Pore water pressure and horizontal stress changes measured during construction of a contiguous bored pile multi-propped retaining wall in Lower Cretaceous clays

The design and construction of a contiguous bored pile propped retained cut on the approaches to Ashford International Station raised some challenging design issues. Design problems associated with under-drainage and groundwater control (including the performance of semi-permeable propped retaining walls) and the effects of wall installation and movement on in situ stresses were compounded by the relatively limited geotechnical engineering experience of the Atherfield and Weald Clay formations. Differences in the permeabilities of these two strata were expected, but the impact of these on the design was only fully established at the start of construction. Some aspects of the engineering behaviour of the Atherfield and Weald Clays are discussed with reference to an instrumented section of the propped retained cut. The changes in total horizontal stress and pore water pressures measured during and over a six-year period following construction of the retained cut are presented, and their significance is discussed