A graphical method for predicting ground movements from pipe jacking

The need for a relatively simple graphical technique for predicting the likely ground movements caused by pipe-jacking operations is established. The two analysis methods used to derive the graphs are briefly described. The first of these methods is based on the Gaussian distribution curve analysis and the second uses an analysis based on constant volume shearing (termed herein ‘modified Sagaseta analysis’). The derivation of the graphs used for predicting ground movements, based on these two methods, is then discussed. Two graphs are presented: one enables the immediate vertical surface and subsurface ground deformations to be predicted; the other enables the immediate horizontal surface and subsurface deformations to be predicted for a plane perpendicular to the direction of pipe-jacking operations. These two graphs, together with the application notes, allow the complete immediate two-dimensional ground displacement field associated with pipe-jacking operations to be determined. The graphs are applicable to tunnel diameters in the range 0·h.5–3·h.0 m and depths up to 15 m. Good quality field monitoring data associated with pipe-jacking operations are quite limited. However, the accuracy of the graphical method presented in this paper is tested using the data from three instrumented pipe-jacking operations described in the literature. It is shown that the predictions made by the proposed graphical method are reasonable, although there are some anomalous results. It is envisaged that as more field monitoring data become available the graphical method can be updated to incorporate new findings, thereby improving the accuracy of the predictions obtained. The practical need for establishing the ground movements for pipe-jacking operations is shown in terms of the likely effects these movements have on adjacent existing services, such as cast-iron pipelines.