DRILLING AND PREPARATION OF REUSABLE, LONG RANGE, HORIZONTAL BORE HOLES IN ROCK AND IN GOUGE. VOLUME I. STATE-OF-THE-ART ASSESSMENT
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The objective of this study is to assess horizontal drilling as an alternative to pilot tunneling in geological investigation prior to the design and construction of highway tunnels and to identify means to increase the penetration capability and accuracy and decrease the cost of horizontal drilling. This volume assesses the horizontal penetration capabilities of available drilling equipment. The drilling of horizontal holes to a maximum length of 5000 ft. (1524 m) is found to be technically feasible and to offer an order of magnitude cost reduction over pilot tunneling. Limitation present day equipment and techniques are identified and means to overcome these limitations are indicated. This is the first of three volumes. Volume II is published as FHWA-RD-75-96, subtitle: Estimating Manual for Time and Cost Requirements. Volume III is published as FHWA-RD-75-97, subtitle: A Development Plan to Extent Penetration Capability, Increase Accuracy, and Reduce Costs. /FHWA/