Backfilling of Sewer Sanitary Trench - Considerations and Compaction Degree

October 16, 2017


The effluent pipes are in place, the bedding material is packed, and the line has been tested for leaks. The backfilling stage comes next. Take a moment to consider the procedure. Remember, if this job isn't done right, the pipe could break. Sewage leaks stink. Worse still, they're a health hazard. Backfill that sewage sanitary trench with caution, with step-by-step professional care.

Sewage Pipe Trenches: The Backfilling Considerations

Toxic fluids move inside sewage pipes, but let's not dwell on this nasty discharge. Let's just say an unpleasant environmental nightmare could occur overnight if this trench isn't properly backfilled. The damaged line allows its effluent load to discharge as a mucky, stinky sludge. The land above the damaged pipe is then transformed into a boggy mess, and a health hazard is spreading through the soil. The course of action is clear: the backfill stage must be prudently conducted so that no pipe damage occurs.

Establishing the Embedment Zone

A layering approach works best. The first layer is the support bedding, which is made from sand or crushed rock. Compact the embedment material and remove any stress-causing crests from the smooth fill. Next, increase the volume of the backfill by layering a granular spread of haunching, then add an upper layer of soil backfill. All the while, each deposited layer uses its own weight to push down the pipe and eliminate void areas. That's a critically important part of the work, especially if the land has a high water table.

What about Compaction Degree?

This is a soil-based variable, one that alters when different backfilling factors are assessed. For example, a simple pipe run across a grassy parcel of land employs natural settlement, the weight of the backfill, because there's not likely to be any traffic on top of the ground. What if this is a high traffic site or a paved area? Then a higher degree of granular compaction is applied during each strip layering stage. In this manner, the structure weight and traffic will not impact pipe integrity.

The backfilling of a sewer sanitary trench isn't quite this easy, but we thought a close look at the different layers would serve to illustrate the importance of this graded closing procedure. The different sands and soils alternate until the lower backfill strip tops off at 30cm above the sewage line. Of course, there are slightly different layering materials and mediums when the pipe type changes. Flexible pipes and rigid pipes occupy the effluent channelling industry, so the trench filling procedures must adapt to consider these alternative pipe types.

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