Excavation of Surface Installed Pipeline

A research program was undertaken to investigate the behavior of high-density polyethylene pipe during surface installation by horizontal directional drilling. In the fall of 1997, an instrumented high-density polyethylene pipe [55 m (180 ft) long, 200 mm (8 in.) in diameter, and dimension ratio of 17] was installed and monitored. Approximately 2 years later, three test pit excavations were completed to obtain in situ information along the bore, including pipe subsurface profile, characterization of site soils and bore slurry surrounding the pipe, location of the pipe in the bore, and pipe rotation and ovality. Research results indicate that pilot bore and in situ pipe profiles agree well, pipe buoyancy forces are small, drilling practice and fluid flow characteristics influence the slurry composition, well-designed drilling fluids provide bore support during and for extended periods following installation, significant voids are not created within the bore, slurry consolidates to a density similar to the surrounding soil (when the bore is located above the groundwater table), pipe torsion loading is inferred to be low, and pipe ovality is less than specified long-term deflection limits.