Impact of Lateral Confinement on Seismic Bearing Capacity of Shallow Foundations in Saturated Sand

The majority of high-rise buildings have basements in their substructures. Basement walls, such as diaphragm walls, "skirts," or secant pile walls, are commonly used to support basement construction and provide lateral confinement. Moreover, the performance of shallow foundations is significantly influenced by this lateral confinement. Skirted foundations have proven to be an effective alternative to piles, piers, and surface foundations for offshore works, jacket structures, oil platforms, and wind turbines. Confined or skirted foundations ensure overall foundation strength and effectively increase subgrade stiffness during earthquake shaking. The behavior of shallow foundations resting on laterally confined saturated sand is investigated under earthquake loads and also under static conditions using numerical modelling by PLAXIS 3D. For the purpose of determining the ultimate seismic bearing capacity, a full validation is presented. The results are presented in a series of charts estimating the bearing capacity enhancements. The results demonstrated that, for the 6 m width square footing, the improvement in the ultimate seismic bearing capacity in the confined case can reach 7.6 times that in the unconfined case. Also, with the increase of Peak ground acceleration in the dense saturated sand, the enhancement of the ultimate seismic bearing capacity ratio increases. However, in loose sand, the effect is less pronounced. The stress settlement curves showed that the confinement system reduces the impact of the earthquake on the soil subgrade, including the settlement that occurs during the earthquake, by a ratio that ranges from 56 to 76%.