The importance of physico-chemical processes at the particle scale for the engineering scale behaviour of fine-grained geomaterials is undisputed. Yet, despite great advances in the discipline, experimental evidence that fully resolves the clay micromechanics i.e. linking the evolving microstructure and interparticle actions under loading, is lacking. This paper will discuss the challenges ahead in quantifying the evolving kinematics and interparticle interactions of finegrained geomaterials. As such, the current limitations, and the potential opportunities of experimental methodologies for manipulating, monitoring and (post-mortem) analysing fine-grained materials at the particle scale will be discussed. In addition to the need of integrating multiple experimental techniques that span several length scales and modalities, the critical role of advanced data reduction and analysis is highlighted, as required for a measurement as opposed to qualitative observation. Throughout the paper, the link between experimental clay micromechanics and modelling will be discussed.

Additional in-situ measurements during piezocone penetration tests can provide important information at a low cost due to recent advances in measurement technology. Resistivity measurements, commonly used in geophysical measurements, can be adapted to a standard piezocone penetration test (CPTU) to supply data about the in-situ properties of the soil. Change in soil density in extensive sand layers can therefore be determined. A series of laboratory multi-frequency AC resistivity tests with a novel electrode configuration have been performed with a model probe to investigate possibilities of in-situ measurement of volumetric properties of sand in a controlled saturated sand sample. The results show that soil density change of saturated sand can be measured efficiently and with relative accuracy with resistivity measurements at multiple frequencies. A measurement frequency spectrum of 100 Hz to 100 kHz is recommended for in-situ tests.

This paper presents the results of model pile penetration in a photoelastic material. The soil in this test is represented by an assembly of photoelastically sensitive glass particles. This allows for the determination of stresses in the assembly by the photoelastic method. Displacements around the pile are measured using digital image correlation. Tests were performed in a medium dense particle assembly. The development of stresses and strains, in particular the development of horizontal stress, around the pile tip and pile shaft is quantified and presented in this paper.