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M4 in Wales. Pontardulais by-pass (J46 to J49)

This was the most westerly contract on the M4. Its eastern end joined the western end of the Morriston By-Pass, where a new bridge and east bound on slip road was constructed. The western termination, at Pont Abrahm, is a surface roundabout with a connection running west along the realigned A48 towards Carmarthen and a northerly exit along a newly constructed section of the A483(N) towards Ammanford. The contract consisted of 13.5km. of dual two lane motorway plus a further 5.1km. of single and dual carriageway trunk road.

M4. Pontardulais by-pass. Penderi interchange (J47)The Penderi Interchange at Penllegaer provides the motorway with a new link into Swansea, the A483 (S) whilst also maintaining a connection to the existing A48. An access onto the A4138 at Hendy provides a road connection for Llanelli and Pontardulais.

The scheme, financed by the Welsh Office (Roads) was designed by W S Atkins & Partners. The scheme was published in April 1971 and there were 42 objections. The line was fixed in November 1972 without a public inquiry. The contract was awarded to Sir Alfred McAlpine & Son Ltd and the tender price was £15.4m. The works commenced on 1 August 1974. The motorway was opened to traffic on 29 April 1977, the opening ceremony being performed by Joel Barnett, MP. In attendance was John Morris, QC, MP, who at that time was Secretary of State for Wales. At the start of the contract, Mr. Morris had performed the 'sod cutting' ceremony by driving a twin-engined motor scraper, not only along the motorway trace but, somewhat over enthusiastically, beyond and onto private land.

M4. Pontardulais by-pass. River Loughor crossingsThe contract included the construction of 25 structures - 16 overbridges and 9 underbridges. The contract also included the almost complete reconstruction of an existing 300 year old bridge over the river Llan to provide access into a private house.
R Loughor crossings

The contract was bisected by the river Loughor the centre line of which was the boundary between West Glamorgan and Dyfed. The approaches to this bridge, on both banks, required the excavation of up to 20 ft depth of peat, the peat deposits on the Dyfed being tidal. The contractor decided that it was not worthwhile contemplating the provision of a temporary crossing over the Loughor so this river remained a physical barrier until the permanent bridge was completed. The Engineer had foreseen this situation arising at the design stage as the bills of quantities uniquely provided for sources of imported fill, the locations of which were specified by the Employer. The existing collieries of Bryn Lliw on the east and Morlais on the west were the designated sources of fill the approximate billed volumes being 97,000m³ and 393,000m³ respectively. It was, however, left to the contractor to decide whether he would utilise these sources and if so, to negotiate with the NCB's Minestone Executive regarding the price, methods of working and the timing of the extraction. Because these sources were readily available, the earthworks balances were worked out accordingly and no other source of common imported fill utilised.

Access to the river Loughor crossing over the peat marsh from the A4138 was made more difficult as the railway line from Llandeilo to Llanelli crossed the works at the western edge of the peat marsh, which was also the high water mark for spring tides. In the design stage the Engineer had started negotiations for a level crossing at the northern edge of the motorway trace and an outline design was provided in the contract for this level crossing. The details and approval by BRB had to be arranged by the contractor and also the accommodation for British Rail watchmen, safety and signalling operatives once the occupation of the site had been taken. Nevertheless, this partially arranged access was crucial to commence the construction of the railway bridge and to gain access to the peat excavation and thus to the major river crossing.

Physically, Pontardulais By-Pass was an extremely difficult site to work due to poor and very limited access. Although for about a mile in Dyfed it ran close to the A48, the roads and tracks across the trace at this and all other areas were often no more than field accesses or lanes which were not permitted routes under the contract. The problems were exacerbated as the majority of the fill areas were underlain, in the worst cases by tidal peat, by shallow peat hag or by soft sandy clays. The cuttings varied from sandy clays to hard gritstone and shale - all typical of the coal measures. In addition, unworked coal was encountered unexpectedly in the largest cutting on the job at Penderi, which was excavated and taken to Morlais colliery for washing and subsequent sale. This operation slowed down the completion of this cut at a time when the fill was urgently needed to complete the embankment to the west. Old mine workings west of Bridge 7, Tal y Clun, which consisted of open galleries of pillar and stall workings at a number of different levels, were plugged with concrete and the whole excavated to 15m. below formation level. Old workings west of Penderi at Llysnini, indicated in the contract to be grouted, were also excavated and backfilled and two additional and previously uncharted workings - one on the A4138 and one in the Ty'r ffordd cutting - were excavated and backfilled.

