Model test and numerical simulation on the dynamic stability of the bedding rock slope under frequent microseisms

Shake table testing was performed to investigate the dynamic stability of a mid-dip bedding rock slope under frequent earthquakes. Then, numerical modelling was established to further study the slope dynamic stability under purely microseisms and the influence of five factors, including seismic amplitude, slope height, slope angle, strata inclination and strata thickness, were considered. The experimental results show that the natural frequency of the slope decreases and damping ratio increases as the earthquake loading times increase. The dynamic strength reduction method is adopted for the stability evaluation of the bedding rock slope in numerical simulation, and the slope stability decreases with the increase of seismic amplitude, increase of slope height, reduction of strata thickness and increase of slope angle. The failure mode of a mid-dip bedding rock slope in the shaking table test is integral slipping along the bedding surface with dipping tensile cracks at the slope rear edge going through the bedding surfaces. In the numerical simulation, the long-term stability of a mid-dip bedding slope is worst under frequent microseisms and the slope is at risk of integral sliding instability, whereas the slope rock mass is more broken than shown in the shaking table test. The research results are of practical significance to better understand the formation mechanism of reservoir landslides and prevent future landslide disasters.

Microseismic monitoring and numerical simulation on the stability of high-steep rock slopes in hydropower engineering

For high-steep slopes in hydropower engineering, damage can be induced or accumulated due to a seriesof human or natural activities, including excavation, dam construction, earthquake, rainstorm, rapid riseor drop of water level in the service lifetime of slopes. According to the concept that the progressivedamage （microseismicity） of rock slope is the essence of the precursor of slope instability, a microseismicmonitoring system for high-steep rock slopes is established. Positioning accuracy of the monitoringsystem is tested by fixed-position blasting method. Based on waveform and cluster analyses of microseismicevents recorded during test, the tempo-spatial distribution of microseismic events is analyzed.The deformation zone in the deep rock masses induced by the microseismic events is preliminarilydelimited. Based on the physical information measured by in situ microseismic monitoring, an evaluationmethod for the dynamic stability of rock slopes is proposed and preliminarily implemented bycombining microseismic monitoring and numerical modeling. Based on the rock mass damage modelobtained by back analysis of microseismic information, the rock mass elements within the microseismicdamage zone are automatically searched by finite element program. Then the stiffness and strengthreductions are performed on these damaged elements accordingly. Attempts are made to establish thecorrelation between microseismic event, strength deterioration and slope dynamic instability, so as toquantitatively evaluate the dynamic stability of slope. The case studies about two practical slopes indicatethat the proposed method can reflect the factor of safety of rock slope more objectively. Numericalanalysis can help to understand the characteristics and modes of the monitored microseismic events inrock slopes. Microseismic monitoring data and simulation results can be used to mutually modify thesensitive rock parameters and calibrate the model. Combination of microseismic monitoring and numericalsimulation provides a more objective basis for the numerical model and parameters and a solidmechanical foundation for the microseismic monitoring.

Numerical simulation study of the influence on stability of slope by underground mining under opencast coal mine slope

In view of the study on mining transferred from open-pit to underground, the research on the problem of the stabil- ity of slope is less. This article combined the actual situation of the Gaohai Coal Mine in Fuxin City and set up a three-dimensional model of the part of Huizhou open-pit slope by the finite difference software. Through the three-dimensional numerical simulation study of the influence on the stability of slope by underground mining, the basic characteristics of the open-pit slope deformation and the situation of basic stability were discussed. The simulation results of the mining slope of the displacement and deformation analysis of the state for mining provide a reference to the slope stability research.

Numerical Analysis of the Stability of Embankment Slope Reinforced with Piles

The effects of stabilizing piles on the stability of an embankment slope are analyzed by numerical simulation. The shear strength reduction method is used for the analysis, and the soil - pile interaction is simulated with zero-thickness elasto-plastic interface elements. Effects of pile spacing and pile position on the safety factor of slope and the behavior of piles under these conditions are given. The numerical analysis indicates that the positions of the pile have significant influence on the stability of the slope, and the pile needs to be installed in the middle of the slope for maximum safety factors. In the end, the soil arching effect closely associated with the space between stabilizing piles is analyzed. The results are helpful for design and construction of stabilizing piles.

