A stability evaluation method for deep-seated toppling in the upper Lancang river,Southwestern China

Deep-seated toppling in the upper reaches of the Lancang River,southwest China involves deformations exceeding 100 m in depth.The slope deformation is initiated by river downcutting and evolves distinctive characteristics with a depth of river incision.In this study,we propose a system for evaluating the stability of deep-seated toppled slopes in different evolutionary stages.This system contains identification criteria for each evolutionary stage and provides the corresponding stability evaluation methods.Based on the mechanical and kinematic analysis of slope blocks,the specific stage of slope movement can be identified in the field through outcrop mapping,in situ tests,surface displacement monitoring,and adit and borehole explorations.The stability evaluation methods are established based on the limiting equilibrium theory and the strain compatibility between the undisturbed zone and the toppled zone.Finally,several sample slopes in different evolution stages have been investigated to verify the applicability and accuracy of the proposed stability evaluation system.The results indicate that intense tectonic activity and rapid river incision lead to a maximum principal stress ratio exceeding 10 near the slope surface,thus triggering widespread toppling deformations along the river valley.When considering the losses of joint cohesion during the further rotation process,the safety factor of the slope drops by 7%e28%.The self-stabilization of toppling deformation can be recognized by the layer symmetry configuration after the free rotation of the deflected layers.Intensely toppled rock blocks mainly suffer sliding failures beyond the layer symmetry condition.The factor of safety of the K73 rockslide decreased from 1.17 to 0.87 by considering the development of the potential sliding surface and the toesaturated zone.

Deep-seated large-scale toppling failure in metamorphic rocks：a case study of the Erguxi slope in southwest China

Deep-seated large-scale toppling failure presents unique challenges in the study of natural slope deformation process in mountainous regions.An active deep-seated toppling process was identified in the Erguxi slope located in southwest China,which affected a large area and damaged critical transportation infrastructure with the volume of the deforming rock mass exceeding 24×10~6 m^3.It poses significant risks to the downstream Shiziping Hydropower Station by damming the Zagunao River.Field investigation and monitoring results indicate that the deformation of the Erguxi slope is in the advanced stage of deep-seated toppling process,with the formation of a disturbed belt but no identifiable master failure surface.It was postulated that the alternating tensile and shear strength associated with the hard/soft laminated rock strata of metasandstone and phyllite layers preclude the development of either a tensile or shear failure surface,which resulted in the continuous deformation and displacement without a catastrophic mass movement.The slope movement is in close association with the unfavorable geological conditions of the study area in addition to the construction of transportation infrastructure and the increase of the reservoir level.On the basis of the mechanism and intensity of the ongoing toppling deformation,a qualitative grading system was proposed to describe the toppling process and toevaluate the slope stability.This paper summarized the field observation and monitoring data on the toppling deformation for better characterizing its effect on the stability of the Erguxi slope.The qualitative grading system intends to provide a basis for quantitative study of large-scale deep-seated toppling process in metamorphic rocks.

Investigation of the block toppling evolution of a layered model slope by centrifuge test and discrete element modeling

Primary toppling usually occurs in layered rock slopes with large anti-dip angles.In this paper,the block toppling evolution was explored using a large-scale centrifuge system.Each block column in the layered model slope was made of cement mortar.Some artificial cracks perpendicular to the block column were prefabricated.Strain gages,displacement gages,and high-speed camera measurements were employed to monitor the deformation and failure processes of the model slope.The centrifuge test results show that the block toppling evolution can be divided into seven stages,i.e.layer compression,formation of major tensile crack,reverse bending of the block column,closure of major tensile crack,strong bending of the block column,formation of failure zone,and complete failure.Block toppling is characterized by sudden large deformation and occurs in stages.The wedge-shaped cracks in the model incline towards the slope.Experimental observations show that block toppling is mainly caused by bending failure rather than by shear failure.The tensile strength also plays a key factor in the evolution of block toppling.The simulation results from discrete element method(DEM)is in line with the testing results.Tensile stress exists at the backside of rock column during toppling deformation.Stress concentration results in the fragmented rock column and its degree is the most significant at the slope toe.

