Instability of iron ore tailings–geotextile interface: a direct simple shear study

To investigate the potential for flow instability in the interfaces between iron ore tailings and woven geotextile (GTX), direct simple shear (DSS) tests covering a wide domain of initial states, volume change boundary conditions and static pre-shear stresses were carried out. Accordingly, constant normal load (CNL), constant normal stiffness (CNS) and constant volume (CV) tests on the loose, medium and dense tailings prepared using the moist tamping method in contact with GTX under two initial vertical stresses were conducted. CV tests on statically pre-sheared loose and medium tailings–GTX interfaces further highlighted the impact of initial shear stress on flow instability. The testing programme included complementary drained tests in which a gradual unloading of effective vertical stress under fixed shear stress led to instability of the loose tailings–GTX interfaces. The results of this study suggest that flow instability in loose and medium tailings–GTX interfaces was triggered under the CV, CNS and constant shear drained tests at low mobilised friction angles not greater than 48–60% of the tailings critical state friction angle. Consequently, neglecting the possibility of the flow instability in the interfaces may cause an overestimation of stability of geosynthetic reinforced earth structures under certain conditions.