scholarly journals Coupled Hydro-Mechanical Analysis of Rainfall-Induced Instability of Non-Uniform Soil Slopes

2021 ◽  
Author(s):  
Manyu Wang ◽  
Yong Liu ◽  
Lu Yang ◽  
Jing Wu ◽  
Guilin Niu
Keyword(s):  
Hydraulic Conductivity ◽  
Flow Rate ◽  
Large Scale ◽  
Slope Failure ◽  
Water Pressure ◽  
Mechanical Analysis ◽  
Soil Slope ◽  
Arithmetic Average ◽  
Average Value ◽  
Soil Slopes

In recent years, more considerable attentions are paying on the hazards of large-scale landslides induced by heavy rainfall. However, the heterogeneity in hydraulic properties of soils may affect the seepage pattern of water infiltrated into soil slopes. Inspired by this fact, this paper aimed to evaluate the effect of the spatial variability in hydraulic conductivity on failure mechanism of an unsaturated soil slope subjected to rainfall infiltration, being implemented in the framework of a transient coupled hydro-mechanical analysis. The concept of random field was adopted to model the spatial randomness of saturated hydraulic conductivity ks following a uniform distribution. The finite element method was then incorporated to conduct Monte Carlo simulations. The resultant findings show that the mode of shallow slope failure is more likely to occur than the deep one due mainly to the highly variable distribution of ks near slope surface. Note that the decrease in the effective stress of soils resulting from the increase of pore water pressure is the most critical reason for the occurrence of slope failure. In addition, from the random element analyses results, it indicates that the value of Qari calculated by performing a deterministic analysis based on arithmetic average value kari gives a prediction of flow rate on average, but the calculated Qmax based on maximum value kmax provides a more conservative assessment on total flow rate across soil slope, which can offer useful suggestions for practitioners to take available measures to drain in advance.

scholarly journals Numerical Analysis of the Effects of Crack Characteristics on the Stress and Deformation of Unsaturated Soil Slopes

Water ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 194 ◽  
Author(s):  
Liuxin Yang ◽  
Enlong Liu
Keyword(s):  
Pore Water ◽  
Unsaturated Soil ◽  
Crack Width ◽  
Evaporation Rate ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Infiltration Rate ◽  
Soil Slope ◽  
Soil Slopes ◽  
Stress And Deformation

Cracks induced by evaporation or rainfall have a great influence on the stability of unsaturated soil slopes, which can lead to landslides during the rainfall process. In order to study the effect of crack characteristics on the evolution of stress and deformation of unsaturated soil slopes, a series of numerical analyses under different conditions were performed using a coupled elastoplastic finite element program that we developed for unsaturated soil. When carrying out the numerical analyses, the effective stress for unsaturated soil proposed by Bishop and an elastoplastic double-hardening constitutive model for the soil skeleton were employed. The varying parameters, including the crack location, the discharge speed, evaporation rate, infiltration rate, and tensile strength, were investigated to study the coupling process of pore water pressure and deformation in the process of evaporation and rainfall infiltration. The numerical results showed that the minimum pore water pressure of the soil slope at the end of evaporation/rainfall decreased gradually and the crack width increased gradually as the crack set closer to the slope; the larger the discharge speed of pore air, the greater the crack width. With the increase in the evaporation rate, the pore water pressure of the soil slope reduced and the crack initiated earlier and became wider. As the infiltration rate increased, the pore water pressure of the soil slope and the crack width increased, but the decreasing duration became shorter. The change of tensile strength had little effect on the pore water pressure, but the development of the crack width changed with evaporation and rainfall infiltration.

scholarly journals Influence of Rainfall Intensity on the Stability of Unsaturated Soil Slope: Case Study of R523 Road in Thulamela Municipality, Limpopo Province, South Africa

2020 ◽  
Vol 10 (24) ◽  
pp. 8824
Author(s):  
Fhatuwani Sengani ◽  
François Mulenga
Keyword(s):  
Slope Failure ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Extreme Rainfall ◽  
Limpopo Province ◽  
Slope Instability ◽  
Soil Slope ◽  
Numerical Software ◽  
The Impact