Influence of joint spacing and rock characteristics on the toppling stability of cut rock slope through a simplified limit equilibrium method

Toppling failure of rock mass/soil slope is an important geological and environmental problem.Clarifying its failure mechanism under different conditions has great significance in engineering.The toppling failure of a cutting slope occurred in a hydropower station in Kyushu,Japan illustrates that the joint characteristic played a significant role in the occurrence of rock slope tipping failure.Thus,in order to consider the mechanical properties of jointed rock mass and the influence of geometric conditions,a simplified analytical approach based on the limit equilibrium method for modeling the flexural toppling of cut rock slopes is proposed to consider the influence of the mechanical properties and geometry condition of jointed rock mass.The theoretical solution is compared with the numerical solution taking Kyushu Hydropower Station in Japan as one case,and it is found that the theoretical solution obtained by the simplified analysis method is consistent with the numerical analytical solution,thus verifying the accuracy of the simplified method.Meanwhile,the Goodman-Bray approach conventionally used in engineering practice is improved according to the analytical results.The results show that the allowable slope angle may be obtained by the improved Goodman-Bray approach considering the joint spacing,the joint frictional angle and the tensile strength of rock mass together.

Toppling and sliding in volcanic bimrocks around Bayrakli(Izmir, Turkey)

Discontinuities have significant role on the behavior of rock masses with respect to several types of instabilities. Excavability, deformability, bearing capacity and slope stability of the rock masses should be investigated considering the discontinuity characteristics with particular emphasis on the geomechanical properties. Kinematic analyses mostly provide an insight to the instabilities, however the dimensions of the blocks bounded by discontinuities, their geomechanical properties and the geometry of the slope should also to be taken into account. The study area is in the abandoned stone quarry in Bayrakl? district of ?zmir residential area. Due to the excavations and discontinuity orientations, instabilities have occured. Miocene aged andesites and altered agglomerates of Yamanlar Volcanics form the bimrock mass. The study area is located within a sheared zone, bounded by strike slip fault zone. Intact andesite blocks were encountered in altered agglomerate matrix, forming a volcanic bimrock. Wedge and planar sliding and block toppling were observed within the area. Detailed discontinuity surveying was conducted, combined with core drillings. Several typical locations were detected where prismatic blocks of andesites are bound to experience block toppling. Such locations are nearby the top of the steep slopes. Agglomerates are subjected to mainly sliding and the blocks have been formed not by gravity but by peculiarities of thevolcanic sedimentation and, probably by subsequent tectonics. In order to determine the mechanism of the sliding and toppling in more details, the relation of the blocks and the slope geometry were investigated. Bimrock type volcanic rock masses sometimes do not tend to accommodate the general rules of toppling and sliding due to their anisotropic settings.

Geophysical-Geological Interpretation and Deep-Seated Gold Deposit Prospecting in Sanshandong-Jiaojia Area, Eastern Shandong Province, China

Integrated gravitational, electrical-magnetic surveys and data processing carried out in the Sanshandao-Jiaojia area, Eastern Shandong Province, northeast China, aim to illuminate the geological characteristics of this shallow-covered area and delineate deep-seated gold prospecting targets. In this region, altogether 12 faults exert critical control on distribution of three types of Early Precambrian metamorphic rock series, i.e. those in the metamorphic rock area, in the granitic rock area underlying the metamorphic rock, and in the remnant metamorphic rock area in granites, respectively. Additionally, the faults have major effects on distribution of four Mesozoic Linglong rock bodies of granite, i.e. the Cangshang, Liangguo, Zhuqiao-Miaojia and Jincheng granites. The Sanshandao and Jiaojia Faults are two well-known regional ore-controlling faults; they have opposite dip direction, and intersect at a depth of 4500 m. Fracture alteration zones have striking geophysical differences relative to the surrounding county rocks. The two faults extend down along dip direction in a gentle wave form, and appear at some steps with different dips. These steps comprise favorable gold prospecting areas, consistent with a step metallogenic model. Six deep-seated gold-prospecting targets are delineated, i.e. Jincheng-Qianchenjia, Xiaoxizhuang-Zhaoxian, Xiyou-Wujiazhuangzi, Xiangyangling-Xinlicun, Panjiawuzi and Miaojia-Pinglidian.

