effect of subsurface cavities on the bearing capacity of shallow strip foundations in soft clay: a numerical study

Subsurface cavities, both natural and anthropogenic, pose significant geotechnical challenges by altering stress distribution beneath shallow foundations. conventional design approaches for strip footings often neglect the effects of such voids, potentially resulting in unsafe or overly conservative designs. this study employs a numerical investigation using the finite element software plaxis 2d to assess the impact of underground cavities on the bearing capacity of shallow strip foundations resting on soft clay. a parametric analysis was conducted to examine the effects of cavity diameter, embedment depth, and both horizontal and vertical offsets relative to the footing center. the results indicate that increasing cavity diameter markedly reduces the ultimate bearing capacity. additionally, increasing the cavity diameter from 0.25 to 0.5 times the footing width led to a 25%–40% decrease in load-bearing capacity. the study also identifies a critical influence zone beneath the footing where the presence of voids most significantly compromises performance. these findings underscore the importance of incorporating subsurface cavity effects into geotechnical design, particularly in urban areas, to enhance the safety and reliability of shallow foundations on soft clay. the parametric study covered cavity diameters d = 0.5–1.0 m, embedment depths y = 2, 4, and 10 m, and horizontal eccentricities x = 0, 1, 6, and 10 m for a strip footing of width b = 2.0 m. quantitatively, increasing d from 0.5 m to 1.0 m at y = 2 m reduced the ultimate bearing capacity by ≈200 kpa (≈56.7%).