PSI - Issue 64

Tom Argyle et al. / Procedia Structural Integrity 64 (2024) 1376–1385 Argyle et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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Based on a certified assessment of the structure a sensitivity study on the capacity of the structure for reduced plate effectiveness in the hogging region was undertaken, with consideration to both normal traffic and special type abnormal vehicle loading. This identified that 50% or greater plate effectiveness was required to support normal traffic on the West deck, with 25% plate effectiveness required on the East deck. Due to the higher loading imposed by the abnormal vehicle types, a restriction to these vehicles was placed on both structures. 3. Structure Interim Measures Management On identification of the potential debonding to the plates, and subsequent sensitivity study, both structures have been subject to the National Highways CS470 ‘Management of sub - standard highways structures’ process, to manage the risk posed by the deteriorated plate condition. In addition to the Load Mitigation Interim Measures (restricting abnormal vehicle movements on the structures) a regime of Monitoring Interim Measures was put in place. 6-monthly visual inspections of the carriageway surfacing were undertaken, and, where break-up/deterioration in the road surface condition was identified, intrusive investigation to expose the strengthening plates and conduct hammer-tapping was conducted. Identified areas of potential debonding from the intrusive surveys were mapped and quantified on the as-built plate records and subsequently compared against minimum plate effectiveness requirements. Through this process, the level of risk posed to the structure from plate debonding was able to be monitored which allowed an appropriate priority to be given to the implementation of a long-term remediation solution. The exact causation of the debonding was not confirmed at this point, but was considered likely to be as a result of a number of factors including; raised level of strengthening plates resulting in reduced surfacing thicknesses, broken and failed grout and waterproofing surrounding the plates and hydrostatic pressures imposed under axle loading from sub-surface water within the porous surfacing material.

Fig. 3. Exposed top of waterproofing showing de-bonded waterproofing and minor infill grout break up (left), and exposed top of strengthening plates (right) from interim measures monitoring investigations. 4. Remediation approach Alongside the Interim Measures to manage the asset, a collaborative optioneering process and subsequent design development of a remediation solution was undertaken. The objectives of the remediation were to: • Minimise (or eliminate) the risk of the observed de-bonding mechanism in future. • Restore the original structure load rating to allow full Normal Traffic and necessary Abnormal Vehicles. • Maintain network availability for the travelling public (National Highways customer) during construction. The options study considered several costed strengthening solutions (the discussion of which are outside the scope • Eliminate future potholing / breakup of the carriageway surfacing. • Allow full reinstatement of sound waterproofing system across the deck.