Although the entire common imported fill came from the two collieries, a major problem arose over the provision of rock fill, SF1 and free draining materials to stabilise areas beneath embankment construction. The major areas of free draining were each side of the Loughor bridge and at the east end of the job west of the Felindre Road, although areas around the crossing of the river Gwili at bridge 4, along the A483(N), and land adjacent to and east of Bryn Lliw Colliery, all required treatment. The tender documents anticipated an excavation quantity below embankments of 179,000m³ stretching along an aggregate of 2.3km. of the motorway. The final account measure for this excavation was 354,000m³ over 4.8km.

In order to provide these materials, particularly in the early part of the construction process, the Contractor elected to purchase a quarry in the limestone region north of Ammanford, at Llandybie. This quarry, about 9 miles from the centre of the contract, remained as a productive quarry in the company's ownership until 1995 when McAlpines sold all their quarrying interests. This source also provided the sub-base, lean mix, structural concrete aggregates and the bulk of the limestone for the blacktop. Due to the large quantities involved and partly also due to the shortage of lorries to haul the materials, other quarries in the area were used from time to time.

At the eastern end of the job, free draining materials were acquired from Margam Steelworks, Port Talbot and it was a condition of the order that this fill would come from the old and weathered slag banks in the works. Regrettably, the suppliers, after a few weeks work and unbeknown to the contractor, decided it was easier to provide fresh slag from the furnaces, much of it arriving on site still hot enough to cause the paint to blister on the sides of the wagons. Although this practice only carried on for a few days, the area became a major source of ground water pollution for many months. As the slag had been deposited below standing water, the toe of batter french drains began showing signs of leachate and jet black water appeared at the outlets and in the outfall ditches which led into the river Llan. The outfall to the river was immediately blocked off and a temporary storage lagoon constructed between the motorway and the river. Air from compressors was pumped into the lagoon and after many months of treatment, the black effluent turned from black to dark green to yellow and eventually white. Initially the ph of the effluent was in excess of 11 when in the form of ferrous sulphide, gradually reducing to 7-8 as the leachate absorbed oxygen to become ferrous thiosulphate. In this state the contractor was allowed to discharge the water into the river. However, when discharged, a white precipitate was deposited and coated the bed for many hundreds of yards downstream. Throughout this long and costly operation there was no observable fish-kill, but ironically, some two months after the motorway discharge had been controlled, there was a total fish-kill along long lengths of the river which resulted from an acid discharge upstream of the motorway from the Felindre Steelworks.

During the design stages of the scheme the Engineer's staff had difficulty obtaining access to lengths of motorway trace and also that of the A483(N), all in the county of Dyfed. It appears that the landowners had been unable to reach agreement with the District Valuer regarding their compensation and as a result the permanent stations that controlled the setting-out had been established along side roads and on the verges of the A48. Whereas this system was eminently satisfactory for design purposes and for use by the aerial survey sub-contractors, the contractor found that the permanent markers could not be used to transfer the centre line to the motorway. A number of landowners and tenants remained sufficiently irritated with the lack of agreed compensation that the contractor's personnel were ejected forcibly from the site, which prevented setting-out and ground level checking. Delays were caused while negotiations were concluded.

The land negotiations in West Glamorgan were, whilst not free of these disagreements, certainly better, although there were one or two instances where access was not possible when required. One particular area was for the removal of anthracite 'duff' on NCB land adjacent to Bryn Lliw colliery. Although this type of irritating behaviour does occur on most motorway contracts, in this case it occurred when there was also a fundamental change in setting-out techniques. In establishing the permanent setting out markers, the engineer had not used standard theodolites but the more sophisticated geodometers and distomats. The advantages of these improved techniques were thus lost and delays occurred, all outside the control of both the resident engineer and contractor. The Employer's negotiations for land entry and the subsequent additional instructions for accommodation works bedevilled the construction processes, which had a knock-on effect on the way land was acquired for tips and temporary access roads. The root cause is that most landowners and unfortunately, their agents, do not understand the relationship that exists between the parties in the standard form of contract and tend to take out their frustrations on the resident engineer and the contractor.

