The M6 through Westmorland (J35 to J40)

The various small-scale plans proposed during the 1930s for a network of motorways showed a line for the North-South route through Westmorland. It was, however, diagrammatic in that no detailed investigations had been carried out at that time.

The perennial difficulties of communications between Scotland and England because of the weather problems of the existing A6 route over Shap Saddle (approximately 1390ft), and keenly felt during the Second World War led to the concept of an alternative route via Tebay and the Lune valley. After the War this was taken up by the Ministry of Transport, and the route was surveyed and set out on the ground.

In 1959 a local resident called a meeting in Kirkby Lonsdale to protest at the route on environmental grounds. The unanimous conclusion of the meeting to condemn the route through the Lune valley was conveyed to the Ministry, who called in Consulting Engineers Scott & Wilson Kirkpatrick & Partners, "to consider all possible and practical alternative routes between the end of the Lancaster By-pass and Penrith, and recommend the one to adopt".

Any route had to deal with an East-West mountain barrier at mid-point that was only relieved by a glaciated valley to the East epitomised by a length near Tebay known as the Lune Gorge. Either use had to be made of this valley or a more direct route had to be found using tunnels and/or high viaducts. In addition to the use of the Lune Gorge, tunnel routes making use of the Long Sleddale valley plus the Lowther or Hawerswater valleys, or along the line of the existing A6 to Shap village were identified: a viaduct route also on the line of the A6 was also identified. Numerous alternatives were found South of the mountain barrier, that could be combined with these resulting in some 30 possibilities to consider. These alternatives were discussed in an Interim Report submitted in mid-August 1960.

A number of special studies were undertaken. Aerial photographs viewed stereoscopically reduced the choice of routes to a few in number. Newly established techniques enabled maps to be drawn of probable depths of rock and the extent of various soil formations. An Origin and Destination survey was carried out so that traffic could be assigned to alternative networks.

Traffic on the A6 was frequently brought to a halt by wintry conditions with bad visibility a particular problem. For the first time on a motorway project, a meteorological study was, therefore, undertaken to judge the effects of wind, low temperature, snow and reduced visibility on traffic using the alternative routes.

The Final Report, in 2 volumes, was submitted by the Consultants in March 1962. In addition to the matters described above, the Report analysed the results of the various surveys and studies, and how they led to three alternatives for final comparison viz;-

* Direct Route

* Killington Route

* Lune Valley Route

The alternatives were described in detail, and the effects of the following factors were assessed:-

* Weather

* Land Use and Landscaping

* Capital and Maintenance Costs

* Traffic Operating Costs

As a first stage, the Killington Route was compared in detail with the Lune Valley Route, and the conclusion was drawn that the Lune Valley Route was to be ruled out and that, if the chosen route was to pass through the Lune Gorge, then it should be the Killington Route.

The Killington Route was then similarly compared with the Direct Route. The choice here was less clear-cut. The Direct Route was shorter, but its capital cost was greater, due to the use of tunnels. A short single 3-lane, unventilated tunnel under Hucks Brow was to carry the climbing North-bound carriageway. Further North at the head of Crookdale, twin ventilated 2-lane tunnels 6,800 ft.long were proposed, one for each carriageway; a third 2-lane tunnel between these two was to be added when justified by traffic growth. This central tunnel could then be bi-directional, used only for climbing traffic, or tidal flow.

Emergency crossing places within and outside the tunnels were proposed. However, the total recurrent costs, comprising traffic operating costs, road maintenance costs, and, in the case of the Direct Route, tunnel operating costs, were shown to be less for the Direct Route even after the construction of the third tunnel.

A cost-benefit analysis showed a return of almost 9% on the additional cost of the Direct Route. Provided the extra capital was available the Direct Route was recommended as the best route from long term, and strategic points of view.

However,

1. it was not possible to rank these returns with those from other road schemes for which the additional funds might be used,

2. the Direct Route was less effective from a weather viewpoint, and

3. the tunnels placed restrictions on the movement of dangerous goods.

For these reasons the Killington Route was selected.

Apart from the terminal interchanges, it was only necessary to provide four junctions with existing roads along the 36 miles of the route.

Separated carriagewaysIn carrying out the design, great care was taken to fit the motorway to the landscape, and the designers found that the motorway alignment standards were particularly suited to the terrain, which mean that North-bound traffic would encounter long climbs along certain lengths and desirable constant gradients were achieved in all of these. The reduction of earthworks achieved by stepping carriageways in steep sidelong ground was utilised for 2.5 miles south of Killington, and for 3.5 miles in the Lune Gorge. In the latter case the vertical separation reached 30 ft.

North of Tebay the carriageways are separated over a distance of 4.5 miles, the maximum separation being 800 ft. North of Shap Interchange separation of carriageways occurs over a length of 2.5 miles. It was concluded that sheep farming could continue between the carriageways, and sheep "creeps" were designed along established sheep "corridors" to facilitate this. Protection from drifting snow for the vulnerable lengths North of Tebay was generally achieved by designing embankments with a minimum height of 2 ft and cuttings with side slopes flatter than 1 in 6.5.

It was decided to separate surface water and sub-soil drainage, the former being effected by a specially designed channel section, with an in-line graded approach with slotted steel covers to gulleys. The latter were buried and comprised standard porous pipes together with filter material designed to prevent clogging from the surrounding soil. In one area north of Dillicar Knott larger, deep intercepting sub-soil drains connected to the motorway drainage system were designed to prevent slips in the steep boulder clay slopes.

