Abstract
Micropiles are reinforced grouted piles that have small diameters commonly not higher than 30 cm. They are widely used for slope stabilization, controlling structural settlement, and in some cases, as retaining structures. Also, they are used for resisting dynamic uplift loads, seismic retrofit mainly in restrictive and low headroom areas, and retrofitting of historical monuments. The main goal of this research is to develop a finite element model that can capture the different aspects of seismic behavior of multi-story structure supported with deep foundation via using of micropiles. Also, a main target for the executing numerical modelling is to show the influence of the surrounding soil on this system and vice versa. Firstly, a representative two-dimensional finite element model is conducted to represent the soil-structure interaction system under seismic excitation supported with proper boundary conditions in PLAXIS 2D V20 for dynamic analysis based on previous recommendations considering the nonlinear soil behavior. The behavior of micropiles is studied and verified using previous results. Based on these models, the effect of lateral dynamic loads on the response of a structure with different foundation types is investigated. Also, a wide range of parametric studies, considering structure properties, earthquake magnitude, micropile diameter, micropile length, and the number of micropiles, have been carried out in order to investigate the actual interaction between soil, substructure, and superstructures. The study results showed that the seismic response of the structure is highly affected by the properties of the sub-surface soil layer. Consequently and similarly, analysis results established that underpinning using micropiles is an efficient technique for controlling the seismic response of existing structures.
Highlights
INTRODUCTIONEarthquakes can be described as a sudden strong ground shaking resulting in damages and deaths as a result of strong shaking and fault rupture
It differs in intensity according to the frequency of the motion, earthquake magnitude, and source of the earthquake
Soil properties, micropiles distribution, micropiles properties, and superstructure properties on the seismic response of structures with micropiles foundations have been studied to investigate their effect on the seismic interaction in terms of: a) Structure’s fundamental periodic time. b) Free field acceleration change. c) Overall displacement. d) Induced piles’ bending moment
Summary
Earthquakes can be described as a sudden strong ground shaking resulting in damages and deaths as a result of strong shaking and fault rupture. Pile foundations were designed mainly to support axial loads only while the loading condition in case of earthquake excitation transfers lateral forces and moments to the piles. Earthquakes are not the only type of dynamic lateral loading that can affect pile foundations, but there are other types such as wind load, braking forces from moving vehicles in bridge abutments cases, and water action on offshore structures 2. The other mode is called bending mode due to soil deformation, which results in high deformation of pile till reaching its moment of resistance. Micropiles are reinforced piles that have small diameters commonly not higher than 30 cm They should be well grouted, as they are designed to transfer loads mainly by skin friction. It's noteworthy to mention that inclined micropiles have a positive effect under seismic conditions 7
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