Effect of soft soil on the engineering properties of sandy soil

Abstract

Improving the geotechnical properties of soil remains one of the primary challenges in the field of geotechnical engineering, particularly when designing structural foundations on sandy soils, which often exhibit low bearing capacity and limited support strength. This research paper aims to analyze the effect of adding fine soil in varying proportions (4%, 8%, and 16%) to sandy soil and to assess its impact on the physical and mechanical properties of the soil. The objective is to enhance soil stability and load-bearing capacity, thereby improving the performance of foundations constructed on such soils. A series of laboratory tests were conducted on both the sandy soil and the fine soil additives. Physical tests on the sandy soil included sieve analysis, which classified the soil as silty sand (SM), in addition to specific gravity measurement. Mechanical tests included the Standard Proctor compaction test, which yielded a maximum dry density of 17 KN/m³, and the direct shear test, which was used to determine the angle of internal friction and cohesion. Compaction and shear tests were also conducted on the fine soil to determine its effect when blended with sandy soil. the results showed that the addition of 4% fine soil reduced the dry unit weight to 16.9 KN/m³, increased the internal friction angle to 35.678°, and yielded a cohesion value of 4.22 Kpa. When 8% fine soil was added, the dry unit weight remained at 17 KN/m³ (equal to the unmodified sandy soil), but the internal friction angle decreased to 32.639°, while cohesion increased to 17.947 kPa. With a 16% addition of fine soil, the dry unit weight significantly increased to 18.74 kN/m³, the internal friction angle rose to 34.11°, and cohesion reached 37.867 Kpa.