Siming He

A MacCormack-TVD finite difference method to simulate the mass flow in mountainous terrain with variable computational domain

A two-dimensional mountainous mass flow dynamic procedure solver (Massflow-2D) using the MacCormack-TVD finite difference scheme is proposed. The solver is implemented in Matlab on structured meshes with variable computational domain. To verify the model, a variety of numerical test scenarios, namely, the classical one-dimensional and two-dimensional dam break, the landslide in Hong Kong in 1993 and the Nora debris flow in the Italian Alps in 2000, are executed, and the model outputs are compared with published results. It is established that the model predictions agree well with both the analytical solution as well as the field observations.

Seismic Displacement of Slopes Reinforced with Piles

The seismic stability of slopes reinforced with a row of piles is analyzed using the kinematic theorem of limit analysis within the framework of the pseudostatic approach. An existing method which is based on the theory of plasticity is used to determine the lateral forces provided by the piles. Expressions for calculating the yield acceleration coefficient are derived. Then, based on Newmarks sliding block concept, the permanent displacement induced by an earthquake shocking can be calculated by the integrals of seismic records. An example is investigated to illustrate the validity of this method and the effects of piles on a restraining slopes dynamic deformation.

MacCormack-TVD Finite Difference Solution for Dam Break Hydraulics over Erodible Sediment Beds

AbstractCoupled shallow water equations integrated with sediment transport and morphological evolution are presented in this paper. The momentum exchange terms that originated from the interaction between flow and sediment, which were ignored by several researchers, are taken into account. The time and space second-order, MacCormack total variation diminishing (TVD) finite difference method is used to solve these equations. A series of numerical simulations compared with laboratory dam-break experiments were carried out. The simulated results are in good agreement with experimental measured results, which demonstrates that the current computational framework is able to determine the dam-break hydraulics over erodible sediment.

Seismic stability analysis of soil nail reinforced slope using kinematic approach of limit analysis

Prediction of the critical seismic yield acceleration coefficient and the seismic permanent displacement of soil nail reinforced slope under seismic loading has been playing an important role in helping design in the earthquake-prone areas. In this paper, the seismic stability of soil nail reinforced slope is analyzed using the kinematic theorem of limit analysis. The log-spiral failure mechanism is considered and the corresponding analytical expressions are derived to calculate the critical seismic yield acceleration coefficient and the permanent displacement of slope subjected to earthquake loading. A series of calculations are carried out to illustrate the influence of inertial force on the stability of a nail-reinforced slope. Parametric studies indicate that the strength and geometry of slope as well as characteristic parameters of soil nail have a significant effect on the critical seismic yield acceleration coefficient and the permanent displacement of soil nail reinforced slope.

Numerical modeling and dynamic analysis of the 2017 Xinmo landslide in Maoxian County, China

A catastrophic landslide occurred at Xinmo village in Maoxian County, Sichuan Province, China, on June 24, 2017. A 2.87×106 m3 rock mass collapsed and entrained the surface soil layer along the landslide path. Eighty-three people were killed or went missing and more than 103 houses were destroyed. In this paper, the geological conditions of the landslide are analyzed via field investigation and high-resolution imagery. The dynamic process and runout characteristics of the landslide are numerically analyzed using a depth-integrated continuum method and MacCormack-TVD finite difference algorithm. Computational results show that the evaluated area of the danger zone matchs well with the results of field investigation. It is worth noting that soil sprayed by the high-speed blast needs to be taken into account for such kind of large high-locality landslide. The maximum velocity is about 55 m/s, which is consistent with most cases. In addition, the potential danger zone of an unstable block is evaluated. The potential risk area evaluated by the efficient depth-integrated continuum method could play a significant role in disaster prevention and secondary hazard avoidance during rescue operations.

Prediction of impact force of debris flows based on distribution and size of particles

A debris flow is a solid–liquid two-phase flow; the composition and gradation of the particles within have a significant influence on its impact force. This paper proposes a new method for studying the impact force according to the composition of a debris flow based on analysis of existing calculation methods. The impact force is divided into three parts: (1) the dynamic pressure provided by the debris flow slurry, which is composed of fine particles and water; (2) the impact force of coarse particles; and (3) the impact force of boulders. This paper analyzes the established formulations used to calculate the impact force by using hydrodynamic theory and contact mechanics to propose a debris flow impact model according to the debris flow type. The results show that the impact force is closely related to the solid volume fraction, composition of particle materials, motion velocity, and depth of a debris flow. Among all the components of the impact force, the boulder impact force is the largest followed by the impact force of coarse particles; the dynamic pressure is minimal.

