TRENCHLESS TECHNOLOGY- -THE NEED FOR ACCURATE GEOLOGIC INFORMATION: CASE STUDIES OF FAILURE AND SUCCESS

Trenchless technology may be described as: techniques and methods which do not rely solely on the use of a trench or excavation for placement of near-surface utility product pipe; methods of utility inspection; and renewal of in-situ product pipe or other type of installation. This technology is used worldwide, and represents a new frontier for needed geologic information.

Horizontal environmental remediation and monitoring wells and municipal water supply wells may be drilled with better success and subsequent higher outputs than comparable vertical applications. Coal bed methane may be successfully collected using “blind” horizontal wells. This technology is environmentally friendly: sensitive environmental areas, commercial areas, and residential areas experience little or no disturbance. Vehicular and pedestrian traffic may flow unimpeded over an area being crossed. Lack of disruption lessens commercial impacts, allowing business owners to conduct normal activity. Governmental income is maintained when business receipts are unaffected, because sales tax collection continues uninterrupted. Even metered parking revenues may remain unchanged during trenchless operations.

Knowledge of surficial and subsurface geology is the single most important factor insuring the success of all new horizontal product pipe installations, either by the collective set of techniques known as horizontal boring, or by a pipe replacement technology known as pipe bursting. Geologic criteria such as; soil and rock type, depth to water table, strength of soil or rock, and particle size should be considered in order to determine proper equipment type and capacity, need for specialized tooling, and drilling fluid formulation.

Two case studies illustrate how knowledge of geologic materials affects the possibility of success or failure of a project. The first case study is a horizontal bore which damaged I-270, a major thoroughfare in St. Louis, Missouri. The contractor responsible for the damage had not sought geologic knowledge prior to attempting the bore. The second example is a pipejack installation under U.S. 63 in Macon, Missouri. The contractor, Keith Contracting, Inc., was supplied adequate advance geologic information and completed the bore successfully, with no adverse impact.