Engineering characterization of tire derived aggregate for geotechnical applications

According to the Rubber Manufacture Association about 230.7 million scrap tires are generated in the United States every year. Reduction of scrap tire disposal, through recycling and reutilization, has become an important environmental priority. In this regard, several reutilization options of scrap tires have been implemented within the field of civil engineering. This dissertation examines one of these reutilization alternatives involving shredded scrap tires that are processed to produce a granular material often referred to as tire derived aggregates (TDA). The specific civil engineering application that this research investigates is the use of TDA as a potential sustainable backfill for retaining walls. The backfill of retaining walls induces lateral pressures which are a key input in the design process. For conventional mineral soils these lateral pressures are computed using classical theories of lateral earth pressures. The applicability of these theories to TDA materials, which have deformable particles, needs to be confirmed due to the very limited experimental data available on TDA generated lateral pressures. The work plan involved centrifuge laboratory experiments, geotechnical laboratory testing, and finite element analyses designed to help fill this important knowledge gap.;Results from the Centrifuge laboratory experimental program revealed that the at-rest lateral pressures generated by TDA and TDA/sand mixtures (50/50 by volume) were found to be approximately 80% and 35% lower than those induced by a conventional Nevada sand backfill, respectively. This large reduction in lateral pressures by TDA and TDA/sand mixtures has the potential to translate into important cost savings associated to reduced material amounts of a likely smaller cantilever wall associated to the lower TDA backfill load demand. The centrifuge tests confirmed that classical earth pressure theories for at-rest (Jaky 1944) and active conditions (Rankine theory) considerably overpredict the measured lateral pressures generated by TDA and TDA/sand mixtures.;The geotechnical laboratory experiments indicate that TDA backfills exhibit a high degree of compressibility which may be an important design consideration for retaining walls where surcharge loading acts on the backfill. The triaxial compression tests on TDA indicated that this material is contractive and did not exhibit a marked peak deviatoric stress. Additionally friction angle values are highly dependent on the axial strain level used. Friction angle values varying from 8 to 21 degrees were found for axial strains between 5% and 27%, respectively. For design purposes it is recommended that the TDA shear strength be based on a limiting axial strain value associated to allowable deformations or service limit states. The granulated rubber TDA tested showed a significant apparent cohesion attributed to particles deforming and pressing against each other to develop some interlocking. A 50/50 by volume TDA/sand mixture was found to have improved mechanical properties, shear strength, and a drastically reduced compressibility compared to the 100% TDA.;The finite element analyses (FEA), carried out using three different constitutive models, suggest that FEA is reasonably good approach for predicting geotechnical behavior of TDA materials within certain limitations.