Ground movements associated with trenchless pipelaying operations
A comprehensive review of the published work is presented on field, laboratory modelling and theoretical data relating to ground movements associated with trenchiess pipelaying techniques. Due to the similarities with convergent trenchiess techniques, soft ground tunnelling work is also reviewed. The factors that influence these ground movements are isolated and the ability to investigate these considered in terms of model tests. A test facility based on a l.5m long,l.5m high and l.Om wide steel tank has been developed and this is described together with the philosophy behind its use. The development of appropriate methods of simulating both pipejacking and pipebursting trenchiess techniques using the test facility, based on the installation of a 200mm diameter semicircular steel pipe section, are described. The use of a stereo-photogrammetry technique for the ground movement data acquisition is also reported and assessed. Three programmes of model tests were conducted: open shield pipejacking, closed shield pipejacking and pipebursting. The test programmes included investigations into the effects on the soil movements of variations in cover depth, overcut ratio (pipejacking tests), bursting ratio (pipebursting tests) and the effect of using different dry sands at different densities. From the photographs obtained during the tests, the sand displacements were determined in both the longitudinal and perpendicular planes to the pipe installation. These displacements allowed contour plots to be produced for the horizontal and vertical components of these displacements. This allowed the interaction of the various areas of sand movement to be appreciated, and the extents and magnitudes to be investigated for the changes in the factors made between each test. The extension of the results to other test conditions not directly investigated and also to the limited field data available, is made by using interpolation and extrapolation of graphical plots of the test data. These graphical plots also allowed trends in the data to be highlighted. This project involved a fundamental study of ground movements. However, guidance is given on how the results obtained from the tests can be used to determine the effects on adjacent services and structures. This is presented bearing in mind that the test results were for laboratory model simulations rather than prototype operations. Two simple theoretical analyses are described, one based on the error function curve and one using a fluid flow method. The error function analysis is used to predict ground movements in the perpendicular plane to the installation, while the fluid flow analysis, with dilation and compression capabilities, is developed to enable ground movements to be predicted in both the perpendicular and longitudinal planes. The analyses were applied to the laboratory model tests and the results correlated very well. The results of the laboratory model tests and the theoretical analyses developed, considerably extend the understanding and knowledge on the ground movements associated with trenchless pipelaying techniques.