An approach for determination of lateral limit angle in kinematic planar sliding analysis for rock slopes

Planar sliding is one of the frequently observed types of failure in rock slopes.Kinematic analysis is a classic and widely used method to examine the potential failure modes in rock masses.The accuracy of planar sliding kinematic analysis is significantly influenced by the value assigned to the lateral limit angleγlim.However,the assignment ofγlim is currently used generally based on an empirical criterion.This study aims to propose an approach for determining the value ofγlim in deterministic and probabilistic kinematic planar sliding analysis.A new perspective is presented to reveal thatγlim essentially influences the probability of forming a potential planar sliding block.The procedure to calculate this probability is introduced using the block theory method.It is found that the probability is correlated with the number of discontinuity sets presented in rock masses.Thus,different values ofγlim for rock masses with different sets of discontinuities are recommended in both probabilistic and deterministic planar sliding kinematic analyses;whereas a fixed value ofγlim is commonly assigned to different types of rock masses in traditional method.Finally,an engineering case was used to compare the proposed and traditional kinematic analysis methods.The error rates of the traditional method vary from 45%to 119%,while that of the proposed method ranges between 1%and 17%.Therefore,it is likely that the proposed method is superior to the traditional one.

Effect of slope angle on fractured rock masses under combined influence of variable rainfall infiltration and excavation unloading

Intense precipitation infiltration and intricate excavation processes are crucial factors that impact the stability and security of towering and steep rock slopes within mining sites.The primary aim of this research was to investigate the progression of cumulative failure within a cracked rock formation,considering the combined effects of precipitation and excavation activities.The study was conducted in the Huangniuqian eastern mining area of the Dexing Copper Mine in Jiangxi Province,China.An engineering geological investigation was conducted,a physical model experiment was performed,numerical calculations and theoretical analysis were conducted using the matrix discrete element method(Mat-DEM),and the deformation characteristics and the effect of the slope angle of a fractured rock mass under different scenarios were examined.The failure and instability mechanisms of the fractured rock mass under three slope angle models were analyzed.The experimental results indicate that as the slope angle increases,the combined effect of rainfall infiltration and excavation unloading is reduced.A novel approach to simulating unsaturated seepage in a rock mass,based on the van Genuchten model(VGM),has been developed.Compared to the vertical displacement observed in a similar physical experiment,the average relative errors associated with the slope angles of 45,50,and 55were 2.094%,1.916%,and 2.328%,respectively.Accordingly,the combined effect of rainfall and excavation was determined using the proposed method.Moreover,the accuracy of the numerical simulation was validated.The findings contribute to the seepage field in a meaningful way,offering insight that can inform and enhance existing methods and theories for research on the underlying mechanism of ultra-high and steep rock slope instability,which can inform the development of more effective risk management strategies.

Numerical study on gas production via a horizontal well from hydrate reservoirs with different slope angles in the South China Sea

It is important to study the effect of hydrate production on the physical and mechanical properties of low-permeability clayey–silty reservoirs for the largescale exploitation of hydrate reservoirs in the South China Sea.In this study,a multiphysical-field coupling model,combined with actual exploration drilling data and the mechanical experimental data of hydrate cores in the laboratory,was established to investigate the physical and mechanical properties of low-permeability reservoirs with different slope angles during 5-year hydrate production by the depressurization method via a horizontal well.The result shows that the permeability of reservoirs severely affects gas production rate,and the maximum gas production amount of a 20-m-long horizontal well can reach186.8 m3/day during the 5-year hydrate production.Reservoirs with smaller slope angles show higher gas production rates.The depressurization propagation and hydrate dissociation mainly develop along the direction parallel to the slope.Besides,the mean effective stress of reservoirs is concentrated in the near-wellbore area with the on-going hydrate production,and gradually decreases with the increase of the slope angle.Different from the effective stress distribution law,the total reservoir settlement amount first decreases and then increases with the increase of the slope angle.The maximum settlement of reservoirs with a 0°slope angle is up to 3.4 m,and the displacement in the near-wellbore area is as high as2.2 m after 5 years of hydrate production.It is concluded that the pore pressure drop region of low-permeability reservoirs in the South China Sea is limited,and various slope angles further lead to differences in effective stress and strain of reservoirs during hydrate production,resulting in severe uneven settlement of reservoirs.

