This paper discusses the wide range of behavior possible in argillaceous soils and rocks and how this behavior can affect the success of horizontal directional drilling (HDD) projects. Much of North America is dominated by argillaceous deposits making it necessary to understand and to recognize when the conditions are good, bad or ugly and to develop appropriate solutions for the potential problems they may pose to HDD.HDD design and good practice guidelines are necessary to reduce the overall risk impact to HDD installations, however the properties of argillaceous soils and rocks are only considered in a limited and qualitative sense. This requires extensive experience from the design team and contractor to determine whether construction conditions will be favorable or unfavorable to HDD and what mitigative measures are necessary to address the risks presented by unfavorable conditions. A geotechnical investigation that defines the relevant material properties of the argillaceous materials are a necessary requirement to HDD feasibility and design. Furthermore, by communicating the potential risks or opportunities presented by the argillaceous material to the HDD design team and construction contractor, linkages between HDD design and risk mitigation construction strategies, particularly relating to annular pressures, can be made. Three case studies are presented to examine the range in behavior in argillaceous soil and rock, design inputs, construction outcomes and recommendations for improvement.
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