United States Department of Transportation
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Abstract:The purpose of this study was to examine the current state of the practice of state highway agencies regarding methods
and specifications for using trenchless technologies. From the perspective of the Virginia Department of Transportation
(VDOT), the paramount concern associated with trenchless construction is the safety of the traveling public. Since such
construction typically takes place without the re-routing of traffic, any sudden and substantial surface displacement of the
overlying roadway has the potential for catastrophic consequences. Surface monitoring during and after construction is a critical
activity to ensure successful installation.
The study focused on the most commonly used trenchless methods for new construction, including the selection of the
most appropriate trenchless technology for specific applications, the identification of minimum geotechnical investigation
requirements, design considerations, construction monitoring, costs, and performance. The study did not address all potentially
available methods of utility construction and rehabilitation.
To achieve the study objective, two tasks were performed: (1) the literature on the current state of the practice with
respect to the use of trenchless technology in other states was reviewed, and (2) identified specifications and design guidelines of
various state transportation agencies were analyzed and examined for potential applicability to trenchless construction activities
administered by VDOT.
The study concluded that trenchless technologies have been widely adopted but design guidelines and construction
specifications vary significantly. Accurate subsurface characterization is critical to the selection of the most appropriate
technology for a specific project. Obstructions pose a significant risk for all types of trenchless work. In general, the risk of
using the directional drilling method increases with pipe diameter. The opposite is usually the case for microtunneling.
Unguided trenchless methods are suitable only for short drives. Monitoring of trenchless construction is usually limited to
observations of installation procedures and surface monitoring. For the most part, a high level of expertise is required for
operators of trenchless equipment.
The study recommends that VDOT’s Materials Division, Location and Design Division, and Construction Division
jointly develop and approve the criteria for selection of trenchless technologies. Specific technical recommendations for
inclusion in VDOT special provisions and the VDOT Materials Division Manual of Instructions are enumerated.
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