Durham, "one of the most splendidly sited medieval cities in Britain, its rocky outcrop, washed on three sides by the River Wear was from the earliest times a secure fortress against invading Scots and Danes. The town grew up in the shelter of the towering cathedral and castle, both built by the Norman Prince Bishops who ruled Durham as a City State. The unique powers which succeeding Bishops held were not relinquished until 1836. They did much to enhance the city we find today."
The by-pass whilst improving access to Durham from the north and south also initially brought relief to traffic in the city.
The route of the Durham Motorway, from Aycliffe to Chester-le-Street, was first published in the County Development Plan in 1954. In 1958 the County Council, as the Agent Authority of the Minister of Transport, was invited to carry out the detailed location work to line order stage, and subsequently to undertake the complete design in 1961.
Over the 22 miles length between Aycliffe in the south and Chester-le-Street in the north, the route of the motorway crosses three Principal Roads, the A.689 Bishop Auckland to Hartlepool, the A.177 Durham to Stockton and the A.690 Durham to Sunderland. The major interchanges planned on these roads broke the whole project into four sections of between five and six miles each, estimated to cost £3 - £4 m and contracts for these were let over a period of two years from October, 1965 to October, 1967. In addition new side road totalling some 13 miles of new construction were necessary. The individual sections of the motorway were progressively opened to traffic when completed thereby easing congestion on heavily overloaded sections of the Trunk Road A.1.
The project had a large measure of public support in the County over the whole 22 miles length; in only one instance did the Minister have recourse to a Public Hearing.
It has been recognised in the earliest stages of the location of the route that ground conditions were bad. In the event they turned out to be rather worse than expected when combined with a succession of wet summers during the construction period, thus providing major worries for those directly involved.
On the Aycliffe-Bradbury section, Contract 1, let to A Carmichael Ltd., the route crossed the site of a post-glacial lake, the Skerne Lake. Bore holes and probes proved depths of up to fifty feet of soft silty clays, with the consistency of toothpaste, underlying a crust of firm material three or four feet thick. Investigations spread over a band of several miles width to locate an optimum narrowest crossing point of this prehistoric lake. This was found, but even so a length of a quarter of a mile was involved, and 300,000 cu. yds. of the material was removed. This was dumped on 45 acres of adjoining land and the excavation backfilled with slag and other waste material. The slag came mainly from a reclamation scheme in Spennymoor; the silty-clay after drying out for three years was levelled off and soiled over and later returned to agriculture. The main excavation works were carried out by Dowsett Engineering prior to the letting of Contract 1.
The co-operation of the landowners, the church Commissioners, the Eldon Estate and their tenant farmers in this area was much appreciated without which the work could not have been undertaken. There was another story in this area.
Ricknall Carrs was a lake of fine grained silt, on the line of the motorway about ¾ mile across. The Durham engineers had decided that the silt should be excavated and backfilled with Colliery shale.
The Bradbury-Bowburn section, Contract 2 was let to Cementation Construction Ltd. On this section the outcrop of Permian geological series is crossed with its extensive dolomite quarries. Here the motorway was routed to sterilise a minimum amount of this valuable mineral. North and south of the magnesium limestone ridge the usual Durham County patterns of soft laminated clays and silts was encountered which, near the interchange on the A.177 at Bowburn necessitated considerable extra land acquisition during the contract works to deal satisfactorily with a perched water-table as well as water-logged silty sand which had not been revealed by the preliminary soils investigations.
The third contract, Bowburn to Carrville, undertaken by W & C French Ltd. crosses the recent alluvium of the Wear Valley where soil conditions were expected to be particularly difficult. At the design stage approximately one-third of the excavated material had been identified as potentially unsuitable for fill, but with an unusually wet summer during the works more than half had to be removed from the site. Because of the poor ground conditions cutting slopes of 1 in 4 and 1 in 3½ were adopted and produced an easy blending of the motorway into the undulating countryside which it crosses. The main problems on this section were in obtaining that stability of the embankments formed from definitely marginally suitable material, and the underlying weak sub-soils. A number of slips occurred, to contain which embankment slopes were graded out over the adjoining land and the thick drainage layers were incorporated at 10 to 15 ft. intervals to reduce pore water pressure building up on the high embankments.
