This letter presents data from triaxial tests conducted as part of a research programme into the stress-strain behaviour of clays and silts at Cambridge University. To support findings from earlier research using databases of soil tests, eighteen CIU triaxial tests on speswhite kaolin were performed to confirm an assumed link between mobilisation strain (c M52 ) and overconsolidation ratio (OCR). In the moderate shear stress range (0?2c u to 0?8c u ) the test data are essentially linear on log-log plots. Both the slopes and intercepts of these lines are simple functions of OCR.

This paper reports the results of four centrifuge model tests that were undertaken to investigate behavior of floating piles subjected to negative skin friction (NSF) and to study effects of axial load on the load-transfer mechanism along single floating piles and shielded center piles inside a group of sacrificing piles. In addition, three-dimensional numerical analyses of the centrifuge model tests were carried out with elasto-plastic slip considered at the pile–soil interface. Prior to applying load, the measured neutral plane position of the single floating piles was located at approximately the three-quarter depth level of the embedded pile length. The neutral plane elevation shifts lower down the pile shaft as the distance of pile tip above the bearing stratum decreases. Under the application of axial load, the dragload generated by excessive soil settlement decreases and is eventually eliminated. The amount of axial load for complete NSF elimination does not seem to be significantly affected by the presence of sacrificing piles, but it does increase with end-bearing stiffness of the pile. Numerical simulation revealed that the hang-up effect is not altered by the application of axial load.

Finite-element analyses (FEA) and case histories of deep excavations in soft clay are used to validate a decision-making tool based on an extended mobilizable strength design (MSD) method that permits the designer an extremely simple method of predicting ground displacements during an undrained excavation. This newly extended MSD approach accommodates a number of issues that are important in underground construction between in situ walls, including alternative base heave mechanisms suitable either for wide excavations in relatively shallow soft clay strata or narrow excavations in relatively deep soft strata, the influence of support system stiffness in relation to the sequence of propping of the wall, and the capability of dealing with stratified ground. In addition, a simplified MSD framework is proposed for analyzing a database of 110 deep excavation case histories worldwide. The approach examines the governing factors controlling deformation in deep excavations and offers simple guidelines for designing support structures for deep excavations. These developments should make it possible for a design engineer to make informed decisions on the relationship between prop spacing and ground movements or the influence of wall stiffness and on the need for and influence of a jet-grouted base slab, for example, prior to conducting project-specific FEA.