In order to make use of wet material, and as a result of experience gained from a full scale trial embankment constructed on the line of the motorway, embankments were designed to be laid in 8.5 ft layers separated from one another by drainage layers. In one area of steep sidelong ground deep intercepting sub-soil drains were used above the motorway for additional protection. In pre-determined areas excavation to a vertical face in cuttings was specified to minimise "suitable" material becoming "unsuitable", after periods of rain.

Extensive use was made of computer programs in the calculation of horizontal alignment, intersection and merging geometry, and the setting out of horizontal control lines from setting out beacons. For the first time in this country, actual computer print-out was incorporated into contract drawings.

Borrowbeck viaductThere are 160 structures on this section of motorway of which 77 are bridges or underpasses. Cost studies led to open abutments being selected generally, so that for standard situations overbridges have three or four spans, but most underbridges have single spans. In one case an overbridge carrying a minor road was designed with 3 spans rather than 4, so as to frame a magnificent early view of the approach to the Lune Gorge for North-bound travellers.

Within a length of 2.5 miles in the Gorge, 8 underbridges were required to carry the motorway, and 3 to carry the diverted A685. The 73 ft high Borrowbeck viaduct is close to and 10 ft higher than the stone arch railway viaduct carrying the West Coast main line to Glasgow. The central span of the curved motorway viaduct was designed to frame the railway viaduct when viewed from the realigned A685, itself on a new curved bridge over Borrow Beck.

The railway line had to be crossed in three places. These were all skew crossings, one having an extreme skew of 70°. Precast reinforced concrete beams square to the tracks were used to minimise temporary works over the railway. For the smaller skews, the free edges followed the skew and a trapezium of reinforced concrete lapped with the precast beams to form a portal construction. For the extreme skew the bridge has beams square to the track throughout, with sections protruding on either side of the motorway construction above.

The location of Service Areas was treated as an environmental as well as an amenity matter. Connecting overbridges were avoided, and sites were selected alternately for North- and South-bound traffic with the two southernmost ones widely separated. However, where the carriageways are separated North of Tebay they are opposite one another. All are designed to provide views away from the motorway, and at Killington the Service Area overlooks the Reservoir and is well screened from the motorway by ground contours.

Construction was to be carried out under five separate contracts for each of the five sections. Contract periods allowing for two full winters of earthwork construction were considered essential. The contract for the section through the Lune Gorge, because of its major structures and large quantities of rock excavation, was given a lead time of 10 months over the other contracts when tenders for it were invited in October 1966. Construction commenced in October 1967.

Rock Face at Jeffrey's Mount

Jeffrey's Mount provided a 'planning' challenge for the Contractor. The A685 was on the line of the M6, and had to be diverted up-hill to the West as an initial task prior to the construction of the motorway itself. Both A685 and M6 had to be excavated to form ledges in the steep rock with the West Coast line immediately below the latter. Pre-splitting techniques were suggested to tenderers as a suitable technique for avoiding overbreak, and to maintain the stability of up-hill slopes or construction. This technique was used extensively and successfully in this location.

In the event, the condition of the exposed rock proved more difficult than could have been anticipated from visual examination of exposed surfaces, and drill-hole results. The adopted solution was to use rock bolting, previously a little known technique. It was used extensively to good effect.

Where the motorway runs close to and above the railway on steep sidelong ground near Dillicar Knott, a safety fence comprising anti-submarine netting fixed to steel rails concreted into the ground was erected prior to commencing earthworks. It was tested successfully by using a "runaway" D6 crawler tractor.

 

The Lune Gorge

Also in the Lune Gorge, site access was very difficult, and a preconstructed continuous haul road off the motorway alignment was considered to be imperative. Imported rock from a disused quarry was used to supplement the rock excavations through Jeffrey's Mount and around Dillicar Knott at the entrance to the Gorge. The former provided a continuous source of input to a crusher sited nearby. Material from the haul road was subsequently re-excavated to provide material for drainage layers elsewhere.

Bailey and Callendar Hamilton temporary bridges capable of taking 35 ton loads were used where the haul road crossed the River Lune. The 8,300 ft realignment of the A685 was a first priority, and intricate programming was involved in completing this section.

The motorway was opened in October 1970 with a maximum elevation of 1036 ft compared with that of the A6 it replaced of 1390 ft. It received a Civic Trust Award and the following wording appears on a plaque in a lay-by off the A685 overlooking the Lune Gorge:-

"This award for an outstanding contribution to the appearance of the Westmorland landscape relates to the 36 miles of M6 Motorway between the Lancaster and Penrith by-passes".

From the interchange at the junction with the A65, it was the intention to provide a new high-standard dual-carriageway road running in a north westerly direction as an improved means of access to South Lakeland. To be known as the Kendal Link, it was to be an 'all-purpose' road and not a 'motorway'. In accordance with Ministry policy, the future maintenance of the boundary fence would, therefore, be the responsibility of the adjoining landowners.

The road was to pass through a deer park and special deer-proof fences would be required. Initially, the landowner concerned raised no objection to the principle of providing the road, but was not prepared to accept responsibility for the fences which were to be erected as accommodation works with the cost met by the Ministry. He, therefore, formally objected at the various stages of the statutory procedures, which led to other objections by interested parties. This resulted in the need for a Public Inquiry and, although the objections were over-ruled in the Minister's decision, it was to be several years before the Link was opened to traffic.