Yu Huang

Run-out analysis of flow-like landslides triggered by the Ms 8.0 2008 Wenchuan earthquake using smoothed particle hydrodynamics

Flow-like landslides have caused significant damage and casualties worldwide. However, studying such phenomena with traditional simulation methods is made difficult by their complex fluidization characteristics. In this paper, we use smoothed-particle hydrodynamics (SPH) for the run-out analysis of flow-like landslides. Compared with conventional methods, the proposed SPH modeling technique is the combination of a Bingham flow model and Navier–Stokes equations in the framework of computational fluid dynamics. At first, two benchmark problems of dam break and granular flow are simulated and verified to evaluate the accuracy of the SPH model. Then, run-out analyses are performed for flow-like landslides triggered by the Ms 8.0 Wenchuan earthquake that occurred on 12 May 2008 in Sichuan Province, China. Run-out analyses of the Tangjiashan, Wangjiayan, and Donghekou landslides are conducted by the application of SPH models to real flow-like landslides. All simulations show good agreement with characteristics of flow-like landslides observed in the field. We have found that numerical modeling can capture the fundamental dynamic behavior of these flow-like landslides and produce preliminary results for hazard assessment and site selection for reconstruction in earthquake-prone areas.

Review of soil liquefaction characteristics during major earthquakes of the twenty-first century

Liquefaction, which can be defined as a loss of strength and stiffness in soils, is one of the major causes of damage to buildings and infrastructure during an earthquake. To overcome a lack of comprehensive analyses of seismically induced liquefaction, this study reviews the characteristics of liquefaction and its related damage to soils and foundations during earthquakes in the first part of the twenty-first century. Based on seismic data analysis, macroscopic phenomena of liquefaction (e.g., sand boiling, ground cracking, and lateral spread) are summarized, and several new phenomena related to earthquakes from the twenty-first century are highlighted, including liquefaction in areas with moderate seismic intensity, liquefaction of gravelly soils, liquefaction of deep-level sandy soils, re-liquefaction in aftershocks, liquid-like behavior of unsaturated sandy soils. Additionally, phenomena related to damage in soils and foundations induced by liquefaction are investigated and discussed.

Secondary geological hazard analysis in Beichuan after the Wenchuan earthquake and recommendations for reconstruction

The Wenchuan earthquake, also known as 2008 Sichuan Earthquake, occurred along the Longmenshan fault zone on 12 May 2008 at 14:28:01.42 CST (06:28:01.42 UTC). It caused serious damage to structures in the region. Beichuan is a town which is within these severely damaged areas. According to the earthquake intensity distribution map of 2008 Wenchuan earthquake officially released by the China Earthquake Administration, the earthquake intensity in Beichuan was XI on the China seismic intensity scale. As the earthquake occurred in a mountainous area, there were thousands of landslides, rockfalls, debris flows, and surface ruptures triggered by the earthquake over a broad area. These secondary geological hazards substantially increased the human, social and economic impact of the earthquake. This paper presents a post-earthquake analysis on the secondary geological hazards in Beichuan. The risk analyses associated with construction of the National Earthquake Memorial Museum in Beichuan are assessed and recommendations on risk mitigations for the mass reconstruction over the ruins are also provided based on this field study.

SPH-based numerical simulations of flow slides in municipal solid waste landfills

Most municipal solid waste (MSW) is disposed of in landfills. Over the past few decades, catastrophic flow slides have occurred in MSW landfills around the world, causing substantial economic damage and occasionally resulting in human victims. It is therefore important to predict the run-out, velocity and depth of such slides in order to provide adequate mitigation and protection measures. To overcome the limitations of traditional numerical methods for modelling flow slides, a mesh-free particle method entitled smoothed particle hydrodynamics (SPH) is introduced in this paper. The Navier–Stokes equations were adopted as the governing equations and a Bingham model was adopted to analyse the relationship between material stress rates and particle motion velocity. The accuracy of the model is assessed using a series of verifications, and then flow slides that occurred in landfills located in Sarajevo and Bandung were simulated to extend its applications. The simulated results match the field data well and highlight the capability of the proposed SPH modelling method to simulate such complex phenomena as flow slides in MSW landfills.

