GSI

Definition of Geotechnical Seismic Isolation (GSI)

“Structural” vs. “Geotechnical” Seismic Isolation

The term GSI was coined in 2009 based on an analogy between conventional "Structural" seismic isolation and new "Geotechnical" seismic isolation. GSI has diversified and gained momentum through a decade of development.

3 Branches of GSI Systems

GSI systems can be categorised into three main branches based on their isolation mechanisms.

A New Design Philosophy

GSI will lead to a paradigm shift in earthquake-resistant design and retrofit of structures. 

Traditionally, earthquake protection techniques have focused on enhancing the strength and/or ductility of structural members, increasing flexibility of the structural forms, reducing plan and vertical irregularities, strengthening and retrofitting vulnerable structural elements, or installing external devices for modifying structural response or introducing supplementary damping. 

GSI does not require changes to the structural systems or architectural features. Instead of designing deformability within the structures, e.g. plastic hinges, that inevitably lead to damage in earthquakes, compliance, intervention and/or separation at the interface between the foundation and surrounding geomaterials does not damage the structure. Seismic energy is dissipated, by different means, before getting into the structure. This can fulfil the low-damage performance requirement as part of the resilience-based seismic design. 

A New Research Area

GSI shifts the focus from altering the structures to making beneficial use of geomaterials or facilitating the beneficial interaction between the structure and surrounding geomaterials, which can be based on different mechanisms: 

(1) Dynamic soil-foundation-structure interaction can be facilitated in a controlled manner to lengthen the natural period of the system. 

(2) Sliding between the structural foundation and surrounding geomaterials can be designed to limit the amount of seismic energy that is transmitted onto the structure. 

(3) Vibration scattering or filtering, or various forms of damping can be adopted to dissipate seismic energy outside the structure. 

GSI has opened and will continue to open unlimited opportunities to geotechnical engineers, as well as structural/material engineers, to harness their creativity, uncover their complementary expertise and ignite a new passion.

A New Scientific Approach 

GSI research requires multi-disciplinary approaches that involve interweaving of knowledge and skills from various sub-disciplines in civil (geotechnical and structural), construction, environmental and material engineering, and beyond. 

The isolation mechanisms are built upon various specialised areas in earthquake engineering, namely, non-linear material properties, dynamic soil-foundation-structure interaction, seismic wave propagation, soil improvement, rocking isolation and traditional seismic isolation. 

Different kinds of materials can also be explored, which include EPS beads, geofoam, tyre-derived aggregates, mixtures of soil and waste tyre rubber granules, ductile nylon fibres, geotextiles, polyurethane, super absorbent polymers (SAP) and metamaterial. GSI research also covers sustainability and environmental impact assessment, e.g. investigating the leachate potential of mixing end-of-life tyre rubber into soils. 

Research on GSI requires advanced research tools and skills such as cutting-edge multi-scale analysis of multi-phase geomaterials at the particle scale, advanced numerical modelling of soil-foundation-structure systems, large-scale experimental testing and field measurement. Advanced construction and site formation techniques, e.g. injection, might be involved too. 

UN Sustainable Development Goals (SDGs)