Evaluation of tyre products as ground improving geomaterials

Applications of scrap tyre-derived recycled products (such as tyre chips and tyre shreds) in geotechnical engineering projects have been increasing largely because of their potential economic and environmental benefit. This paper first addresses and evaluates two novel Japanese experiences of tyre-derived recycled products in ground improvement applications. It then discusses and evaluates the deformation mechanism of such materials through non-destructive testing techniques. Direct shear testing procedures are first described, in which sand as well as layers of sand and tyre chips were examined to compare the deformation behaviour. The shear behaviour of the materials could be investigated through X-ray computed tomography (CT) during the testing. The particle image velocimetry (PIV) technique was then used to visualise the deformation properties. In addition, triaxial shear testing of tyre chips as well as tyre chip-sand mixtures is described, in which the compressibility and the deformation of the tyre chip particles were examined by X-ray CT scanning and PIV. Based on these test results, the mechanical properties and the internal structure during the deformation of tyre chips were finally evaluated for their applications as ground improving geomaterials. Model test results indicate that the presence of tyre chips (either as cushion or as reinforcing material) could substantially reduce the earthquake-induced permanent displacement of structures. Non-destructive test results indicate that the deformation characteristics of mixtures of tyre chips and sand are different from those of pure sand. Less shear strain is generated in tyre chips and tyre chips mixed with sand than that in pure sand, and the potential of onset of localisation diminishes with decreasing sand fraction. Also, it was found that tyre chips- sand mixtures do not undergo liquefaction if a suitable mixing percentage (sand fraction) is used. Therefore, tyre chips can be successfully used as a reinforcing material to help prevent the liquefaction of sandy soils.