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Modelling the soil pipeline interaction during the pull back operation of horizontal directional drilling

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The pull back operation is the most important stage of horizontal directional drilling (HDD). The cost of jammed pipelines, damaged pipelines and the costs for additional measures during and after the pull back operation can be considerable. Recently in the Netherlands several problems occurred during the pull back operation at some locations where relatively large diameter pipelines where installed. The objective of the Delft Cluster Horizontal Directional Drilling (HDD) project, is to find a detailed method for modelling the pulling of pipelines through a borehole created using HDD’s. The main objective is to get a better understanding of the behaviour of the pipeline in the borehole. Penetration of the borehole wall during the pullback operation and friction in between the pipe and the borehole are important parameters. The current Dutch method for calculating the pull back force on the product pipe was developed more then 10 years ago. For global design purposes and global engineering practice it is a quick and relative simple method which gives a reasonable estimate of the maximum pull back force. But large differences with field measurements have also been observed, hence a more detailed analysis of the processes occurring in the soil-pipe interaction during the pullback operation is required. Such analysis has been made from which a new model for the pull back operation is developed. In this report first the various processes occurring during pull back are described in Chapter 2. In Chapter 3 the model is presented, what elements are included in the model, what processes they describe. Chapter 4 presents pull back simulation results for a variety of cases, from simple to extensive. Simple cases are used to compare the model to analytical solutions, and to compare geometrically linear to nonlinear behaviour. More detailed cases include more and more phenomena and processes. The complexity is increased gradually to better understand the influence of various parameters. Chapter 5 presents conclusions that can be drawn from the simulations. In Chapter 6 a study is presented that investigates the soil-pipe interaction behaviour for various combinations of pipe dimensions and soil types. From this study a better understanding is obtained for the behaviour of soil springs in pipe-soil interaction contact as used in the model. Chapter 7 gives some general conclusions about the model and the project, including suggestions for future research.