Inadvertent Slurry Returns during Horizontal Directional Drilling: Understanding the Frequency and Causes

摘要

Horizontal Directional Drilling (HDD) is an innovative and attractive construction method forinstalling pipelines and utilities within rights-of-way. Regulatory agencies often consider HDDas the least environmentally disruptive alternative because construction operations can be iso-lated from environmentally sensitive areas. However, bentonite slurries used in HDD are knownto inadvertently migrate to the surface, which may introduce foreign material into wetlands orincrease turbidity in surface waters. The Gas Research Institute (GTI) sponsored a survey of largeHDD installations to identify the frequency and possible causes of inadvertent returns. Survey re-sults would provide planners information to aid in critical decision making. Questionnaires weresent to HDD Contractors to assimilate information about crossing parameters and inadvertent re-turn details. Ultimately, 54 individual HDD installations of various lengths and in an assortmentof geotechnical conditions were studied. Inadvertent return events occurred on approximatelyhalf of the HDD installations. Inadvertent returns occurred most frequently within 200 ft. of theentry or exit point and where there was less than 40 ft. of overburden. No correlation was ob-served between lack of normal returns, slurry properties, or pumping rates and the inadvertentreturn events. Disturbed ground (tree roots, pilings, burrows, etc.) increased the likelihood of in-advertent returns. Inadvertenteturns are a phenomenon which cannot be ignored. Constructionrights-of-way should be obtained for remedial clean-up in the first and last 200 ft. of any HDDalignment. Most events studied produced manageable amounts of material that can be containedand disposed without interrupting the construction operations.