The Durham Motorway contract 3, Bowburn - Carrville, was obtained by French in April 1967, at a figure in the region of £3,500,000. The work started in May 1967, and was programmed for a two-year completion.
It comprised the construction of a further 4½ miles of the Durham Motorway from north of its junctions with the A177 at Bowburn to half a mile north of the two level interchanges with the A690 at Carrville. Included with the motorway works were several structures, including overbridges, underpasses, Armco culverts, and an extension to the existing railway bridge at Carrville.
The route lay through the Durham coalfield, an active mining area, and particular attention had to be paid to possible surface settlement in the future.
A breakdown of the main items of the work at the tender stage was: earthworks, fencing and site clearance, £900,000; drainage and services, £500,000; pavement construction, £900,000 and bridge construction, £600,000.
The earthwork team excavated and stockpiled approx. 200,000 cu. yds. of topsoil, 900,000 cu. yds. of cut and fill to embankments and 1,250,000 cu. yds. of unsuitable filling materials off site to a tip adjacent to the site. Over and above these enormous quantities, 100,000 cu. yds. of rock was excavated and broken down to size for re-use as filling in the embankments. Topsoiling operations were completed in time to enable the seeding contractor to complete his contract.
The drainage had its share of difficulties of working in bad ground, including running sand. Pumping was necessary and at one time up to 40 pumps of varying diameters were employed, also dewatering equipment was necessary to enable work to proceed south of Bridge 42 for approx. 1,000 feet run of trench. Storms on three occasions flooded the site, but despite these difficulties the work forged ahead and completion time was as programmed.
The formation team on the motorway alone (excluding side roads) dealt with approx. 250,000 cu. yds. of shale filling and 100,000 cu. yds. of imported common fill. Both shale and common fill were excavated and carted to site by means of 657's under extreme weather and site difficulties, but eventually these were overcome.
The fourth section, Carrville to Chester-le-Street, awarded to A. M. Carmichael Ltd., crosses an area of generally rather better soil conditions than was expected but was complicated by the presence of ancient coal workings, only partly collapsed, at a depth of about 25 ft., two areas of opencast backfill, a brickyard, and a half mile length of low-lying river flood plain with underlying compressible clays to a depth of over sixty feet. This latter section was the site of advanced earthworks carried out by the County's Direct Labour organisation, working in close association with the Opencast Coal Executive. The northernmost opencast site was worked where the motorway was to be in about twenty feet of cutting, the land was restored to this level and the surplus hauled to form the motorway embankment further north, after removal of 80,000 cu. yds. of soft surface layers. The anticipated settlement of the embankment as calculated had largely taken place by the time the carriageway works were commenced under the main contract. Ameys were the surfacing contractor for this section with the same team under Gibbs.
There are a total of 60 bridges on the four sections of the motorway and their overall cost was almost £4 million.
In November, 1964, a contract was awarded for the advance construction of two crossings of the River Skerne, three bridges over the main London-Edinburgh railway and two other bridges, and these were completed in time to provide accesses over these obstacles for the earthmoving equipment of the main contracts.
Possessions of the track were available only for periods of over seven hours early on some Sunday mornings, and the bridges were designed largely for speed of erection. Two railway bridges on Contract 1 were underlain by some 30 ft. of soft laminated clay, and were designed to be supported on bored piles but the alternative of using steel H-piles was accepted. A very close watch was kept during the driving of the first piles to ensure that there was no excessive heave of the track. In fact no measurable movement of the rail track was detected at any time. A speed restriction was enforced during piling operations but the foundations of these bridges, and the two bridges at Nunstainton on Contract 2, which were founded on boulder clay, were given sufficient clearance from the track to enable them to be constructed while trains were operating at full speed.
