Effect of deformability of ridges on interface shear strength



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Tire bales have become an innovative and cost effective fill material that can be used for the construction of geotechnical structures, like embankments for highway projects. The mechanical and physical properties they present allow them to be suitable for this type of structures, as long as they are provided with an appropriate drainage system. Stability of these structures is controlled by the interface shear strength existing in the contact surfaces between the bales. However, the tire bale has a jagged, uneven and highly variable surface and it presents a number of irregular tire ridges with random dimensions that are difficult to quantify. Due to the flexibility of these ridges, deformation of the interface occurs when a horizontal shear load is applied, and following this deformation the actual displacement of the interface takes place. Freilich (2009) performed large scale tests in the field and in the laboratory to observe the behavior of the whole tire bale structure, which is composed of the tire bale mass and the tire bale interface. Due to the irregular and highly variable surface of the tire bale, the deformations that occur on the ridges along the interface cannot be directly measured and quantified.

Following similar concepts of some rock mechanic models, Freilich characterized the tire ridge interface using three parameters and came up with a model. Using these parameters, an ideal interface was constructed where the variability was reduced by incorporating a known geometry, and it can still be characterized in the same manner as that for the tire bale interface.

Loads, deformations and displacements occurring along the interface were measured and recorded. From this data, shear strength parameters are defined and incorporated into Freilich’s tire ridge interface model that is used to predict the geometric and mechanical behavior of the irregular ridges controlling the interface shear strength. The behavior predicted from the model is then compared to the recorded data representing the actual geometric and mechanical behavior of the interface with known geometry, where the deformations on the asperities are approximated. This comparison verifies that the consideration of the flexibility from the tire ridges is not entirely described by the tire ridge interface model. Therefore a possible modification, based on the observations recorded, could be found.