Study Of Landslides And Landslide-Induced Waves Based On Meshfree Methods

Landslides,rock avalanches,snow avalanches,pyroclastic flows and debris flows(for simplicity,they are collectively called landslides in this thesis)manifesting in the vicinity of water bodies such as reservoirs,lakes,rivers,fjords and the sea can generate mega tsunamis posing a big threat to people's life and property.Rainfalls,earthquakes and human activities all can trigger landslides.Study on the landslide and its generated surge waves(tsunamis)is of great importance for the prediction and assessment of hazard zonation(tsunami inundation area).Further,more destructive hypermobility characteristics would emerge when the slide volume exceeds 10~6 m~3 since conventional analysis methods are no longer applicable,the study on the mechanism of hypermobility landslides in depth and the improvement of the existing numerical models are crucial important for correctly predicting their velocity,runout distance and deposits.Landslide tsunamis involve multiple time and space scales and exhibit a series of processes such as slide initiation and penetration into the water,wave generation and propagation,runup along the shore and inundation.With regard to the mechanism of hypermobility landslides,investigators proposed many hypotheses such as acoustic fluidization,fragmentation,air cushion lubrication,slide liquefaction(the generation of excess pore water pressure due to heat pressurization or basal shear zone contraction)and friction coefficient reduction.The quantitative research on landslide tsunamis is mainly focused on theoretical derivations,physical experiments and numerical simulations.With the development of computer performance,more and more attentions are paid to numerical simulations as it is not restricted by experiment sites and has good repeatability.The relation between slide velocity and friction coefficient is implemented into discrete element method to handle the issue of hypermobility landslide.Based on hybrid DEM-SPH model and open source software DualSPHysics v4.0,this thesis studies landslide generated surge waves and their near field propagation from four aspects inclusive slide rigidity,initial position,slide velocity and dimensionality.The main research results are achieved as follows:(1)Highlights of the thesis.Current research status of landslide and its induced tsunamis is summarized and the limitation of mesh-based methods in numerical simulations is indicated.A new hybrid DEM-SPH model combining two meshfree methods namely discrete element method and smoothed particle hydrodynamics is proposed to study the landslide tsunamis.(2)Study on rigid landslide tsunamis.Numerical simulations are conducted to replicate the experiments with different block shapes,initial conditions and transition types.One single block and multi-block landslides and their generated waves and other complex hydraulic phenomena such as the formation of impact crater are modeled.The rigid slide motion is resolved via block DEM and its trajectory does not need to be prescribed.Sensitivity analyses are further conducted with respect to three empirical coefficients inclusive block friction angle,drag coefficient and added mass coefficient to investigate their effects on landslide motion.Block buoyancy calculation algorithm is improved such that it is applicable to partially submerged block.(3)Study on deformable landslide tsunamis.Submarine,slow and fast subaerial deformable landslide tsunamis are modeled and their numerical results are compared with experimental data to validate the effectiveness of the hybrid model.The deformable slide motion is resolved via particle DEM that can take the slide deformation into account.Meanwhile,the rolling friction is introduced to constrain the rotation between particles.The approach for irregular slide mass is proposed.Sensitivity analyses are further conducted with respect to rolling friction coefficient,global damping coefficient and artificial viscosity coefficient.(4)Study on hypermobility landslides.The mechanisms such as acoustic fluidization,fragmentation,air cushion lubrication and slide liquefaction are all attributed to the reduction of friction coefficient that changes dynamically according to slide velocity.Based on this postulation,hypermobility landslides are numerically investigated by block and particle DEM.(5)Application to practical engineering problems.Based on open source software DualSPHysics v4.0 and with the acceleration of GPU graphics card,scenarios of rigid landslide tsunamis in three dimensions are conducted for the Spanish island of Es Vedrà.The lateral wave propagation with a form of semicircle is reproduced and the characteristics of surge waves generated by hypermobility landslide is preliminarily revealed too.