How do changes in soil composition affect the stability of structures in civil engineering projects? Explore the relationship between soil mechanics and foundation design, considering factors such as soil type, moisture content, and compaction methods. Discuss the implications of soil settlement, bearing capacity, and soil$-$structure interaction on the overall performance and longevity of engineered structures. Additionally, analyze the role of geotechnical investigations and laboratory testing in assessing soil properties and determining appropriate engineering solutions. Consider various scenarios, such as building on expansive clay soils or constructing in seismic zones, to illustrate the significance of understanding soil behavior in civil engineering operations.