A38(M). The Aston Expressway
History and Background
In the 1960's Birmingham was reaching its peak as a heavily industrialised manufacturing city. The principal road network was becoming progressively congested due to increased business activity and growth in road transport. One of the key routes affected was the A38 between Birmingham City centre and Salford Bridge, which served as the transport corridor to the north and north-east of the city.
The A38 (Lichfield Road) operated as a sub-standard four-lane single carriageway serving locally generated and long-distance traffic. Commuter traffic from the north Birmingham suburbs and the townships of Lichfield, Tamworth and Sutton Coldfield caused peak flows along the closely developed Lichfield Road. Studies confirmed that a new dual three-lane carriageway was needed to relieve the A38 and to provide for future traffic growth.
On-line improvements to Lichfield Road were out of the question and with the decision to route the new M6 through north Birmingham, the case for the Aston Expressway linking the city centre and the M6 at Gravelly Hill was made. Consultation with Government confirmed that a 75% grant would be available for the Expressway provided that it would be ready for the M6 opening. This left barely six years to carry out a full detailed design, acquire land and build it through the densely populated inner city of Birmingham.
The City of Birmingham Public Works Committee formally approved the Aston Expressway in principle on 2 December 1965. Also, approval was given to apply to the Ministry of Transport (MOT) for an order under S.11 of the Highways Act 1959 to designate the Aston Expressway a 'Special Road'. Sir William Halcrow and Partners were appointed as structural. By January 1968 the highways drawings were complete and a provisional sequence of works and construction programme had been developed. Quantities, billing and contract documents followed in preparation for a late 1968 start.
At the City end, the plan line of the Expressway follows Corporation Street, Aston Road and the former A38, northwards, crossing the canal near the junction with Aston Road. Then it goes into cutting to form the underpass at the junction with the A45, Birmingham Middle Ring Road (Dartmouth Street- Bracebridge Street). It departs on the west side of Lichfield Road continuing northwards into the South Aston. Queens Road and Salford Park Comprehensive Development Area.
The line crosses the Hockley Brook, which is prone to dramatic rises in water level (4m+) and occasional flooding. The brook marks the site of a very deep, buried glacial valley. Further north, the main carriageway passes through the former Rippingilles (Valor Works) site where heavy press and machinery bases had been left in-situ. The next section is in deep cutting (approx. 9m) where it passes under Park Road and Tower Road, skirting the HP Sauce factory.
Curving north-east the Expressway passes under Victoria Road at the Park Circus junction, emerging onto an embankment that gives way to a long span viaduct. On the west side this gives a panoramic view of Aston Hall, a Jacobean mansion, and Aston Church. The viaduct is curved to bypass the Ansells Brewery site. Ironically, the brewery was demolished before the Expressway was finished. The viaduct continues at high level carrying the Expressway over the River Tame, and two railway lines that are themselves on high embankment.
The highway terminates south of Gravelly Hill Interchange (more widely known as Spaghetti Junction) at the viaduct expansion joint. The short remaining length of the Expressway through to the A38 at Gravelly Hill was part of the Interchange design undertaken by others (for M6).
The main carriageway was designed as a single seven-lane highway to be used on a tidal flow basis. The original intention was to operate the tidal flow with four lanes and three lanes morning and evening depending on the direction of the rush hour traffic. This was never tried out since it was thought too dangerous to have traffic travelling in opposite directions on adjacent lanes. For many years it was used as dual three lanes with a buffer lane but in recent years tidal flow has operated during the commuter periods on a four and two basis whilst always maintaining the clear buffer lane.
Initially, it was concluded that the new junction between the Expressway (A38M) and the Middle Ring Road (A45) would require three levels with a roundabout at the intermediate level. The layout was complicated by the need to maintain north-facing slips for free-flow links to Lichfield Road.
At Park Circus 1 km. north of the junction with the MRR another locally important and strategic traffic route, Victoria Road, crosses the line of the Expressway to join the Lichfield Road (A38). Victoria Road serves cross-city traffic and a two level grade separated junction with the Aston Expressway was justified. Access and egress at the Victoria Road Junction were restricted to north facing slip roads in the direction of the proposed M6 and the Gravelly Hill Interchange.
Identified constraints & problems
On the Expressway main alignment these included a Canal crossing (Aston Road), a 132 kV electricity supplies in gas filled pipes, extensive major primary services along the existing A38, the need to minimise overall cross section due to land and property constraints, the . need to minimise the threat of main carriageway flooding from Hockley Brook, the HP Sauce factory and Tower Road vinegar mains the need for a large volume of high quality material for retained fill on slip roads, two existing railway lines on high embankment on viaduct approach to Gravelly Hill and the River Tame crossing.
