Performance of push-in pressure cells in overconsolidated clay

Abstract

Low-profile push-in pressure cells (spade cells) are commonly used to measure total horizontal stresses in both normally and overconsolidated clays. It is known that spade cells over-read the in situ stress in such deposits as a result of the complex localised stresses created during installation. Previous investigations into the magnitude of over-read are limited in number and have produced scattered results. During construction of the Channel Tunnel Rail Link at Ashford, Kent, a spade cell was installed horizontally in an overconsolidated clay, aligned to measure initial vertical stress, and the change in vertical stress due to excavation of material above the cell. The results of this experiment are presented and interpreted with reference to a finite element analysis and a comparison of spade cell and self-boring pressuremeter test data of horizontal stresses at the same site, to assess the performance of this type of spade cell in the Atherfield Clay.