thumb_hts-pepperhill_bridge_a2_hyder-46Two previous Phase III investigations of the structure by Kent County Council during 1995 were inconclusive and further works at the Pepperhill A2 Overbridge required another Phase III investigation in accordance with BA 50/93 (“Post-Tensioned Concrete Bridges - Planning, Organisation and Methods for Carrying Out Special Inspections”) including interim Advice Note IAN3 and BA 35 90 (‘The Inspection and Repair of Concrete Highway Structures”). The investigation was required to determine the condition of the post-tensioning system at locations considered to be vulnerable to deterioration. The contract period of 5 weeks comprised 2 weeks for site works and 3 weeks for completion of laboratory tests and submission of reports.

Hydra Technical Services (HTS) were awarded the contract by Hyder Consulting Ltd and prepared a network diagram & Gannt chart identifying the critical path, showing the level of detail appropriate to each stage of the works and all activities and restraints. In particular, the works requiring traffic management on the A2 were completed as early as possible to minimise risk of disruption to the works being undertaken beneath the bridge by the Channel Tunnel Rail Link contractor.

HTS completed the following operations:-

Traffic Management, including Varioguard.
Duct and tendon location, exposure and investigation, reinstatement and repair. Grout samples taken for chemical analysis (chloride, alkali, cement and sulphate content).
Anchorage location, and inspection and, where necessary, exposure (including reinstatement and repair) at 7 No. locations. Anchorages, longitudinal and transverse, were exposed and inspected by forming a hole through the curtain wall and edge of the deck. Reinstatement and repair incorporated works to the road joints in the carriageway.
Ducts were located then tendons exposed at 42 No. locations and investigated and a representative number of grout samples taken for chemical analysis. Any voids were probed to determine approximate length, inspection was carried out using a flexible endoscope.
Reporting of the results and the findings of the investigation.
Replacement of carriageway road joints above the pier supports and the south abutment. Over the north abutment it is intended to replace the neoprene insert component of the existing joint.
The realignment of kerbing, lighting column removal and replacement, relocation of gullies and the installation of temporary safety barriers.
Reinstatement of footway and carriageway surfacing.
Reinstatement of road markings and removal of TM.