Doctor of Philosophy
School of Civil, Mining and Environmental Engineering
Mashiri, Maria Soledad, Monotonic and cyclic behaviour of sand-tyre chip (STCh) mixtures, Doctor of Philosophy thesis, School of Civil, Mining and Environmental Engineering, University of Wollongong, 2014. http://ro.uow.edu.au/theses/4267
Stockpiling of scrap tyres is a significant environmental hazard. In recent years, considerable amount of research attentions have been devoted to explore viable solutions to the recycle and reuse scrap tyres in Civil Engineering projects. At present, only a relatively small amount of scrap tyres has been used in Civil Engineering applications compared to the amount of scrap tyres generated annually. Experimental investigation reports suggest that inclusion of tyre chips (TCh) in sand increases the shear strength and decreases the dilatancy of sand, implying a promising and environmentally sustainable use of the sand-tyre chip (STCh) mixtures in Civil Engineering applications. The reuse of scrap tyres as tyre chips in sand (STCh mixtures) can effectively address the growing environmental concerns and at the same time provide solutions to geotechnical problems associated with low soil shear strength and high dilatancy.
In this thesis, the monotonic behaviour of STCh mixtures has been investigated. Importantly, three behavioural zones of STCh mixtures have been identified: sand-like, sand-rubber, and rubber like. The experimental investigation results of a series of monotonic triaxial tests on sand mixed with varying proportions of TCh demonstrate that TCh increase the shear strength and decrease the dilatancy o f sand. The effects of confinement and relative density on the shear strength, dilatancy, and initial tangent modulus of the STCh mixtures have also been investigated. These tests demonstrate that the greatest improvement is obtained in the sand-rubber behavioural zone in which sand and tyre chips (TCh) form the skeleton of the mixture. Considering the importance of a suitable constitutive model for wide applications of STCh mixture in Civil Engineering applications, a semi-empirical constitutive model for STCh mixtures has been developed based on a critical state framework incorporating the constant stress ratio (CSR) and the state parameters ( ^), which captures the key features exhibited by the STCh mixtures during shear loading. The model has been validated with the results of extensive laboratory investigations. The developed semi-empirical model can effectively simulate the monotonic behaviour of STCh mixtures.
Recently, STCh mixtures were proposed to be used for seismic isolation of low-tomedium- rise buildings. In such seismic isolation methods, a large amount of scrap tyres can be reused in an environmentally friendly way. Moreover, it was reported that scrap tyres can reduce the liquefaction potential of sand. However, investigations into the cyclic behaviour and dynamic properties of STCh mixtures are limited. In this study, the effects of the gravimetric proportion of TCh, the cyclic shear strain, and the number of cycles on the cyclic behaviour of STCh mixtures (such as liquefaction potential and maximum shear stress) have been investigated by strain control cyclic triaxial tests. The dynamic properties (shear modulus and damping ratio) of STCh mixtures for a medium to a large range of shear strain levels (0.15% to 0.50%) have also been determined.
The importance o f the monotonic and the cyclic behaviours together with the static and dynamic properties of STCh mixtures presented in this thesis is paramount, especially in increasing the confidence for the use of tyre chips in Civil Engineering applications. Hence, the reuse of potentially hazardous scrap tyres can be significantly increased by the environmentally friendly and sustainable applications of STCh mixtures in Civil Engineering applications.