Predicting ground displacements caused by pipe splitting

Pipe splitting is used for the on-line replacement of pipelines made from ductile materials, for example ductile iron and steel. It is a relatively new technique, and so there is limited knowledge about the associated ground displacements, in contrast to the pipe-bursting operations used for pipelines constructed of brittle materials, such as clay, concrete or cast iron. Understanding, and hence predicting, the ground displacements generated by pipe splitting is of vital importance when considering safe distances to other services and controlling possible damage to the road surface. This paper describes the results from some analytical studies that have been conducted in an attempt to develop such a method of prediction, and follows on from a series of full-scale laboratory experiments and an instrumented field trial. The observed ground displacements obtained from this work showed that an elliptical expansion of the soil locally to the existing pipe best represented the general behaviour of the ground for the most common types of pipe splitter currently used in practice. Consequently the analytical work has concentrated on assessing this assumption. The results from these analyses suggest that the elliptical assumption for the localised displacement is generally valid as a first estimate. However, pipesplitting operations cause more complicated ground displacements than pipe-bursting operations as the displacements are less symmetrical in nature, and are controlled to some extent by the way the pipe-splitting device is used in practice.