Performance of a propped retaining wall at the CTRL, Ashford

This thesis is based on the field monitoring of a propped bored pile retaining wall installedin an overconsolidated clay. Pile bending moments, prop loads, pore water pressures andlateral earth pressures were logged automatically at intervals of up to 5 minutesthroughout construction (and for 4 years afterwards) and wall deflections were measuredduring construction, making this the most comprehensive instrumentation project of itskind.The magnitude of the over-read associated with the use of spade cells (used to measurelateral earth and pore water pressures) in overconsolidated deposits was determined bycomparing readings from a spade cell aligned to measure vertical stress with the estimatedoverburden acting on it as the overburden was excavated. This study adds significantly tothe previous data as spade cells have not previously been \lsed in the Atherfield Clay, andthe performance of spade cells under a known changing load has not previously beenmeasured in the field.Analysis of the changes in lateral stress and pore water pressure during the wallinstallation process showed significant reductions in horizontal stress during wallinstallation, reducing the ratio of effective horizontal to effective vertical stress, K, fromabout 1 to nearly the active condition. Following wall installation there was no furtherchange in horizontal stress over a period of about 10 months, during which time no furtherconstruction work took place.Analysis of the data yielded good agreement between pile bending moments estimatedfrom inclinometer and strain gauge measurements in the piles, and the onset of concretecracking was identified. The components of strain measured in the reinforced concreteprops due to shrinkage, creep and applied load were also identified, allowing prop loads tobe estimated. A simple equilibrium calculation showed that these agree with the measuredwall bending moments and total horizontal soil stresses, demonstrating the overallconsistency of the data collected.Simple equilibrium analysis of the behaviour of the wall during construction shows thatthe soil stresses measured are compatible with the measured structural loads. The longtermhorizontal soil stresses, bending moments and RC prop loads show no increase overthe 6 years since construction began