| Summary: |
The proposed research project aims at studying the potential of the use in geosynthetic reinforced structures of cohesive soils and by-products instead of high quality granular soils.
The soil reinforcement technique appeared in the 1960s with the proposal, by Henri Vidal, of the constructive technology "Terre Armée". This technology demands a granular cohesionless backfill soil and metallic reinforcements.
Later, geosynthetics began being used instead of metallic reinforcements, especially due to the low cost and easier application of geosynthetics.
An important feature of the rapid growth in the use of geosynthetic reinforced soil structures, was that they were first successfully applied in practice and then later researched and standardised within design methods. As a result of this, over the last thirty-five years, the need to maintain the confidence of the construction industry practitioners has been of primary concern, with the risk of failures always minimised by the adoption of conservative design methods. In this context, the backfill soil characteristics had to be as demanded for "Terre Armée" (that is, granular, without cohesion) and the safety factors for geosynthetics were extremely conservative due to the lack of knowledge on geosynthetics durability and long term behaviour. Moreover, the design methods were based on Limit Equilibrium principles. However, the research developed over the last thirty-five years leads, nowadays, to a much greater understanding of the operational behaviour of the materials and of the overall structures, which indicates that more economic and technically efficient structures can be built in the future. Soil-geosynthetic interaction is of the utmost relevance for soil reinforcement, because it is through the interfaces between the soil and the reinforcements that the stress transfer becomes effective. As geosynthetics are bi-dimensional reinforcements the contact area with the soil available fo  |
Summary
The proposed research project aims at studying the potential of the use in geosynthetic reinforced structures of cohesive soils and by-products instead of high quality granular soils.
The soil reinforcement technique appeared in the 1960s with the proposal, by Henri Vidal, of the constructive technology "Terre Armée". This technology demands a granular cohesionless backfill soil and metallic reinforcements.
Later, geosynthetics began being used instead of metallic reinforcements, especially due to the low cost and easier application of geosynthetics.
An important feature of the rapid growth in the use of geosynthetic reinforced soil structures, was that they were first successfully applied in practice and then later researched and standardised within design methods. As a result of this, over the last thirty-five years, the need to maintain the confidence of the construction industry practitioners has been of primary concern, with the risk of failures always minimised by the adoption of conservative design methods. In this context, the backfill soil characteristics had to be as demanded for "Terre Armée" (that is, granular, without cohesion) and the safety factors for geosynthetics were extremely conservative due to the lack of knowledge on geosynthetics durability and long term behaviour. Moreover, the design methods were based on Limit Equilibrium principles. However, the research developed over the last thirty-five years leads, nowadays, to a much greater understanding of the operational behaviour of the materials and of the overall structures, which indicates that more economic and technically efficient structures can be built in the future. Soil-geosynthetic interaction is of the utmost relevance for soil reinforcement, because it is through the interfaces between the soil and the reinforcements that the stress transfer becomes effective. As geosynthetics are bi-dimensional reinforcements the contact area with the soil available for stress transfer is much higher than that available when the reinforcements are metallic and also one-dimensional. This fact, linked to the very good behaviour of geosynthetic reinforced structures observed to date, leads to anticipate of the possibility of using low quality soils or, even, by-products, instead of high quality granular soils. This substitution will have a huge repercussion on construction savings and on environmental protection. On the other hand, in the last 15 years the behaviour of granular soil-geosynthetic interfaces have been deeply researched and the efficacy of that interaction proved. It is now imperious to advance in another direction, that is the research on poor backfill material-geosynthetic interaction.
To achieve this objective, different cohesive soils and different types of geosynthetics will be selected and the experimental study will be carried out of the mechanical behaviour of soil in isolation and reinforced soil by triaxial tests and of the behaviour of soil-geosynthetic interfaces in pullout, direct shear and inclined plane shear for different soil water content and compaction degree and confinement pressure.
This research is expected to contribute to a better understanding of the behaviour of different types of geosynthetic reinforced backfill material and of different types of backfill material-geosynthetic interfaces, to the clarification of the validity of current design methods, as well as to construction savings. |