Mechanism of toppling and deformation in hard rock slope: a case of bank slope of Hydropower Station, Qinghai Province, China

Recently, various toppling slopes have emerged with the development of hydropower projects in the western mountainous regions of China. The slope on the right bank of the Laxiwa Hydropower Station, located on the mainstream of the Yellow River in the Qinghai Province of Northwest China, is a typical hard rock slope. Further, its deformation characteristics are different from those of common natural hard rock toppling. Because this slope is located close to the dam of the hydropower station, its deformation mechanism has a practical significance. Based on detailed geological engineering surveys, four stages of deformation have been identified using discrete element numerical software and geological engineering analysis methods, including toppling creep, initial toppling deformation, intensified toppling deformation, and current slope formation. The spatial and time-related deformation of this site also exhibited four stages, including initial toppling, toppling development, intensification of toppling, and disintegration and collapse. Subsequently, the mechanism of toppling and deformation of the bank slope were studied. The results of this study exhibit important reference value for developing the prevention–control design of toppling and for ensuring operational safety in the hydropower reservoir area.

A two-dimensional limit equilibrium computer code for analysis of complex toppling slope failures

Evaluation of blocky or layered rock slopes against toppling failures has remained of great concern for engineers in various rock mechanics projects.Several step-by-step analytical solutions have been developed for analyzing these types of slope failures.However,manual application of these analytical solutions for real case studies can be time-consuming,complicated,and in certain cases even impossible.This study will first examine existing methods for toppling failure analyses that are reviewed,modified and generalized to consider the effects of a wide range of external and dead loads on slope stability.Next,based on the generalized presented formulae,a Windows form computer code is programmed using Visual C#for analysis of common types of toppling failures.Input parameters,including slope geometry,joint sets parameters,rock and soil properties,ground water level,dynamic loads,support anchor loads as well as magnitudes and forms of external forces,are first loaded into the code.The input data are then saved and used to graphically draw the slope model.This is followed by automatic identification of the toppling failure mode and a deterministic analysis of the slope stability against this failure mode.The results are presented using a graphical approach.The developed code allows probabilistic introduction of the input parameters via probability distribution functions(PDFs)and thus a probabilistic analysis of the toppling failure modes using Monte-Carlo simulation technique.This allows calculation of the probability of slope failure.Finally,several published case studies and typical examples are analyzed with the developed code.The outcomes are compared with those of the main references to assess the performance and robustness of the developed computer code.The comparisons demonstrate good agreement between the results.

Evaluation of toppling rock slopes using a composite cloud model with DEMATEL–CRITIC method

Safety evaluation of toppling rock slopes developing in reservoir areas is crucial. To reduce the uncertainty of safety evaluation, this study developed a composite cloud model, which improved the combination weights of the decision-making trial and evaluation laboratory (DEMATEL) and criteria importance through intercriteria correlation (CRITIC) methods. A safety evaluation system was developed according to in situ monitoring data. The backward cloud generator was used to calculate the numerical characteristics of a cloud model of quantitative indices, and different virtual clouds were used to synthesize some clouds into a generalized one. The synthesized numerical characteristics were calculated to comprehensively evaluate the safety of toppling rock slopes. A case study of a toppling rock slope near the Huangdeng Hydropower Station in China was conducted using monitoring data collected since operation of the hydropower project began. The results indicated that the toppling rock slope was moderately safe with a low safety margin. The composite cloud model considers the fuzziness and randomness of safety evaluation and enables interchange between qualitative and quantitative knowledge. This study provides a new theoretical method for evaluating the safety of toppling rock slopes. It can aid in the predication, control, and even prevention of disasters.

Numerical modeling of deep-seated landslides interacting with man-made structures

This paper describes the interaction between deep-seated landslides and man-made structures such as dams, penstocks, viaducts, and tunnels. Selected case studies are reported first with the intent to gain insights into the complexities associated with the interaction of these structures with deep-seated landslides(generally referred to as deep-seated gravity slope deformations, DSGSDs). The main features, which characterize these landslides, are mentioned together with the interaction problems encountered in each case. Given the main objective of this paper, the numerical modeling methods adopted are outlined as means for increase in the understanding of the interaction problems being investigated. With the above in mind, the attention moves to an important and unique case history dealing with the interaction of a large-size twin-tunnel excavated with an earth pressure balance(EPB)tunnel boring machine(TBM) and a deep-seated landslide, which was reactivated due to the stress changes induced by tunnel excavation in landslide shear zone. The geological and geotechnical conditions are described together with the available monitoring data on the landslide movements, based on the advanced and conventional monitoring tools used. Numerical modeling is illustrated as an aid to back-analyze the monitored surface and subsurface deformations and to assist in finding the appropriate engineering solution for putting the tunnel into service and as a follow-up means for future understanding and control of the interaction problems. The simulation is based on a novel time-dependent model representing the landslide behavior.

