Highways Agency - Safe roads, Reliable journeys, Informed travellers

Related pages

• 2.1 General
• 2.2 Mainline Layout
• 2.3 Junctions
• 2.4 Traffic Flows
• 2.5 Engineering Standards
• 2.6 Highway Features
• 2.7 Structures
• 2.8 Ground Conditions

2.7 Structures

Since the original construction of the structures on this section of the A2 the design standards have changed but all the structures have been assessed for current assessment loading standards under the Highways Agency 15-year rehabilitation programme. The 15 year programme was announced in 1987 and includes works to enable all structures to carry lorries up to the EC limits of 40 tonnes (gross) and 11.5 tonne drive axles. The programme also includes works relating to safety and durability of the structures.

All the structures on this section of the A2 are maintained by WS Atkins on behalf of the Highways Agency. They are subject to regular inspections and routine maintenance as required by the Highways Agency's Trunk Road Maintenance Manual (Vol 2 part 2).

Hyder Consulting have carried out an inspection of all the structures. Previous assessments have been reviewed and additional assessments have been carried out as required to verify the load capacity of the structures in accordance with current design standards.

2.7.1 Bean Road Overbridge (CH600 - Figure A2.1)

Bean Road Overbridge is a 3 span continuous overbridge that carries the B255 Bean Lane over the existing A2. The deck is an insitu voided post-tensioned concrete slab deck supported on bank seats and concrete columns, the latter being located in the verge and protected from vehicle impact by vertical concrete barriers.

A ground anchored retaining wall was constructed at the southern abutment to accommodate the realignment of the slip road through the side span in 1998.

2.7.2 Sandy Lane Subway (CH1340 - Figure A2.1)

Sandy Lane Subway is a single span rectangular box structure that carries the existing A2 (dual three-lane carriageway with hardshoulders) over Sandy Lane at approximately 26 degrees of skew. The structural form of the subway comprises a simply supported, solid reinforced concrete deck slab supported on mass concrete walls that are pinned at foundation level. Parallel rectangular wingwalls form the vertical legs to discrete reinforced concrete portal frames at both ends of the subway.

2.7.3 Swanscombe Footbridge (CH1830 - Figure A2.2)

Swanscombe Footbridge has a Grade II listed status, having been listed in 1997. The structure comprises a three pinned post-tensioned parabolic arch with post-tensioned cantilevered side spans. Abutments are buried in the cutting slopes and support the arch via concrete hinges buried just beneath the cutting slope. The abutments also support the ends of the cantilevers on rubber bearings. Vertical concrete barriers protect the piers from vehicle collision loading.

2.7.4 Northfleet Retaining Wall (CH2500)

This retaining wall has been amended from its original form to accommodate the addition of the fourth coast bound lane in 1998. The wall measures nearly 150metres long and was constructed using 600mm diameter contiguous bored concrete piles with the pile capping approximately level with the top of the carriageway, and approximately 1m above the adjacent footpath level. However, from site inspections the pile capping is now no longer visible either having been demolished down to a level beneath the widened carriageway or buried by the amended soil slopes.

2.7.5 Park Corner Underbridge (CH3200 - Figure A2.3)

Park Corner Underbridge is a single span, twin deck concrete bridge carrying four coast bound lanes and three London bound lanes (plus a hardshoulder) over the B259 at a skew angle of approximately 17 degrees. Deck construction comprises longitudinal precast concrete I beams and transverse insitu diaphragms acting compositely with an insitu concrete deck slab. Beams and diaphragms are post- tensioned and are supported on piled counterfort type abutments.

2.7.6 CEGB Tunnels (CH4100 - Figure A2.2)

The original horizontal twin service tunnels were constructed at an approximate depth of six metres below the carriageway level of the A2 and had vertical access shafts at each end sited outside the highway boundary. Their depth however was not sufficient to pass beneath the new CTRL construction to be built adjacent to the A2 at this point and they were replaced in 1998 by two new service tunnels constructed and commissioned alongside the original ones. These will pass beneath the new CTRL cut and cover tunnel construction at an approximate depth of 15m below carriageway level. The original tunnels were abandoned and filled in with foamed concrete.

2.7.7 Pepperhill Overbridge (CH4200 - Figure A2.3)

Pepperhill Lane Overbridge, is a four span bridge carrying the A2260 Hall Road and adjacent footpaths over the A2. Each of the spans are simply supported and comprise precast post-tensioned concrete beams with transverse post-tensioned diaphragms and an insitu concrete deck slab. The substructure comprises reinforced concrete spill-through abutments and with three-span frame piers hinged at the top and bottom. The piers are located in the verges and the central reserve. The footpaths across the bridge are protected from accidental wheel loading by temporary bollards at the kerb.