Dynamic simulation of landslide based on thermo-poro-elastic approach

Catastrophic landslides often extend for surprisingly long distances, a trend consolidated by a decrease in the apparent friction coefficient with an increasing landslide volume. However, there is not yet a physical model able to predict the long distances traveled by landslides in the condition of deformation. A two-dimensional model for simulating catastrophic landslide motion is presented in this paper and is based on a lump model for thermo-poro-elastic mediums. The model can concurrently simulate landslide dynamic processes, and pore pressure and frictional heating evolution in the shear zone at the bottom of a landslide. These are based upon the shallow-seated groundwater table assumption and depth-averaged integration, as well as the thermo-poro-elastic approach. A combined computational method based on the finite volume method and Crank–Nicolson method is proposed to solve the coupled equations. Four computational experiments have been run and the numerical results indicate that frictional heating enhances pore water pressure and reduces the friction, resulting in higher mobility and longer distances traveled. The value of pore water pressure can also influence the deformation process of a landslide.

An Angle-Based Method Dealing with Vertex-Vertex Contact in the Two-Dimensional Discontinuous Deformation Analysis (DDA)

Due to the discontinuity of the direction of a normal vector at the corner, vertex–vertex contact is indeterminate in numerical modelling. Two classes are indeterminate in two-dimensional discontinuous deformation analysis (DDA), designated as “genuine indeterminacy” and “pseudo indeterminacy”. While examining these indeterminacies, it is necessary to pre-process quasi-vertex–vertex contact and determine contact or entrance edges. On one hand, improper pre-processing not only changes the equilibrium equations of the system, but also increases the burden on open–close iteration. On the other hand, there are two kinds of quasi-contact edges, i.e. the same and different block quasi-contact edges. Certain previous distance-based methods, which are used to seek the correct entrance edge, lead to some forced contacts, including vertex–vertex or vertex–edge. New pre-processing and angle-based methods for determining entrance edges are developed in this study. Additionally, the new concept of strengthening the movement trend of blocks is presented in DDA. The new pretreatment method combining the angle-based method and a strategy for strengthening the movement trend of blocks are intended to reduce forced contacts, maintain the movement trend of blocks, and speed up open–close iterations to a certain extent. Furthermore, the new method only depends on the orientation of quasi-contact edges and the movement trend of convex corners. The effectiveness of these improvements is verified by translational motion, rotation trend, and time-step size effect tests.

Progress in stability analysis of submarine slopes considering dissociation of gas hydrates

Gas hydrates have the potential to be a new energy source and a submarine geohazard. Though researchers generally agree about the association between gas hydrate dissociation and submarine slope failures, the processes and mechanism of submarine slope failure caused by gas hydrate dissociation are not clearly understood. In the last few years, some authors have tried to analyse submarine slope stability by considering the existence and dissociation of gas hydrate, and a few researchers have presented quantitative models. This paper presents a review of the various causes of submarine slope failures associated with gas hydrate dissociation. Also, analysis models of submarine slope stability associated with gas hydrate dissociation that are documented from the literatures including the infinite slope model, wedge model, slump and retrogressive failure model are interpreted and illustrated, respectively.

Stability Analysis of Slopes Reinforced with Piles Using Limit Analysis Method

A simplified methodology is proposed for the stability analysis of slopes reinforced with one row of piles. To account for the presence of piles, an existing method which is based on the theory of plasticity is used to determine the lateral forces acting on the piles. Then, the kinematic approach of limit analysis is used to analyze the stability of the slope. The rate of external work due to the pile force is added to the energy equation and expressions are derived to calculate the safety factor of slope reinforced with piles. Using the proposed method, a study is carried out to illustrate the effect of piles on slope stability. Finally, the most suitable location of piles within the slope and the effect of pile spacing and diameter on the safety factor are discussed.