Influence of Dense Granular Columns and Liquefiable Soil Stratigraphic Variations on the Performance of Overlying Structures
Publication: Geo-Congress 2024
ABSTRACT
The current state of practice for designing dense granular columns (DGCs) relies heavily on simplified procedures that assume free-field conditions (no structure or slope) and uniformly layered, level soil deposits composed of clean sand. These guidelines ignore stratigraphic variabilities in the permeability, groundwater table, layer thickness, or relative density of soil layers commonly found in natural deposits. Prior research has shown that such variability can significantly influence the contribution of different mechanisms of displacement, excess pore water pressure generation and redistribution, formation of soil ejecta at the ground surface, accelerations, and subsequent damage to the foundation and structure. These effects and the implications on system performance are poorly understood and, hence, not considered in the design of mitigation strategies. In this paper, fully coupled, three-dimensional (3D), nonlinear dynamic finite-element analyses in OpenSees, validated with centrifuge models, are performed to evaluate fundamentally how DGCs influence the seismic performance of sites with realistic stratigraphy and their overlying shallow-founded structures. The effectiveness of drainage and reinforcement provided by DGCs is shown to depend strongly on the heterogeneity of the soil profile. Draining DGCs are shown to have the potential to effectively reduce the permanent settlement of the foundation compared to an unmitigated structure. In addition, drains with an area replacement ratio (Ar) greater than 20% significantly reduced the severity of ejecta (quantified through hydraulic gradients) and excess pore pressure ratios in the liquefiable layers. This reduction was especially effective in the case when DGCs were accompanied by densification. However, treatment could adversely impact the acceleration demand transferred to the superstructure due to reduced damping and increased soil stiffness. The results highlight the critical importance of considering stratigraphic variations in the design of mitigation strategies that holistically improve the performance of the soil-foundation-structure system.
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Information & Authors
Information
Published In
Geo-Congress 2024
Pages: 62 - 72
History
Published online: Feb 22, 2024
ASCE Technical Topics:
- Analysis (by type)
- Clays
- Continuum mechanics
- Dynamics (solid mechanics)
- Engineering fundamentals
- Engineering mechanics
- Geology
- Geomechanics
- Geotechnical engineering
- Granular soils
- Layered soils
- Models (by type)
- Pressure (type)
- Soil liquefaction
- Soil mechanics
- Soil properties
- Soils (by type)
- Solid mechanics
- Three-dimensional analysis
- Three-dimensional models
- Water pressure
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