Experimental observations and theoretical interpretation of the mechanical behaviour of a grouted pyroclastic silty sand

This paper deals with the mechanical characterisation of an artificially structured material, obtained by grouting a low permeability pyroclastic silty sand (pozzolana) with a sodium silicate solution. Notwithstanding the low permeability of pozzolana (k(sat) = 10(-6) divided by 10(-7)m/sec), a preliminary set of laboratory tests has shown that the very diluted silicate grouts adopted are effective in enhancing its mechanical behaviour. The paper refers on a detailed experimental programme carried out to investigate the stress-strain behaviour of the grouted soil in order to outline its peculiar mechanical properties. With this aim, oedometer, CID and CIU triaxial tests were carried out. The whole set of results shows the typical behaviour of a structured material, with a brittle behaviour at low stress levels, and structural degradation at higher stresses. A first attempt to explain the experimental observations is proposed in the light of the classical Critical State Soil Mechanics theory and some preliminary conclusions are discussed.