Winnipeg watermain backfill studies

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Mishtak, John David
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Previous studies have indicated that movements of watermains in the Winnipeg area are of sufficient magnitude to cause flexural failures in corrosion weakened watermains. It was suspected that the type of backfill material, state of density of the backfill, and techniques of backfilling and compacting had an appreciable effect on the resulting movements. A field investigation was conducted to study backfill material, obtain quantitative densities in backfill and for comparison, in adjacent undisturbed soils; effects of various methods of compaction were also studied. Results indicated that densities produced were highest when the backfill was compacted by mechanical apparatus then decreased as compacted by the hand tamper and water jetting, loosely placed backfill compacted at surface by moving tractor, and by hand tamping, respectively. Trial compaction by the Barco Rammer compactor resulted in densities higher than those produced by any other method of compaction and higher than densities in undisturbed soils. It was concluded that to backfill and compact in the ideal manner required a very strict moisture content and compaction control, the cost of which would be prohibitive. However, suggestions were made for improvements in the manner of backfilling and compacting which it is believed would effectively lower the number of flexural breaks in watermains and reduce maintenance costs.