On the A45 (Middle Ring Road), horizontal curvature on overpass section, a Canal crossing in Dartmouth Street and major utilities on Dartmouth Street including 3 No. 36 inch and I No. 30 inch gas mains.
Much of the design required slip roads on retained fill. Retaining walls were insitu reinforced concrete mainly of the cantilever type, with a key below the base. At the deepest parts of the underpass and in the main cutting the walls were counterforted with a key below the base.
Due to the number and large physical size of the utilities crossing the canal at Aston Road and the limited headroom available. it was decided to construct a utilities tunnel under the canal. Vertical shafts close to the canal provide access to the tunnel.
Most of the bridges carrying road crossings and footways over the Expressway are reinforced concrete with cantilever abutments supporting pre-stressed pre-cast beams. Two exceptional structures are the bridge (B7) carrying the road link from Dartmouth Circus to Lichfield Road, and the main viaduct (BI) carrying the Expressway from Queens Road to Gravelly Hill Interchange. Bridge B7 is a box beam design deck. A novel feature is the steel spiral ramp footway connecting to B7.
Viaduct (BI) is a long span design in steel, having twin parallel box beans and a steel deck. The deck is fixed at the Queen's Road abutment and there is a single large expansion joint at the Gravelly Hill end. Both of the box beam structures were designed before the Merrison Committee rulings. This introduced post-design problems and had a significant impact during the late stages of construction.
In view of the complexities at the city end mentioned previously, it was decided to divide the construction into two separate contracts.
Contract A ran from the Gravelly Hill connection with the M6 to a point just north of the Tower Road footbridge and included the junction at Park Circus. Contract B ran from Tower Road to the start of the Lancaster Circus overpass (at the inner Ring Road) and included the junction with the Middle Ring Road.
Even with the 200m. Salford Viaduct, Contract A was seen as a three-year job being the less difficult of the two. Completion to the Park Circus junction offered a traffic outlet via Victoria Road to Lichfield Road, if the M6 opened on time. Contract B was more complex and was considered to be at least a four-year job and realistically would not be ready for the M6 opening.
Due to the structural content, the design contract was awarded to Sir William Halcrow and Partners with the City of Birmingham as the Employer. The works contract was awarded to Taylor Woodrow Construction. The viaduct foundations were a critical and difficult operation as the River Tame was directly underneath the new structure for half its length. The deck design used hollow box beams allowing long spans and a visually more acceptable structure. Construction over the two railway crossing points required the usual track possessions.
RM Douglas Construction Ltd tendered for Contract B of the Aston Expressway in the autumn of 1968 and was awarded the Contract for commencement on 1st January 1969. This contract was supervised directly by the City if Birmingham.
Contract B, Construction
Essentially the Expressway runs in retained cutting for most of its length. With some 3½ miles of retaining walls, two canal bridges, four bridges over the expressway, five subways, foundations for the Middle Ring Road Flyover and a service tunnel, the structural content dominated the operations.
Although a substantial volume of imported fill was required, it was only in the latter stages when retaining walls had been completed that the embankment areas became available for filling. Equally there were no areas on site where temporary stockpiles could be formed. Consequently most of the structural excavation had to be removed from site although it was returned at a later date. A redundant sand quarry some seven miles away was established both as a permanent and temporary tipping site.
Most of the excavation was in sand or sandstone. Near the surface the sand was soft and easily excavated but at greater depths the sandstone became harder. Generally larger heavy hydraulic excavators could dig the rock but some blasting was necessary. In the areas of rock the sides of excavations remained stable without any restraints and this proved to be very advantageous.
The total requirement of concrete on the Contract was in the order of 60,000 cu.m. The Contractor deemed it economic to batch this on site. Having the exclusive use of a batching plant gave great advantages in quality control and service. However, the economic justification did depend on achieving the three-year programme. It was also important to ensure that all of the concrete did come from the site plant without use of ready-mix.
Another feature of the concrete operation was that a concrete pump was allocated permanently to the site and a small gang of three operatives using the pump for the most part, placed virtually all of the structural concrete on the job. Programming of the structures was carefully controlled to balance these resources in the most economical way. In practice this worked extremely well and almost no concrete had to be imported and additional pumping was rarely required.
With the considerable length of retaining walls that had to be built, there was a great deal of repetition and scope to devise a standard formwork system. The retaining wall shutters were made to standard heights of 10 foot, 20 foot and 32 foot. Since in these days, there were no suitable shuttering supports on the market, these were designed and manufactured by the Contractor. The tallest retaining walls had counterforts and unusually the Contractor elected to construct the counterforts first and complete the walls as a separate operation.
