ORIGINAL PAPER Study of the Bearing Capacity of Closely Spaced Square Foundations on Granular Soils William Fuentes . Jose ´ Duque . Carlos Lascarro . Melany Gil Received: 5 March 2018 / Accepted: 5 September 2018 / Published online: 7 September 2018 Ó Springer Nature Switzerland AG 2018 Abstract In the present study, the effect of the interaction between two closely spaced square foot- ings is analyzed through finite element simulations. The numerical analyses were performed through the construction of three-dimensional 3D Boundary Value Problems constructed with the software Abaqus Standard. Several values for the foundation embed- ment and separation between footings were consid- ered. The behavior of the granular soil was simulated through an extended Drucker–Prager constitutive model. The results were used to calibrate an extended bearing capacity equation through a multiple variable regression analysis, and accounts for the effect of the embedment depth and separation between footings. Finally, the proposed relation was compared with some reported values in the literature, including experimental tests and numerical results, and showed a better agreement with the experimental data than other reported studies. Keywords Closely spaced footings  Bearing capacity  Finite element simulations  Granular soils 1 Introduction The determination of the bearing capacity of the soil is of high importance for the stability of shallow foundations. The literature offers several methods based on the limit equilibrium approach to assess this issue. Since the pioneer work of Terzaghi (1943), a number of enhanced methods, incorporating empirical factors, have been proposed accounting for different effects, such as load inclination, ground inclination, among many others, e.g. Hansen (1961), Meyerhof (1963), Vesic (1973). Nevertheless, very few methods consider the interaction between closely spaced foot- ings. Stuart (1962) studied the effect on the bearing capacity for closely spaced shallow foundations on granular soils and developed an analytical method. This analysis was based on the slip surface proposed by Terzaghi (1943) and assumed limit equilibrium conditions. The authors introduced two new factors in an extended bearing capacity equation, known as the efficiency ratios n q . and n c , such that: q u ¼ qN q n q þ 1 2 cBN c n c þ cN c ð1Þ where q u is the ultimate bearing capacity, N q ; N c and N c are factors depending on the friction angle u, B is the shortest dimension of the footing, q is the initial effective stress at the footings base and c is the soil cohesion, which for granular soils is set to c ¼ 0. Later, West and Stuart (1965) carried out large- scale experimental tests in order to validate the effect W. Fuentes (&)  J. Duque  C. Lascarro  M. Gil University del Norte, Barranquilla, Colombia e-mail: fuentesw@uninorte.edu.co 123 Geotech Geol Eng (2019) 37:1401–1410 https://doi.org/10.1007/s10706-018-0694-5 Journal: Geotechnical and Geological Engineering Year: 2019