Predicting the friction angle of clays using a multi-layer perceptron neural network enhanced by yeo-johnson transformation and coral reefs optimization

The accurate prediction of the friction angle of clays is crucial for assessing slope stability in engineering applications.This study addresses the importance of estimating the friction angle and presents the development of four soft computing models:YJ-FPA-MLPnet,YJ-CRO-MLPnet,YJ-ACOC-MLPnet,and YJCSA-MLPnet.First of all,the Yeo-Johnson(YJ)transformation technique was used to stabilize the variance of data and make it more suitable for parametric statistical models that assume normality and equal variances.This technique is expected to improve the accuracy of friction angle prediction models.The friction angle prediction models then utilized multi-layer perceptron neural networks(MLPnet)and metaheuristic optimization algorithms to further enhance performance,including flower pollination algorithm(FPA),coral reefs optimization(CRO),ant colony optimization continuous(ACOC),and cuckoo search algorithm(CSA).The prediction models without the YJ technique,i.e.FPA-MLPnet,CRO-MLPnet,ACOC-MLPnet,and CSA-MLPnet,were then compared to those with the YJ technique,i.e.YJ-FPA-MLPnet,YJ-CRO-MLPnet,YJ-ACOC-MLPnet,and YJ-CSA-MLPnet.Among these,the YJ-CRO-MLPnet model demonstrated superior reliability,achieving an accuracy of up to 83%in predicting the friction angle of clay in practical engineering scenarios.This improvement is significant,as it represents an increase from 1.3%to approximately 20%compared to the models that did not utilize the YJ transformation technique.

Development of a DFN-based probabilistic block theory approach for bench face angle design in open pit mining

In open pit mining,uncontrolled block instabilities have serious social,economic and regulatory consequences,such as casualties,disruption of operation and increased regulation difficulties.For this reason,bench face angle,as one of the controlling parameters associated with block instabilities,should be carefully designed for sustainable mining.This study introduces a discrete fracture network(DFN)-based probabilistic block theory approach for the fast design of the bench face angle.A major advantage is the explicit incorporation of discontinuity size and spatial distribution in the procedure of key blocks testing.The proposed approach was applied to a granite mine in China.First,DFN models were generated from a multi-step modeling procedure to simulate the complex structural characteristics of pit slopes.Then,a modified key blocks searching method was applied to the slope faces modeled,and a cumulative probability of failure was obtained for each sector.Finally,a bench face angle was determined commensurate with an acceptable risk level of stability.The simulation results have shown that the number of hazardous traces exposed on the slope face can be significantly reduced when the suggested bench face angle is adopted,indicating an extremely low risk of uncontrolled block instabilities.

Mass-front velocity of dry granular flows influenced by the angle of the slope to the runout plane and particle size gradation

The mass-front velocities of granular flows results from the joint action of particle size gradations and the underlying surfaces.However,because of the complexity of friction during flow movement,details such as the slope-toe impedance effects and momentum-transfer mechanisms have not been completely explained by theoretical analyses,numerical simulations,or field investigations.To study the mass-front velocity of dry granular flows influenced by the angle of the slope to the runout plane and particle size gradations we conducted model experiments that recorded the motion of rapid and long-runout rockslides or avalanches.Flume tests were conducted using slope angles of 25°,35°,45°,and 55° and three particle size gradations.The resulting mass-front motions consisted of three stages:acceleration,velocity maintenance,and deceleration.The existing methods of velocity prediction could not explain the slowing effect of the slope toe or the momentum-transfer steady velocity stage.When the slope angle increased from 25° to 55°,the mass-front velocities dropped significantly to between 44.4% and59.6% of the peak velocities and energy lossesincreased from 69.1% to 83.7% of the initial,respectively.The velocity maintenance stages occurred after the slope-toe and mass-front velocity fluctuations.During this stage,travel distances increased as the angles increased,but the average velocity was greatest at 45°.At a slope angle of 45°,as the median particle size increased,energy loss around the slope toe decreased,the efficiency of momentum transfer increased,and the distance of the velocity maintenance stage increased.We presented an improved average velocity formula for granular flow and a geometrical model of the energy along the flow line.

