M62. Boundary to Pole Moor (J22 to West of J23)
In both its design and construction this contract from the Lancashire County boundary to Pole Moor incorporating the Scammonden Dam, to carry the M62, the largest rockfill dam in the United Kingdom, was unique. It presented the West Riding Engineers and the contractors with the greatest of challenges in working under extreme climatic conditions and of overcoming unparalleled physical problems.
In motorway history it must rank as one of the great feats of engineering and worthy of a more detailed record than can be given here. A far more detailed account, particularly of the dam construction, can be found in the Executive Summary, details of which can be found in the pages "about the motorway archive".
Although having successfully tendered for the M1 contract outside Wakefield in consortium with Fairclough(AMEC), Sir Alfred McAlpine & Son Ltd had decided to 'go it alone' and were awarded the £10.5 million contract. It was the first motorway contract in this country to involve large-scale rock-shifting and, at that time, probably entailed the most impressive concentration of large excavators assembled on one project in the UK.
Where the M62 passes from Lancashire into Yorkshire the county boundary is marked by the Pennine Way footpath. The westernmost structure in the West Riding contract is the slender concrete arch that carries the ancient path over the six-lane motorway at a height of 65ft. At this point the M62 is at its highest elevation and deep in the Pennine hills. The next 7 miles, across the moors to the edge of Huddersfield, presented the motorway builders with their greatest challenges - five major rock cuttings, the removal of impassable peat bogs, a major dam, as well as some of the worst weather in the country.
Just east of the Windy Hill cutting the M62 crosses the Halifax-Oldham Road A672 at the Rockingstone Moss Interchange - the first on the Yorkshire side and the only one on the actual Pennine section.
This interchange is also used for access to the maintenance depot which was sited nearby, because the existing road is unfenced across the moors it was necessary to provide "cattle" grids to prevent the sheep, which freely graze on the moor, from wandering onto the motorway which is bounded by specially designed stock fences.
From Rockingstone the motorway strikes out across the high open peat-covered hills of Moss Moor, over 1,000 ft. above sea-level. Viewed from the side here the motorway can be seen as a series of embankments and cuttings levelling out the very irregular landscape it has to cross. And the embankments are built of the material excavated from the cuttings.
Some 12 million cu. yds. of material, 8 million cu. yds. of it solid rock - had to be handled over nearly 7 miles of very inhospitable terrain to prepare the way for the carriageways which when built could be traversed in just under 6 minutes.
Because of the scarcity of solid stable features such as buildings to act as reference points for the original survey a comprehensive system of monuments had been positioned over the whole site by three dimensional co-ordinates to an accuracy of less than one inch. These monuments were located in places unlikely to be disturbed by the construction and were used as bases from which to set out accurately the construction of the motorway.
Access to the parts of the site where the contractor wanted to start working was the major headache. On Moss Moor the first job was the removal of some 650,000 cu. yds. of peat on the line of the motorway. The average depth of peat was 5ft. but pockets of up to 20 ft. depth were met and this sort of terrain presented a major obstacle to the job of simply getting about the site. Once the vegetation was stripped from the surface of the moor the peat had virtually no bearing weight capacity and could hardly support the weight of a man. Conventional vehicles, even tracklayers, simply could not negotiate it.
After coming close to losing a couple of excavators to the bog the contractor eventually evolved a satisfactory method for digging out the peat. This involved cutting straight through it and running the plant and equipment on the underlying, more solid strata, then excavating the peat from the exposed vertical face."
The peat itself had no agricultural, horticultural or other commercial value and was stacked in specially selected disposal areas on the hill sides adjacent to the Motorway and later landscaped to blend in with the surrounding countryside. It was so glutinous that dump-trucks with heated bodies had to be used to ensure a clean discharge and thus a full payload each trip. After lime fertilising and seeding the only way the disposal sites can now be identified is from an aircraft.
The motorway dam was the biggest single job and its rate of progress determined the time of completion for the whole scheme, therefore access to the dam area was a first priority. To operate vehicles and heavy plant into and out of the steep sided valley, over 400 ft. deep, haul roads were built which zig-zagged down the hillside with a maximum gradient of 1 in 5.
McAlpine's earthworks required a major investment in heavy excavation plant of £3,500,000, the key items of which were three 150RB 6 yd. face shovels, three 110RB's (4½ yd.), three 71RB's (3½ yd.) and fifty 30 ton, 35 ton and 45 ton rear dump trucks made by GM, Aveling-Barford, Caterpillar and International.
