Contract 2 was let in January 1975 to Dowsett Engineering Construction Ltd and traverses undulating farmland and woodland throughout its length. Its rural nature, and lack of interchanges presented ideal conditions for "rigid" pavement construction with a minimum of discipline from structural requirements. It was not surprising therefore that the contractors chose this Contract to establish themselves in the field of paving quality carriageway construction, even though the southern 1.7km was specified, without option, as flexible construction because its alignment was close to the River Roding, where settlement was anticipated.
The Specification for Road and Bridgeworks, as amended by Technical Memorandum H 10/71, issued by the DoE formed the basis of the design. The contractor elected to construct the carriageway in unreinforced concrete. The slab thickness was 280mm nominal except where the CBR was expected to be 2 per cent or less when a 305mm slab was specified.
The three lane dual carriageway is designed to rural motorway standards with a 4m central reservation, 11.2, carriageways including hardstrips and 3.1m hard shoulders. The contractor chose to build the hardshoulders in flexible construction. The sub-base throughout was Group N (granular material complying with Clause 804 Type 2 of the specification).
Longitudinal joints were specified adjacent to lane divisions but the contractor was permitted certain choices for transverse joints. Since construction was programmed for completion within the specified summer months, the contractor elected to omit expansion joints. Transverse contraction joints spaced at 5.0m intervals, with no warping joints, were chosen. For longitudinal joints, 10mm dia. x 750mm long high yield deformed bars were required at 600mm centres whilst for contraction joints 25mm dia MS bars 400mm long at 330mm centres were specified. The concrete carriageway, was curtailed where underbridges were traversed; this assisted in avoiding possible settlement damage behind abutments.
Contract 2 was the first major motorway awarded in the south-east to Dowsett Engineering Construction Ltd., little was known of their abilities with respect to concrete carriageways which apparently resulted in a desire on their part to show that they were more than capable of competing with established contractors in this field. Good cooperation between contractor and engineer needed to be established at an early stage so that mutual understanding can prevail.
The initial decision by the contractor to invest in a new SGME rail-mounted paving train and batcher undoubtedly provided an essential pre-requisite to good construction. Inadequate, ineffective or troublesome plant only leads to interruption to paving and unsatisfactory work.
A constant high standard of supervision, both on the part of the contractor and resident engineer, was essential for smooth operation. Dowsett appointed a paving agent and sub-agent, and the supervision and inspection for the whole length of the Contract was provided by an engineer and inspector working in conjunction with respective section engineers.
This procedure eliminated differing attitudes by section engineers in the field and maintained a constant standard of supervision throughout.
(No information is available on any other aspects of this contract)
