Effect of fines content on critical state parameters of sand matrix soils

Abstract

Natural sand does always contain significant amounts of fine particles, known as sand matrix soils. The development of critical state for sand and clay are both well established. However, limited researchers focused on the sand matrix soils. This paper discusses the effect of fines content on the critical state parameters of sand matrix soils. Two types of plastic fines with different plasticity (kaolin and bentonite) were mixed into poorly graded Johor clean sand at different percentages to form the sand matrix soils. The critical state was obtained from the strain controlled triaxial compression test. All tested soils had been isotropically consolidated to four different effective confining pressures and sheared under consolidated undrained condition until the critical state was ascertained. The critical state line was plotted for each sand matrix soils on space and compression spaces. Based on linear regression analysis, the critical state parameters, M, λ and Γ were obtained and the ranges are from 0.807 to 1.102, 0.062 to 0.160 and 1.732 to 2.431, respectively. The trend of the critical state lines of sand matrix soils in both stress and compression space coincides with the concept of threshold fines content. The threshold fines content identified for sand-kaolin mixtures is 25 % kaolin while it is 20 % bentonite for sand-bentonite mixtures.