The main cuttings and the quantities yielded were Windy Hill 120 ft. deep, 2,500 ft. long, 1.2 million cu. yd., Deanhead 150 ft. deep, 2,600 ft. long, 4.65 million cu. yd., Croft House 90 ft. deep, 1,700 ft. long, 1.3 million cu. yd. and Wholestone 50 ft. deep, 5,000 ft. long, 1.2 million cu. yd. The material from Windy Hill formed the embankment over Moss Moor. Most of the material from Deanhead went eastwards to form Scammonden embankment/dam, as did Low Platt, Croft House and Wholestone cuttings.
Scammonden embankment/dam is 240 ft. high, 2,100ft. long, 1,220 ft. wide between toes, and consists of some 4.5 million cu. yd. of rockfill, in addition to the filter material and clay core. During the winter of 1968/69 some 52,000 tons of clay from Dowsett's Gildersome - Lofthouse Contract was transported to Scammonden and used in the construction of the Dam.
The optimum quantity of rock to be blasted out in any single operation was up to 40,000 tons. Rockfill was compacted by large vibrating rollers, the largest of which, weighing 11½ tons dead weight, were developed on site specially for the contract. The micro delay blasting techniques and borehole patterns established in the trials which produced the maximum fragmentation with little need for secondary treatment proved to be very successful on the actual contract.
For two of the three summers worked on this contract the Pennines were lashed by some of the heaviest rains on record, with 66 in. falling during the first year twice the national average - and as much as 4 in. in 2 days on at least one occasion. Moreover the cloud here is often down to around 1,000 ft. and much of the site was frequently lost in cloud which at times reduced visibility almost to nil.
This amount of rainfall, over the large areas of the motorway site, amounts to a huge volume of water. Really effective drainage was one of the main priorities of the contract, not only for the carriageways themselves but also for all the surrounding hillsides. Carriageway drainage is by continuous channels built into the marginal haunch and covered with pre-cast slotted concrete slabs. At intervals the channels are intercepted by catchpits from which water is piped into adjacent streams and ditches. Where the motorway embankments have to be protected from heavy run-off from the hillsides paved cut-off ditches have been built which channel the water under the carriageways via culverts.
These moors are a major water catchment area for the Wakefield and District Water Board and it was necessary to ensure minimal interference with the existing catchwater system during construction of the motorway. Running the full length of Moss Moor and Moselden Pasture is an open catchwater which is crossed by the M62 in two places, once on embankment and once in cutting. In the cutting, at Deanhead, the catchment water is taken under the motorway through an inverted syphon consisting of twin prestressed concrete pipes, 3 ft. in diameter, tested to a head of 200 ft.
On the embankment, in the middle of the Moss Moor stretch, the building of the motorway caused a constriction in the catchwater. This made necessary the construction of a further outflow weir and spillway just upstream of the crossing. At times of heavy rain the weirs discharge water from the catchwater into the adjacent valley, which already contains a reservoir, so that it is retained in the Wakefield collecting system.
The extrusion machines used to lay the marginal haunch and the drainage channel were also improved by the manufacturer in the course of this contract. The carriageway sub-base was spread and laid to a fine tolerance by a Rahco finishing machine handling 2,000 tons of material a day. Levels and tolerances were automatically set by the machine using information fed back through a feeler in contact with a preset wire.
Because of the low ph value of the moorland, water special protective treatments were given to steel corrugated culverts and steel mesh boundary fencing. High strength dense concrete and air entrainment were used in drainage works and structural concrete in contact with the ground protected with a bitumen treatment.
The moorland stretch of the M62 was built on geologically creeping side long ground and each embankment had to be anchored and benched into the underlying sandstone base. This called for separation of the carriageways over three-quarters of a mile which fortuitously enabled Wildes farm and buildings to be retained together with several acres of rough grazing. Access tunnels were provided under each carriageway for maintenance of the Water Authority catchwater, which also provided access to the farm.
It was also the first use of a tensioned wire barrier in the central reserve to avoid snow build up. The embankments which were aerodynamically designed to minimise snow deposits already referred to and the motorway has never closed due to driven snow in the 29 years it has been in operation. It was closed once through industrial action when salting and gritting was not carried out.
The motorway carriageway construction consists of 7 in. of imported type 1 sub-base, a 7 in. asphalt base and 4 in. of two course rolled asphalt surfacings.
There are eleven structures on the contract. The Pennine Way Footbridge which carries the 250 mile Pennine Way footpath across the motorway. The bridge consists of a reinforced concrete three pin arch of 220 ft. span with side cantilevers. Each cantilever supports prestressed concrete approach spans each 85 ft. long.
Rockingstone Interchange Underbridge which carries the motorway over the Halifax - Oldham Road A672. This skew bridge has two spans having a deck of pretensioned pre-cast concrete 'I' beams with an in situ concrete slab supported on reinforced concrete abutments and a central pier.
