#Christmas wallap series
However unlike the River Kennett Bridge, the decks frame into contiguous piled abutment walls and so a series of analyses were carried out to determine the required pile sizes. Drawing upon the design of the River Kennett Bridge on the Newbury Bypass (an integral bridge with a 20♶ m clear span and 27° skew designed by Mott MacDonald and built by Costain), precast Y6 and YE6 beams with cast-in-situ composite top slabs were selected for the bridge decks. Contiguous bored pile walls that also serve as integral abutments for the bridge decks retain the cut. The bid team developed a design for the M4 crossing whereby the A34 is effectively in retained cut spanned by separate bridge decks for the M4 and the two slip roads.
The M4 crosses the A34 at a skew of 18°, requiring a clear span of 24♷ m.
#Christmas wallap Offline
With some temporary widening of the M4 embankment, three successive phases of traffic management would allow construction of one-third of the M4 bridge at a time in a top-down sequence while the slip road bridges would be built with the slip roads temporarily diverted offline (see Fig. To minimise disruption to the travelling public, Costain proposed to construct the M4 bridge while keeping three lanes of traffic moving in each direction on the motorway. Taking into account the traffic management that would have to be in place for the resurfacing works, the alternative structure constructed in a top-down sequence showed a capital cost advantage in excess of £4 million over box-jacking, the prerequisite being that all the ‘top works' could be constructed concurrently with the resurfacing works and so would incur no additional lane rental charges. Initially the Costain/Mott MacDonald bid team evaluated both options for the M4 crossing.
Also included in the contract were extensive resurfacing works on the M4 under lane rental. An alternative structural configuration was also shown, which comprised bored pile abutments with a high-level bridge for the M4 and separate lower-level bridges for the slip roads. The illustrative design shown in the tender documents was a two-cell box underpass that could be constructed either in open cut or by box-jacking. The subject of this paper is the design of the crossing under the M4 motorway and the adjacent slip roads.ĭesign-and-build tenders were invited in August 2002 by the Highways Agency. The design of the works was carried out by Mott MacDonald working with Costain under a design-and-build contract. The existing roundabout is retained for interchange movements between the M4 and A34, with new slip roads linking to the realigned A34 (see Fig. The improvement entails realignment of a 3 km section of the A34 to the west of junction 13 allowing the new A34 to pass beneath the existing west-facing slip roads and the M4 embankment. Traffic growth in the intervening years, particularly following the opening of the Newbury Bypass in 1998, has led to increasing congestion at junction 13 with long tailbacks occurring at peak periods. When the M4 was built in the early 1970s, the motorway was raised on an embankment while the A34 was kept at grade, and all north–south traffic was forced to negotiate the roundabout at junction 13.
#Christmas wallap full
This Highways Agency scheme provides full grade separation between the A34 and the M4 at Chieveley.
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