Xinpo Li

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.

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.

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.

Effects of segregation in binary granular mixture avalanches down inclined chutes impinging on defending structures

This study investigates the segregation processes and impact response of binary granular mixtures with identical densities but different sizes particles subjected to gravity. Deposition was compared using discrete element method (DEM) numerical experiment and laboratory experiment to determine the material parameters in the particle flow code in three dimensions (PFC3D). With proper material parameters, many numerical experiments were performed on an idealized binary granular mixture avalanche to reveal its kinetic properties, with a particular focus on the results of the final run-out distance, fluid velocity, and impact force exerted on defending structures. The simulation results show that the energy dissipation in granular avalanches is higher with uniform particle sizes than with mixed particle sizes, indicating lesser energy dissipation in segregation processes. Coarse particles also play an important role in determining the kinetic properties of binary granular mixture avalanches; specifically, they obviously affect the maximum impact force when the storage area length is small. On the other hand, fine particles play an important role when the storage area length is large. These results suggest that the effects of coarse particles in granular avalanches containing more than one particle size may be at least as important.

A finite volume method for two-phase debris flow simulation that accounts for the pore-fluid pressure evolution

The temporal and spatial evolution of pore-fluid pressure exerts strong control on debris flow motion because it can counteract normal stresses at grain contacts, reduce friction, and enhance bulk flow mobility. In Iverson’s two-phase debris flow model, the depth-averaged pore pressure equation, which takes into account the effect of shear-induced dilatancy, was combined with a previous model to describe the simultaneous evolution of flow velocity and depth, solid mass, and pore-fluid pressure. In this work, a high-resolution scheme based on the finite volume method was used to solve the system of equations. Several numerical tests were performed to verify the ability of the presented model and the accuracy of the proposed numerical method. Numerical results were compared with experimental data obtained in a laboratory, and the effectiveness of the proposed numerical method for solving practical problems has been proven. Numerical results indicated that increases of the pore-fluid pressure could enhance the motion of debris flow and expand the spread area. Furthermore, results showed that the debris shear-induced dilatancy could affect the evolution of pore-fluid pressure, thus further influencing the motion of debris flow.

Assessment of prospective hazards resulting from the 2017 earthquake at the world heritage site Jiuzhaigou Valley, Sichuan, China

On August 8, 2017, a Ms = 7.0 magnitude earthquake occurred in the Jiuzhaigou Valley, in Sichuan Province, China (N: 33.20°, E: 103.82°). Jiuzhaigou Valley is an area recognized and listed as a world heritage site by UNESCO in 1992. Data analysis and field survey were conducted on the landslide, collapse, and debris flow gully, to assess the coseismic geological hazards generated by the earthquake using an unmanned aerial vehicle (UAV), remote-sensing imaging, laser range finders, geological radars, and cameras. The results highlighted the occurrence of 13 landslides, 70 collapses, and 25 potential debris flow gullies following the earthquake. The hazards were classified on the basis of their size and the potential property loss attributable to them. Consequently, 14 large-scale hazards, 30 medium-sized hazards, and 64 small hazards accounting for 13%, 28%, and 59% of the total hazards, respectively, were identified. Based on the variation tendency of the geological hazards that ensued in areas affected by the Kanto earthquake (Japan), Chi-chi earthquake (Taiwan China), and Wenchuan earthquake (Sichuan China), the study predicts that, depending on the rain intensity cycle, the duration of geological hazard activities in the Jiuzhaigou Valley may last over ten years and will gradually decrease for the following five to ten years before returning to pre-earthquake levels. Thus, necessary monitoring and early warning systems must be implemented to ensure the safety of residents, workers and tourists during the construction of engineering projects and reopening of scenic sites to the public.

Seismic Stability of Gravity Retaining Walls Under Combined Horizontal and Vertical Accelerations

The seismic sliding limit condition of gravity retaining walls with cohesionless soil backfill is investigated and analytical solutions for the critical acceleration coefficient are provided in this paper. The solutions have been derived in the framework of the upper bound theorem of limit analysis. The retaining walls and the backfill soil are taken as a whole system and the combined action of horizontal and vertical accelerations are considered. For retaining walls with horizontal backfill, the effects of the inclination of the wall internal face and of the soil–wall friction were investigated. The effects of vertical component of the seismic acceleration on the yield horizontal acceleration coefficient were discussed in detailed. Based on a limited parametric study, it is shown that both the roughness and inclination of the internal wall face have some effects to the seismic stability of the wall–soil system. And under some conditions, the effects of vertical acceleration are considerable large and can’t be neglected.

A physical model considered the effect of overland water flow on rainfall-induced shallow landslides

BackgroundIt is well know that many shallow landslides are triggered by rainfalls. In previous studies of shallow landslide models, the effect of overland water flow on slope stability was ignored.ResultsIn this paper, a physical model considered the effect of overland water flow on rainfall-induced shallow landslides is derived and applied to predict the landslides. The slope stability model is developed by considering the depth of overland water flow in infinite slope stability theory. Hillslope hydrology is modelled by coupling the overland uniform water flow equation with Rosso’s seepage flow equation. And then, the model is used to assess the slope stability in Dujiangyan of China, and the results is compare with Rosso’s model.ConclusionsThis model is simple, but has the capability of taking into account the effect of overland water flow in the triggering mechanism of shallow landslide. The results of case study show that the overland water flow can make an obvious effect on shallow landslides, so it is quite important to consider the overland water flow in shallow landslide hazard assessment.

Numerical simulation of landslide over erodible surface

BackgroundEstimating the magnitude and intensity of landslides is a fundamental requirement in quantitatively evaluating the risks involved, and preparing a mitigation strategy. Though the physics-based dynamic model of landslide can predict the travel distance, kinematic velocity, and hazard zone, the effects of erosion and the excess pore water pressure during the dynamic process of landslide are often ignored.ResultsIn order to study these factors, a physics-based dynamic model of landslide considering erosion and excess pore water pressure is presented in this paper. A high-precision numerical method based on the finite volume method is proposed to solve the model equations. Several numerical tests are performed to verify the numerical method and the model. The effects of erosion and excess pore water pressure on the dynamic process of landslide are also analyzed.ConclusionsThe numerical results indicate that the scale and mobility of a landslide are influenced by the effect of erosion and excess pore water pressure. The excess pore water pressure can reduce the resistance to shear stress from the erodible bed and lead to a higher erosion amount and longer moving distance of the landslide. It also affects the degree of erosion and further affects the dynamic process of the landslide. The sensitivity analysis of the parameters that influence excess pore water pressure indicate that these parameters have a significant impact on the evolution of excess pore water pressure, and that the degree of saturation of bed sediment has the highest influence on excess pore water pressure.