Geotechnical Properties and Numerical Analyses for Socketed Pile Design in Weak Rock

Abstract

This research project involved laboratory and theoretical studies relevant to the performance of piles socketed into the Melbourne mudstone. The laboratory studies consisted of detailed investigations into the geotechnical properties of the intact Melbourne mudstone using both soil mechanics and rock mechanics concepts, theories and testing procedures. The theoretical studies involved the development of mathematical models for both the intact mudstone and concrete-mudstone interface on the basis of the laboratory findings, to enable the prediction of pile behaviour.The laboratory investigations included the study and development of rock testing techniques with special attention given to saturation, and the effects of strain-rate and specimen length to diameter ratio on the measured stress-strain behaviour of the mudstone. The strength and deformation properties of the mudstone were then determined, including its consolidation, uniaxial stress, direct shear and drained and undrained triaxial stress characteristics.The mathematical models examined for the mudstone were the critical state, elastic-ideally plastic and variable moduli models, with the latter two especially in relation to finite element analyses. Various finite element techniques using these two models, e.g. reduced integration and use of higher order elements, were developed. A model for the mudstoneconcrete interface was also formulated.Finite element analyses were performed to establish design curves for elastic analyses of end-bearing only, side-resistance only and complete piles in a homogeneous, 2-layer and 3-layer rock mass. In addition, the effects of a soft layer underlying rock and limiting tensile stresses on pile behaviour were theoretically examined beyond the elastic range [...]