Analysis of tunnel face stability with advanced pipes support

To keep the tunnel face stable is very important for tunnel construction.In this paper,the tunnel face stability under the advanced pipe was analyzed using the Winkler foundation model and rigid limit equilibrium.The tunnel face deformation characteristics were also analyzed using the numerical simulation.The influence of parameters on the deflection of the pipe roof and the stability of the tunnel face were discussed.The results show that the tunnel face stability can be improved through increasing the pipe diameter,decreasing the initial displacement at the beginning of the pipe seat,and adopting the short round length and small excavation height.With the increase of tunnel burial depth,the safety factor of tunnel face stability first decreases,then increases,and then remains unchanged.The deformation at the center of the tunnel face is larger than the deformation at the surround sides and at the corner.The horizontal displacement varies little with the increasing of the pipe length.The horizontal displacement at the center of the tunnel face increases with the increase of the pipe ring spacing and the pipe longitudinal spacing.There is an optimum external angle.

Influence of blasting load directions on tunnel stability in fractured rock mass

Tunnels in fractured rock masses are typically damaged by dynamic disturbances from various directions.To investigate the influence of blasting load directions on the stability of a tunnel with a precrack nearby,blasting tests were conducted on the physical models of an external crack around a tunnel(ECT)in this study.Failure modes of the tunnels were analysed based on stress wave theory.The Riedel-Hiermaier-Thoma(RHT)material model was employed to perform the numerical simulations on ECT models.Stress distribution around the tunnels and final failure patterns of the tunnels were characterised.The results show that,under blasting loads,the pre-crack propagates and then new cracks initiates on the incident side of the tunnel.These cracks extend towards each other and eventually coalesce.Blasting load directions significantly influence the ultimate failure mode of the tunnel in the fractured rock masses.The new cracks on the shadow side of the tunnel appear at different positions when the blasting stress waves come from various directions.The results are meaningful to the analysis of tunnel stability and optimisation of the tunnel support scheme.

Development of a new type of foam concrete and its application on stability analysis of large-span soft rock tunnel

The long-term stability of large-span soft rock tunnel is influenced greatly by the creep effect of surrounding rock.The development of a new type of foam concrete which has the property of high compressibility and low ductility was introduced.And it was made as filling material of reserved deformation layer between the first lining and the second lining used in large-span soft rock tunnel.The effect of the new type of foam concrete was simulated as filling material of reserved deformation layer using numerical simulation.Through the comparison with the common large-span soft rock tunnel,the vault settlement and surrounding convergence are reduced by about 61% and 45%,respectively,after creep of 100 a.And in the second lining,the plastic zone reduces apparently and the maximum equivalent plastic strain decreases relatively.So,it can be found that the application of the new type of foam concrete as the filling material of reserved deformation layer can relieve the excessive force in second lining induced by rock creep,reduce its deformation and improve the stability of tunnel.

Stability of inner dump slope under coal pillar support:case study in an open‑pit coal mine

The stability of an inner dump slope was investigated under the efect of coal pillar support considering the development position of dumping.Based on the instability mechanism and load distribution characteristics of the supporting coal pillar,the three-dimensional mechanical efects of the supporting coal pillar are characterized.Using the two-dimensional equivalent principle and the residual thrust method,the stability of the inner dump slope was analyzed under the efect of pillar support at diferent dump development positions.The quantitative efects of various factors on the inner dump slope stability were revealed,and the coal pillar shape parameters were optimized through numerical simulations.The results indicate that the slope stability coefcient is linearly related to the top width and height of the coal pillar,slope angle,and base inclination angle,and has an exponential relation with the coal pillar strike length and slope height increment.There are quadratic and absolute value relations with the coal pillar outer and the inner bottom angle,respectively.The top width of the coal pillar in the inner dump of Shengli East No.2 open-pit coal mine should be at a level of+824 m,and the optimal top width and height are 15 and 36.7 m,respectively.The instability mechanism of the supporting and retaining coal pillar obtained by numerical simulations and the stability of the inner dump are in good agreement with the theoretical analysis.Our results provide a theoretical basis for the design,treatment,and safe implementation of similar open-pit mine slope engineering.