Seismic responses of slopes with different angles in coral sand

This paper investigates the seismic responses of slopes in coral sand taken from a reef island in the South China Sea.A series of shaking table model tests were conducted to explore the responses of soil acceleration,excess pore pressure,and slope displacement for three slope angles(5°,10°,and 15°).The results show that the excess pore pressure ratio of the slope decreases due to an increase in the initial shear stress when the slope angle increases.The acceleration response of the soil increases with the increase of the slope angle.The slope displacement presents substantial increments as the excess pore pressure ratio increases.In addition,the lateral movement,and slope settlement present substantial increments as the slope angle increases.No liquefaction is observed under a dynamic excitation of 0.2 g in the coral sand site.Under a dynamic excitation of 0.4 g,the site liquefies quickly,the acceleration amplification factor decreases,and the lateral movement and the settlement of the slope surface both increase compared with that under 0.2 g excitation.For the slope with an angle of 15°at 0.4 g,the flow distance of the sand strip increase by 289.47%compared with that in the 5°case.The lateral movement of the slope surface near the water level line is substantially larger than that away from the water line.The largest settlement is observed near the middle section of the slope(below the water level)under a dynamic excitation of 0.2 g.In contrast,the largest settlement under a dynamic excitation of 0.4 g occurs at the top of the slope.

Optimization of Slope Angle and Its Seismic Stability: A Case Study for the Proposed Open Pit Coalmine in Phulbari,NW Bangladesh

The present study reflects upon the results of substantial program of two-dimensional Finite Element Method （FEM） numerical analyses of the open pit that links to slope angle optimization associated with the safety factor of the pit slope of a coal mine in Bangladesh. In the present analyses, two types of models have been presented. The first model estimates safety factor without seismic effect on the overall pit slope of the model; the second model incorporates safety factor with seismic stability of the model. The calculated optimum slope angle of the first model is 31% with a rational safety factor of 1.51, prior to the seismic effect. However, the value is reduced to 0.93, 0.82, and 0.72, after we applies the seismic effect in the second model with M6, M6.5, and M7, respectively. Finally, our modeling results emphasize that for the case of the proposed Phulbari coalmine, there is extremely high prospect for causing massive slope failure along the optimum pit slope angle with 31% if the mine area felt seismic shaking, like the Sikkim （in northern India） earthquake with M6.9 on September 18, 2011.

Design of Overall Slope Angle and Analysis of Rock Slope Stability of Chadormalu Mine Using Empirical and Numerical Methods

In engineering projects associated with rock mechanic science like open pit mines, assessment and slope stability of mine walls is one of the important performance in generate of these structures. Estimating and knowledge of stable slope angle is one of main parts that should be occurring to special attention in open pit mines studies phase. Considering the importance of economic costs in mining issues, the need for appropriate design slope angle that can cause an adverse minimize project costs and throws the other hand, the stability conditions in the safe walls of the mine life will provide essential and seems obvious. Therefore, in this study to determine the optimal slope angle of overall and bench of west wall of the Chadormalu ore iron mine, has been trying, first, done field studies on the discontinuity of western wall, engineering classification and geomechanical properties of rock masses of wall, then assess the amount of optimal slope angle using empirical method. Finally, in order to ensure stability and accuracy of the wall slope angle based on the obtained (empirical method) tries to analysis is amount of Factor of Safety (FOS), displacements and mean stress condition atwalls calculated from drilling use Phase2D powerful software.

Impact of the slope angle of hummocks on the ride-up of finger ice in the Liaohe Estuary

The ride-up and pile-up of sea ice have effects on the ice load of marine structure. The ride-up angle is an important parameter to study the process of ride-up and to determine the possibility of the ride-up to occur. Some conclusions about the ride-up angle are drawn based on field-survey data in this paper. Thirty hummocks with full structure, formed by 0.4-1.6 cm ice layers, were investigated in the Liaohe Estuary of the north of Liaodong Bay. After analyzing the cross-sections of the pile-up body, some concfusions on the ride-up angle are reached. The results indicate that whether the ride-up occurs or not is associated with the slope angle of the hummock. If the slope angle is greater than 10.31°, the ride-up can take place. With the development of riding-up and piling-up, if the slope angle increases to 40.0°, the climbing-up process will stop and the drifting ice begins to accumulate in front of the hummock. The climbing process does not continue until a new slope angle, which is less than 28.0°, is formed. Meanwhile, the forming process of hummocks, which are made up of 10.0 cm or 22.0 cm ice layers, is proved to follow the rule.

