The purpose of the research described in the report is to examine the effects of eight trench reinstatements, built to the HAUC (Highway Authorities and Utilities Commission) Specification, on the long-term performance of a Type 3 road and the effects of traffic loads on buried pipes. A trial was constructed at TRL's Pavement Test Facility to study the structural performance of granular and foamed concrete backfill materials and their effects on overall pavement performance, pipes and the wetting up of the subgrade. A typical Gaussian distribution of trafficking, at 11.5t axle load, was applied across each of the trenches. Performance measurements were carried out at simulated 6 month intervals over a simulated 4 and a half year test period and included the recording of visual condition, deflection, surface profile and strains in the pipe and structure due to traffic loading. Within the HAUC guarantee period, no consequential damage was observed using either backfill material and no premature maintenance was required to the trenches or the original pavement. No significant changes were found in deflection, visual deterioration on the control or trenched sections. Settlement within the trenches was 5 per cent of that allowed under HAUC. The good performance of the trenches and the pavement indicated that sustained sound performance is likely to be achieved throughout the design life of the pavement. (A)

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