Experimental study on shear failure mechanism of loose spoil soil considering the adverse factor of water

Loose spoil soil (LSS) is a kind of granular material with unstable structure, for which the deformation and even failure should be induced by changing of water conditions. This research was conducted based on an engineering spoil dump, and considered the relative density ( D r ) and existed stress environment of LSS, the authors designed detail experimental plans and improved experimental equipment, a comprehensive study focused on adverse factor of water in shear failure mechanism of LSS has been achieved, conclusions were obtained as follows: 1. Under the three selected Dr 0 (0.35/0.40/0.45), LSS showed strain hardening during whole shear process, shear deformation mechanism could be summarized as the big friction deformation of unstable granular materials; 2. the adverse effect of water on LSS was significant, as the increase of main shear strain ε s0 , volume strain ε v under wet and saturated states showed continuously shrinkage in whole process, while under dry state, ε v showed an evolution characteristics of contractancy–stable–dilatancy, and based on specific ε s0 –ε v curves, the concept of critical equilibrium normal stress (CENS) was proposed; 3. The shear strength of LSS could be considered to fully follow a linear relationship, and it is greatly affected by dry/wet states, for three determined Dr 0 (0.35/0.40/0.45), their internal friction angles φ were 33.1°–38.0°, 22.9°–27.7° and 20.9°–27.3°, respectively, under dry, wet and saturated states, and it showed that strength deterioration of LSS had been basically released in wetting process; 4. LSS showed characteristics of relatively uniform friction deformation under dry state, while under wet and saturated states, thickness of shear zone narrowed significantly, and when shear stress level exceeded 0.70, local strain increment of shear zone increased sharply, localized strain should be the main reason in strength attenuation; 5. 3D particle flow method was considered to make a simple shear numerical test of LSS with a rapid shear process, it was found that under lower normal stress condition, LSS exhibited semi-fluid characteristics, which could help us to reveal the phase transition of LSS from a mechanistic perspective.