Behavior of Sand–Tire Chip Mixtures in Constant Shear Drained Stress Path

This paper presents the potential of scrap tire in controlling the onset of instability of sand in the constant shear drained (CSD) stress path. A series of triaxial tests in the constant shear drained stress path was conducted on the sand and sand––tire chip (STCh) mixtures. All the tests were performed following the conventional consolidated drained (CD) test up to a predefined deviator stress (onset of CSD). The CSD test then was carried out on samples at the onset of CSD by reducing the confining pressure while maintaining the deviator stress and backpressure constant. The effect of different deviator stress ($q_{\mathrm{CSD}}$), initial mean stress ($p_o^{\prime }$) levels, and tire chip content (TCh) on the onset of instability were investigated. The instability of sand and sand–tire chip mixtures was determined based on the decrease in the constant deviator stress ($dq<0$) and second-order work criteria ($d^{2}W<0$). Both approaches were found to be consistent in determining the onset of instability of STCh mixtures. The onset of instability of sand is influenced by the TCh content and $q_{\mathrm{CSD}}$. On other hand, a unique value of $p_f^{\prime }$ was found for different values of $p_o^{\prime }$. The optimum performance in controlling the onset of instability of sand was found for $\mathrm{TCh}=20\%$ for the tire chip considered in this study. The mobilized effective friction angle also exhibited improved performance for TCh = 20%. In addition, the modified state parameter had good correlation with the mobilized effective friction angle in the CSD stress path.