Deformation characteristics and mechanism of an impoundment-induced toppling landslide in Baihetan Reservoir based on multi-source remote sensing

Impoundment and water level fluctuations in reservoirs can induce landslides,especially during initial filling and drawdown.Since the initial impoundment in April 2021,multiple landslides have occurred within the Baihetan(BHT) reservoir,which is located at the boundary of Sichuan and Yunnan province in southeast China.However,due to the complex terrain conditions of reservoir banks,traditional landslide research methods,such as surveys,deformation monitoring,and geotechnical experiments,cannot be effectively conducted in a timely manner.In recent years,the development of remote sensing technology has addressed the shortcomings of traditional landslide research methods that may not be promptly carried out.In particular,interferometric synthetic aperture radar(InSAR) technology,capable of measuring subtle deformations,and portable small unmanned aerial vehicles(UAVs) have played a significant role.This study integrates multiple remote sensing data sources,including InSAR results,optical remote sensing images,digital elevation model(DEM),and UAV imagery,to investigate and elucidate the deformation characteristics and mechanisms of the Xiaomidi(XMD) landslide developed on the left bank of Jinsha River,about 100 km from the BHT hydropower dam site.The spatial deformation distribution of the landslide before and after impoundment and the deformation time series during filling were examined.Monitoring water level variation and analysing the deformation process of the landslide were achieved by employing continuous synthetic aperture radar(SAR) intensity images and DEM.UAV photography was utilized to assist in the verification of ground deformation.The findings suggest that the weak strength of the reversed bedding strata structure and the steep slope eroded by the Jinsha River are inherent factors that contribute to the development of the landslide.The rise in the water level leads to softening of the rock mass at the slope toe,thereby directly facilitating the acceleration of landslide deformation.The toppling deformation of the lower rock mass initiates the formation of surface cracks and localized uneven subsidence in the overlying colluvial deposits.

Deep-seated rock fracture of valley slopes in China:A review

Deep-seated rock fractures(referred to as DSRF hereafter)in valley slopes are uncommon geological phenomena that challenge our previous understanding of slope unloading processes.These fractures weaken the strength and integrity of the rock mass,potentially forming unstable block boundaries with significant volume,thereby affecting the stability of slopes,chambers,and dam abutments.DSRF has emerged as a critical environmental and engineering geological issue that hinders large-scale projects in deep canyon areas.Despite the attention and practical treatment given to DSRF in engineering practice,theoretical research on this topic still lags behind the demands of engineering applications.To garner widespread attention and promote the resolution of DSRF-related problems,this review aims to redefine DSRF through comprehensive data collection and analysis,engineering geological analogies,and field investigations,and provide a summary and analysis of the research progress on DSRF,along with future research directions.The study defines DSRF as the intermittent tension cracks or relaxation zones within a slightly weathered or fresh,and intact or relatively intact rock mass distributed below the surface unloading zones of a deep canyon slope,and should be distinguished from"loose rock mass"and"deep-seated gravitational slope deformations".The article provides an overview of the development and distribution,rupture characteristics,and genesis mechanism of DSRF.It proposes that DSRF is formed based on the fluvial deviation-undercutting evolution mode,wherein the energy accumulated in the rock mass is violently released when the river further down cuts the slope after the rock mass has undergone cyclical loadingunloading.However,further research is necessary to establish a comprehensive database for DSRF,refine exploration techniques,understand evolutionary processes,develop engineering evaluation methods,and predict the distribution of DSRF.

