In 1945, although the Second World War was over, conscription for men into the armed forces was to continue for two years and, at the age 18, John, given his public school background, joined the Army as an officer cadet in the Royal Engineers and held a regular army commission, being promoted to Second Lieutenant in June 1947. After he was demobbed, he gained a place at Trinity College Cambridge as an undergraduate in the Autumn of that year to study for a law degree followed by a post graduate degree.
In the same year, John was on a visit to Milan to advise a contractor on tunnelling through the city’s gravel deposits who was laboriously using traditional methods. However, while there, he was able to see how the city's first metro line had been built, using the ‘cut and cover’ method, rather than bored tunnels. In this, Italian engineers had developed diaphragm walls, an ingenious method of constructing vertical retaining walls in non-cohesive ground by exploiting the properties of bentonite clay to support trenches during excavation.
Bentonite was a commonly available clay material that, when activated by chemical treatment to form a slurry, became 'thixotropic', which was a gel when at rest, but a liquid when agitated. On his flight back to London, John, in a stroke of brilliance, visualised how slurry trenches and mechanical digger technologies could be combined to create a new type of tunneling machine, with fluid support of the working face.
In technical terms, the new machine used pressurised bentonite slurry in a sealed bulkhead behind the cutting face to balance the water pressure in the ground and stabilised the tunnel while supporting rings were installed. The excavated soil was then separated from the slurry, which was recirculated to the cutting face. The experiment was deemed to be a great success, with tunnelling rates of four metres per 10-hour shift achieved. The invention, and the prototype, included all of the essential ingredients of a whole new class of slurry tunnelling machines (STMs) that were to follow all over the world, with many improvements were made on the way and by the end of the 1970s more than 1000 had been used worldwide. Unfortunately, further development happened outside Britain, since – apart from a single sewer contract in Warrington – no suitable projects emerged here for a decade or more.
In 1966 John became the partner for Mott, Hay and Anderson and director responsible for the firm’s transport and tunnelling work, including further projects in Toronto, advisory appointments in Madrid, Brussels and the Melbourne Underground Rail Loop. He also headed the project management of the Tyne and Wear Metro, coordinating its design and construction.
In 1971 John became a founding member of the British Tunnelling Society (BTS), a professional association established in London by tunnelling professionals, led by Sir Harold Harding. A 'Learned Society of the Institution of Civil Engineers', its mission being to provide a forum for meetings and discussion on tunnel-related matters. It subsequently took part in the founding of the International Tunnelling Association in 1974 and by 2016 it had 800 members.
The origins of the London Underground's Victoria Line can be traced back to the 1943 County of London Plan, but the shortages of the post-war years had caused delays. Parliamentary powers to build the line were obtained in 1955, but further funding delays meant that construction work did not start until 1962. (link) In his mid 30's, John was appointed as the 'Project Engineer' and was 41 when he saw it opened in 1968 between Walthamstow Central and Highbury & Islington and on to Warren Street a few months later and then saw the line was completed to Victoria in 1969.
John now faced the greatest challenge of his career as the 'Engineer with 'Design Responsibility' for the British side of the Channel Tunnel, first as a Principal Designer for the scheme and following the project's revision in the early 1970s, as a 'Principal Design Consultant' for all civil and geotechnical engineering on the British section. Digging began on both sides of the Strait of Dover in 1987–88 and was completed in 1991 and the tunnel was officially opened on May 6, 1994.The digging was done by huge tunnel boring machines, known as TBMs, which cut through the chalk, collected the debris and transported the debris behind it using conveyor belts.(link)
The descendants of John's original machine have been used in many major civil engineering projects. They include 'Ada' and 'Phyllis' (left), named after Ada Lovelace, the world's the world's first computer programmer, and Phyllis Pearsall, who created the London A-Z, the giant boring machines used by Crossrail to construct tunnels between Royal Oak and Farringdon. Also 'Busy Lizzie', which was used to cut the Lee Tunnel, the first section of London’s Thames Tideway ‘super sewer’. 'Mary' and 'Sophia' (right), the two tunnelling machines which completed the Thames Tunnel, were named after the wives of Isambard and Marc Brunel who constructed London’s first Thames Tunnel over 150 years ago. (link)
In a congratulatory letter to John, Ivor Thomas, the Chair of the British Tunelling Society wrote : 'Your invention of the slurry machine and its subsequent development has made a tremendous difference to how and where we can tunnel. Slurry tunneling has allowed us to develop tunnels in geology that would previously have been either very difficult and costly or impossible. Much of the Jubilee Line to the south of the River, the Channel Tunnel Rail Link Crossing and the Crossrail River Crossing were only made possible by the use of slurry machines'.
Lord Robert Mair, President of the Institution of Civil Engineers, echoed these sentiments with : 'There can be no doubt that a major revolution in the worldwide tunnelling industry was triggered by John Bartlett's invention of the bentonite tunnelling machine. It has enabled a rapid increase in tunnel construction around the world, particularly in urban areas, for water supply, sanitation and transport with remarkable benefit to humanity'.
On receiving the award, John said, with perfect self-effacement :
"Civil Engineering today is a team game. I hope members of my team will enjoy sharing the recognition given by this award. Many thanks to those who put me forward".