Trench backfills not only impact buried utilities, but are also required to support surface pavements. Forces generated by traffic loads, frost loads as well as soil loads are transmitted through the pavement as well as to the buried pipes. While some of the materials are as old as trenching itself, others are completely novel. The sites are variously instrumented to monitor temperature, thermal conductivity, moisture content and compaction of the backfill itself as well as loads on the pipe, water temperature and flow rates in the active water line. Clay is a good insulator but the road settles.
Cementitious materials support the roads but promote frost penetration deeper into the trench.
What we're trying to do is to show the efficiencies and deficiencies of each kind of material.