LGW Stand 51

Project summary

Pavement defects had manifested on Stand 51 at Gatwick Airport over several years with ad-hoc repairs being carried out over that time period. The frequency of the repairs and their specific location under the main gear wheel paths suggested there was an inherent inability of the pavement to adequately support the range of aircraft now using it. The investigation sought to ascertain the usable life remaining of the pavement and recommend appropriate remedial treatment to ensure future serviceability.

Scope of assessment

A visual inspection was initially undertaken where pavement defects were photographed, their location logged, and the information plotted in AutoCAD with wheel path locations of various aircraft. Historical records were also examined to understand the local pavement profile which consisted of block paving construction laid on existing pavement from a general aviation apron built in the 1970s. Publicly available site investigation data was also gathered to develop an understanding of the local ground conditions.

An ACN-PCN analysis was undertaken to understand the current suitability of the pavement to accommodate aircraft using Stand 51 using subgrade CBR values of 3% and 6% and results contrasted with the visual condition. The results showed that as the assumed subgrade CBR value tended toward 3%, overloading was likely to be a contributing factor while at 6% this was not the case. The 777-300ER was also found to be having a disproportionate effect on the pavement with loading in excess of 40% potentially occurring. Further consideration was also given to the underlying historical pavement make-up. This consisted of Hot Rolled Asphalt (a binder rich material susceptible to creep) and the possible presence of a sand carpet, a non-structural regulating material which would likely fail early in a pavement’s life and lead to above ground visual defects.

Aerial overview of Stand 51

ACN-PCN analysis

The investigation concluded with summarising options to remedy the stand and return it to full serviceability. These options included full-depth reconstruction with contrasting methodologies from the BAA pavement design guide and DMG 27; the localised construction of concrete pads/strips under the main gear wheel paths; and the implementation of a hybrid Densiphalt solution with properties similar to concrete and already employed in various locations on the airfield.

Benefit

The report provided a better understanding of the historical pavement profile and likely overloading scenarios being experience by Stand 51. It also provided scope for discussing the most appropriate remedial treatments as well as the future operational necessities and/or restrictions that might need to be implemented to safeguard its long-term serviceability.