Modulus of Soil Reaction Values Measured in Ohio Thermoplastic Pipe Deep Burial Project

The researchers at Ohio University examined various aspects of the buried plastic pipe-soil interaction problem through their thermoplastic pipe deep burial project. This paper addresses one issue that they have not studied before—the modulus of soil reaction of the backfill materials. This modulus is a key parameter of the buried pipe-soil system. However, it has rarely been determined from actual field data. Most engineers and researchers consult publications such as AASHTO specifications or the values reported in the American Water Works Association design manual when selecting its value for any given flexible pipe installation case. A careful analysis made on the deep burial project data showed that the field-based soil modulus values were close to the published values for dense granular backfill materials. For loose granular backfill materials, the field-measured values were higher than those provided by the AASHTO specifications and laboratory one-dimensional compression test results. Other findings of the analysis included the following: (1) no straightforward one-to-one correlation was observed between the relative compaction level and the soil modulus; and (2) the soil stiffness gauge readings could not represent the actual soil modulus values seen in the buried thermoplastic pipe problems.