Postconstruction evaluation of horizontal directional drilling installations

Recently, questions have arisen concerning the compactive nature of drilling fluids within the annular space during horizontal directional drilling (HDD) operations. To address these concerns, a field and laboratory study was conducted to provide both a qualitative and a quantitative assessment of the annular space. The study consisted of installing 61 m (200 ft) bore lengths of 100 mm (4 in.), 200 mm (8 in.), and 300 mm (12 in.) SDR 17 high density polyethylene pipe in two different soil mediums: clay and sand. Subsequently, the pipes were excavated with visual and strength measures of each of the installations taken at time periods of 1 day, 1 week, 2 weeks, 4 weeks, and 1 year after installation to assess the annular space region over time. Additionally, samples of the drilling fluid were evaluated both in the field and at a laboratory. This paper presents the results of this research initiative and provides qualitative and quantitative information on borehole annular space integrity during HDD installations. The study revealed that: (1) the integrity of the annular space was maintained, as little evidence of voids was present; and (2) the strength properties increased over time through apparent consolidation, or equalization, with the native soil.