Implementation of Hypoplasticity for Fast Lagrangian Simulations

The hypoplastic constitutive equations by Wu with and without structure tensor and by von Wolffersdorff were implemented in the finite element with explicit integration program FLAC. The influence of material nonlinearity, mass density and damping factor on numerical solutions with the explicit method were studied and reported. The implementation of hypoplasticity by Wu in FLAC was selected to simulate some laboratory tests i.e. biaxial test and simple shear test. The implementation was also used to simulate some typical geotechnical problems i.e. a spread footing on cohesionless soil, a trapdoor problem and an unlined circular tunnel. The results obtained with hypoplasticity agreed well with analytical solutions and experimental results. The hypoplastic constitutive equations and an elasto-plastic one with Mohr-Coulomb failure criterion were used to simulate normally consolidated Bangkok Clay. The hypoplasticity by Wu was selected for modelling of shield tunnelling in Bangkok Clay because the model gives good predictions of the undrained behavior. The earth pressure coefficient at rest K0 used in the shield tunnelling simulations with FLAC is higher than the K0 obtained from the Jaky's formula. The shield tunnelling was modelled by using actual dimensions from the construction records to generate the mesh. The surface settlements from the simulations are close to the observations. The empirical method by Peck underpredicts the surface settlements from observations.