The purpose of this paper was to analyze the impact of extreme rainfall on the recurrence of slope instability using the Thulamela Municipality roads (R523) as a case study. To this end, the historical rainfall data of the area of study were analyzed between 1988 and 2018. The results show that a significant increase in rainfall is usually experienced in the summer months of December and January. Following this, the factor of safety (FoS) of slopes of silt clay, clay, and clay loam soils were estimated using the SLIDE simulator (Numerical software “Finite Element Method (FEM)”) under sunny to rainy conditions of the area. A complementary model, FLACSlope (Numerical software “Finite Difference Method (FDM)”), was utilized to simulate FoS and pore water pressure in sunny and rainy conditions of the area. Simulation results show that extreme rainfall has the ability to reduce the shear strength and resistance of the soil slope material. This may explain the recurrent landslides noted in the area. Finally, the water pore pressure has been simulated to increase with the increased water table, which generally pushes the soil particles apart and reduces the stress between the particles resulting in soil slope failure. Extreme rainfall alters the phase of the material solid in a manner that may require further research for a better understanding.

scholarly journals Investigation of the Role of Crown Crack in Cohesive Soil Slope and Its Effect on Slope Stability Based on Extended Finite Element Method

2021 ◽  
Author(s):  
Yiding Bao ◽  
Yuchao Li ◽  
Yansong Zhang ◽  
Jianhua Yan ◽  
Xin Zhou
Keyword(s):  
Slope Stability ◽  
Extended Finite Element Method ◽  
Slope Failure ◽  
Slip Surface ◽  
Natural Soil ◽  
Tension Zone ◽  
Soil Slope ◽  
Extended Finite Element ◽  
Soil Slopes

Abstract Tensile cracks in soil slopes, especially developing at the crown, have been increasingly recognized as the signal of slope metastability. In this paper, the role of crown cracks in natural soil slopes was investigated and their effect on stability was studied. A numerical slope model based on the extended finite element method (XFEM) simulating the tensile behavior of soil was used. Before the simulation, a numerical soil tensile test was applied to validate the use of XFEM on tensile behavior of soil. Slope failure was simulated by using strength reduction technique, which can determine the potential slip surface of slope. The simulation results show that the crown crack forms in natural soil slopes when the plastic zone starts penetrating, and therefore it is reasonable to consider the crown crack as the signal of slope metastability. A sensitivity analysis shows that cracks are at the position of the tension zone or very long can obviously affect the slope stability. The stress variation analysis from the initial deformation to slip surface penetration shows that the slope is at a state of compressive stress initially. When plastic zone starts to penetrate, the upper part of slope generates tension zone, but the extent of tension zone is limited until slope failure. This shows why tensile cracks are difficult to form and be stretched in the deep part of the slope. The application of XFEM on slope stability analysis can be used to assess the tensile strength of soil and predict slope failure disaster.

scholarly journals Examples of numerical simulations of two-dimensional unsaturated flow with VS2DI code using different interblock conductivity averaging schemes

Geologos ◽  
2015 ◽  
Vol 21 (3) ◽  
pp. 161-167 ◽  
Author(s):  
Adam Szymkiewicz ◽  
Witold Tisler ◽  
Kazimierz Burzyński
Keyword(s):  
Hydraulic Conductivity ◽  
Unsaturated Flow ◽  
Water Pressure ◽  
Geometric Mean ◽  
Pressure Head ◽  
Richards Equation ◽  
Test Problems ◽  
Simulation Code ◽  
Arithmetic Average ◽  
The Difference

AbstractFlow in unsaturated porous media is commonly described by the Richards equation. This equation is strongly nonlinear due to interrelationships between water pressure head (negative in unsaturated conditions), water content and hydraulic conductivity. The accuracy of numerical solution of the Richards equation often depends on the method used to estimate average hydraulic conductivity between neighbouring nodes or cells of the numerical grid. The present paper discusses application of the computer simulation code VS2DI to three test problems concerning infiltration into an initially dry medium, using various methods for inter-cell conductivity calculation (arithmetic mean, geometric mean and upstream weighting). It is shown that the influence of the averaging method can be very large for coarse grid, but that it diminishes as cell size decreases. Overall, the arithmetic average produced the most reliable results for coarse grids. Moreover, the difference between results obtained with various methods is a convenient indicator of the adequacy of grid refinement.