On the main motorway contract, the same type of bridge design has been used for both sections 1 and 2. North of Bradbury the motorway is built over the coal measures, and the possibility of some movement from old and fairly shallow workings could not be ignored. This consideration, together with a desire to keep obstructions in the motorway to a minimum, resulted in a simply supported single span bridge of robust appearance, which reflects the workmanlike character of the region to visitors approaching from the South, and was in keeping with the semi-industrial nature of the mid-Durham countryside. This theme was continued in the colour scheme of the bridges, where the sombre bulk of the substructure was relieved and given continuity by the lighter shades of fascia and coping.
The bridges on Section 1 were supported by driven in situ concrete piles, founded through the alluvial and laminated clays to the boulder clay below. On Section 2 none of the bridges have piled foundations and, where the ground bearing capacity was insufficient for a normal strip foundation, a cellular foundation was employed which "floats" the bridge in the sub-soil and results in little or no net increase in bearing pressure at foundation level.
The requirements for the bridge decks in the mining areas have resulted in the choice of steel beams acting compositely with a concrete deck slab. All these bridges have provision for jacking to correct the effect of subsidence movement and laminated rubber bearings were used throughout.
On sections 3 and 4 of the motorway there was a change of emphasis on the bridge types. The possibility of mining movement was less general and rockhead approaches nearer to the surface. Thus, although five single span composition bridges were built on these sections in positions where visibility or subsidence requirements made them necessary, there are also six multi-span bridges. These latter have prestressed inverted T-beam decks, with steel beams to provide additional edge stiffening. Once again the deck has been made to appear continuous from bank to bank, while the piers are sufficiently robust to emphasise the stability of the structure.
Two bridges on Section 3 under the Ferryhill and Pelaw branch railway created the usual problems of keeping rail traffic operating during construction. At Whitwell a temporary diversion of the railway was formed so that the bridge could be built in situ but at Belmont railway bridge the problem was to add a second span to an existing bridge. This was done by carrying the railway on way-beams and troughing, erecting the deck on trestles, and rolling in the usual way. The design of the new span followed that of the old span as far as possible. Plans of the existing bridge dated 1890 were obtained from the Railway Board and although the substructure information was rather sparse it was quite accurate.
At the Blind Lane Interchange at Chester-le-Street, two bridges and the embankment between them were built in advance, to allow for the settlement of the embankment over a considerable depth of alluvial material. Steel H-piles were used, the longest being 87 ft. 6 in. To avoid the problem of the bridge being left at its original level while the embankment on either side settled, an extra 1 ft. depth of filling was laid over the bridge which could be removed if it ever becomes necessary to regulate the pavement levels.
The two major structures on the motorway occurred at the crossings of the Lumley Dene and the River Wear. These are the only structures on the Durham Motorway designed by Consultants, and Messrs. R. Travers Morgan and Partners were appointed by the Ministry of Transport with the full approval of the County Council.
Lumley Dene Bridge crosses a deep, steep-sided valley of considerable natural beauty, and, in keeping with this setting, the motorway is carried by this shaped steel arch which soars from 80 ft. above the valley floor. The three-pinned arch has a span of 191 ft. between springing points, and two spans simply supported between the "knees" of the arch and abutments on either side increase the total span to 330 ft. Both the arch and the side spans are of structural steelwork, acting compositely with reinforced concrete deck slabs, with separate structural systems provided for each carriageway. The arch hinges were formed using knuckle pin bearings, and the design provided for the internal inspection of all box girders, bearings and hinges. The foundations of the arch piers were taken down to siltstone.
The River Wear Bridge also has separate structural systems for each carriageway. The bridge is of reinforced concrete construction having a fully continuous five span constant depth deck slab with a total span of 345 ft. between abutments. Each pier under each carriageway consists of two V-shaped supports springing from a common base. Both abutments are of the bank seat type and consist of a shaped bearing beam support on four or five stepped narrow columns to facilitate the construction of the motorway embankments, which were placed after the completion of the bridge. The bridge is supported on steel H-piles driven down to rock level.
