TABLE OF CONTENTS Horizontal Directional Drilling (HDD) is probably the fastest growing technology in the trenchless industry. HDD has gained widespread acceptance in the construction industry over the past decade. Horizontal directional drilling in North America has grown from 12 operational units in 1984 to more than 2000 units operating in 1995. The reason for the popularity is that HDD represents a significant improvement over the traditional open-cut and cover methods for installing pipelines beneath obstacles.
Equipment and installation techniques used in the HDD process are an outgrowth of the technologies from the oil field and water well industries. There is a wide range of directional boring units in use today, from mini drilling rigs, which are used for small pipes and conduits to maxi rigs, which are capable of installing large diameter pipelines. The maximum length of a HDD is determined by many parameters including rig size, soil conditions and pipe diameter. Installations as long as 6000 feet have been successfully completed. Current HDD equipment can operate in a wide range of soil conditions, from extremely soft soils to full-face rock formations with unconfined compressive strengths of 40,000 psi.
Traditional open trenching methods for installing pipe can be expensive, particularly in congested urban areas. Construction involves digging around existing utilities to get to the required depth, which slows down the operation. Also, not only must the trench be backfilled, often sidewalks, pavement, brick paving, sod, or other surfaces must be replaced. In addition, open cut operations often cause interruption...
