Relevant Properties for Reinforcing Products based on Latest Research and Field Measurements
The application of geotextiles as soil reinforcement in roads, embankments and inclined to vertical earth wall constructions has proven a valid and very beneficial technique in the last decades. Many different products are available on the market, such as grids or wovens, made from different raw materials and also different production technologies. Application engineers and customer are sometimes confused about the relevant properties and sufficient design parameters due to the amount of research and publications carried out worldwide. This research aims to summarize and explain the relevant properties of geotextile and provide the application engineers and customers with a guidance how to implement those information in their design approach and it consequences are discussed. For instance, it is well known that parameters such as surface hardness and roughness and geometry of a reinforcement product dominates the interaction behaviour between soil and reinforcement. Depending on the product, the interaction may occur based on friction, interlocking and or the mobilisation of soil strength and passive earth pressure. However, for design purpose only the coefficient of interaction as a result of all resistance components is considered whereas achievement of the expected interaction level is considered in design stage. In this research, these parameters and tensile and/or bending stiffness, will be discussed for general applications for a reinforced retaining wall application based on finite element and limit equilibrium analyses. Finally, the recommendation on the appropriate selection of reinforcement are provided and its influence on the required design tensile strength are discussed.
The influence of reinforcement stiffness (bending and tensile) on the system behavior, mobilization of strength and the forces in geogrid layers in a reinforced retaining wall has been numerically studied. With reference to the obtained results, the following remarks can be highlighted:
1. Using geotextiles with higher bending stiffness in soil can absorb the compaction energy and also eliminate the alignment component of interaction resistance between reinforcement and soil. Both of these aspects can weaken the shear strength of soil-geotextile contact.
2. There is a critical tensile stiffness of reinforcement that reinforcing the backfill with stiffer geotextile beyond that cannot decrease the horizontal deformations of the wall significantly.
3. Using reinforcements with higher axial stiffnesses significantly increases the tensile force in the geotextile due to imperfect mobilization of the stress in backfill material. This definitely can affect process of mobilization of strength in the reinforcement as well.
4. For backfills with low to normal stiffness, the conventional design approaches based on internal stability are not sufficient to be employed for the design of reinforcements with high tensile stiffnesses due to higher loads which are developed in the reinforcement by incomplete mobilization of soil strength.
5. If very stiff material is used in backfilling, the soil strength is fully mobilized at smaller deformations (strains) and therefore using stiffer geogrid does not develop higher loads in the reinforcement.