Instability caused by a seepage impediment in layered fill slopes

2008 ◽  
Vol 45 (10) ◽  
pp. 1410-1425 ◽  
Author(s):  
Y. S. Lee ◽  
C. Y. Cheuk ◽  
M. D. Bolton
Keyword(s):  
Hydraulic Conductivity ◽  
Groundwater Flow ◽  
Slope Failure ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Friction Angle ◽  
Excess Pore Pressure ◽  
Order Of Magnitude ◽  
Numerical Parametric Study ◽  
Fill Slope

The underlying cause of loose fill slope failures in Hong Kong has been attributed to static liquefaction during heavy rainfall. A series of centrifuge model tests and numerical analyses were conducted to illustrate that instability of a fill slope inclined at approximately the internal friction angle of the soil can be triggered by confined groundwater flow due to soil layering in the fill slope. The results also showed that slope failure could occur irrespective of the density of the fill material when seepage was sufficiently impeded leading to a localised buildup of pore-water pressure in the slope. A numerical parametric study was carried out to examine the effect of variations in hydraulic conductivity in the layered fill slopes. The results showed that the excess pore pressure distribution and hence the failure mode were strongly dependent on the location of the inhomogeneous soil layers and their hydraulic properties. It was also demonstrated that layered fill slopes with spatial variation in hydraulic conductivity of as small as one order of magnitude were vulnerable to global failure under confined groundwater flow.

Artificial Rainfall Failure Experiments for a Red Clay Slope

2014 ◽  
Vol 638-640 ◽  
pp. 402-406
Author(s):  
Kai Sheng Chen
Keyword(s):  
Slope Failure ◽  
Water Pressure ◽  
Reference Value ◽  
Soil Slope ◽  
Red Clay ◽  
Artificial Rainfall ◽  
Water Conservancy ◽  
Major Factors ◽  
Slope Displacement ◽  
Fundamental Mechanism

The influence of rainfall on slope stability problem that highway, railway,water conservancy and energy engineering production must consider and study, the rainfall is one of the major factors causing the soil slope failure。Establishing model test of red clay slope, rainfalling the model, the paper analyzing the moist frontal edge, power water pressure, slope displacement under the rainfall. The result has some reference value for fundamental mechanism of rainfall infiltration induced landslides in a red clay slope.

scholarly journals Suggestion of Measurement Management Criteria for Soil Slope Failure Based on Displacement

2021 ◽  
Vol 21 (1) ◽  
pp. 251-260
Author(s):  
Sun-Gyu Choi ◽  
Jae-Wook Suk ◽  
Hyang-Seon Jeong
Keyword(s):  
Literature Review ◽  
Field Data ◽  
Large Scale ◽  
Slope Failure ◽  
Small Scale ◽  
Soil Slope ◽  
Short Term ◽  
Literature Reviews ◽  
Under Construction

This paper describes the Measurement Management Criteria (MMC) of a soil slope failure based on displacement using literature reviews, small-scale experiments, large-scale experiments, and field data. Two types of measurement management criteria were developed, i.e., short-term criteria for slopes under construction or requiring urgent measurements, and long-term criteria for slopes under continuous management. First, the measurement criteria for the short term were determined based on small- and-large scale experiments, and were determined to be “1 mm/min for the watch level,” “4 mm/min for the caution level,” and “21 mm/min for the alert level.” Next, the criteria for the long term were determined through a literature review and field data, and were “2 mm/day for the watch level,” “8 mm/day for the caution level,” and “56 mm/day for the alert level”.

scholarly journals An 84-μG Magnetic Field in a Galaxy at Z=0.692?

2008 ◽  
Vol 4 (S254) ◽  
pp. 95-96
Author(s):  
Arthur M. Wolfe ◽  
Regina A. Jorgenson ◽  
Timothy Robishaw ◽  
Carl Heiles ◽  
Jason X. Prochaska
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Faraday Rotation ◽  
Large Scale ◽  
Dynamo Model ◽  
Magnetic Field Generation ◽  
Interstellar Gas ◽  
Splitting Technique ◽  
Average Value ◽  
The Magnetic Field

