In 1955, it was reported that the County Surveyor had carried out some preliminary work on the design of the motorway within Cheshire. Further investigations were undertaken and, in May 1957, representations were made to the Ministry of Transport for the County Council to be appointed as Agents for the whole of the length between the adjoining County boundaries.
The terrain through which the motorway would pass, is rolling open countryside, containing many high-quality dairy farms. There were no serious difficulties in producing a free-flowing alignment with long sight-lines, to conform with the highest standards applicable at that time. Farm severance was minimised, and only a few cottages would be directly affected.
The Ministry was minded to employ Consulting Engineers and, in view of the resources which were considered to be necessary in order to meet the programme for construction, it was agreed that the work would be divided into two distinct sections. The Southern section between the Barthomley Interchange at the Staffordshire County Boundary and the proposed junction with the A54 at Holmes Chapel, was allocated to the firm of Scott & Wilson Kirkpatrick & Partners. The County Council, was to be responsible for the Northern section as far as the southern end of the proposed Thelwall Viaduct. The Consulting Engineers were also commissioned to design the bridges on the Northern section, thereby ensuring that all the bridges in Cheshire were of a similar 'pedigree'.
However, on the basis of the earlier work carried out by the County Surveyor, the preferred route and vertical profile of the whole of the proposed 25 mile length of the dual three-lane motorway were established to the extent that the statutory procedures were then undertaken, and these were completed without undue difficulty.
On the 9 mile Southern section, only one intermediate interchange was required. At the junction with the A534, it would serve the small but ancient market town of Sandbach one mile to the west of the motorway. For many years, the town had been a popular stopping place for drivers using the A533, the A534 and the north/south trunk road A50. In the design of the motorway, provision was made for a Service Area to be constructed at a later date.
The Northern section intersected three major traffic routes along its 15 mile length. Interchanges were to be constructed, therefore, at the junctions with the A54 at Holmes Chapel, the A556 near Knutsford, and the A50 near Lymm. There was to be a Service Area at Knutsford.
The soil surveys indicated clays varying in plasticity, poorly graded sands with some of uniform particle size, silts, peat and rock. As a result of the high water table over much of the area, many of the sands were saturated and the clays were generally soft.
As a result of these investigations, a major amendment was made to the profile in the vicinity of the valley of the River Dane. This was done in order to reduce, as far as possible, the constructional and subsequent maintenance which would have arisen from a deep cutting through saturated sands overlying highly compressible clays.
A total of sixty one bridges was required along the 25 mile route, of which two carrying railways over the motorway, were the responsibility of British Railways.
It was advantageous to group bridges so that within a group they conformed, in principle, to a single design, although on account of differences in skew and width, variations in detail inevitably arose. Such grouping attracts the consequential advantage of speed of construction and economy. At the same time, it was recognised that it might produce a monotonous uniformity.
Certain bridges, however, required individual treatment. There were 10, of which the largest is a viaduct, 270 feet in length, carrying the motorway over the River Dane. Forty-five bridges carrying local roads over the motorway, and linking farms severed by it, were grouped into four types.
The foundations of the bridges varied according to the ground conditions, as ascertained from boreholes and, in general, either strip footings, driven piles, or cylinders, were used.
With the exception of the two railway bridges, concrete was used as the principal material of construction. The choice as to whether mass, reinforced, prestressed, pretensioned, post-tensioned, precast or cast in-situ design should be adopted was made after careful consideration, bearing in mind suitability, economy and aesthetics.
Separate contracts were awarded for the two Sections and work began in June 1961 with a period for completion of 27 months. However, provision was made in the Northern contract for the early completion within 24 months of the 1½ mile section between the A50, at Lymm, and the Thelwall Viaduct. This was to enable the crossing of the Manchester Ship Canal and the River Mersey to be brought into use as soon as the construction of the motorway between Warrington and Preston had been completed.
As expected, the varied geology caused difficulty in carrying out the major part of the earthworks during 1962. The saturated sands could only be handled following extensive dewatering schemes. In the North, the Keuper Marls, which were classified as rock, required blasting techniques in order to carry out bulk, as well as, trench excavations, particularly in the construction of the Lymm Interchange.
The weather played a major part in the programming of the works when the whole of the site was brought to a standstill during the 'big freeze' during the winter of 1962/63. In order to enable the roadworks to continue, a procedure known as 'Winter Working' was devised by the Contractor and the Resident Engineer whereby only short lengths of formation, of the order of 50 to 100 feet, were exposed each day. These were covered by plastic sheeting, a 3 inch thick layer of sand, and a layer of sub-base as frost protection. Work was able to continue, albeit slowly.
North of Lymm, the motorway was opened to traffic in July 1963. A contract for the construction of 9½ miles of the motorway in North Staffordshire had commenced earlier and the works were completed at the same time as those within Cheshire. The joint opening in November 1963 meant that there was then a continuous length of 87 miles of the M6 in use between Birmingham and north of Preston.