A Study of Shallow Foundations on Expansive Soils (A Case Study of Bojonegoro Soil)

Abstract

Soil plays a vital role as the primary support in structural foundations. However, expansive clay soils often present challenges in construction due to their water-dependent characteristics. When wet, these soils expand; when dry, they shrink, potentially causing cracks in foundations and other structural elements. This study aims to identify the type of soil in the Bojonegoro area and evaluate its impact on stress distribution beneath shallow foundations placed on expansive soils. Laboratory tests were conducted, including plasticity index analysis, Atterberg limits, compaction test, and shear strength test. The focus of the study includes identifying the level of expansion potential, soil activity classification, and analyzing the pattern of vertical and horizontal stress distribution beneath the foundation, particularly in relation to the theoretical 2V:1H approach. Based on the analysis results, the soil in Bojonegoro is classified as highly expansive, with a plasticity index (PI) of 53.92%, a liquid limit (LL) of 84.60%, and a plastic limit (PL) of 30.68%. According to the USCS classification, the soil falls into the CH category (Clay with High Plasticity). Observations on the foundation model showed a settlement of 103.36 mm and an uplift (unloading) of 6.05 mm. The observed stress distribution followed a 6V:3H pattern, which theoretically corresponds to the 2V:1H ratio. These findings are expected to serve as a reference for designing more adaptive and safe foundations in expansive soil conditions.