Synthesis of Trenchless Technologies

About the report:

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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