Pseudo-static Seismic Bearing Capacity of Shallow Foundations in Unsaturated Soils Employing Limit Equilibrium Method
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ORIGINAL PAPER
Pseudo-static Seismic Bearing Capacity of Shallow Foundations in Unsaturated Soils Employing Limit Equilibrium Method Mohammad Amin Nouzari . Reza Jamshidi Chenari Faranak Pishgar
. Meghdad Payan .
Received: 26 July 2019 / Accepted: 26 August 2020 Ó Springer Nature Switzerland AG 2020
Abstract There exist many structures founded on unsaturated soil deposits. Shear strength augmentation due to the evolution of the matric suction within the unsaturated porous media enhances the bearing capacity of the overlying foundation. This paper presents the evaluation of the pseudo-static seismic bearing capacity of the shallow foundations resting on unsaturated soil deposits using limit equilibrium method. Adopting the Coulomb failure mechanism and Bishop effective stress concept, the bearing capacity equations are solved. The distribution of the matric suction beneath the footing is assumed to be linear. The results of the bearing capacity evaluation are validated against some experimental data found in literature for the static condition. For the seismic loading consideration, the pseudo-static method is utilized. The dual effect of the earthquake acceleration vertical component is thoroughly discussed and a suction transition point is introduced in which the minimum M. A. Nouzari Department of Civil Engineering, Rasht Branch, Islamic Azad University, Rasht, Iran R. Jamshidi Chenari (&) M. Payan Department of Civil Engineering, Faculty of Engineering, University of Guilan, Rasht, Iran e-mail: [email protected]; [email protected] F. Pishgar Islamic Azad University, Fouman and Shaft Branch, Fouman, Guilan, Iran
bearing capacity is observed to bear the same value for both upward and downward directions. The increase in the matric suction throughout the soil deposit leads to the increase in the soil shear strength, thus posing more resisting forces as well as higher ultimate bearing capacity. The offered solution is deemed a consistent and useful tool for the accurate prediction of the seismic bearing capacity of shallow footings resting on unsaturated soil deposits. Keywords Unsaturated soil Shallow foundation Seismic bearing capacity Pseudo-static Matric suction List of Symbols B Footing width Cij Resisting force caused by cohesion on the side ij of the failure wedges c; capp Cohesion and apparent cohesion, respectively df Footing depth Peak value of the seismic vertical kv acceleration coefficient kh Peak value of the seismic horizontal acceleration coefficient PA Active force PP Passive force PL Ultimate bearing load Pa Pore air pressure Pw Pore water pressure
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Geotech Geol Eng
Q q qu RA RB save s, s0 se WA WB r; rnet u0 d s Nc , Nq , Nc v b S c, S c c qa ; qb
Overburden load Overburden pressure Ultimate bearing capacity stress Reaction force applied on the wedge A Reaction force applied on the wedge B Average value of matric suction beneath the foundation Matric suction and matric suction value at ground surface Air entry/air
