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A1 Improvement schemes. Wentbridge to Micklefield

Wentbridge to Ferrybridge

This improvement scheme passes close to Darrington and comprised of the duplication of 2¾ miles of existing trunk road carriageway together with the construction of ¾ mile of new dual carriageway and was undertaken by McLauchlan (Knollongly) Ltd. a local contractor. This section of road was completed in 1961 at a cost of £259,000.

Access to the village of Darrington remained at grade for a further twenty or so years until the Darrington Flyover and Junction scheme was undertaken by the West Yorkshire Metropolitan County Council the successor authority.

Fly-over at Darrington Cross Roads

The main contract completed in 1978 was awarded to A. F. Budge (Contractors) Ltd at about £1.5 million. It involved the construction of 1.8km of dual carriageway and the Darrington Fly-over, to carry the A1 Trunk Road over the Darrington to Womersley side road linked by slip roads. 60,000 cu. m of rock and other material was excavated to form the embankments, together with associated side road construction, drainage, fencing and street lighting. Major temporary diversions and a Bailey footbridge for diversion of pedestrians were required.

Of particular note was the use of reinforced earth techniques for the abutment wing walls to the fly-over, based on designs by Dr Colin Jones who later went on to become Professor of Geotechnics at Newcastle University and a recognised expert in reinforced earth structures.

The Ferrybridge By-pass and Aire Bridge

The first Ferrybridge improvement scheme was carried out in the late 20's and permitted through traffic toward the centre of the old village with its coaching inns of the Angel, Greyhound and Swan. In the 60's with peak traffic of some 40,000 vehicles a day it became a notorious bottleneck with three mile queues at busy periods. Within one mile of road there were three major obstacles to traffic:

  • the existing Aire Bridge built in 1803 with single 20 ft. carriageway and 90° approach bends.,
  • a roundabout with the Pontefract to Goole A465 and
  • a signal controlled junction with the Knottingly to Castleford road.

Additionally, the A1 passed under two 35 ft. high railway embankments through narrow arches.

With dual carriageways already constructed and in use to the north and south, the possible alignment was very limited. The route necessitated the demolition of some 15 houses, one petrol filling station, the old derelict Angel Inn the fish and chip shop and the premises of the local bookmaker.

In March 1964, tenders were submitted for the construction of:

  • 1.2 miles of dual carriageway, two-lane trunk road, to motorway standards of construction.
  • the new 480 ft. long bridge over the River Aire.
  • a 190 ft. long flyover at Knottingley, with associated 0.5 miles of embankment and roadworks.
  • the 116 ft. long North Road Bridge, an underline bridge.
  • the 147 ft. long Doncaster Road Bridge, carrying rail traffic over the A.1. together with a footbridge and subway.

The construction of the new Aire Bridge involved bridging the River Aire without interfering with the barge traffic, and was designed for cantilevering from the piers.

The successful contractor, Martin Cowley, commenced work in May 1964 and went into liquidation during the Autumn of 1965, having virtually completed the Doncaster Road Bridge, one span of the North Road Bridge, and some 20-30% of all other work which included the piled foundations for the Aire Bridge. During excavation the ancient timber piles of the pre 1800 bridge were revealed.

Construction having started it had been decided that a fly ash embankment would be constructed each side of the bridge to lighten the load on the ground from 110/130 lbs. cu. ft. The associated problems with "flying ash" - a name conjured up by French engineers during a site visit - brought many complaints in a built up area, as did the heavy piling for the Aire Bridge. This was restricted to the hours of daylight which provided little peace for those on night shift at the nearby power station also under construction.

In December 1965, tenders were invited for the completion of the contract from a few major contractors with experience of cantilever bridge construction. Christiani and Nielsen were awarded the contract and started work in April 1966.

