a significant proportion of sewer renewal, replacement and new construction involves deep trenching in urban areas. studies carried out to assess the likely causes of fractures in shallow buried cast iron gas and water mains have indicated that ground movement is one of the principal reasons. of the many quoted causes of this ground movement, work on other services is frequently mentioned. as part of a study to assess the effect of ground movements due to trench construction on roads and adjacent buried services, observations are first being made of the magnitude and distribution of ground movements produced by deep trenching in a range of ground conditions. this report describes a full-scale field trial involving the construction of a 5m deep by 25m long by 1m wide trench in london clay. information is provided on the effect of the component activities of the trenching operations on the ground movements which develop in the short and longer term and on the pattern of surface and subsurface movements. (a)

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