About GSI

Geotechnical Seismic Isolation (GSI) is an established branch of Earthquake Engineering that focuses on reducing seismic demand by engineering the soil-foundation system and its interaction with ground motion.

Learn more:

State-of-the-Art Paper (Soil Dynamics & Earthquake Engineering, 2025)

Definition of GSI

GSI was first formally defined in 2009 as:

“A category of seismic isolation techniques that are in direct contact with geomaterials and of which the isolation mechanism primarily involves geotechnics”

The concept has since evolved and been consolidated through subsequent research, culminating in the 2025 state-of-the-art synthesis that formalises its classification and governing mechanisms.

Reference: Chapter 3. Geotechnical Seismic Isolation. In: Earthquake Engineering: New Research, Nova Science Publishers Inc, New York, USA, p. 55–87 (2009)

“Structural” vs. “Geotechnical” Seismic Isolation

The term Geotechnical Seismic Isolation (GSI) was introduced in 2009 to articulate a class of isolation strategies in which the primary mechanisms are mobilised within the soil-foundation domain, in contrast to conventional structural seismic isolation systems.

The distinction concerns the location and nature of the isolation mechanism:

Structural isolation mobilises devices installed within or beneath superstructures.
Geotechnical isolation mobilises controlled soil-foundation-structure interaction.

This conceptual differentiation has evolved into a structured framework encompassing multiple governing mechanisms within the soil-foundation system.

Four Branches of GSI Systems

GSI systems are classified into four principal branches based on their governing isolation mechanisms, as synthesised in the current state-of-the-art framework.

1st Branch

Facilitating Dynamic Soil-Foundation-Structure Interaction

2nd Branch

Introducing Low-Friction Interface for Sliding

3rd Branch

Wave Scattering and/or Energy Dissipation

4th Branch

Fully Mobilising Combined Foundation Bearing Capacity

Design Philosophy & Conceptual Positioning

GSI reflects an evolution in earthquake-resistant design by relocating the primary isolation mechanisms from the superstructure to the soil-foundation interface.

Conventional seismic protection strategies typically focus on:

Enhancing structural strength and ductility
Modifying structural stiffness and configuration
Introducing supplemental damping devices
Retrofitting vulnerable structural elements

GSI, in contrast, reduces seismic demand through mechanisms mobilised within the soil-foundation system, including compliance, controlled separation, sliding, rocking, wave modification, and energy dissipation. By modifying the interaction between the structure and its supporting ground, GSI mitigates structural damage while preserving architectural and structural integrity.

Governing Isolation Mechanisms

GSI integrates soil dynamics, foundation behaviour, and seismic isolation principles within a unified mechanism-based framework. The principal isolation strategies can be categorised into four governing mechanisms:

(1) Lengthening the structural system’s natural period by reducing foundation stiffness through controlled soil compliance or softening.

(2) Decoupling the structure-foundation system from ground shaking by introducing low-friction sliding or rolling mechanisms.

(3) Altering incident seismic wave characteristics through impedance contrast and/or dissipating seismic energy via material damping within the soil medium.

(4) Mobilising combined foundation bearing capacity through controlled exceedance or under-design of foundation resistance to permit rocking, uplift, or sliding mechanisms.

These four mechanism families collectively define the technical foundation of GSI and provide a structured basis for research, design, and practical implementation.

An Interdisciplinary Field

The advancement of GSI relies on interdisciplinary collaboration, integrating expertise from geotechnical and structural engineering, construction engineering, materials science, environmental engineering, and related disciplines.

Its governing isolation mechanisms draw upon established domains of earthquake engineering, including nonlinear material behaviour, dynamic soil-foundation-structure interaction, seismic wave propagation, soil improvement techniques, rocking isolation, and conventional seismic isolation theory.

A wide range of geomaterials and engineered materials have been investigated within the GSI framework, including expanded polystyrene (EPS) beads, geofoam, tyre-derived aggregates, rubber-soil mixtures, ductile fibres, geotextiles, polyurethane, superabsorbent polymers, and emerging metamaterial concepts. Research also addresses sustainability considerations, such as circular material use and environmental impact assessment, including evaluation of potential leachate behaviour in recycled-material applications.

Methodologically, GSI research involves advanced numerical modelling of soil-foundation-structure systems, multi-scale characterisation of geomaterials, large-scale experimental testing, and field monitoring. In some applications, specialised ground improvement and construction techniques, such as injection-based methods, may be incorporated.

Contribution to UN Sustainable Development Goals (SDGs)

The engineering principles underlying GSI are aligned with internationally recognised sustainability objectives, particularly those concerning resilient infrastructure and sustainable cities. By reducing structural damage, enabling resource-efficient construction, and facilitating the use of locally available or recycled materials, GSI contributes to:

Infrastructure resilience and disaster risk reduction
Sustainable urban development
Circular material utilisation
Reduction of lifecycle environmental impacts

In resource-constrained or high-seismic regions, foundation-based isolation strategies may provide more accessible pathways to earthquake risk mitigation, thereby supporting more equitable access to structural safety.

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