Scammonden Bridge which spans the Deadhead cutting carries the former A6025 Elland - Buckstone County Road over the motorway. Although originally designed as a flat arch spanning the cutting, further consideration of the aero dynamic and vibration characteristics of the bridge led to a redesign, an important consideration being to minimise disturbances in the air flow through the cutting which would cause snow drifting.
Because the site afforded excellent foundation material, it was decided to build an open spandrel fixed-arch bridge. The final design of the arch was arrived at as the result of a series of computer programmes and proved to be both aesthetically pleasing and economic. It has a span of 410 ft. supporting eight spandrel walls which, with four further walls on the cutting sides under the approach spans, carry a deck 660 ft. long, 120 ft. above the motorway.
All the 18 in. thick spandrel walls have concrete hinges at the top and the shorter ones also have hinges at the bottom; those over 20 feet tall are flexible enough to accommodate thermal and other movements of the deck. The deck is composed of standard M.O.T. inverted T-type pretensioned prestressed beams with in situ concrete infill. The arch which is of twin box section is the largest of its type in the country.
Hey Lane Underbridge carries the Motorway over a district road. Redlane Dyke Bridge is a four span steel box girder bridge over the motorway and required additional stiffening under the Merrison rules. There are also seven reinforced concrete underpasses for agricultural and Water Board use.
It was during the building of Scammonden Bridge that the effects of an exceptionally severe Pennine winter were experienced. The centering of the arch was a conventional scaffolding structure of gigantic proportions. It contained no less than 70 miles of scaffolding tube. And it had to be designed for wind speeds of up to 110 miles an hour. In the sub-zero conditions that prevailed during much of the construction period the worst hazard of all was freezing fog. This left a build up of ice on everything in its path and created unprecedented structural problems as well as almost impossible working conditions. During the first winter the ice build-up was so heavy that the scaffolding framework had an additional load on it estimated at over 1,100 tons.
This type of ice build-up also brought down a nearby television mast, as well as telephone and power cables, and cut off the construction site from the outside world. The site offices were left without heat or light; emergency generators were not powerful enough to combat the intense cold and the offices had to be abandoned. Construction plant and equipment, too, was brought to a standstill.
The building of this bridge gave rise to special problems because rock had to be blasted from the cutting whilst concreting of the arch was continuing. We cast samples of concrete on a trial scaffolding and monitored the effects of vibration from blast effects. The results first of all confirmed our specifications to be a practical one showing that blasting could be carried out close to the structure without impairing its integrity.
An unusual detail of the centering was the anchorage of the thrust rakers to the rock using epoxy resin bonded rag bolts in order that they could cater for both tension and compression.
In addition to the suite of computer programs to aid the engineers designing the arch, another was written to analyse the effects of various construction sequences for the spandrel walls and deck so that the Contractor's proposals could be quickly checked to guard against overstressing the structure during construction.
As the M62 passes under Scammonden Bridge and out of the eastern end of the Deanhead cutting it starts out across the 2,000 ft. rim of Scammonden Dam.
To prevent high sided vehicles from being blown over as they emerged from the shelter of the cutting onto this exposed embankment, the ends of the cutting slopes had to be very carefully arranged. The profile of the motorway on the dam itself was also subjected to rigorous design studies and these led to the provision of simple but effective wind-breaks in the form of slatted fencing on either side, below the level of the carriageways.
From Scammonden the road continues its descent towards the next interchange at Outlane, the last structure on this Pennine section of the M62 built under the adjacent contract.
As with all schemes landscaping was an important consideration and the ledges in the deep cuttings now have flora and fauna of their own.
A major project like the Scammonden Dam changes the whole face of the valley. Huddersfield corporation were conscious of this and were anxious not only that the engineering works should fit well into their background but also that the completed reservoir area should be a source of pleasure and recreation to the whole district. Trees were planted and picnic areas laid out, with parking and other facilities, a sailing club formed and the land immediately around the reservoir used for stock farming.
Through extreme weather it became necessary to extend the contract period leading to completion in 1971.
On Thursday 14th October of that year Her Majesty the Queen inaugurated the Lancashire - Yorkshire Motorway, a historic day for all those involved and said :
"I am very glad to be here this afternoon to commemorate the completion of the Scammonden Dam and Reservoir. To construct a dam on this scale is a fine achievement; to build a motorway across it at the same time is remarkable.
It is and outstanding feat of engineering and also an excellent example of effective partnership between central and local government.
I congratulate all those who have worked so hard to bring this outstanding project to a successful conclusion."
Another plaque was erected on the county boundary, Lovell and Drake had wanted their county boundary signs to be erected but this was not permitted. However, a concrete plinth made with Pennine aggregates embossed with the Lancashire and Yorkshire red and white rosettes was erected and stands to this day.
The final cost of the entire scheme which included additional contracts awarded to McAlpine was £13.98 million - the most expensive rural stretch of motorway in the United Kingdom.