Stability analysis of cohesive soil embankment slope based on discrete element method

In order to study the safety factor and instability process of cohesive soil slope, the discrete element method(DEM) was applied. DEM software PFC2 D was used to simulate the triaxial test to study the influence of the particle micro parameters on the macroscopic characteristics of cohesive soil and calibrate the micro parameters of DEM model on this basis. Embankment slope stability analysis was carried out by strength reduction and gravity increase method, it is shown that the safety factor obtained by strength reduction method is more conservative, and the arc-shaped feature of the sliding surface under the gravity increase method is more obvious. Throughout the progressive failure process, the failure trends, maximum displacements, and velocity changes obtained by the two methods were consistent. When slope was destroyed, the upper part was cracked, the middle part was sheared, and the lower part was destroyed by extrusion. The conclusions of this paper can be applied to the safety factor calculation of cohesive soil slopes and the analysis of the instability process.

Stability analysis of open-pit gold mine slopes and optimization of mining scheme in Inner Mongolia,China

The geological structure of the Changshanhao open-pit mine in Urad Middle Banner,Inner Mongolia,China is extremely complicated,and slope instability has frequently occurred in various forms,such as wedge sliding,bedding sliding,and toppling failure.In order to study the failure mechanisms of these slopes,the geological structure and mechanical rock properties were investigated based on field investigations and laboratory tests.Numerical models for the present mining area and final mining area of the original scheme were established to analyze slope stability.The results showed that the unique geomorphological characteristics of the mining area were generated by geological tectonism,and the north side of the stope is an anti-dip layered rock slope and the south side is a dip layered rock slope.Slope failure is the consequence of endogenic and exogenic integration,including physical and mechanical properties of the rock mass,geological structures such as faults and joints,and human-caused factors such as blasting and excavation disturbances.Then the original excavation scheme was redesigned mainly by optimizing the slope angle and decreasing the final mining depth to maintain slope stability.Finally,the Monte Carlo method was used to analyze the reliability of the slope angle optimization scheme.The open-pit mine excavation plan that meets the stability requirements was obtained eventually.

Stability analysis of complex terrain slope based on multi-source point cloud fusion

Numerical modelling is a common routine for slope stability analysis in the complex terrain,and the accuracy of topographic survey has a great impact on the results.In this study,a combination of unmanned aerial vehicle(UAV)photogrammetry and 3D laser scanning technique was first proposed to establish a high-precision digital elevation model(DEM),which could be accurate to 0.2 m,fulfilling the engineering requirements.Then,a series of 3D/2D finite element models(FEM)were constituted on the basis of DEM to investigate the slope stability in the complex terrain.The results indicate that the deformation of complex terrain slope is chiefly triggered by compression-shear failure and the failure zones are mostly distributed on the middle-upper part and the scarp.Furthermore,the complex terrain slope is divided into concave,convex,concave-convex and convex-concave slope according to the topographical curvature,and the factor of safety(FOS)is as follows:the maximum value 1.8504 for the concave-convex slope,the minimum value 1.1129 for the convexconcave slope,and the median for either concave or convex slope.The inflection points and curvature of the slope jointly determine the shape of nonlinear slope,dominating the morphological effect on the slope stability,so the rational use of section morphological effect will be conducive to the overall stability of the slope.For four representative slopes,the plastic deformation first emerges into the middle,then progressively develops to the upper,and finally forms the connected failure zones.

Stability analysis of slope in strain-softening soils using local arc-length solution scheme

Soils with strain-softening behavior — manifesting as a reduction of strength with increasing plastic strain — are commonly found in the natural environment. For slopes in these soils,a progressive failure mechanism can occur due to a reduction of strength with increasing strain. Finite element method based numerical approaches have been widely performed for simulating such failure mechanism,owning to their ability for tracing the formation and development of the localized shear strain. However,the reliability of the currently used approaches are often affected by poor convergence or significant mesh-dependency,and their applicability is limited by the use of complicated soil models. This paper aims to overcome these limitations by developing a finite element approach using a local arc-length controlled iterative algorithm as the solution strategy. In the proposed finite element approach,the soils are simulated with an elastoplastic constitutive model in conjunction with the Mohr-Coulomb yield function. The strain-softening behavior is represented by a piece-wise linearrelationship between the Mohr-Coulomb strength parameters and the deviatoric plastic strain. To assess the reliability of the proposed finite element approach,comparisons of the numerical solutions obtained by different finite element methods and meshes with various qualities are presented. Moreover,a landslide triggered by excavation in a real expressway construction project is analyzed by the presented finite element approach to demonstrate its applicability for practical engineering problems.

