Zili Dai

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.

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.

Modeling the flow behavior of a simulated municipal solid waste

Flow slides in the municipal solid waste (MSW) landfill are common geological disasters that have the potential to cause loss of life, destruction of property, and damage to the natural environment in the surrounding region. In this work, a mixture of peat, kaolin clay and quartz sand was used as a model test material to simulate MSW. A series of physical model tests on MSW simulant flows was carried out to capture the run-out behavior of the waste and analyze its mobility. The testing assembly consisted of a transparent model box, a steel frame and a high-speed camera. Flow failure was induced by lifting up a baffle to cause the MSW simulant to collapse and flow. Images of the flowing mass were taken by the high-speed camera. The series of images clearly displays the propagation of MSW simulant flows. The final profile of the MSW simulant and the shape of the deposition area were observed and measured. The run-out distances, final deposit shapes, flow depth, velocities and angle of reach showed significant variation between test configurations, indicating the strong influence of moisture content on overall mobility. The test results obtained can aid in the prediction of distal reach, flow depth and maximum velocity of solid waste following a landfill slope failure, which are necessary for hazard assessment and mitigation planning, and also to provide physical data for theoretical and numerical model verification.

Application of virtual earth in 3D terrain modeling to visual analysis of large-scale geological disasters in mountainous areas

Sudden large-scale geological disasters can be triggered in mountainous areas by events such as earthquakes, rainfall, volcanic eruptions, or human activity, leading to serious loss of life and property. Generating digital elevation model (DEM) for such geological disasters allows the rapid identification of affected areas, which is essential for emergency response and hazard mitigation. The main aim of this study is to propose a low-cost and efficient method based on virtual earth to generate a three-dimensional (3D) DEM. Based on the terrain model, numerical simulations can be conducted and the results integrated with virtual earth to perform 3D visualization and visual analysis. The method proposed in this study may solve some limitations existing in other more traditional methods. For example, historical topographic maps exist mostly in paper format, which is not conducive to spatial analysis, while interpretation of remote-sensing images generally requires professional knowledge at a high cost. The emergence of the virtual earth platform of Google Earth (GE) provides new possibilities for generating terrain models. Terrain information can be extracted efficiently and freely from GE using an application programming interface (API) and then used to generate DEM. In this paper, the Donghekou landslide-debris flow triggered by the 2008 Wenchuan earthquake was selected as a case study. 3D visualization of the temporal-spatial dynamic process of a natural disaster was carried out by combination of the numerical results and GE imaging. The comparison of the study case with field survey data proves the validity of the proposed method as it describes the real terrain shape and determines the slide distance accurately, although the elevation error may be large. The free and easy-to-use method proposed here can provide an intuitive basis for hazard assessment and rapid responses to geological disasters.

A three-dimensional model for flow slides in municipal solid waste landfills using smoothed particle hydrodynamics

Flow slides at municipal solid waste (MSW) landfills can lead to a leak of toxic MSW and leachate over a large area, and result in serious pollution to the environment in the surrounding region. It is therefore important to predict the propagation of failed MSW in the environment, and then take protective measures. In this paper, a three-dimensional (3D) model based on the smoothed particle hydrodynamics method, which is an improved version of the previous two-dimensional (2D) model (Huang et al. in Waste Manag Res 31(3):256–264, 2013), is established to reproduce the propagation stage of the failed MSW across complex terrain. The Navier–Stokes equations and Bingham model are adopted as the governing equations and constitutive model, respectively. A no-slip boundary condition is incorporated to consider the effect of a solid boundary on the MSW movement. The 3D performance of the new model is verified and evaluated through the simulation of a MSW flow model test. The established 3D model and the former 2D model are applied to simulate a typical flow slide that occurred at the Ümraniye-Hekimbasi landfill. The final shape of the waste deposit simulated with the 3D model well matches the field observation; the performance of the new model in simulating flow slides for MSW in three dimensions across complex terrain is highlighted. The presented model can play a role in defining and mapping hazardous areas, and provide a means for the identification and design of appropriate protective measures for landfills with potential flow slides.

Geo-disaster modeling and analysis : an SPH-based approach

Introduction.- SPH Concept and Essential Formulations.- Basic algorithm of SPH simulation.- The program realization of the SPH method in geotechnical engineering.- Verification and validation of the SPH program.- Analysis of flow slides in municipal solid waste landfills based on SPH method.- Flow analysis of liquefied soil based on SPH method.- Run-out analysis of flow-like landslide based on SPH method.- Conclusions and Expectations.

Constitutive flow behavior of a municipal solid waste simulant at post-failure: experimental and numerical investigations

Flow slides are relatively common environmental disasters that occur in municipal solid waste (MSW) landfills and can result in serious consequences in surrounding regions. This study presents experimental and numerical investigations into the constitutive flow behavior of a MSW stimulant at post-failure stage. First, a series of ring shear tests on MSW simulant are conducted under varying shear rates; the residual shear strength is observed to grow linearly as the shear rate increased, which behaves like a kind of viscous fluid. Based on the results, the concept of viscosity coefficient is introduced and a viscous fluid model is established to describe the constitutive behavior of the MSW simulant at post-failure stage. This model is finally incorporated into a smoothed particle hydrodynamics (SPH) code to simulate a flow slide model test. The numerical results agree well with the test data, thus verifying the applicability and reliability of the viscous fluid model to describe flow slide disasters in landfills.

SPH Modeling for Propagation of Flow-like Landslides

The extremely strong Wenchuan earthquake triggered thousands of landslides in Sichuan Province, China. Flow-like landslides, such as the Tangjiashan, Wangjiayan, and Donghekou landslides were among the most destructive, causing many casualties and serious economic damage. In this chapter, a three-dimensional SPH model was introduced and numerical modeling of the propagation of the Tangjiashan, Wangjiayan, and Donghekou landslides was performed. The whole flow processes of these flow-like landslides across the 3D terrain are represented. Time-history curves of the velocity and displacement were obtained to analyze the movement characteristics of the landslide mass. The shapes of the deposition zones after slide occurrence were investigated. The prediction of the fluidization characteristics of earthquake-induced flow-like landslides can notably reduce sudden loss of life, as it provides a means for mapping hazardous areas, for estimating the hazard intensity, and for identification and design of appropriate protective measures.