The construction period of the Aire Bridge was the determining factor of the overall contract period, as construction time occupied all but the last three months of the critical path. In order to complete the contract in the specified period, it was necessary for C&N to pick up the proposed construction methods, utilise the partly completed temporary works and engage the consulting engineer, Mr. C. Parry, to complete his temporary works design. The consultants, Drs. Peter Pell and Qwynne Davies of Nottingham University, were also engaged to adapt their deflection calculations to suite C&N's programme, which involved partially stressing the concrete at 3 days to allow earlier movement of cantilever carriages, and longer periods of construction at diaphragms.

Several difficulties were encountered in taking over these works and assembling the right type of men at the start of the contract. Fortunately, C&N had available staff and key-men experienced in cantilever operations, which enabled them to open the bridge to southbound traffic only 3 weeks later than planned.

The good progress being made by the roadworks staff, however, enabled the contract to be completed on time.

Knottingley Bridge is a four-span bridge having a deck formed of pre-cast, pre-tensioned concrete beams weighing up to 25 tons each, laterally stressed with 0.7 in. diameter strands. The deck spans are simply supported, being mounted on laminated rubber bearing pads to allow for any mining subsidence. The bridge is built on a skew and to horizontal and vertical curves. The cantilevered walkways were cast in situ; the deck-surface formed from a copper-lined waterproof membrane coated with ½ in. thick fine cold asphalt, and covered by a variable thickness of cold asphalt base course and 1½ in. thick hot rolled asphalt wearing course. The bridge, which carries four lanes of traffic, was opened twelve weeks ahead of programme.

Wentbridge to MicklefieldNorth Road Bridge a two-span bridge, carries two main railway tracks, has 8 ft. steel plate girders with 27 in. x 10 in. plated Universal cross beams, shear studs and a 7 in. reinforced concrete deck slab supporting 9 in. minimum ballast, the rail tracks and traffic.

The construction of the abutment involved removal of track and part embankment under a railway possession to install way beams over the position of the abutment during a rail possession. This enabled excavation and strutting to take place between the Frodingham 3N sheet piles and the old bridge. On completion of the 45 ft. deep excavation, the piled foundations were undertaken in conditions of limited access and headroom, and the abutment constructed.

The 180 ton bridge deck, which had been constructed on adjacent trestling, was rolled in during another rail possession involving removal of track, way beams and embankment.

The dumpling of earth under the new bridge-span was removed, wing walls constructed, footbridge built, and carriageway opened to traffic. The southbound carriageway and roadworks were completed five weeks ahead of programme.

The constraints imposed on the bridging of the River Aire were many and some quite rigorous. The Rivers Board would not allow any alteration to the regime of the river and the Navigation Authority requirements were most extracting. The closeness of the existing bridge, the hazards of boats, barges and tankers entering and leaving Ferrybridge Lock downstream, required a single span without need for centering in the river. The soil survey showed the bridge site to be composed of sand and gravel overlying badly weathered magnesian limestone.

After careful comparison of costs a concrete bridge was selected as being the most economical and aesthetically in keeping. The pinned cantilever formed a compromise between the suspended span and continuous type bridges.

Wentbridge to Micklefield2The Aire Bridge is an in situ prestressed concrete, balanced cantilever structure of 3 spans, the centre span is 290 ft. long and each side span is 145 ft. The width of the bridge is 83 ft. between the composite handrail crash barriers and includes two 24 ft. carriageways, one 10 ft. central reservation and 12 ft. acceleration lanes. The abutments and "V" leg piers are of reinforced concrete.

The deck of the bridge comprises of 4 box girders of varying depth supporting a continuous slab and cantilevers. The girders are joined together at each pier by a hollow torsion box, and by diaphragms at the abutments, mid span and two intermediate points. The abutments and piers are founded on post-tensioned pre-stressed concrete piles of 21 in. diameter.

Each torsion box is supported by four "V" legs which stem from concrete hinge units having a throat thickness of 6½ in. at ground level. These hinge units support the whole of the dead weight of 5,520 tons, at an average working stress of 4,500 lb. per sq. in., and also resist all horizontal braking and wind loads.