On the Stability of Carbon Shale Slope under Rainfall Infiltration

Carbonaceous shale is a sedimentary rock containing a large amount of dispersed carbonaceous organic material.It is easy to crack and soften when exposed to water.In the present work,the stability of such a rock and its sensitivity to the formation of infiltrations due to rainfall are analyzed numerically using the GeoStudio software.The slope stability coefficient is calculated and verified using the landslide thrust calculation method.The results show that under the action of heavy rainfall,water infiltrates into the slope layer by layer,and,accordingly,the soil volume water content is different with respect to that typical of a homogeneous soil.It is also shown that,although in an initial stage,rainfall infiltration leads to the decline of the slope stability coefficient,with the progress of rainfall,this coefficient can temporarily increase,that is,these phenomena can display a lag phase.

Stability Analysis of Large Section Rocky Tunnel Support Structure

In order to study the stress characteristics of the initial support and secondary lining of the large section tunnel and to solve the problem of secondary lining cracking during operation. Taking the large section tunnel in Zihong village, Qi County as the research object, a numerical simulation method was used to establish a finite element model of the large section tunnel. So as to simulate and analyze the stress characteristics of the support structure of this tunnel. Through the simulation of the initial support and second lining of this large section tunnel in terms of displacement, stress, plastic zone damage and anchor shaft force, the results show that as the excavation progresses, the stress and displacement on the surface of the newly excavated tunnel profile is faster, especially at the side walls and arch footings, the stress and displacement values are slightly larger than other characteristic points, but the final values are stable and converge, and are basically consistent with the field monitoring results, which indicates that this support system is basically in stable state. Therefore, during the tunnel excavation and support process, special attention should be paid to the stability of the sidewalls and footings, and the results of this study will be of great practical significance for tunnel construction and maintenance.

Rock-soil slope stability analysis by two-phase random media and finite elements

To investigate the strong random nature of the geometric interfaces between soil and rock, a rock-soil slope is considered as a two-phase random medium. A nonlinear translation of a Gaussian field is utilized to simulate the two-phase random media, such that the soil(or rock) volume fraction and the inclination of the soil layer can be examined. The finite element method with random media incorporated as the material properties is used to determine the factor of safety of the rock-soil slope. Monte-Carlo simulations are used to estimate the statistical characteristics of the factor of safety. The failure mode of the rock-soil slope is examined by observing the maximum principal plastic strain at incipient slope failure. It is found that the critical surface of a rock-soil slope is fairly irregular, and it significantly differs from that of a pure soil slope. The factor of safety is sensitive to the soil volume faction, but it is predictable. The average factor of safety could be well predicted by the weighted harmonic average between the strength of soil and rock; the prediction model is practical and simple. Parametric studies on the inclination of the soil layer demonstrate that the most instable scenario occurs when the slope angle is consistent with the inclination of the soil layer.

Development of a preliminary slope stability calculation method based on internal horizontal displacements

This paper proposes a horizontal displacement-based approach to determine the potential slip surface of the slope. Firstly, a group of in-situ inclinometers with an appropriate spacing in the horizontal direction is located in the model slope.The equation of horizontal displacement with time for each in-situ inclinometer is fitted during the whole simulation process. Furthermore, the intersection of each inclinometer with potential slip surface is determined by using an optimization model. The slip surface can be obtained by using least square fitting method. Finally, the feasibility and accuracy of the method are validated by a series of numerical simulations. It is noted that the optimization model taking the maximum value of displacement increment gradient as an objective has higher accuracy when compared with other optimization models. This method employed in this study provides a preliminary approach to determine the real-time slope stability based on displacement, which can also be measured by using conventional instruments on site.

Model test and discrete element method simulation of shield tunneling face stability in transparent clay

The stability of the shield tunneling face is an extremely important factor affecting the safety of tunnel construction.In this study,a transparent clay with properties similar to those of Tianjin clay is prepared and a new transparent clay model test apparatus is developed to overcome the“black box”problem in the traditional model test.The stability of the shield tunneling face(failure mode,influence range,support force,and surface settlement)is investigated in transparent clay under active failure.A series of transparent clay model tests is performed to investigate the active failure mode,influence range,and support force of the shield tunneling face under different burial depth conditions,whereas particle flow code three-dimensional numerical simulations are conducted to verify the failure mode of the shield tunneling face and surface settlement along the transverse section under different burial depth conditions.The results show that the engineering characteristics of transparent clay are similar to those of soft clay in Binhai,Tianjin and satisfy visibility requirements.Two types of failure modes are obtained:the overall failure mode(cover/diameter:C/D£1.0)and local failure mode(C/D≥2.0).The influence range of the transverse section is wider than that of the longitudinal section when C/D≥2.0.Additionally,the normalized thresholds of the relative displacement and support force ratio are 3%-6%and 0.2-0.4,respectively.Owing to the cushioning effect of the clay layer,the surface settlement is significantly reduced as the tunnel burial depth increases.