M4. Pontardulais by-pass. Northern terminalThe Pontardulais By-Pass was one of the first contracts let in the UK using the ICE 5th edition Form of Contract, a form substantially different in principle from the 4th Edition. W S Atkins recognised the importance of the bill rates when assessing the tendered bids and clearly examined in detail all the rates. As a result of this examination, they wrote to the favoured bidder seeking clarification on rates deemed to be either too high or too low. In addition a number of the preliminary lump sum rates were queried and the contractor was asked where all the 'on-cost' elements had been included. All of these queries and the contractor's responses were bound into the acceptance of the bid and became part of the contract.

During 1974 legislation was enacted that greatly and continuously affected the construction industry, namely that dealing with Health and Safety at Work and the amended Employment Acts. During the currency of the contract the Contractor was obliged to produce, for the first time, written schedules of site hazards and list those personnel directly responsible for arranging safety. The Resident Engineer's staff and the design staff also were taken into this amended system during their approval of the temporary works designs.

In addition, subsequent to the start of the contract, new regulations were issued for the signing of hazards in and around highway construction sites, particularly where accesses were gained to and from public highways and where site traffic crossed highways. The original contract had contained advice only on these points by Technical Memorandum no. 736. The new regulations involved considerable extra signing and much more direct contact with both the Police and the Highway Authority before operations were allowed to start. Chapter 8 of the Traffic Signs Manual has since become part and parcel of all highway construction sites.

The major river crossing of the Loughor, Bridge 9 was one of seven bridges on the site crossing rivers. The Loughor was by far the widest of the rivers; the other rivers - the Llan, the Lliw and four crossings of the Gwili - although minor were all interesting structures. The Gwili bisects the Pont Abrahm roundabout and also cuts across the A483(N) These three bridges were let as a sub-contract package to Public Works Ltd. from Bristol. Downstream, the Gwili again cuts across the motorway at a very acute angle and at a point where the motorway is elevated across the river valley, bridge 4. Atkins chose at this location, and also at the crossing of the Llan east of Penllegaer, bridge17, to construct a culvert of an interesting and imaginary design. Two simple sloping abutments were constructed along the length of the culvert. A grooved seat was formed in the top surface into which were fitted precast parabolic arch units. The units were approximately 9m in length and rested against their partner on the opposite abutment, the joint being displaced by half a unit, at the crown of the arch. No temporary support was required during the erection other than horizontal constraint.

The construction for the Gwili crossing, Bridge 4, was relatively straightforward once the peat and underlying soft materials had been removed from the bridge site. Bridge 17 at Melin Llan was made difficult as the new structure had to be threaded through an existing viaduct carrying the A48 from Llangyfelych to Penllegaer. Therefore before the A48 could be diverted onto its new alignment the traffic using the existing A48 had to be diverted around the partially completed Penllegaer Interchange, down the east-bound slip road, across the motorway trace, re-emerging on the existing A48. This diversion then enabled the viaduct to be demolished and the permanent A48 diversion constructed.

Structure 14, taking the A48 across the motorway west of the Penderi Interchange and Structure 24 - a half width Bridge 14 - which provided agricultural access, was sited very close to the existing A48 and, quite rightly because of the amount of material in the interchange area, the Engineer had tried to provide a surface crossing of the A48 prior to the contract being let. Regrettably the agent representing the landowner and tenant was not persuaded to agree with this course of action. He said that he would prefer to wait until the contractor was on site, probably reasoning that he might receive more money. When the contractor tried to negotiate a surface crossing and consulted the Highway Authority and the Police, it became apparent that there was a marked reluctance to allow motorway construction traffic to cross the A48 at this point. It was suggested that a bailey bridge be constructed over the A48 which would have required a large volume of fill as a temporary access embankment. Alternatively the contractor was asked to look at driving a tunnel under the A48, but this would have meant providing an opening through the false work of both Bridges 14 and 24 sufficient for large dump trucks. In addition a tunnel would have inevitably disturbed the existing gas, electricity, telephone and water services in the A48. After further discussion and the intervention of the Employer, it was agreed that a surface crossing was the best solution.
Footbridge at Hendy

