This paper presents an extensive series of laboratory works and a prediction model on the design of a road pavement subgrade with Xanthan Gum (XG) biopolymer. The experimental works were carried out using mixtures of conventional aggregate for road pavement construction and XG at the ratios of 0%, 1%, 2%, and 5%, by dry weight. Unconfined compressive strength (UCS) and California bearing ratio (CBR) tests were conducted during the experimental works at the end of the various curing periods (4, 8, 16, and 32 days). An example of an improvement in the UCS values for a specimen with 5% XG addition tested at the end of 4-daycuring yields about a 200% increment by the end of a 32-daycuring. The CBR values of clean aggregates were found to be increased by about 300% by 5% XG addition for all curing periods applied. Furthermore, the energy absorption capacity of the aggregates was observed to be increased significantly by both XG inclusion and curing period. Moreover, scaled conjugate gradient (SCG) training algorithm-based models developed for the prediction of CBR and UCS test results displayed a very high estimation performance with the regression coefficients of R² = 0.967 and R² = 0.987, respectively. Evidently, XG biopolymer is provably of use as an alternative inclusion in road pavement subgrades constructed with conventional aggregates.

The aim of this study is to assess the influences of both the size and shape of sand grains mixed with a clay on shear modulus (Gmax)– and shear wave velocity (vs)–based liquefaction resistance (cyclic resistance ratio, CRR) using an intensive series of bender element (BE) tests. A low plasticity clay (CL) was added to two specific particle gradations (0.15–0.30 mm, and 1.0–2.0 mm) of clean sands with particular shapes (angular and rounded) at the percentages of 5, 10, 15, 20, 30, and 40, by dry weight. The BE tests were performed on the remolded specimens of different size/shape sands containing various amounts of CL in a recently designed mold used specifically for cohesionless soils, and then the values of vs, Gmax, and CRR were investigated. In most of the cases, the testing results indicated that, up to 20 % fines, which is named as transition fines content (FCt), Gmax and CRR values decreased, and then they increased for the specimens tested. Eventually, Gmax and CRR values of the specimens were significantly changed by the physical features (size, shape) of the sand grains with all the clay inclusions and frequencies applied.

This paper presents the results of an intensive series of laboratory fall-cone tests undertaken on mixtures of sand with different grain size/shapes and a low-plasticity clay. The mixtures were prepared with various water contents from a fully dry to a fully saturated condition. The clay was added to two different gradations (0·15–0·30 mm and 1·0–2·0 mm) of clean sand with specific shapes (rounded and angular) at the ratios of 5, 10, 15, 20, 30 and 40% by dry weight. The results obtained suggest that penetration depth primarily depends on water content, size/shape of the sand grains and the amount of clay in the mixtures. The relation between penetration depth and water content displays three distinct behaviours in that the penetration depth (a) is relatively large for dry mixtures, (b) decreases with increasing water content, and (c) increases to values approximately 20% larger than those for dry mixtures. Observations revealed that the transition fines content, the boundary between sand-governed and fines-governed behaviour, was mainly affected by intergranular void ratio.