Stress–strain behaviour and stiffness of lightly stabilised granular materials from UCS testing and their predictability

Abstract

This paper examines the non-linear stress–strain behaviour of lightly stabilised granular materials and stiffness modulus from unconfined compression testing and their predictability based on modified and extended Ramberg–Osgood expression. Unconfined compressive strength (UCS) testing with the internal deformation measurement setup was carried out for the characterisation of two granular materials stabilised lightly with 0.5–3.0% cement–flyash as well as with 1.5–3.0% slag-lime. All the samples were prepared at their respective optimum moisture contents, cured for 28 days and then, tested in a Universal testing machine to obtain the stress–strain relationships of these lightly stabilised materials. The modified Ramberg–Osgood expression was found to be suitable for describing the non-linear experimental stress–strain curves. The parameters involved with this expression were initial elastic modulus E 0, 0.2% proof stress σ0.2, ultimate strain ϵ u and the exponents for quantifying the nonlinearity of the curves n and m. Values of all the parameters were determined from the experimental stress–strain responses and quite reliable linear regression relationships were developed between these parameters and the UCS. This study also shows that all the parameters could be determined from the value of UCS alone and the stress–strain relationship of a lightly stabilised material could be predicted using the modified and extended Ramberg–Osgood approximation proposed in this paper even in the absence of the facilities to measure the vertical deformation internally. Moreover, the secant modulus and tangent modulus were evaluated and their variations were examined, and the modulus at 0.2% proof stress E 0.2 is suggested as the appropriate modulus for pavement design involving lightly stabilised granular base materials. Expressions for estimating both these modulus values were also derived in terms of UCS value. Therefore, it is possible to acquire additional insight regarding the non-linear stiffness modulus of a lightly stabilised granular base material from UCS testing as presented in this paper.