The profile of road is at a noticeable gradient. The retaining wall sections are 60-foot long and since they follow the gradient it meant that the kicker for the walls would be well above the level of the road if the kicker were cast horizontal. To complicate this further the base of the walls had a splay. On Contract B, RM Douglas, contrary to common practice cast the kickers on the slope parallel to the road gradient and this resulted in the joint between wall and kicker being hidden by the road surfacing. To this day some thirty years later it is quite obvious where this practice was not adopted on the adjacent contract and the joint in the concrete is clear to see.
During the first 18 months of construction it must have looked a rather bizarre approach to the building of the job. Odd walls were appearing in different parts of the site for no apparent reason. In fact work had to be progressed wherever it could take place. Demolition of housing, service diversions and traffic considerations dictated this sequence. The movement of traffic at different stages became the targets to meet. Considerable enthusiasm built up before each traffic stage and they provided momentum to the job.
Roadworks on the project were relatively straightforward. One unusual feature was the sub-base. This was 10" of demolition brick hard-core topped with 2" of Type I subbase. As large areas of old housing in Aston were being knocked down there was a plentiful supply of good quality brick hard-core. This is a very good example of recycling. To the writers knowledge this is still carrying traffic some 30 years later.
During the late 1960's labour-only sub-contracting had become a more common method of employing labour. This form of piecework had dramatically improved output from tradesmen and operatives. Outputs had been falling in the late 1950"s and in the 1960's and it became difficult to programme operations when there was no certainty of achieving completion dates.
Labour-only sub-contracting changed all that. Gangs came together often based on family units. They specialised in one activity and would take on work for a price. Outputs rose spectacularly and certainty of completion became normal. It could not be said that these subcontractors took the full responsibilities of a contract and a certain amount of negotiation would take place at the end of each week to create a reasonable return for the subcontractor. Quality in general did not suffer provided management demanded proper standards.
It is interesting that many of these labour-only subcontractors working on the Aston Expressway continued to work for Douglas' for many decades thereafter. One in particular was still working with his gang on motorway bridges until the end of the Century. By this tine it was on DBFO contracts where the responsibility for maintenance and defects were firmly with the contractor.
Contract B - Early completion a Target to Meet
The tender documents for Contract B had stated a Contract period of four years. This unusually lengthy period was due in no small part to the massive amount of service diversions required (36" gas mains entwined like spaghetti) and also to the amount of demolition of housing still required. During the tender period, RM Douglas had devised a shorter works programme and had offered an alternative tender with a three year programme for a cheaper price. The City did not accept this. They believed that the potential delays in making the site available, the uncertainty of the service diversions and the general complexity of the site, made it very unwise to set off on a shorter programme than four years.
This did not stop the Contractor from believing that the best solution for everyone was to complete the work in three years. Not only would it provide an economic solution for themselves, it would reduce the City's supervision costs and most importantly it would reduce the period of disruption to traffic in the area. A further benefit, which was of paramount importance to the City and to the travelling public was that the M6, would be open in three years time disgorging traffic onto Spaghetti Junction. Unless the Expressway was available to receive this traffic there was no adequate alternative road system to deal with it or to link it to the City.
So the three-year works programme was presented and generally accepted although the Contract period remained at four years. This ambitious programme sounded fine until attempts were made to commence work on site. There was hardly any of the site in full possession where construction could take place. As a result of the foreshortened design and lead-in period (outlined elsewhere in the paper), the difficult and time consuming task of re-housing people and moving factories had not been completed. Indeed it had only just begun in January 1969. The problems of occupied premises and homes were to remain until they were finally cleared some 18 months later.
In addition to the delayed site possession, traffic and the difficulties of carrying out work in the middle of a densely congested road system had a major influence on the way the job was organised. One of Birmingham's principal arterial roads, the A38 ran through the length of the site and inevitably it carried considerable traffic. There were few tunes in the day when the local road system was not solid with traffic.
As mentioned previously Service Diversions were also a major factor. The cost of the diversions alone were an order of magnitude equal to one quarter of the cost of the main construction contract and at the dine the contract commenced, "advance"' sewerage, tunnel and other diversions had only just been started.
As a consequence of the contractor's foreshortened programme and the joint teamwork approach to the contract, Contract B was in fact substantially completed some 16 months ahead of the original Contract Programme. This was no mean achievement in view of the many delays and disruptions in the early stages. to say nothing of the inherent complexities of the job.
In practice, due to the complications arising from the Merrison Report additional strengthening work was required both on Contract A (to the Salford Viaduct) and on Contract B (to Bridge 136) as well as on the M6 Motorway (Midlands Links). The Aston Expressway and the M6 were formally opened to traffic on 24th May 1972.