Aurecon Insights | Geogrid Reinforced Soil Abutments by Jan Kupec


Why are Geogrid Reinforced Soil Abutments not more prevalent in New Zealand?

Abutments are geotechnical structures with their primary purpose to transfer stresses from the bridge superstructure into the foundation elements. Other functions include resisting lateral stresses, supporting backfill and approach slabs, and generally maintaining a balance between vertical and horizontal actions from a bridge structure.

Reinforced soil is the combination of alternating layers of compacted earth fill with relatively closely spaced tensile reinforcement elements to create an earth composite structure, whose properties and performance depend on the interaction between the soil and the reinforcement.

Geogrid reinforced soil (GRS) abutments are bridge abutments comprising interlayered granular soil and geogrid materials. They are a special form of earth retaining structure requiring high stiffness to support bridge elements and to resist imposed actions with minimal deformations.

This paper investigates the performance of geogrid reinforced bridge abutments for their use on New Zealand’s State Highway network.


Geogrid Reinforced Soil (GRS) Abutments

Over the past couple of decades, geosynthetics and geogrids, in particular, were employed to create a reinforced soil block. It supports the bridge superstructure and resists lateral earth pressures, especially seismic actions.

Facings panels or segmental block facings are used for aesthetic and urban design reasons, but flexible facing systems such as gabion baskets are available. Many geogrid reinforced soil abutments were built overseas, and they have performed very well, especially during large seismic events. In New Zealand, however, these structures are not prevalent.

This study will define the structure and its performance requirements on the main roading network. International case studies from the past two decades will be reviewed in detail to draw out design and construction issues and potential advantages.

A key focus will be on the seismic performance of geogrid reinforced abutments, including seismic performance in past events. Long-term monitoring and large-scale laboratory testing will also be considered.

This study then reviews current international design best practice and compares them to New Zealand’s design approaches for geogrid reinforced abutments in the context of the New Zealand Transport Agency’s Bridge Manual. Roadblocks to widespread implementation on New Zealand’s roading network are discussed, and potential changes to current design guidance will be provided.

What’s inside?

This thinking paper examines the use and behaviour of geosynthetics, specifically geogrid reinforcement (polymeric reinforcements), in bridge abutments. It introduces the reader to the subject using typology defining the form and function of bridge abutments, including typical materials used and their performance subject to design actions.

The paper will first introduce and define bridge components and abutments. A short literature review will then focus on the critical material behaviour of geogrid reinforcement. A case study review will look at relevant and available literature sources on geosynthetic reinforced abutments and draw out critical items to consider for the design of these structures.

Design approaches, case studies, large scale testing, and numerical modelling will be introduced. The section will also explore how geosynthetic reinforcement form a composite when embedded in soil, a critical behaviour often ignored.

The problem statement has been deliberately placed mid report to provide the reader with background knowledge. It explores and defines the outcomes from information capture and poses the question: Why are these structures not more prevalent in New Zealand and what may be the roadblocks for their use?

Design approaches used in New Zealand and internationally will be reviewed with respect to their use and applicability in high seismic environments and their ability to integrate into the New Zealand design practice.

Following discussions and conclusions, recommendations for further research and development will be presented to allow others to take up this research and continue the development of geogrid reinforced abutments in New Zealand.

About the author

Dr Jan Kupec is a Ground Engineering Principal at Aurecon. He provides subject-matter expertise in national and international projects in an advisory, technical and project management capacity. His expertise includes deep and shallow footings, retaining walls, slip and rockfall remediation, embankments and dams, risk-based assessment of slope stability, and contaminated land investigation and management.

About Aurecon Design Academy

Aurecon Design Academy is Aurecon’s flagship learning program for technical mastery. A major component of the Aurecon Design Academy is the individual project-based research paper. The research involved developing technical innovation and application methods for an actual project through experimentation, prototyping and human-centred design. This research paper is the result of such a project and authored by an Aurecon Design Academy graduate.

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