Optimum Design of Highway Excavation Slope Angle: Evidence from Dawu Section of Jingzhu Highway

The optimum design of the highway excavation slope angle is one of the most important problems to the highway construction and to the slope improvement. The Dawu Section of Jingzhu (Beijing Zhuhai) Highway is taken as an example to illustrate the study method for excavation slope angle design. The analysis of the engineering condition from different angles with different factors shows that the stability of the slope is calculated by using residual pushing force and the Sarma method. Then the sensitive analysis of the slope stability is conducted by using residual pushing force method. Finally, the optimum angle of design is presented on the precondition of ensuring the whole stability of slope and the economic reasonability. The study results show that the most sensitive factors are the shear strength parameter and the seismic force, and that the optimum excavation slope angle is 60°.

Stability analysis of the open-pit mine slope and the study on the incensement of the slope angle

Based on the exploration of the engineering geology and the rock mechan-ics testing, limit equilibrium analysis method was adopted to calculate the stability of the Huogeqi Copper Mine slope, the results show that the original slope angle is too con-servative and the slope have the potential of more preferable slope angle. In order to discuss the possibility of slope angle enhancement, sensitivity analysis of parameters related to limit state slope was made. Quantitatively determined angle value of the add-ing and the optimal slope angle was obtained. The study having performed showed that it is not only useful for the safety control of open-pit mine slope but also for the open-pit mine design for the similar geological condition.

Stability of High Slope Interbedded Strata with Low Dip Angle Constituted by Soft and Hard Rock Mass

Slopes consisting of interbedded strata of soft and hard rock mass, such as purplish red mudstone and grey brown arkosic sandstone of Jurassic age, are very common in Sichuan basin of China. The mudstone is soft while the sandstone is hard and contains many opening or closing joints with a high dip angle. Some are nearly parallel and the others are nearly decussated with the trend of the slopes. Many natural slopes are in deformation or sliding because of those reasons. The stability of cutting slopes and supporting method to be taken for their stability in civil engineering are important. In this paper, the stability and deformation of the slopes are studied. The methods of analysis and support design principle are analyzed also. Finally, the method put forward is applied to study Fengdian high cutting slope in Sichuan section of the express way from Chengdu to Shanghai. The results indicate that the method is effective.

Effects of laser beam divergence angle on airborne LIDAR positioning errors

The influence of laser beam divergence angle on the positioning accuracy of scanning airborne light detection and ranging （LIDAR） is analyzed and simulated. Based on the data process and positioning principle of airborne LIDAR, the errors from pulse broadening induced by laser beam di vergence angle are modeled and qualitatively analyzed for different terrain surfaces. Simulated results of positioning errors and suggestions to reduce them are given for the flat surface, the downhill of slope surface, and the uphill surface.

Influence of deflection angles on flow behaviours in openchannel bends

The deflection angle of a river bend plays an important role on behaviours of the flow within it, and a clear understanding of the angle's influence is significant in both theoretical study and engineering application. This paper presents a systematic numerical investigation on effects of deflection angles(30°, 60°, 90°, 120°, 150°, and 180°) on flow phenomena and their evolution in open-channel bends using a Re-Normalization Group(RNG) κ-ε model and a volume of fluid(VOF) method. The numerical results indicate that the deflection angle is a key factor for flows in bends. It is shown that the maximum transverse slope of water surface occurs at the middle cross section of a bend, and it increases with the deflection angle. Besides a major vortex, or, the primary circulation cell near the channel bottom, a secondary vortex, or, an outer bank cell, may also appear above the former and near the outer bank when the deflection angle is sufficiently large, and it will gradually migrate towards the inner bank and evolve into an inner bank cell. The strength of the secondary circulations increases with the deflection angle. The simulation demonstrates that there is alow-stress zone on the bed near the outer bank and a high-stress zone on the bed near the inner bank, and both of them increase in size with the deflection angle. The maximum of shear stress on the inner bank increases nonlinearly with the angle, and its maximums on the outer bank and on the bed take place when the deflection angle becomes 120°.

Modification Method of Lightning Shielding Angle Calculation for Transmission Lines in Mountain Areas

Shielding angle is one of the main factors influencing lightning performance of transmission lines,which always stays in the focus of the design and the evaluation of lightning protection.A formula for the improved shielding angle is proposed for evaluating the lightning performance in different terrains.The digital elevation model(DEM) is used to obtain the micro-topography data,such as the slope gradient,slope aspect,etc.The following results are obtained by analyzing the influence of topography factors on the improved shielding angle:(1) improved shielding angle non-linearly increases with the increase of the slope gradient and the slope aspect,(2) improved shielding angle is more sensitive to the slope gradient than to the slope aspect,(3) the improved shielding angle in the mountain terrains is much greater than the designed shielding angle.This may be the reason why the designed shielding angle is limited into the rational range,while the shielding faults occur frequently.

