A prominent structural feature of the Lower Oxford Clay near Peterborough is formed by a series of near vertical joints traversing the full height of excavations up to 25 m deep and extending for at least several hundred metres in a north-south direction. The orientations and spacing of these joints were determined by means of a series of stereophotographs taken at intervals from the same three points, as a face was excavated. Using machine contour plots derived from the stereopairs a three-dimensional model was constructed to demonstrate the joint disposition. Although some bifurcation of joints occurs the average spacing is about 8–10 m. A similar, nearly orthogonal, set of joints is also present but less well-developed.

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