Research Projects

Bahia El Refai

Current PhD Student

The design of Geosynthetic Reinforced Soil – Integrated Bridge Systems (GRS-IBS)

Project Background

Geographical obstacles such as valleys, roads, and bodies of water, are the reason behind building bridges which are an essential component in modern infrastructure, to provide passage over these obstacles. Bridges, in their simplest design, consist of two abutments, one on either side of the obstacle, supporting the bridge deck spanning over the obstacle. Moreover, in conventional bridges, expansion joints and bearing are traditionally installed between the bridge deck and the supporting abutments to accommodate the relative movement and prevent the development of stresses generated by temperature between the superstructure and the abutment. These expansion joints require permanent maintenance due to damage from de-icing salts leaking through the deck joints in the superstructure components. This issue leads to corrosion and immobilization of the joints and bearing that represent a major element of conventional bridges, repair, and maintenance costs.

Given the problems with conventional bridges containing joints and bearings, the concept of physically and structurally connecting the superstructure and abutment to create an integral bridge have become very popular. For integral bridges all the problems associated with joints and bearings are avoided.

A new solution evolved for an economical and faster way to construct a system that blend geosynthetic reinforced soil system (GRS) supporting a bridge superstructure without any joints. The Geosynthetic Reinforced Soil – Integral Bridge System (GRS-IBS), uses alternating layers of compacted granular fill with layers of geotextile reinforcements alternating layers of compacted granular fill with layers of geotextile reinforcement, rather than relying on a conventional bridge support system beneath the bridge.


This project aims to address some of the deficits in the understanding of the mechanisms of action in GRS-IBS and how this affects the overall design of these systems. The core aims and objectives of this study were to:

  • To identify the failure mechanisms in GRS-IBS.
  • Develop and validate a numerical model in Plaxis 2D that can capture the response of GRS walls and GRS-IBS.
  • To better understand the behaviour of GRS-IBS through numerically modelling of the system under vertical and horizontal loads.
  • To conduct a numerical parametric study of GRS-IBS to identify the pertinent parameters including reinforced soil abutment geometry, bridge geometry and bridge loading that influence the performance of the system.
  • To provide design guidance for the safe design of GRS-IBS.


  • Using Plaxis 2D to investigate the influence of soil properties, location if the bank seat, geogrid stiffness and arrangement and the magnitude and direction of horizontal load on the behaviour of GRS-IBS.
  • Further validation of the numerical model using a geotechnical centrifuge.
  • Effect of phased loading to several thousand phases to represent actual traffic and temperature variations experienced in Ireland & UK.
  • Further modelling to optimise the location of the bank seat relative to the back of the wall.
  • Finally, to propose a method of design to reduce or eliminate the deformation created behind the bridge seat to increase the service life of the bridge and decrease the cost of maintenance.