Numerical simulation of flow processes in liquefied soils using a soil-water-coupled smoothed particle hydrodynamics method

Liquefaction can result in the damage or collapse of structures during an earthquake and can therefore be a great threat to life and property. Many site investigations of liquefaction disasters are needed to study the large-scale deformation and flow mechanisms of liquefied soils that can be used for performance assessments and infrastructure improvement. To overcome the disadvantages of traditional flow analysis methods for liquefied soils, a soil–water-coupled smoothed particle hydrodynamics (SPH) modeling method was developed to analyze flow in liquefied soils. In the proposed SPH method, water and soil were simulated as different layers, while permeability, porosity, and interaction forces could be combined to model water-saturated porous media. A simple shear test was simulated using the SPH method with an elastic model to verify its application to solid phase materials. Subsequently, the applicability of the proposed SPH modeling method to the simulation of interaction forces between water and soil was verified by a falling-head permeability test. The coupled SPH method produced good simulations for both the simple shear and falling-head permeability tests. Using a fit-for-purpose experimental apparatus, a physical flow model test of liquefied sand has been designed and conducted. To complement the physical test, a numerical simulation has been undertaken based on the soil–water-coupled SPH method. The numerical results correspond well with the physical model test results in observed configurations and velocity vectors. An embankment failure in northern Sweden was selected so that the application of the soil–water-coupled SPH method could be extended to an actual example of liquefaction. The coupled SPH method simulated the embankment failure with the site investigation well. They have also estimated horizontal displacements and velocities, which can be used to greatly improve the seismic safety of structures.

Analysis of geoenvironmental hazards in urban underground space development in Shanghai

Underground space is becoming increasingly more utilized in the fast urbanization process of Shanghai. However, many geoenvironmental hazards, including land subsidence, slip flow, methane gas, piping, and quicksand, are occurring more frequently, as underground space development enters the state of “big, deep, long, fast, and dense.” In this paper, based on our investigation and studies of construction project cases, we analyze the possible factors causing geoenvironmental hazards and propose corresponding measures for their prevention. From the viewpoint of earth system science, the geoenvironmental hazards are caused by anthropogenic factors coupled with natural factors. Shanghai is built over layers of soft soil that were deposited during the Holocene. The paleogeographical environment of the Holocene produced soft soil with high water content, large void ratio, high sensitivity, thixotropy, low shear strength, and high compressibility; these characteristics lead to a geoenvironment that can be easily disturbed by underground engineering construction. To achieve sustainable development of underground space, a series of prevention and control measures are presented, especially awareness of the need for geoenvironmental protection and risk management should be enhanced, as well as incorporating technology including global positioning system, geographic information system, and synthetic aperture radar interferometry, and information construction in underground development projects.

SPH model for fluid–structure interaction and its application to debris flow impact estimation

On 13 August 2010, significant debris flows were triggered by intense rainfall events in Wenchuan earthquake-affected areas, destroying numerous houses, bridges, and traffic facilities. To investigate the impact force of debris flows, a fluid–structure coupled numerical model based on smoothed particle hydrodynamics is established in this work. The debris flow material is modeled as a viscous fluid, and the check dams are simulated as elastic solid (note that only the maximum impact forces are evaluated in this work). The governing equations of both phases are solved respectively, and their interaction is calculated. We validate the model with the simulation of a sand flow model test and confirm its ability to calculate the impact force. The Wenjia gully and Hongchun gully debris flows are simulated as the application of the coupled smoothed particle hydrodynamic model. The propagation of the debris flows is then predicted, and we obtain the evolution of the impact forces on the check dams.