The out-of-balance loads are taken by the abutments and the shear pin joints at mid-span; the pin is designed to resist vertical forces, while accommodating most of the horizontal movements (caused by thermal and shrinkage forces) of the deck. It was the first time a joint of this type had been used on a bridge at least in this country. Relatively small movements occur at the abutments where the deck is supported on leaf hinge units through which pass the 1¼ in. Macalloy anchor bars which are stressed to 30 tons and transmit any live load uplift from the deck to the abutment base.

Wentbridge to Micklefield3The centre span was constructed by cantilevering out over the river from each pier, whereas the land spans were cast on movable shutters supported from the ground level. The deck was cast in 9 ft. sections, each section being stressed back to the torsion box by 1 3/8 in. Macalloy bars. The land span was constructed in advance of the river span, the out-of-balance moment being countered by eight temporary A-frames and eight 250 ton jacks positioned 24 ft. from the pier under each land span.

362 Macalloy bars, 1 3/8 in. diameter, are incorporated in the deck slab at the torsion boxes, in two layers. Each bar is anchored at the torsion box with an anchorage on either the land or riverside of the box. This enabled construction to proceed independently on the river and side spans. Each bar was stressed to 67 tons, using Christiani and Nielsen patented Mini-Jack. This jack proved invaluable, as the spacing of the bars did not permit the use of the standard Macall jack.

The applied longitudinal super elevation to the bridge deck was calculated with the aid of a computer for each concrete pour, to allow the bridge to creep to its true alignment in ten years time. The maximum super elevation applied near the centre of the bridge was 3¾ in. Today there is no evidence of "cusping" at the pin joint which has occurred on some early continental bridges.

A few bars were partially stressed on the third day after casting, to 22 tons, and in a few cases to 33 tons each, to facilitate striking movement of carriages. The specification called for 3,600 lb. per sq. in. cube strength and not less than three days for partial prestress, and 6,000 lb. per sq. in. and not less than five days for final stressing to 67 tons. During the winter electric blankets were used for curing the deck which ensured that the concrete obtained the necessary early strength.

The whole section of the deck was cast in one pour using temporary stop ends between the boxes in the desk slab to avoid any possibility of initial sets occurring at the top of the eight webs prior to casting the deck. The maximum size of pour was 110 cu. yd. The concrete was placed using half-yard capacity skips in conjunction with half cu. yd. Winget Mixers. The tower cranes were mounted on tracks to cover almost the entire bridge deck. The concrete was compacted with immersion type vibrators.

In addition to horizontal tendons in the top deck there were a number of tendons in the bottom support of the box beams near the hinge and at the abutments to cater for the changes in bending moment. 1¼ in. diameter Macalloy bars at 18 in. centres were positioned in 9 in. thick webs to accommodate the shear forces. Each concrete pour required the placing of between 430 to 5,020 lin. ft. of Macalloy bars, and the stressing of between 112 to 140 bars.

Wentbridge to Micklefield4The completion of the temporary works left by the previous contractor and construction of 60 complete 9 ft. concrete sections of the bridge took approximately one year. The cycle time for each concrete pour varied widely from seven to twenty-six days. This was largely the result of having to launch into complicated cantilever construction without the opportunity of building up gangs of men on less arduous work such as the construction of foundations and piers, Abnormal loadand was a peculiar feature of this contract.

The final contract cost with disruption and the re-assignment cost was of the order of £2 million with the Aire Bridge accounting for about one quarter of this sum.

The completion of the bridge enabled an abnormal load of a transformer to be delivered to Eggborough Power Station.

Although successfully completed in 1967 the settlement of the final account occupied the contractor and Resident Engineers staff somewhat longer. This was the last major contract of the improvements of the Great North Road in the West Riding in the 60's.

Brotherton By-pass

North of Ferrybridge lies the village of Brotherton known for its ancient manor house of the Archbishops of York.