Boundary effect of toppling failure based on three-dimensional mechanical model

Previous researches on the mechanical model of toppling failure mainly concentrated on twodimensional mechanical model(TwDM) analysis. The TwDM analysis assumes the width of the slab beam is unit width without considering the lateral constraint force. The assumed conditions are obviously different from the site conditions, thus there is a certain difference between the calculated results and the field work. A three-dimensional mechanical model(ThDM)of toppling failure was established, considering that the slab beam was mainly subject to self-weight, the frictional resistance of interlayer and lateral constraint force. Due to the progressive characteristics of toppling failure, the concept and the formula of the first fracture depth(FFD) of toppling was raised and constructed. The case study indicates that the ThDM is more effective and can be accurately used to calculate the toppling fracture depth of the slab beam. The FFD decreases proportionally with the increase of slab beam width. FFD grows fast when the slab beam width is less than 2.0 m and it tends to be stable when the slab beam width is above 2.0 m. The FFD decreases with the increase of the lateral constraint coefficient, indicating that the boundary condition of the free space is positively correlated with the stability and depth of toppling. This is a good explanation of the free space effect. This study provides a reference for the stability evaluation and prevention-control design of toppling slope in the future.

THE MECHANICAL RELATIONSHIP TO THE FORMATION AND DISTRIBUTION OF THEBURIED HILLS AND THE DEEP-SEATED FRACTURAL ZONE IN THE DIWA-TYPE FAULTED BASIN IN CENTRAL HEBEI PROVINCE,CHINA

The author proves the existence and movement of a deep-seated fraetural Zone located in the eenter zone of the diwa-type faulted basin in central Hebei Province. This deep-seated fraeturai zone tending in NNE direction is a structural effect of the mtodle East Asin Grustobody in the Mexozoic-Cenozoic. This paper will diseuss the formation, evolution and the meehanism of the deep-seated fraetural zone, faulted basin and the buried hills as well as their relationships. The uthor expounds that the deep geological process is the major factor of the structural effect.

Geological and geochemical indicators and prediction of deep-seated ore bodies in Jiudian gold deposit of Pingdu,Shandong Province

Based on the geology and geochemistry of gold-bearing quartz veins in the Jiudian gold deposit of Pingdu,Shandong Province,the geological and geochemical indicators of occurrence of deep-seated ore bodies in the Jiudian gold deposit have been summarized.Extent occurrence of wide,intensive,varied alteration zones around the gold-bearing quartz veins and continual presence of diorite porphyrite and lamprophyry indicate the probable occurrence of deep-seated ore bodies at depth of gold lodes.As,Sb and Hg belong to the head halo elements, and their anomalies could reveal the probable occurrence of the deep-seated ore bodies below.

适合机械化收获的油菜新品种秦优1618的选育

为选育高油高产强优势适宜机械化栽培的杂交油菜,为生产提供优良油菜品种及创新强优品种的推广模式,通过多年多点试验和定向选择,以化学杀雄不育系“H04A”为母本,综合抗性较好的优质种质资源“DC2R”为父本,育成了适宜机械化收获的强优势甘蓝型双低杂交油菜新品种秦优1618。该品种在国家黄淮区域试验中平均产量3 468.75 kg/hm^(2),比对照秦优7号增产8.5%,含油量46.76%;长江下游区域试验中平均产量2 854.05 kg/hm^(2),比对照秦优10号增产10.67%,含油量49.68%;在大田生产中表现出发育快长势强、耐迟播、耐密植、抗病性好、株高适中(160 cm)、抗倒性强、适合机械化收获的特点。秦优1618适宜在黄淮和长江下游区冬播种植。

黄河玛尔挡水电站库区Qd04倾倒体稳定性评价及涌浪分析

玛尔挡水电站库区发育的Qd04倾倒体距离上游抽水蓄能电站下水库进水口较近,考虑到该倾倒体潜在失稳体积较大,宏观稳定性较差,水库蓄水后可能沿软弱面或折断面发生失稳,准确评价其稳定性及涌浪风险至关重要。为了准确评价该倾倒体稳定性,分析涌浪情况,采用M-P(Morgenstern-Price)法进行稳定性分析,并采用常用的3种滑速计算方法与3种涌浪计算方法9种组合进行涌浪计算,使用数值模拟法对涌浪值进行验证。结果表明:结合新滩滑坡实测的涌浪数据,得出使用经验公式法时采用能量守恒法计算滑速和潘家铮法计算涌浪高度的组合计算成果更贴近实测值,即在死水位、正常蓄水位时倾倒体整体失稳产生涌浪至上游抽蓄电站的涌浪高度分别为11.3、11.5 m。研究成果可为玛尔挡水电站库区相关工程的风险预测提供借鉴。

