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Road works ahead - of its time

Jubilee Projects

In postwar Britain the country had its eyes on the horizon. Some of the dreams bloomed - and some withered away. Alan Sparks looks at two 1950s visions, one of which lit the blue touchpaper.

Although just 13.3km in length, the Preston bypass paved the way for the vast motorway network that today stretches across the UK.

As road traffic levels doubled after the Second World War, pressure on the UK road network threatened to hamper the progress of the recovering economy. Most county councils sharank awat from the prospect of the bridge maintenance burden that a new motorway brings, but in June 1956, echoing British industrial history, Lancashire was once again first to grasp the nettle of progress.

Today part of the M6, the bypass was built by Tarmac in 29months at a cost of £2.5M. Initially consisting of two, dual lane highways, enough room was left over in the central reservation - with no dividing barrier - to add an extra lane in each direction eight years after opening.

In 1963 the hard shoulder was brought up to the same specification as the rest of the carriageway. Until then it had only a thin sub-base with a grass topping, which had made it a popular picnic venue.

Ironically, the official ceremony to mark the start of the job witnessed a sight that reflected the climate for motorists at the time. After driving a bulldozer through a hedge to continue along the planned route after Minister for Transport and Civil Aviation Hugh Molson switched a traffic light from red to green, Tarmac foreman fitter Fred Hackett's machine came to a sudden standstill - having run out of fuel.

The effects of the Suez Crisis of 1956 demanded that every litre of fuel be spent wisely. Just to visit each section of works required a 56km round trip. This made the weekly ration of 150 litres of fuel shared between 12 members of staff particularly limiting.

Contractors had to deal with a 2.3M. m 3muckshift in arguably the most arduous conditions ever faced on a UK road job.

Undulating ground, including both the Ribble and Darwin river valleys, had to be traversed.

Embankments and cuttings up to 20m high needed to be formed from what turned out to be very sloppy ground.

Except for a large peat bog, initial surveys showed predominately sandy clay with occasional wet sand and silt lenses.

However, these lenses were found to be far more widespread than first thought and after two notably wet summers the site became a quagmire.

The local county surveyor insisted on a burnt red shale subbase. This was wet-mixed with crushed and graded limestone and laid 225mm thick. A 63mm tarmacadam base course was then applied, with 18mm fine cold asphalt overlaid as a wearing course.

Contractors dubbed the silty sludge of the Ribble Valley 'cow belly'. One junior engineer nearly lost his life as he sunk into the swampy mire. According to John Cox, Tarmac's site agent for the project and later a director, lessons learnt included the poor quality of the prescribed burnt red shale and importance of having sufficient drainage.

To keep costs low, the strip of land bought for the site was just 46m wide - the eventual width of the highway. As construction advanced neighbouring land had to be purchased by the contractor in order to dump spoil. One landowner drove a particularly hard bargain, demanding a fur coat in exchange for the right to dump on his land.

Such was the magnitude of the challenge, those involved were delighted when the project was delivered only five months late.

But, sad to say, just six weeks after then prime minister, Harold MacMillan, had opened the pioneering highway - it had to be closed due to frost damage.

John Cox is the author of a book on the Preston by-pass which is to be published by Thomas Telford later this year.

. . . and one that didn t quite work Creating a pioneering dome full of wondrous exhibitions on the south bank of the Thames was not a novel way of marking a special celebration. Back in 1951, the largest dome in the world sat close to where the London Eye stands today and formed the centrepiece of the Festival of Britain.

So fantastic was the gleaming aluminium Dome of Discovery that it even featured in the futuristic Eagle children's magazine. The reason it is not now listed as a landmark architectural and engineering structure is because just 11 months later the newly elected Conservative government ripped it down.

Despite this, an aluminiumpaved future based on wartime technological advances seemed assured. Surely the success of the Dome would spawn a succession of aluminium roof structures. But the hopes of the aluminium industry foundered, with only sporadic projects surfacing over the past half a century.

Ralph Freeman of Freeman Fox, best known as the designer of the Sydney Harbour Bridge, was appointed to carry out structural design on the 109m diameter dome.

Although 70 years old, Freeman retained an enthusiasm for what was a massively challenging project, not just because of the novel caption structural riddles, but because it was essential that a speedy erection was achieved at an economic price.

Due to welding limitations, connection design and construction, aluminium was much trickier than steel or timber. But it was decided that its lightness would be a massive advantage and it would be plenty strong enough for the job.

Predicting the wind effects on such a complicated structure was abetted by wind tunnel tests that were carried out at Queen Mary College. A system of 132 triangular rib sections, arranged in concentric circles, was eventually chosen for the dome's main structure. Each of the 864mm deep triangular lattice members were made of aluminium, and with a maximum length of 18.3m, were the longest extruded sections to have been made at that time. These were then overlain with 2,100 aluminium sheets. A steel box-section ring beam was used to contain the outward thrust of the dome.

Shaping the aluminium to match the dome's curvature needed special consideration.

Bending each member cold seriously reduced its strength, so moulding had to be done while the metal was still hot, innovative for the time. The engineers had to get to grips with what was basically a material completely new to the construction industry.

Minimising work on site and maximising the erection time meant that as much prefabrication as possible was needed. Bolt holes for each joint were drilled in the shop and the frame was put together on site like a big Meccano kit.

Freeman Fox engineers Oleg Kerensky and Gilbert Roberts had to make sure that all 133 rib sections met precisely.

Today an engineer would plug the data into a 3D framework package and pull out infinitely accurate co-ordinates.

Kerensky and Roberts, however, had to tackle this with tables of logarithms - and be accurate to seven decimal places.

In total, 232t of aluminium was used at a cost of £100,000, 133t of steel was supplied for £60,000, and erection by specialist contractor, Carter Horseley cost just £23,000.

Alongside the dome stood another aluminium-clad icon, the 91m tall Skylon. This unlikely steel framed structure achieved its improbable stability thanks to heavily posttensioned ground anchors.

Brilliant structural engineer Felix Samuely made the cigarshaped structure possible by using hydraulic jacks from three smaller pylons to stress the whole structure.

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