Influence of surface roughness on the development of moss-dominated biocrusts on mountainous rock-cut slopes in West Sichuan, China

Since natural restoration combined with artificial auxiliary measures may achieve a relatively rapid restoration effect at a lower cost, it has become an essential measure for the ecological restoration of rock slopes. Previous studies have focused heavily on the relationship between substrate nutrients and water conditions and the development of mosses on the rock surface, but quantitative characterization of substantial effect of rock surface texture(e.g., microrelief) on moss growth is absent. The undulating microrelief on the rock surface can increase the heterogeneity of the microhabitat, which may be an important factor affecting the development of mossdominated biocrusts. In this study, the roughness of rock surfaces, moss coverage and biomass, weight and major nutrient contents of soils within the biocrusts were measured in the western mountainous area of Sichuan Province, Southwest China to further examine the role of rock surface microrelief in the biocrusts. The results showed that three main factors affecting the development of the biocrusts were bryophyte emergence, soil accumulation, and lithology. The presence of moss accelerates soil formation on rock surfaces and lead to the accumulation of nutrients so that all parts of the moss-dominated biocrusts system can develop synergistically. It was found that a microrelief structure with a roughness between 1.5 and 2.5 could gather soil and bryophyte propagules effectively, which may have a strong relationship with the angle of repose. When the roughness is 1.5, the corresponding undulation angle is very close to the theoretical minimum value of the undulation angle calculated according to the relationships between the undulation angle of the protrusion, slope and angle of repose.

公路改扩建高边坡既有锚杆受力特性离心试验

为研究改扩建边坡二次开挖下既有锚杆的受力特性及边坡稳定性,基于自主研发的模型试验锚杆角度支护装置,采用离心试验研究了锚固角度分别为10°、20°、30°、45°、60°及锚杆横向密度分别为1根/(18 cm)、1根/(12 cm)下顺层岩质高边坡开挖全过程中坡顶水平位移、锚杆轴力及坡内土压力变化规律。结果表明:相同锚固角度下,随着边坡开挖卸荷,坡顶累计水平位移非线性增加,且开挖坡顶增幅较开挖坡中大;锚杆轴力呈单峰分布,在开挖坡顶及坡脚时轴力增幅较大,轴力峰值靠近软弱面且随开挖卸荷先减小后增大,开挖后轴力峰值仍为开挖前的61%以上;随锚固角度的增加,坡顶水平位移先减小后增大,坡内土压力先增大后减小,即存在最佳锚固角度;建议边坡开挖宜采用分级开挖,并在开挖坡顶及坡脚时适当降低速率,综合考虑边坡坡度、岩层及软弱面倾角等因素,合理设计锚固角度。研究成果有助于工程技术人员在改扩建边坡二次开挖工程中选择合适的支护措施。

考虑粒径分布的某大型排土场坡角设计

排土场具有成分复杂、粒径分布不均匀、孔隙率大、黏聚力小等特点,极易产生滑坡,为此对大型排土场边坡坡面碎石土粒径分布进行现场调查。研究发现,大粒径碎石从坡顶到坡底的含量逐渐提高,在坡底部含量占80.12%,粒径的分选性显著,决定了排土场力学性质下部强、上部弱的分布特点。在此基础上通过对给定坡高所允许最大坡角进行研究,得出随着坡角增大边坡稳定系数逐渐减小,两者之间近似呈线性关系,最终得到了180 m坡高允许的最大坡角为30°。研究为排土场设计工作提供依据。

多分支水平井岩屑运移模型与实验研究

随着多分支水平井及复杂结构井钻井技术的不断发展,井眼清洁技术面临着新的困难和挑战。如何解决复杂地质条件与复杂井型条件下的岩屑床问题,对于判断与处理井下复杂情况是当前钻井工程面临的重要科学问题之一。通过岩屑颗粒受力分析建立了岩屑运移环空临界流速模型;基于室内可视化岩屑运移实验,探究了岩屑运移影响规律。结果表明:井斜角为36°时岩屑临界启动速度最大,携岩最为困难;模型预测结果与实验结果吻合度较好,且基于实例井的预测结果与现场作业情况一致,验证了所建模型的可靠性。该研究可为大位移大井斜井及水平井井眼清洁提供理论依据和技术支持。