M4. Pontardulais by-pass. Footbridge at HendyThe structures in general were a mixture of in-situ and precast units for the decks. The piers, columns and abutments had some similarities in surface finish so standard panel shutters had some re-use. The balance of economic shutter use, i.e. cheap formwork and the aesthetics of the finished motorway meant that there was certainly no boredom in planning. The Contractor would have preferred to have had greater repetition of his formwork resources, thereby improving both the costs and programme. The Contractor did attempt to sub-let groups of structures, but was only successful in letting Bridges 1, 2 & 3. However, he was able to sub-let the steel fixing and formwork to a labour only company from the north-west of England who were at that time deeply involved in a prison contract for McAlpines. In the first twelve months, when very few of the bridges had been started, the sub-contractor went into liquidation due to his commitments elsewhere, so the Contractor took on all the labour and supervision up to completion

The pavement construction for Pontardulais By-Pass was the standard for the early 70's - 40mm of hot rolled asphalt wearing course, 60mm of DBM base course, 75mm of DBM base and 210mm of lean mix with varying depths of Type 1 sub-base. However, the hard shoulder was of reduced strength, with only 100mm of DBM surfacing on a wet mix road base. The finish to the shoulder was specified as red slurry seal, which during the course of the contract was changed to red schlammé. On embankment areas an extruded asphalt kerb provided passage for water to a positive gulley system.

During the currency of the works, the contractor proposed and the Engineer accepted a change to the standard cross-section by the addition of a 300mm. concrete haunch on both edges of the carriageway. Where the extruded kerb was specified the haunch was raised to top of kerb level. The standard MOT design at this time had open edges to the carriageway but the contractor reasoned that this amended cross-section enabled works in the verges and central reserve to be programmed earlier than would normally have been the case. The overall completion of the works was thus improved.

As the years have gone by it is sometimes difficult to recall that in the early decades of the motorway building programme there were immense problems of getting contractors underway owing to the difficulties of acquiring sites for the main offices, plant yards, batching plants, etc. Pontardulais By-Pass was particularly difficult. Contractors generally tried to find sites that were contiguous with the works as, in this case, planning permission was not required within the general development orders. However, all the likely sites, and there were very few anyway, were impossible to use as there were not sufficient telephone lines available. Mobile phones were not then in use. Eventually the telephone managers department were asked bluntly in what areas could they provide the necessary lines - and that proved to be in one location only - in the village of Grovesend between Pontardulais and Gorseinon. Unfortunately the only land in this area which was suitable and which could be obtained relatively quickly, required planning permission. Many weeks were lost whilst local councillors and other interested parties were consulted. Groups of councillors and officers visited the site on at least four occasions before permission was granted and the site was made available to fill with colliery shale. In the interim, the resident engineer's and the contractor's staff were housed in highly unsatisfactory conditions around Pontardulais and Penllegaer at a time when important decisions and construction planning matters were at their most critical. Water was supplied to the site with reasonable ease; power initially was generated and sewage disposal was provided. The site also provided accommodation for up to 50 caravans, homes for the itinerant staff. Smaller caravan sites were located at the east and west section offices.

As the contract period was longer than 24 months, the monthly valuations were done using the Baxter price variation formula. Prior to this time variations of price had been calculated on market prices using a basic price list deemed to be correct at the time of tender. The Baxter formula, based upon rises calculated on standard commodity prices relevant to the specific contract, had been designed to limit the amount of administrative time involved in the submission and checking of monthly valuations. The Baxter certainly proved easier in administrative terms, each monthly calculation being done by the respective quantity surveyors. The final Baxter percentage for the Pontardulais By-Pass was nearly 70%.

On most motorway contracts, monthly valuations were normally under-measured by the resident engineer's surveyors. The reason given for this dubious practice was to ensure that the Employer was not paying for items of work which may not ultimately be valued, for example the measurement for imported fill. Since the introduction of the Standard Method of Measurement for Roads and Bridgeworks, imported fill was measured as the difference between the total volumes of embankment less the volume of suitable arising from cuttings and other sources. Earthworks, drainage and accommodation works were generally under-measured, whereas structures and pavement construction very easily measured from the drawings and were normally accurately computed. Claims based upon bill rates and any accumulated under-measure produced surges in the monthly valuations towards the end of the job, being affected by the 70% Baxter multiplier. In addition because the 5th Edition had turned the 'balancing sum', not into a sum, but a percentage addition to all bill rates, under-measure or claims paid after the completion of the works produced a multiplier of 92% on basic rates.

