Shear characteristics of fly ash improved sand as an embankment material for road infrastructure purpose

This study examines the influence of the fly ash material on the shear strength characteristics and stress-dilatancy response of two categories of sands with different maximum grain sizes (D-max = 4.00 mm and 0.63 mm) mixed with four fly ash fractions (FA = 0, 5, 10 and 15%). To achieve this goal, a series of direct shear tests was carried out on reconstituted samples at an initial relative density (D-r = 90%) and subjected to three normal stresses (sigma(n) = 100, 200 and 300 kPa). The obtained test results show that the fly ash content enhances greatly the shear strength characteristics of the granular soils. It is found for a given normal stress, the peak friction angle and maximum dilatancy angle increase with the increase of fly ash content. In addition, the excess friction angle (phi(ex)) increases with the increase of the maximum dilatancy angle (psi(max)) of the tested materials. New developed strength-dilatancy equations incorporating the influence of fly ash proportions were proposed for the tested materials. In general, it is found that these strength-dilatancy equations could well predict the mechanical characteristics and shearing response of the different sand classes mixed with various proportions of fly ash leading to a systematic better understanding of the tested soils to be used in the road embankment constructions.