Effects of particle size and grading characteristics on sand matrix soils under monotonic and cyclic loadings

Abstract

Since 1964, liquefaction resistance of sand matrix soils or sand-fine mixtures has been extensively studied by researchers. These extensive studies were done/conducted following dramatic damages due to liquefaction caused by earthquakes in Niigata and Alaska. However, until the end of the 2010s and the latest major liquefaction occurrence in September 2018 at Palu, Indonesia, little research effort had been made to focus on the effects of particle shape and size, grading characteristics, particle arrangement and fines content of sand matrix soils. Although sand is the dominant material in sand matrix soils, there have not been enough efforts to elucidate the effects of particle size and grading characteristics of sand as the main factor in altering liquefaction resistance. Moreover, some results previously reported are still contradictory. This research aims to determine the effects of particle size and grading characteristics of sand on liquefaction resistance of sand matrix soils. To achieve the aim, three (3) objectives have been identified; (1) to evaluate the particle size, the grading characteristics and the physical properties of sand matrix soils at various compositions of sand and fines, (2) to establish the critical state line as the failure envelope of sand matrix soils from the results of monotonic undrained triaxial tests, and (3) to characterize the liquefaction susceptibility of sand matrix soils from the cyclic triaxial tests and validate through the centrifuge tests. The material used in the research was selected clean sand, which was sieved into three ranges of grain size that were coarse, medium and fine. Sand matrix soils were reconstituted by mixing these three-grain sizes of sand with low plasticity fines (kaolin) at 0% to 40% by weight. The results showed that the threshold fine content for coarse sand matrix soil and medium sand matrix soils were 30%, while for fine sand matrix soil, the percentage was 10%. From cyclic triaxial tests, it also indicated that the liquefaction resistance of sand matrix soils decreases with increases in fine content and showed a reverse trend after reaching threshold fine content. The threshold fines content (fth) for coarse sand matrix soils and medium sand matrix soils was 30%, whereas, for fine sand matrix soils, it was 10%. Threshold fines (fth) were observed to change the transition behaviour of sand dominates to fines dominates which occurred at different percentages of fines content depending on the grain size of sand. Less number of cycles was required to initiate soil liquefaction of sand matrix soils with a higher value of the coefficient of curvature and coefficient of uniformity. In general, the sand matrix soil has higher liquefaction resistance at larger sand particles. By using the centrifuge test, similar trends were observed as a result of the cyclic triaxial test. Some of the equations were generated to provide a new outcome for this research.