The influence of loading rate on excess pore pressures in triaxial tests
The research described in this dissertation is concerned with coupled loading and consolidation in triaxial tests and with selection of rates of loading in routine tests to avoid errors due to incomplete drainage or non-uniform pore pressures in fine grained soils. The work consisted of a combination of laboratory tests in which pore pressures were measured within triaxial samples, numerical analysis using the CRISP geotechnical finite element program and theoretical analysis. Both constant strain rate and constant stress rate loading were considered. The work demonstrates the applicability of CRISP to coupled loading and consolidation analyses and its limitations are discussed. The influence of loading rates on pore pressures in triaxial tests and upon the soil parameters obtained from them is investigated and deficiencies in the current procedure for choosing rates of loading are revealed. A new method is proposed which permits a rational choice of loading rate based on the drainage characteristics of the sample and on the magnitude of the errors which can be accepted. Non-uniformities of stress, strain and specific volume in triaxial samples and the influence of loading rate on these non-uniformities is also investigated.