Sewer installation, repair or replacement frequently involves deep trenching through roads that contain other services, for example, shallow buried gas and water mains. Such works induce ground movements which may adversely affect the adjacent road pavement and services. This report describes the third in a series of full-scale field trials carried out to investigate the magnitude and distribution of ground movements caused by deep trenching in a range of ground conditions. A 5.2 m deep by 20 m long by 1.3 m wide trench was constructed in boulder clay and the ground movements occurring during and subsequent to the trenching works were monitored. Details are given of the pattern of surface and subsurface movements, the changes in porewater pressure, the convergence of the trench sides and the loading on the struts. Also included is a brief summary of the strains induced in an instrumented shallow buried pipeline installed parallel to the line of the trench. Based on the observations suggestions are made concerning possible amendments in working practice required to minimise ground movements in critical situations. (Author/publisher)
Abstract