Field Measurements of Surface Displacements from Pipe Bursting
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Two field studies of surface displacements during pipe bursting were conducted. The first field study consisted of a controlled experiment in clay soil. Three vitrified clay pipelines, each at a different burial depth, were up-sized to high density polyethylene (HDPE) pipes using static pipe bursting techniques. Surface displacements during the pipe bursting process were monitored using digital imaging techniques as well as surveying. It was found that ground displacements were largest in the vertical direction, such that the maximum vertical displacements measured during pipe bursting ranged from 71.8 ± 7.5 mm at a depth of cover of 0.6 m and 11.2 ± 1.2 mm at a depth of cover of 1.5 m. Transverse displacements generated during pipe bursting were found to correspond to tension cracking of the ground surface above the pipe. The second field study examined pipe bursting installations which took place at the Royal Canadian Mounted Police College campus in Ottawa, Ontario. During this study, five pipe bursting installations were monitored. Each installation varied in terms of the surface and subsurface conditions, host pipe size and material, replacement pipe size, and depth of cover. The pattern of displacements distributed in all three directions was consistent with the results from the controlled study. However, greater variability in results was found during the Ottawa project. Vertical displacements were found to range from 0.6 ± 0.1 mm to 11.3 ± 0.2 mm for pipe bursts carried out to the same up-size dimension, at approximately the same depth of cover, surrounded by similar surface and subsurface conditions. In general, pipe bursting in clayey soils with an unpaved surface resulted in larger displacements having a narrower distribution over the ground surface than the paved installations. Additionally, increased variability in results occurred under real construction conditions due to inherent variability in subsurface and host pipe conditions.