also facilitate the demolition, piece by piece, of Rennie’s old granite five span arch bridge. Our new bridge is actually four bridges joined together laterally and is twice as wide as the old bridge.
The construction sequence involved taking the corbels off the edge of the old bridge on the western side, so we could build a new bridge beside it and divert some traffic here. We then repeated this on the eastern side of the bridge. After one side of the old bridge was demolished, a third bridge was built in its place. Finally, the old bridge was completely demolished, and the fourth bridge put in place. The four new bridges were then joined together into one structure.
Another big challenge was that the greater part of the work was carried out from below from barges in the fast-flowing tidal river. Understanding the state of the tides was very important due to the very strong currents (7 to 8 knots) between tides. Certain operations had to be scheduled at high or low tide. The current was increased due to the new piers not aligning with old. At one point, a barge crashed into the cofferdam doing a lot of damage.
What is your favourite memory of working on London Bridge?
My favourite memory would be the opening of the bridge on Friday 16th March 1973 by Her Majesty the Queen, who presented me with a medal coined by the City of London to mark the occasion. There was a reception afterwards at The Guildhall and a Service of Thanksgiving at St Magnus the Martyr. It was wonderful to have all these ceremonies to mark the culmination and achievement of some six years of hard work.
I also won’t forget the challenges of taking the old bridge down, numbering each piece so that it could be sent to America and re-erected at Lake Havasu in Arizona. As only a 4 or 7 inch slice of the face of the stones was sent to America, we had to devise a system to mark the face to survive the cutting, the journey to the States and its placement on the new structure.
How was the bridge’s structure determined?
The architect’s concept for the bridge was a slender structure that had to accommodate the constraints of the existing road network and surrounding ancient buildings. A reinforced concrete structure like Waterloo Bridge would not meet the requirements – our bridge needed to be constructed in prestressed concrete. This was a relatively new construction method which had come to the fore after the war.
Could you tell us about the range of materials that were sourced for this bridge?
The new bridge’s cement was originally going to contain local Thames Valley gravel aggregate. However, the project architect decided that as the previous bridge, designed by John Rennie, had been constructed with Cornish granite, the new bridge should match this style. Much research was carried out to find suitable aggregate which was eventually sourced from Scotland, many tons of which had to be transported down to London. The parapets are also made of polished granite with a stainless-steel handrail above. Heating cables were installed under the asphalt surfacing during the construction with the plan to melt ice on both the carriageway and the pavements. I understand that they never used this technology due to the cost.
Where is your favourite spot to view London Bridge and admire its architecture?
For me, the best spot is probably from the river itself, on a boat.
What do you think the Illuminated River project will bring to London and its bridges?
Originally, the Thames was a commercial river with many warehouses turning their back on the riverfront. Access was very limited and there was a decline in pleasure traffic traveling on the water. Today, walkways have been constructed along the river banks and new pedestrian bridges have been built; while old warehouses have been turned into museums, shops, residential and office accommodation. We see far more pleasure craft and commuting traffic. Londoners are beginning to be proud of their river and use it once again.
The Illuminated River project will continue this process and do much more. It will emphasise the corridors of infrastructure joining the areas south of the river to the West End and the City. It will highlight the work of many eminent engineers who have built these great structures over the Thames.
In this project, engineers will also be seen to be facilitating public art. London Bridge has become almost insignificant against neighbouring Tower Bridge. The lighting up of London Bridge by the Illuminated River artwork emphasises its slenderness as a ribbon of light across the river, a gateway to the shining city of London, putting it in its place amongst other landmarks such as the 'Gherkin' and the Shard. It is wonderful to see a bridge I spent many years working on celebrated in this way. I heartily endorse the Illuminated River project.