The by-pass scheme which has a length of 1.01 miles traverses an area extensively quarried for limestone. The dual carriageway has an overall width of 87 ft. varying to 102 ft. at two points where the central reservation is widened to 30 ft. on either side and the carriageways also have in situ concrete marginal strips.

The construction of the carriageway is similar to other schemes but the final surface constructed of 2½ in. thick dense tar base course with 1½ in. thick dense tar surfacing.

The earth works involved some 200,000 cu. yds. of cut and fill.

Wentbridge to Micklefield5Major features were the construction of four bridges (a railway bridge, two over-bridges and a footbridge) and the extension of three large flood culverts at the southern end, which traverse the flood plans of the River Aire.

The decks of the Fox Bridge and the railway bridge consisted of Universal Beams placed side by side with steel mesh top and bottom and the whole encased in a concrete slab. The purpose of this type of deck was to reduce the construction depth to a minimum in order to take the motorway under the road at the Brotherton Fox Inn and then over the railway.

Dish Hill Flyover was on very poor ground and very long. BSP cased piles were used. When drilling for site investigation, the auger went down 15 or 20 ft. under it's own weight and the wash water on one bore hole was found to bubble out through another 10's of feet away.

The deck of this bridge was of steel construction despite Lovell's prejudice against steel. It was certainly quicker to design. The largest Universal Beams were used and stretched to their ultimate (about 73 ft.). There was no CP117/2 in those days, so the studs were designed in accordance with rules in an American design book by I.M. Viest.

The studs had to be individually welded on site by a stud gun. The testing of suspect studs took the form of swinging a 5 lb. hammer against them. The contractor felt this was not very scientific when they started to go over like nine pins. So in collaboration with McCalls, an attachment to the Lee McCall jack was devised and used to test the pull out strength of the weld.

The contract for construction was awarded in 1960 to Harbour and General Works Ltd. In the sum of £486,000. The by-pass was opened to traffic in 1962.

Brotherton to Micklefield

This scheme involved the dualling of the existing road between Brotherton By-pass and Micklefield By-pass, a length of 4½ miles. It comprised dual carriageways a 13 ft. minimum central reservation and two verges with a 4ft. 6in. hardened section adjacent to the carriageways.

Grade separation of all junctions was achieved throughout together with the segregation of local traffic and pedestrians in the village of Fairburn. All junctions were provided with acceleration and deceleration lanes.

Three major interchanges occur at the southern junction with A.63, B.1222 and again at the northern junction of A 63.

The road was designed for a speed of 60 m.p.h. The maximum grade was 3% and vertical curves were designed to give a minimum visibility of 950 ft.

The Contract, awarded to Dowsett Engineering Construction Ltd., commenced on 2nd July 1962 and was completed in November 1964. This was the first of many contracts to be undertaken by Dowsetts in the West Riding and later West Yorkshire.

Construction commenced and was undertaken in three sections.

The first section extended from Brotherton By-pass to Selby Fork. Phase 1 included a new carriageway forming the ultimate southbound carriageway of the dualling. This section of road was opened to traffic in the July. Reconstruction of the existing carriageway was constructed under phase 2, and provided the north bound carriageway of the duals.

The second section contained the bulk of the excavation required for embankments. To enable an early start to be made with this operation a temporary diversion was immediately constructed from Selby Fork south utilising part of the existing Trunk Road A.63 Leeds to Selby and part new construction. This diversion was taken into use on the 10th September 1962 and from that date until end of October 1962 marl from the area was compacted into embankments in the immediate area and at the northern area end of the works in the Boot and Shoe Flyover embankments.

The third section extended to Micklefield By-pass. Mention must be made of the drainage outfall along the Sherburn in Elmet road which was dug in solid rock.

Pavement construction consisted of crusher run stone sub-base in depths of 6in. to 18in. according to the C.B.R. values of the sub-grade. In situ marginal haunches with white top were constructed using the Parry type road form enabling approximately 1000 lin ft. of haunch to be completed in a 10 hour shift. Base construction included a 7½ in. depth of tar bound base in three 2½ in. layers and a 2½ in. depth of bitumen bound base, to give a completed finished thickness of 10in. The surfacing was of a 2½in. compacted thickness of hot rolled asphalt and ¾in. pre-coated chippings to a minimum compacted thickness of 1½ in. This flexible type of pavement was selected because of the possibility of settlement due to mining subsidence.

