Assessment of the Performance of Trial Trenches Backfilled with Cementitious Materials

Abstract

Longitudinal and transverse trial trenches backfilled with unbound graded granular material. Lytag:cement and PFA:sand:cement were monitored over a period of one year. Permanent deformation, elastic deflection and ease of break-out of backfill were used to assess the performance of the trenches. Granular backfill exhibited settlement of 2 and 5mm for the transverse and longitudinal trenches respectively. The corresponding settlement for cementitious backfill was 1 and 2mm. For all types of backfill materials, longitudinal trenches showed greater settlement than the corresponding transverse trenches. Settlement of the trenches took place mainly in the first two months after construction and the rate of settlement became insignificant after that period. Field trials showed that cementitious materials performed better than granular backfill both in terms of permanent deformation and less elastic deflection.

Falling weight deflectometer tests were conducted to estimate the elastic modulus of the backfill. It was found that after about one year the deduced elastic modulus of granular backfill became similar to that of the surrounding soil. The deduced elastic modulus of the two cementitious backfille became higher than for the control section, but poor bond between fill and trench wall may have limited the deduced value for Lytag cement mix. One metre length of each transverse trench was excavated to assess ease of break-out. Whilst the granular backfill was the quickest to excavate, Lytagxement backfill was favoured by the operatives as it could be broken out and handled as easy as the granular backfill.

The initial cost of PFA:sand:cement was very close to the granular backfill whereas Lytagxement was 12–28% more expensive. If long-term performance is considered, cementitious backfill may be more economical even though the initial cost is higher.

Keywords:

• Trench
• fill
• utility cut
• permanent deformation
• lytag
• fly ash