Improvement of the geotechnical properties of Yenikent (Ankara) settlement area clays with lime and fly ash

Swelling clays with the potential to shrink or swell are found throughout the Turkey. Volume change potential of swelling clays cause vertical movement which are generally responsible for structural damage. Lightly loaded structures are very susceptible to differential soil movement which cause important damages due to their low vertical pressures. Predetermining the swelling behaviors and affecting factors of them prevents possible damage occurrences. The mineralogic composition of the expansive clay minerals determine the amount of volume change. In this study, improvement of the geotechnical properties of swelling clays of Yenikent settlement by using hydrated lime and fly ash additives were investigated. For this purpose, samples were taken from 5 bore holes in different locations representing the study area and laboratory tests were conducted in order to be determine engineering properties of the site soil. The physical characteristics of the disturbed specimens were determined by making water content, specific gravity, grain size distribution tests on them. The plasticity characteristics of the cohesive clay specimens were found by the liquid limit and plastic limit tests. By using USCS classification system, it was determined that all the samples were CH clays. Swelling properties of the CH samples were evaluated both by indirect and direct methods. For indirect methods, some empirical approaches are used to interprete swell potential of the samples, whereas in direct methods, swell properties of the soil are measured by laboratory tests. The results of indirect and direct methods showed that all the clayey samples have high swelling potential. For direct measurement in the laboratory, swelling tests were conducted on compacted specimens with additives of hydrated lime at %1, 3, 5, 7, 9 and fly ash at %5, 10 by dry weight. According to the swell test results, from 5% of lime swell potential were significantly decreased and for 7% ,9% of lime additive swell percentage and pressure were reduced by %89, %65 and %94, %75 respectively, they reached to very low values. In contrast to lime additive, it was observed that fly ash additive had limited improvement effects for swelling improvement. In order to determine the effect of lime and fly ash additives on unconfined strength of swelling clays in the site, unconfined compression (UC) tests were conducted on compacted specimens at %5 and %10 additives for curing duration of 1, 14, 28 days. According to the UC tests results, at the end of 28 days of curing obtained higher strength for %5 and %10, using average values, UC strength was increased by %78, %181 for lime additive and %41, %84 for fly ash additive respectively. Finally, it was determined that lime additive is much more effective on stabilizing of the CH clays of the site and optimum lime additive can be used as 7% for Yenikent clayey soils for improvement. And it was determined that fly ash additives for %5 and %10 have a considerable effect on the strength of UC strength of the soil, but have small effect to stabilize CH clay samples at swelling properties.