Study of the Composition of Roadbed Soils in the Foothills of Kyrgyzstan for Salts and Minerals

ABSTRACT The purpose of this study was to determine the specific features of chemical and mineralogical composition, along with the physical and mechanical properties of saline soils of roadbeds in the foothill zone of southwestern Kyrgyzstan. Four samples were taken at altitudes of 1556, 1345, 1672, and 2406 m Above Sea Level (ASL) from Naukat, Taldysuu, Chiyyrchyk Pass, and Batken and studied. The results of X-Ray Fluorescence (XRF) analysis showed that samples 1 and 4 had elevated salinity of 165 and 133 mg/100 g, respectively, exceeding the acceptable limits for road construction (≤60 mg/100 g). The same samples exhibited reduced density (1.44 and 1.48 g/cm3), high water saturation (34–36%), and maximum swelling coefficients (1.18–1.21), indicating instability under load. Mineralogical analysis revealed a predominance of chlorite and gypsum, which contribute to swelling, macropore formation, and a decrease in structural integrity when moistened. On the other hand, samples 2 and 3, which had a salinity level of 39 and 51 mg/100 g, respectively, were characterised by a greater density (1.65–1.72 g/cm3), low water saturation (21–23%), and slight swelling (1.03–1.05). These samples were dominated by kaolinite, quartz, and feldspar, minerals that provide structural stability and low vulnerability to changes in humidity. A spatial pattern was identified: with increasing altitude and precipitation (from 440 to 875 mm/year), the level of soil salinity decreases, which is associated with the effectiveness of atmospheric flushing and the type of geological base. According to the assessment results, only samples 2 and 3 were suitable for use as a natural road base without additional stabilisation. Samples 1 and 4 require engineering reinforcement using lime, fly ash, or cement additives. The obtained criteria can be considered in regional standards and used for modelling road infrastructure.