Direct Pipe—Installation Force Evaluation of Recent Direct Pipe Installations

摘要

In the last few years, the direct pipe method of trenchless installation has moved from an emerging technology to a viable alternative to horizontal directional drilling (HDD) for relatively large diameter pipe in difficult soil conditions. In some cases, direct pipe is a more appropriate solution. In 2014, Robison, et al. evaluated installation thrust force data for 20 completed direct pipe installations; however, only the maximum thrust force, diameter, length, and general soil/rock type were available for the data analysis. As a result of the limited information, the estimation of maximum thrust force for direct pipe installations was somewhat impeded and resulted in a broad range of maximum thrust force instead of a specific recommendation for maximum thrust force. Currently, more than 100 direct pipe installations have been completed worldwide and more than 40 have been completed in North America. Of these, eleven were completed by Laney Directional Drilling. Because the authors were unable to obtain permission to use project data from other direct pipe contractors, this paper will present a detailed evaluation of the installation thrust forces based on data compiled for the eleven direct pipe installations completed by Laney. The thrust forces are evaluated and compared considering pipe length, pipe type, pipe diameter, and subsurface soil conditions. The paper also evaluates several factors that can affect the total installation thrust force. Understanding the installation thrust force during construction and its importance in evaluating the axial, bending, and combined stresses, and elastic buckling is critical to proper direct pipe design. Using the state-of-the-practice design procedures, the measured installation thrust forces are compared to the installation loads estimated during the design process. By comparing the estimated design installation thrust forces with the measured installation thrust forces, the authors evaluate the current design procedure and suggest ways the design procedure can be improved.