Analysis of the fabric of undisturbed and pluviated silty sand under load over time

Microstructure of two undisturbed silty sands with 4% fines and 35% fines is described and quantified. The materials were sampled by the gel push sampling method. Upon reloading to their in situ stresses, the material fabric was fixed by resin impregnation. A qualitative and quantitative comparison of the microstructure was made with laboratory prepared dry deposited specimens (15% fines) which were loaded over different periods of time. The microstructure is quantified statistically by measuring particle orientation and the distribution of spatial distance between particles. Both undisturbed and reconstituted specimens show a preferred horizontal particle orientation, with little detectable change over time in the reconstituted samples. Spatial microstructural change was assessed using new parameter called index of dispersion. A greater index of dispersion suggests a more interlocked structure (hence, more structurally stable sample). Analysis of the reconstituted samples show that index of dispersion tends to increase with ageing, with the denser sample displaying greater change over time than the looser sample. Values of index of dispersion of reconstituted samples (15% fines) tend to lie between those of the undisturbed sample with 35% silt fines and with 5% fines, showing that this measure is not independent of the particle size distribution.