<p>The smoothed particle hydrodynamics (SPH) method is employed to investigate tunnel face instability using a hypoplastic constitutive model incorporating the critical state concept. The proposed approach is validated against three benchmark problems, including a direct shear test, the classical sand column collapse and a series of laboratory tests on tunnel face instability. Subsequently, the influence of the displacement- and stress-controlled boundary conditions on the tunnel face instability is examined. The results show that both boundary conditions yield reasonable estimates of the limit support pressure, while the displacement-controlled scheme demonstrates advantages in computational efficiency and objectivity. Furthermore, a comprehensive parametric study is performed to study the progressive failure of tunnel face, with particular emphases on the stress state evolution in front of the tunnel face and post-failure behaviors. The results indicate that the void ratio plays a dominant role in determining both the limit support pressure and shear band formation, while having a limited influence on the extrusion distance after collapse, which is mainly governed by the critical friction angle.</p>