SPH-based numerical simulation of catastrophic debris flows after the 2008 Wenchuan earthquake

Post-earthquake debris flows that have occurred in Sichuan Province in southwestern China following the Wenchuan earthquake on May 12, 2008, have caused significant damage and casualties. Previous earthquake-induced landslides produced large amounts of loose material that remained on the steep slopes and in the gullies. As a consequence of heavy rainstorms during the rainy seasons, the existing loose material was transformed into numerous debris flows. Research has shown that the debris flows in the Wenchuan earthquake disaster areas have been characterized by their large scale, high speed, long run-out, and destructive impact. In order to identify the areas potentially at risk and to predict the flow severity, an accurate numerical method is needed to simulate these debris flows. In this paper, we have proposed a smoothed particle hydrodynamics (SPH) modeling technique—a meshfree particle method—to simulate the post-earthquake debris flows in the Wenchuan earthquake disaster areas. The SPH modeling technique introduces a Bingham model to analyze the relationship between material stress rates and particle motion velocity. Compared to traditional numerical methods, the SPH modeling technique is a true meshfree method of a pure Lagrangian nature. It can instantaneously track the motion of each particle, accurately predict the velocity, and naturally handle problems with extremely large deformations. In addition, the SPH method is based on continuum mechanics, and is therefore an efficient method to simulate large-scale debris flows. In this work, first, a viscoplastic fluid was simulated and verified with experimental results in order to evaluate the accuracy of the SPH model. Then propagation analysis of two typical post-earthquake debris flows in earthquake-hit areas was carried out, applying the SPH model. The simulation results showed good agreement with the limited field observation data. Our proposed SPH numerical modeling is able to capture the fundamental dynamic behavior of post-earthquake debris flows and can partially explain these complex phenomena. These simulation results can provide a preliminary scientific basis for hazard assessment and site selection for reconstruction in earthquake-prone areas.

Analysis of the mechanism of seabed liquefaction induced by waves and related seabed protection

As one of the most serious offshore hazards, wave-induced seabed liquefaction can trigger massive landslides on the ocean floor and pose a great threat to submarine structures (e.g., coastal levees, oil platforms, drilling platforms and seabed pipelines). In view of the complexity and practicability of the problem, this study systematically analyzes the mechanism, factors and remedial measures of liquefaction. Compared with seismic liquefaction, waved-induced liquefaction varies in many respects, such as the load pattern, loading position, drainage condition and characteristics of pore water pressure, resulting in different mechanisms of seabed liquefaction under the action of waves. Both wave characteristics and soil characteristics, including the wave period, water depth, wave height, degree of saturation, seabed thickness, permeability and stress history, affect the degree of seabed liquefaction. Moreover, to ensure the sustainable development of the ocean, a series of remedial measures against liquefaction, including evaluation of the liquefaction potential, management of disaster prevention, ocean monitoring and forecasting, are proposed.

Simulation of flow slides in municipal solid waste dumps using a modified MPS method

AbstractnFlow slides in municipal solid waste (MSW) dumps have caused serious damage to structures and casualties all over the world. Therefore, much attention should be paid to this type of disaster to elucidate the flow mechanisms and fluidization characteristics of MSW, which are essential for the assessment and prevention of flowlike hazards. To bypass the deficiencies of the traditional analysis methods that use the mesh method and are based on a framework of solid mechanics, the moving particle semi-implicit (MPS) method, which is a purely Lagrangian meshless method and proposed for incompressible flow, is introduced to study flow slides in MSW landfills. Considering the no-physical pressure fluctuation that affects the simulation accuracy in the original MPS, the original MPS is revised in three ways: the kernel function, the source term of the Poisson equation and the search for free surface particles. Two benchmark problems, the dam break problem and the static pressure problem, are computed to illustrate the improvement of the pressure stability of the modified MPS. The Bingham constitutive model combined with the Mohr–Coulomb failure criterion is adopted to depict the dynamic features of MSW flow slides, and the equivalent viscosity is employed to bridge the gap between Bingham fluid models and Newtonian fluid models. This method, ultimately, is applied to simulate real flow slides in the Umraniye–Hekimbashi landfill and the Payatas waste dump. The numerical results show good consistency with the field data, indicating that the modified MPS method is capable of capturing the essential dynamic behavior and reproducing the entire process of complicated flow slides in MSW dumps.