Grain breakage affects a number of geotechnical engineering problems. In this research study, the breakage of an artificial, porous granular material (light-expanded clay aggregate (LECA)) has been studied in one-dimensional compression with both standard laboratory techniques and in situ X-ray tomography during loading. X-ray tomography has revealed that there is a wide distribution of internal porosity among LECA particles, and particle tracking has been used, for the first time, to give an objective measurement of each particle's life expectancy. Links between micro- and macro-scale quantities are discussed.

The paper presents an interpretation of the temperature monitored during the application of artificial ground freezing in the Isarco River Underpass tunnel, within the Brenner Base Tunnel project. The observations gathered in the in situ monitoring provided an opportunity to (1) examine the response of a heterogeneous glacial and river deposit composed of gravelly loose sand and boulders subject to seepage, upon freezing; and (2) set up a coupled (thermohydraulic) theoretical formulation, which accounts for the water retention curve and relative permeability function, able to properly simulate the artificial ground freezing process on a heterogeneous coarse subsoil under seepage. The simulation was able to provide a satisfactory representation of the development of the in situ monitoring data and it revealed the dependence between the freezing process, the retention properties of the subsoil, and the seepage velocity. A sensitivity analysis was also carried out to examine the potential effect of water retention parameters on the frozen wall formation in terms of thickness and closing time. The critical examination of in situ observations and the results of the numerical analyses allowed the definition of a new criteria to define the freezing temperature of the soil based on the water retention curve features and the residual degree of saturation, with the aim to optimize the design of the artificial ground freezing process by maintaining the safety level against waterproofing of the excavation area.

The presented experimental study, from micro to macro scale, assesses the effects of grain shape on the strength-dilatancy behaviour and physical properties of seven natural sands of different origins and mineralogical composition. The micro-scale has been characterised by processing two-dimensional image of grains, using the fractal analysis of particle contour to define their shape. The macroscopic material properties are evaluated performing direct shear tests at three different normal stresses, and measuring void ratios limit and angles of repose. An innovative method to interpret the experimental data obtained has pinpointed interesting relationships linking the morphological features of grains to the mechanical and physical properties of sands. Data confirm that the increase in grain shape irregularity produces an increase in all the variables investigated: void ratios limit, friction angles and dilatancy parameters.