All but the southernmost section of the Motorway, Contract 1, Aycliffe to Bradbury, cross the Durham Coal Field. At an early stage discussions with the National Coal Board were opened in an endeavour to relate coal extraction to the programme of motorway construction.
The co-operation of the Coal Board in re-phasing their work and so ensuring that subsidence was virtually complete under long lengths of Contracts 2 and 4 was very much appreciated by all concerned. No further extraction was planned that would affect the motorway but in line with the then Ministry of Transport's policy of not sterilising coal, the structures and motorway construction were designed to withstand subsidence without serious damage should this occur in the future.
The assistance of the Board's mineral surveyors and geologists was invaluable in the location of shallow coal workings and in Contract 4 a section of these was dug out and refilled by opencast methods. Quantities of unstable coal were uncovered in the pillars between the old workings and the Board met the cost of selecting, digging, and transport.
At the River Wear Bridge site on Contract 4, boreholes penetrated old workings only twenty ft. below river bed level. It is unlikely that the river was in that position at the time of the workings as there is evidence of substantial movement of the channel at that point. The bridge, one of the major structures on the motorway, was sited clear of the workings, built in the dry and then the river was diverted back to its original course of several hundred years' ago under the new bridge.
This, however, still left the workings, but sited under a forty feet approach embankment. The closeness of the River Wear, the waterlogged ground, and the likelihood of connections with current workings precluded the possibility of opening them up and the area was therefore slabbed over in heavily reinforced concrete.
With the possibility of mining subsidence on Contracts 2, 3 and 4, and the extensive alluvial deposits on Contract 1 with its long term settlement problems, a fully flexible construction for the carriageways was adopted with the contractors selecting either tar, bitumen or asphalt bound road based material. Contract 1 has asphalt, Contract 2 tar, Contracts 3 and 4 asphalt bound base. The 4-in. two-coat hot-rolled asphalt was common throughout with sub-base thickness of between 12 and 20 in. of crushed rock, depending upon the bearing value of the sub-soil.
A positive system of drainage was adopted throughout the carriageway draining into pre-cast concrete channels and normal road gullies. On the Durham Coalfield section flexible pipe-joints were specified and the system was designed to function with a 1 in 250 change of level. French drains were provided in the verges and the central reserve.
The emergency telephones provided at one-mile intervals along the whole length of the Motorway connected with Durham Police Authority's control room at Aykley Heads. When a call is made from one of the telephones, its position on a large display map on the motorway is illuminated, enabling immediate identification of the site of the breakdown or emergency.
The main Service Area, initially planned for building concurrently with Contract 2, was unable to go ahead due to difficulties in land-acquisition and was built later. Service Area facilities were also provided north of the Durham Motorway north on Birtley By-pass.
From the beginning of Motorway Construction on the Darlington By-pass, full-scale laboratory and testing services were supplied by the County Council with the agreement of the Ministry. Field testing personnel and laboratory technicians were trained in the Central Highways Laboratory at Durham and employed in a well equipped site laboratory at Bowburn, under the supervision of an experienced materials engineer, and with apparatus provided by the Ministry of Transport.
Durham Police Authority provided valuable assistance at all stages of the Motorway construction by way of advice on traffic diversions and traffic control. Roadworks of this magnitude inevitably inconvenience road users but the close association between the Police Authority's staff, the resident engineers and the contractors went a long way to minimising this.
The Royal Automobile Club and Automobile Association also gave valuable advice on signing of diversions and accepted the responsibility of providing the many additional temporary signs necessary as each section of the motorway was opened to traffic.
The construction of this Motorway network involved the excavation of some 5,800,000 cu. yds. of material, 870,000 cu. yds. of imported fill, and 930,000 cu. yds. granular and free draining special fill. The road pavement was 1,140,000 sq. yds.
The cost of the whole scheme excluding land and preparation costs was estimated at £18,330,000.
The Durham Motorway A1(M) consisting of four sections constructed respectively by Carmichael, Cementation, French and Carmichael, was officially opened by the Rt. Hon. Richard W. Marsh, PC, MP, Minister of Transport, on the 17th September 1969.