The earthmoving plant on the job was fairly typical for this period of motorway construction and for the terrain to be traversed. Caterpillar 637 motor scrapers formed the backbone of the fleet with the addition of 22 RB, 30 RB, and 38 RB draglines, which were used almost exclusively for the peat excavation. D8s, tractors and boxes took off the topsoil that was available on the site. The Contractor managed to negotiate tips on lands adjacent to one side or other of the peat areas so that it was possible for the excavation plant to cast into the tips, the material having to be handled up to six times. Gradually, as it dried out, low ground bearing pressure dozers were used to push the top layers of peat away from the motorway towards the extremities of the tip. All the draglines started their work on mats until the backfill was of sufficient area to allow it to be used as a working platform. Poclain face shovels and Cat.769 dump trucks were used in the rock cuttings assisted by D9 rooters. There was no blasting required for the removal of the rock. A number of front loaders were utilised, the largest being the Cat 992, which was rated at 10 cu.yds, which was used to excavate the rock cuts in Penderi Interchange. The total quantity of all earthworks materials excavated from cuttings and below embankments, excluding topsoil, was 2,285,400m³

This brief summary of Pontardulais By-Pass can only touch upon the major factors that affected the works. Very many other and possibly less significant points of interest will be contained in other archival documents produced by individuals who were involved in the scheme. All of these will be personal recollections and will reflect individuals' perspective of working on this contract. However, one point of interest does require to be noted and although it is a problem often occurs on motorway contracts, the effect on the Pontardulais By-Pass was considerable - the weather.

In August 1974 when work started, it immediately became obvious that due to ground conditions, obtaining a stable access through the site and to the bridges would be difficult. There was little or no arable land along the length, and large sections were in the ownership of commoners - a sure sign of poor ground conditions. In September of that year the rains arrived and continued to such a degree that the bulk of the site was impassable. The only areas capable of being worked were the peat areas, which were excavated either below standing water or in tidal conditions and therefore not affected by the heavy rain. The site was not opened up properly until the late spring of 1975. However, what caused additional difficulty, and never anticipated, was the summer of 1976, which was one of the hottest on record. The dust was almost impossible to suppress and the operatives working on site were in some discomfort for most of the day. Bowsers and the concrete mixer trucks were filled with water at night and the site haul roads were doused heavily from about 6.00am. By 11.00am the site was again like a desert. The site huts, always poorly insulated, were barely habitable and open windows did little to ease the discomfort. Site meetings started at 7.00am and finished by mid-morning.

A large proportion of the contractors staff were transferred from recently completed contracts, mainly from the north of England whilst Atkins also had to recruit site staff. Key plant operatives, foremen and gangers were brought in from other contracts but very large numbers of men were recruited locally, the directly employed labour force reaching over 500. In spite of the Contractor's desire to carry out most of the works with his own labour, large numbers of sub-contractors and suppliers were also used, especially for the more specialist works.

Losingers were employed to carry out the post tensioning, an operation that may have jeopardised the progress of the contract as in 1974/75 an immense amount of work was being carried out nationally on the construction of oil rigs for the developing North Sea oil fields. As a consequence there was a shortage of stressing strand. Losingers were able to obtain sufficient strand from their own resources to complete the works.

Steel H piling was done by C Evans and the specialised pre-cast in-situ piles - Wests - was changed to Steel H piles when Wests claimed that they were unable to comply with their tender offer. Concrete beams were supplied from Kingsbury Concrete and the parabolic precast units for Bridges 4 & 17 from Ferro Concrete & Stone. Holgates erected all the fencing and safety fencing, a firm which had been long associated with Alfred McAlpines; whilst the largest sub-contract was for the surfacing - the laying done by United Asphalt, an Alfred McAlpine subsidiary. The materials were provided from the company's own quarry at Llandybie. The bulk of the structural concrete was mixed on site, and all the reinforcement provided from ASW in Cardiff, a supplier not without problems. The hand-railing for the bridges was provided and erected by a local company from Port Talbot, Vervox. The lighting columns were supplied by Petitjean and the electrical work by Baileys. Charlesworth in 'The History of British Motorways' in a rare note dealing with the process of construction, states that the parapets on the bridge over the river Loughor were constructed of glass reinforced cement, also provided by a local firm from Llanelli. Charlesworth could also have mentioned that this same bridge, cast in two halves, used sand jacks as part of the support system. This system, mounted on transverse rail track, was lowered using the sand jacks, eased gently sideways and re-raised for the second half of the deck support.