Geotechnical and Statistical Assessment of Compacted Silty Sand for Rural Road Subbase Applications

Abstract

Soil compaction is a critical process in road construction because it directly affects structural stability, load-bearing capacity, and long-term pavement performance. This study aimed to assess the suitability of compacted silty sand for use as a rural road subbase through an integrated geotechnical and statistical approach. The dataset was obtained from soil property testing and field dry density testing using the sand cone method in a case study area in Pathum Thani Province, Thailand, comprising 20 field test samples. Soil classification results indicated that the material was silty sand (SM) according to the Unified Soil Classification System (USCS), with a liquid limit of 49.16, a plastic limit of 45.27, a plasticity index of 3.89, and a specific gravity ranging from 2.65 to 2.75. These properties indicate low plasticity and suggest that the soil has potential for subbase application when moisture content and compaction are properly controlled. Statistical analysis of the field dry density results showed that the average relative compaction was 93.46%, with a coefficient of variation of 6.61%, indicating generally acceptable compaction quality with some variability in field performance. Furthermore, comparison between test groups A and B using Welch’s t-test revealed a statistically significant difference, with Group A exhibiting higher compaction performance than Group B. The 95% confidence interval for the mean difference ranged from 8.41 to 13.56. The findings suggest that the studied silty sand has preliminary potential for use as a rural road subbase material; however, stricter control of moisture content, compaction procedures, and field-testing practices is necessary to improve consistency and reliability in construction quality.