The USA and USSR jointly constructed a special test section of 915-mm diameter Reinforced Plastic Mortar (RPM) fiberglass pipe in June 1979 near Riga, Latvia. This experiment was part of the working agreement of the US-USSR team “Investigations of Effectiveness of Plastic Pipe in Drainage and Irrigation.” Measurements were made of pipe deflections, soil properties, and in-place densities. Six different embedment conditions were used. The pipe deflections were measured during each state of construction and over a 4-year period.
Data of particular interest is the increase in the vertical diameters caused during soil compaction at the sides of the pipe and the frequent deflection measurements in the few weeks following the final placement of the 3 m of backfill over the pipe. The ratio of the vertical deflection after 4 years to the vertical deflection on the day the backfilling was completed ranges from 1.6 to 1.7 for the dumped side support, 4.5 for a side support with a moderate degree of compaction, and 2.2 to 2.9 for the side support placed to a high degree of compaction.