AbstractThe magnetic field pervading our Galaxy is a crucial constituent of the interstellar medium: it mediates the dynamics of interstellar clouds, the energy density of cosmic rays, and the formation of stars (Beck 2005). The field associated with ionized interstellar gas has been determined through observations of pulsars in our Galaxy. Radio-frequency measurements of pulse dispersion and the rotation of the plane of linear polarization, i.e., Faraday rotation, yield an average value B ≈ 3 μG (Han et al. 2006). The possible detection of Faraday rotation of linearly polarized photons emitted by high-redshift quasars (Kronberg et al. 2008) suggests similar magnetic fields are present in foreground galaxies with redshifts z > 1. As Faraday rotation alone, however, determines neither the magnitude nor the redshift of the magnetic field, the strength of galactic magnetic fields at redshifts z > 0 remains uncertain.Here we report a measurement of a magnetic field of B ≈ 84 μG in a galaxy at z =0.692, using the same Zeeman-splitting technique that revealed an average value of B = 6 μG in the neutral interstellar gas of our Galaxy (Heiles et al. 2004). This is unexpected, as the leading theory of magnetic field generation, the mean-field dynamo model, predicts large-scale magnetic fields to be weaker in the past, rather than stronger (Parker 1970).The full text of this paper was published in Nature (Wolfe et al. 2008).

scholarly journals The Hydromechanical Interplay in the Simplified Three-Dimensional Limit Equilibrium Analyses of Unsaturated Slope Stability

Geosciences ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 73
Author(s):  
Panagiotis Sitarenios ◽  
Francesca Casini
Keyword(s):  
Analytical Solution ◽  
Slope Stability ◽  
Slope Failure ◽  
Failure Modes ◽  
Pore Water Pressure ◽  
Limit Equilibrium ◽  
Water Pressure ◽  
Three Dimensional ◽  
Stability Limit ◽  
Smooth Transition

This paper presents a three-dimensional slope stability limit equilibrium solution for translational planar failure modes. The proposed solution uses Bishop’s average skeleton stress combined with the Mohr–Coulomb failure criterion to describe soil strength evolution under unsaturated conditions while its formulation ensures a natural and smooth transition from the unsaturated to the saturated regime and vice versa. The proposed analytical solution is evaluated by comparing its predictions with the results of the Ruedlingen slope failure experiment. The comparison suggests that, despite its relative simplicity, the analytical solution can capture the experimentally observed behaviour well and highlights the importance of considering lateral resistance together with a realistic interplay between mechanical parameters (cohesion) and hydraulic (pore water pressure) conditions.

scholarly journals Analysis of Seepage Characteristics of a Foundation Pit with Horizontal Waterproof Curtain in Highly Permeable Strata

Water ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1303
Author(s):  
Chenghua Shi ◽  
Xiaohe Sun ◽  
Shengli Liu ◽  
Chengyong Cao ◽  
Linghui Liu ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Theoretical Calculation ◽  
Calculation Method ◽  
Design Method ◽  
Water Pressure ◽  
Water Inflow ◽  
Deep Foundation ◽  
Foundation Pit ◽  
Deep Foundation Pit ◽  
Seepage Characteristics

At present, jet-grouted horizontal waterproof curtain reinforcement has become an essential method for deep foundation pit groundwater control. However, there is still a lack of an effective theoretical calculation method for horizontal waterproof curtain reinforcement, and there is little research on the seepage laws of foundation pits under different horizontal waterproof curtain conditions. Based on Darcy’s seepage theory, theoretical analysis models of deep foundation pit seepage were established considering the effect of a horizontal curtain in a highly permeable formation. Through the established models, the calculation method of the water inflow and the water pressure under the condition of a horizontal curtain was derived. Then through indoor tests, the reliability of the theoretical calculation method was verified. Furthermore, the established theoretical calculation method is used to analyze the influence of various factors on the water inflow and the water pressure, such as the ratio of hydraulic conductivity of the horizontal curtain to surrounding soil, thickness, and reinforcement position of the horizontal curtain. It is found that the hydraulic conductivity ratio has the most significant influence on the seepage characteristics of the foundation pit. Finally, the design method was applied to an example of the horizontal waterproof curtain of the foundation pit, which is located at Juyuanzhou Station in Fuzhou (China). The water inflow per unit area is 0.36 m3/d in the foundation pit, and this implies that the design method of the horizontal waterproof curtain applied for the excavation case is good and meets the requirements of design and safety.

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