Impact of parameter fluctuations on RF stability performance of DG tunnel FET

This paper presents the impact of parameter fluctuation due to process variation on radio frequency （RF） stability performance of double gate tunnel FET （DG TFET）. The influence of parameter fluctuation due to process variation leads to DG TFET performance degradation. The RF figures of merit （FoM） such as cut-off frequency （ft）, maximum oscillation frequency （fmax） along with stability factor for different silicon body thickness, gate oxide thickness and gate contact alignment are obtained from extracted device parameters through numerical simulation. The impact of parameter fluctuation of silicon body thickness, gate oxide thickness and gate contact alignment was found significant and the result provides design guidelines ofDG TFET for RF applications.

Forming condition of transient saturated zone and its distribution in residual slope under rainfall conditions

Rainfall, as one of the most significant factors triggering the residual soil slope failure, leads to not only the reduction of soil shear strength, but also the increase of soil weight and the decrease of matric suction as well. All these modifications in soil properties have important influence on the slope stability. The water infiltration and redistribution inside the slope are the preconditions of the slope stability under rainfall conditions. Based on the numerical simulation via finite element method, the water infiltration process under rainfall conditions was studied in the present work. The emphases are the formation, distribution and dissipation of transient saturated zone. As for the calculation parameters, the SWCC and the saturated permeability have been determined by pressure plate test and variable head test respectively. The entire process(formation, development, dissipation) of the transient saturated zone was studied in detail. The variations of volumetric water content, matric suction and hydraulic gradient inside the slope, and the eventually raise of groundwater table were characterized and discussed, too. The results show that the major cause of the formation of transient saturated zone is ascribed to the fact that the exudation velocity of rainwater on the wetting front is less than the infiltration velocity of rainfall; as a result, the water content of the soil increases. On the other hand, the formation and extension of transient saturated zone have a close relationship with rainfall intensity and duration. The results can help the geotechnical engineers for the deeper understanding of the failure of residual slope under rainfall condition. It is also suggested that the proper drainage system in the slope may be the cost-effective slope failure mitigation method.

Interaction between anti-shear galleries and surrounding rock in the right-bank slope of Dagangshan hydropower station

The fight-bank slope of the Dagangshan hydropower station located in Southwest China is a highly unloaded rock slope. Moreover, large-scale natural faults were detected in the slope body; some excavation-induced unloading fractures were discovered at elevations between lo75m and 1146m. Because of poor tectonic stability, the excavation work was suspended in September 2009, and six large- scale anti-shear galleries were employed to replace the weak zone in the slope body to reinforce the fight- bank slope. In this study, based on microseismic- monitoring technology and a numerical-simulation method, the stabilities of the slope with and without the reinforcement are analysed. An in-situ microseismic-monitofing system is used to obtain quantitative information about the damage location, extent, energy, and magnitude of the rocks. Thus, any potential sliding block in the fight-bank slope can be identified. By incorporating the numerical results along with the microseismic-monitoring data, the stress concentration is found to largely occur aroundthe anti-shear galleries, and the seismic deformation near the anti-shear galleries is apparent, particularly at elevations of 121o, 118o, 115o, and 112om. To understand the interaction mechanism between the anti-shear gallery and the surrounding rock, a 2D simulation of the potential damage process occurring in an anti-shear gallery is performed. The numerical simulation helps in obtaining additional information about the stress distribution and failure-induced stress re-distribution in the vicinity of the anti-shear galleries that cannot be directly observed in the field. Finally, the potential sliding surface of the right-bank slope is numerically obtained, which generally agrees with the spatial distribution of the in-situ monitored microseismic events. The safety factor of the slope reinforced with the anti-shear gallery increases by approximately 36.2%. Both the numerical results and microseismic data show that the anti-shear galleries have a good reinforcement effect.