The success of any street resurfacing is, to a large extent, dependent
upon proper backfilling. To obtain maximum load-bearing capacities and to
prevent settlement, it is necessary that the backfill be made of good material,
properly placed and completely compacted. In backfilling around and over a
structure, the loads of heavy compacting equipment may exceed those for which
the structure was designed. Therefore, it is always advisable that the structure
be covered adequately before direct loads are applied.
Selected, drainable backfill material is preferred, but most local fill
material can be used, provided that it is carefully placed and compacted.
It should be free from large rocks and hard lumps or clods larger than three
inches in diameter. Do not use frozen fill, sod, cinders or earth containing
a high percentage of organic material. Granular material containing a small
amount of silt or clay is ideal, since it makes a dense, stable fill. In instances
where the excavated material is unsuitable for backfill and the opening is
soon to be repaved, use sand for the backfill material.
Fill material under haunches and around the structure should be placed
alternately in six-inch layers on both sides of the pipe to permit thorough
tamping. The fill is placed alternately to keep it at the same elevation on
both sides of the structure at all times. The fine material should be tamped
in these uniform layers with a small tamper under, around and over the structure
to a depth of two feet above the top. It should proceed evenly on each side
of the structure so that injurious side pressures cannot occur. Until two
feet of fill has been placed, earth must be dropped very carefully into the
opening.