Modelling rate-dependent behaviour of structured clays

Due to the desire of reducing the embedded CO2 in construction and the pressure in public finances to get more value for money in big infrastructure projects, the demands for the accuracy of deformation predictions increase. Instead of piling, alternative environmentally friendly and cost effective solutions, such as preloading via surcharge, vertical drains and column methods, such as deep-mixing, are becoming increasingly attractive. Installation of piles and ground improvement into the ground will modify the state of the soil. This is sometimes beneficial, and sometimes detrimental, and so far this effect has been rarely taken into account. One reason for this is that the numerical techniques and the constitutive soil models have not been able to represent the changes in soil structure and state in a satisfactory manner. The aim of the European GEO-INSTALL project has been to develop numerical techniques that can be used to model installation effects in geotechnical engineering. A key part of this has been constitutive model development, and their robust implementation. The aim of this paper is to discuss some recently developed rate-dependent constitutive models for structured clays, which formed the basis for new developments, resulting in a new rate-dependent model able to represent the complex rate-dependent stress-strain behaviour of soft structured clays. The importance of modelling key features of soil behaviour in the context of rate-dependency are discussed in the light of experimental evidence, and demonstrated through a series of numerical benchmark simulations.