All main drains were laid and jointed with Cornelius type joints to ensure flexibility for the same reason.

The earthworks involved approximately 400,000 cu. yds of excavation including rock, and 120,000 cu. yds of imported granular filling material, which includes pulverised fuel ash.

Moisture content of PFA was very critical to achieve full compaction. During the winter of 1962-3 the site was closed down for over two months due to snow which commenced a week before Christmas, and then severe frosts until March 1963. Tests were taken and frost had penetrated the embankment fill to a depth of some 3 ft.

During the construction of the works a disused tunnel was found near Brotherton Village. It had apparently been used years ago to transport materials from a quarry to the canal. No ownership could be found, and as the tunnel was under the carriageway, it was decided to brick wall each end at the road boundary and pump a mixture of PFA and cement in a 20 to 1 mix to fill the tunnel section between the walls.

Wentbridge to Micklefield6The A.1 passes through the centre of Fairburn Village and Fairburn Footbridge was constructed to provide a link between the two communities. To allow for traffic of cycles and perambulators, approach ramps at a gradient of 1 in 10 were provided and span between a central spline wall and two circular columns in the form of an elongated spiral. The combined weight of ramps and supporting structure were used as an anchor block for the bridge deck, which pivots about a pier situated 15 ft. away from the spline wall. The deck was designed on the cantilever balanced arm principal with a central freely supported span of 45 ft. The overall length of the bridge is 145 ft. with a span between centres of pivot columns of 115 ft. Approach ramps and deck supports were constructed in reinforced concrete and post-tensioned beams were used with an in situ concrete deck slab. The vertical faces of the columns, piers and spline walls were treated with matt black "Arpon" paint and the soffits of approach ramps and deck beams with white Inertol, which was considered quite novel at the time.

Rawfield Lane is a single span overbridge consisting of three post-tensioned T-beams with in situ concrete make-up strips between the flanges, giving an overall width with cantilever edges of 31 ft. The bridge has a clear span of 98 ft. between the abutments which were constructed in mass concrete with reinforced concrete wing walls. The deck beams were cast in three segments at the manufacturers works and stressed together on site prior to erection. An impacted anchorage caused concern, but was cut out, reconcreted and restressed.

At Selby Fork two bridges carry the A1 dual carriageway over the Leeds-Selby Trunk Road. Each bridge has a central span of 53 ft. and two outer spans of 33 ft. The deck consists of pre-tensioned inverted T-beams with a transverse stressed in situ slab, supported on skeleton abutments, and slender reinforced concrete piers.

Whitecoat Lane Bridge is similar to those in Selby Fork but with reduced centre span of 47 ft.

Adjacent to the Boot and Shoe Inn a two span bridge supports a 24 ft. carriageway and 8 ft. hard shoulder and connects the Leeds Road (A.63) with the south bound lanes of the A.1. Pre-tensioned inverted T-beams with in situ slab form the deck, which is supported by mass concrete abutments and a reinforced concrete pier. Each span is 61 ft. Staircases have been provided at each abutment for pedestrians.

The site of the Brotherton Micklefield Improvement overlies extensive areas of mineral deposits which were expected to be worked following construction and bridges were designed to accommodate 18 in. of differential settlement with facilities for jacking.

The surface finish of the exposed abutment faces of all bridges were formed by the use of plastic moulds and the surfaces treated with a silicone solution. Darvic fascia panels were used to provide an artistic feature along the edge beams and to form a continuation strip across the faces of wing walls.

Sub-Contractors for the bridgeworks were Yorkshire Hennibique Ltd. and for surfacing, Messrs. Clugston Civil Engineering Ltd.

The cost of the final work was £1.6 million.