Reinforcement of completely decomposed granite with discrete fibres

Abstract

The use of discrete fibres as reinforcing material for soils has been researched by many, e.g. Gray and Al-Refeai (1986), Maher and Ho (1994), Crockford et al. (1993), Santoni et al. (2001), Consoli et al. (2009a), but these studies have been generally done independently and have not always been consistent. Silva dos Santos et al. (2010) used data gathered through many years of study to develop a framework of behaviour for a poorly graded quartzitic sand reinforced with polypropylene fibres. In Hong Kong, the construction industry has used reinforcement with continuous fibres for some time, but it is mainly applied to landscaping of otherwise stabilised slopes, for example as a green cover on an existing shotcreted slope. Using randomly distributed short discrete fibres in Hong Kong completely decomposed granite (CDG) could help stabilise the soil while keeping the density low enough to allow growth of vegetation. It is not guaranteed, however, that a well graded residual soil like CDG would behave in the same way as sands used by previous researchers. Laboratory tests have been carried out on completely decomposed granite using short discrete polypropylene fibres as a reinforcing material. The fibres are randomly distributed in the soil. It was found that the fibres increase the unconfined compressive strength of the CDG prepared at its maximum dry density by up to tenfold for fibre contents less than 1%. The behaviour of the fibre-CDG mixture during drained triaxial compression changed from dilative to compressive, with more effects at low confining pressures. These tests seem to indicate that discrete fibres could be considered for improving the performance of CDG.