基于优化支持向量回归的磨古倾倒变形体参数反分析研究

岩土体力学参数的确定将直接影响对倾倒变形体稳定性的分析判断,野外原位监测数据作为反映倾倒变形体现场条件的重要信息,利用原位监测数据能有效地获得倾倒变形体岩土体参数.本文针对雅砻江两河口近坝库区磨古倾倒变形体,提出以海洋捕猎者优化算法对支持向量回归反分析模型参数进行寻优,构建MPA-SVR岩土体参数反分析模型.以倾倒变形体现场安全监测数据为输入信息,反分析得到适用于两河口磨古倾倒变形体折断带的力学参数,其反分析结果可为变形体稳定性分析提供重要数据基础.结果表明磨古倾倒变形体不同高程监测点具有相似的变形规律,变形速率发展趋势与水位变化趋势一致,变形累计值整体呈增长趋势,变形尚未完全收敛;随着分期蓄水进程的推进,倾倒变形体水动力作用特征明显,反分析得到的折断带力学参数逐渐降低,从第二阶段蓄水到第三阶段蓄水,折断带黏聚力下降3.68%,内摩擦角下降1.98%.

倾角变化条件下反倾层状斜坡倾倒变形演化研究

倾倒变形是反倾层状岩质边坡的一种典型破坏模式,为了研究不同岩层倾角对反倾层状岩质边坡倾倒变形的影响,以澜沧江上游古水水电站坝前倾倒变形体为原型,从岩层倾角变化的角度出发,利用大型土工离心机试验分析了反倾层状岩质边坡的失稳破坏过程、变形演化特征与最终失稳模式等。结果表明:①反倾层状斜坡的变形演化过程基本概括为岩层压密-坡脚压裂阶段、弯折面形成-部分失稳阶段和弯折面贯通-彻底失稳3个阶段,岩层倾角的改变并不会影响斜坡阶段性演化过程;②岩层倾角越大的斜坡,斜坡形成弯折面所需时间越短,失稳破坏发生后坡体贯通性倾倒破坏深度更大,对应的变形范围越大,折断岩层的破坏程度越剧烈;③岩层倾角变化会导致斜坡的倾倒变形过程与最终失稳模式存在一定差异。倾角较小的55°和70°模型斜坡前部岩层在重力作用下发生明显弯曲倾倒变形,最终以“倾倒-弯曲-滑移”的失稳模式发生破坏;倾角最大的85°斜坡岩层发生的弯曲变形较小,最终以“倾倒-折断-崩塌”的模式发生破坏。研究结果对大型工程项目的顺利开展具有一定指导意义。

澜沧江中上游反倾斜坡倾倒变形影响因素敏感性及斜坡易倾倒几何模型研究

倾倒是反倾岩质斜坡常见的失稳类型,其变形破坏受多种因素影响。为探究各类因素对反倾斜坡倾倒变形的影响程度及其对变形模式的控制作用,本文以澜沧江中上游反倾岩质斜坡为研究对象,建立了反倾斜坡倾倒变形影响因素体系,结合离散元数值模拟试验结果及改进灰色关联分析理论,对各类影响因素的敏感性进行了研究。在此基础上,以斜坡几何特征参数为输入,基于支持向量回归(SVR)理论对研究区反倾斜坡倾倒变形易发几何模型进行预测。结果表明:(1)反倾斜坡的几何特征参数敏感性最高,水平构造应力次之,岩体力学参数敏感性最弱。(2)反倾斜坡的变形量与变形深度与上下坡角呈正相关,变形深度与岩层倾角呈正相关,但变形量随岩层倾角的增大先增大后减小。(3)研究区内的反倾斜坡存在4种变形模式:稳定斜坡、潜在变形斜坡、浅层倾倒斜坡及深层倾倒斜坡。(4)在研究区内,岩层倾角小于57°的斜坡总体保持稳定;超过57°有产生浅层倾倒变形的可能;超过63°时有产生深层倾倒的可能;达到81°,岸坡普遍产生倾倒变形。本研究成果可为此类斜坡变形体的野外早期识别与灾害危险性评估提供可靠理论参考。