Author: Ashkan Faghih

Publisher:

Published: 2022

Total Pages: 0

ISBN-13:

Horizontal directional drilling (HDD) technology is becoming a popular option for steel pipeline construction and replacement projects. During installation, the pipe is subject to a combination of loads and the long-term performance of a pipe installed by HDD is linked to the stresses that develop during installation. With increasing demand for steel pipeline installations using HDD, a more detailed investigation of the stress conditions that develop during installation is required to evaluate the reliability of current design guidelines. This dissertation aims to identify and address topics related to the analysis of the loads imposed on steel pipes during HDD installation. In North America, the load calculations recommended by the Pipeline Research Council International, PRCI (2015) are widely used for steel pipeline installation by HDD. Therefore, more attention is given to investigating the stress analysis method suggested in this widely accepted guideline. Pull force estimation in HDD is essential during the planning phase. As part of current design practice, simplifications and assumptions need to be made to approximate the pull forces expected during HDD pullback. However, to date, a comprehensive assessment of the accuracy of pull force predictions has not been completed. A review of current design practice based on PRCI and industry accepted engineering assumptions for pull force calculations is presented in this work. Data from two hundred recent commercial HDD projects were collected and studied to compare actual and predicted pull forces in chapter three of this thesis. The accuracy of the pull force prediction for these crossings was investigated based on different project characteristics such as pipe size, crossing length, geotechnical conditions, and equipment size. This study indicates that the underlying assumptions for pull force estimations need to be selected based on project-specific characteristics to increase the accuracy of pull force predictions. In some HDD applications, multiple product pipes can be bundled together and installed inside a single hole. In the absence of detailed analytical solutions for bundled pipe projects, a simple approach can be used based on current calculation methods, which involves approximating the bundled pipes by using a single equivalent pipe to calculate the required pull force. Chapter four of this thesis reviews the concept of using a single equivalent pipe and applies it to the pull force calculation method recommended by PRCI. Five HDD case studies-including installations of bundles comprising two to six steel pipes of different sizes-were investigated to determine the accuracy of the proposed pull force estimation method. The simple method proposed in this work was found to result in pull force predictions that were close to actual loads measured during installation. Chapters five and six of this thesis describe a strain monitoring program which was utilized for two major HDD installations over a kilometer long to analyze the axial and circumferential stresses and strains imposed on the product pipe during HDD installations. Strain measurements were presented in the form of pipe strains along the drill path during the time of the installation. The stress-strain relationships were developed for the pipe installation and installation stresses were calculated using the strain measurements. Then, the stresses calculated from the strain data were compared with the expected theoretical values determined based on current design practice. The strain monitoring and stress calculation discussed in this thesis provides some details on the expected behavior of steel pipes during HDD installations. Finally, this thesis presents a new method to model the geometric path of the pipe inside the borehole based on Bézier curves, using drilling survey data collected while drilling the pilot hole. A large-diameter HDD project in dense soil where the actual geometry of the installed pipe was determined using an in-line inspection tool is presented as a case study. The analysis of bend radii indicates that for most locations along the bore path, the installed pipeline had a larger bend radius than the as-drilled hole. The application of the proposed geometric modeling is tested in the case study project. The smallest bending radii determined by the proposed geometric modeling method using Bézier curves was found to be closer to the actual pipe curvature as opposed to simply using the geometry of the pilot hole to determine the pipe bend radii.