Geological analysis of gravitational rock slope deformation: a case from Nujiang River,China

This paper presents a study on the gravity-induced rock slope deformation observed along the Nujiang River in China. We performed a comprehensive field investigation and analysis to identify the deformation pattern of the slope and its triggering factors. Moreover, a geological-evolutionary model was developed, and it considers the effects of river incision and rock mass degradation caused by weathering and simulates the mechanisms underlying the initiation and progression of the slope deformation. The results support the proposed failure mechanism in which fractures within the slope are induced by rock mass degradation caused by weathering. Importantly, the modeling reveals that compressional deformation at the toe of the slope results in a tensile failure in the upper portion of the slope, demonstrating that the rock mass in the slope toe is the key factor inducing slope deformation. This analysis of slope deformation and its spatial and temporal correlations with rock weathering and river incision reveal the main triggering factors that control the evolution of the studied slope and provide insights into the deformation process.     

碳酸盐岩裂缝研究进展及发展趋势

裂缝对碳酸盐岩储层油气产能有重要的影响。在总结碳酸盐岩裂缝的分类、成因、主控因素、识别与预测等方面的基础上,认为对非构造缝的分类、命名及其含义仍存在较大争议。裂缝成因主要包括构造作用、成岩作用、异常高压作用、剥蚀作用和风化作用。粒度和孔隙度对构造缝发育的影响机理有待进一步深入研究。沉积相对构造缝发育有一定的影响,但同一沉积相内岩性组成复杂,难以准确揭示裂缝发育的影响机理。直接研究岩性对裂缝发育影响更利于揭示裂缝形成机理。基于成岩演化序列对裂缝进行研究可明确裂缝形成时的岩石特征,为深入讨论构造缝发育的主控因素提供了基础。层间缝、缝合线、异常高压缝和溶蚀缝等非构造缝发育的主控因素有待进一步深入研究。近几年地震技术识别裂缝突破不大,非常规测井识别裂缝领域以声波远探测技术发展最快。常规测井识别裂缝一直是研究的热点问题,不同学者提出了40余种裂缝识别方法。测井、地震信息裂缝预测法预测结果可靠性高,是目前主流的裂缝预测技术。规范裂缝分类、梳理裂缝成因、深化构造缝发育机理研究、加强非构造缝主控因素探讨、提高常规测井裂缝识别率、综合现有不同裂缝预测技术预测裂缝是下一步裂缝研究的重要发展方向。      

Failure mechanisms of post-earthquake bedrock landslides in response to rainfall infiltration

Among the triggering factors of post-earthquake bedrock landslides,rainfall plays an important role.However,with slope variation,the mechanism of its effects on the failure of rock landslides is not clear.Here,from the viewpoint of fracture mechanics,and based on post-earthquake conditions,the mechanisms of crack propagation,water infiltration and development of the sliding surface were investigated.Then,according to the upper boundary theorem,the effects of water infiltrated into fractures on the stability of rock slopes were analyzed quantitatively.Finally,an example is presented to verify the theory.The results show that the propagation and coalescence of cracks and the lubrication of incipient sliding surfaces are the main causes of the failure of post-earthquake rock landslides in response to rainfall.     

湖北省阳新县基岩滑坡变形因子及其破坏模式

斜坡变形受众多因子综合控制, 不同因子的敏感性与作用规律在变形过程中差异明显。以湖北省阳新县顺层基岩滑坡为研究对象, 通过正交试验结合离散元数值模拟的方法, 研究多个影响因子对应顺层滑坡变形的敏感性并确立主导因素, 随后基于响应面拟合主导因素与滑坡不同部位变形程度间的量化关系, 揭示主导因素交互作用对滑坡变形破坏模式的影响规律。结果表明, 在研究区内坡度与岩层倾角分别为影响顺层滑坡变形的主导与次主导因素, 滑坡的变形破坏模式受控于二者的交互作用。在中-陡倾顺层滑坡中, 当坡度小于岩层倾角时, 滑坡变形主要集中在坡顶, 且变形程度随岩层倾角的增加而增大, 表现出滑移-弯曲的变形破坏模式; 在缓倾顺层滑坡中, 当坡度大于岩层倾角时, 滑坡坡脚位移较坡顶显著, 其坡脚变形程度随坡度的增加而增大, 以滑移-拉裂变形为主。研究成果可为该类滑坡的防治工作提供参考。      

Evaluation of mountain slope stability considering the impact of geological interfaces using discrete fractures model

The stability of rock slope is often controlled by the existing discontinuous surfaces, such as discrete fractures, which are ubiquitously distributing in a geological medium. In contrast with the traditional approaches used in soil slope with a continuous assumption, the simulation methods of jointed rock slope are different from that of in soil slope. This paper presents a study on jointed rock slope stability using the proposed discontinuous approach, which considers the effects of discrete fractures. Comparing with traditional methods to model fractures in an implicit way, the presented approach provides a method to simulate fractures in an explicit way, where grids between rock matrix and fractures are independent. To complete geometric components generation and mesh partition for the model, the corresponding algorithms were devised. To evaluate the stability state of rock slope quantitatively, the strength reduction method was integrated into our analysis framework. A benchmark example was used to verify the validation of the approach. A jointed rock slope, which contains natural fractures, was selected as a case study and was simulated regarding the workflow of our framework. It was set up in the light of the geological condition of the site. Slope stability was evaluated under different loading conditions with various fracture patterns. Numerical results show that fractures have significant contributions to slope stability, and different fracture patterns would lead to different shapes of the slip surface. The devised method has the ability to calculate a non-circular slip surface, which is different from a circular slip surface obtained by classical methods.     

Effect of the inclined weak interlayers on the rainfall response of a bedded rock slope

Engineering experience shows that outward dipping bedded rock slopes, especially including weak interlayers, are prone to slide under rainfall conditions. To investigate the effect of inclined weak interlayers at various levels of depth below the surface on the variation of displacements and stresses in bedded rock slopes, four geo-mechanical model tests with artificial rainfall have been conducted. Displacements, water content as well as earth pressure in the model were monitored by means of various FBG (Fiber Bragg Grating) sensors. The results showed that the amount of displacement of a slope with a weak interlayer is 2.8 to 6.2 times larger than that of a slope without a weak interlayer during one rainfall event. Furthermore, the position of the weak interlayer in terms of depth below the surface has a significant effect on the zone of deformation in the model. In the slope with a high position weak interlayer, the recorded deformation was larger in the superficial layer of the model and smaller in the frontal portion than in the slope with a low position weak interlayer. The slope with two weak interlayers has the largest deformation at all locations of all test slopes. The slope without a weak interlayer was only saturated in its superficial layer, while the displacement decreased with depth. That was different from all slopes with a weak interlayer in which the largest displacement shifted from the superficial layer to the weak interlayer when rainfall persisted. Plastic deformation of the weak interlayer promoted the formation of cracks which caused more water to flow into the slope, thus causing larger deformation in the slope with weak interlayers. In addition, the slide thrust pressure showed a vibration phenomenon 0.5 to 1 hour ahead of an abrupt increase of the deformation, which was interpreted as a predictor for rainfall-induced failure of bedded rock slopes.     

Experimental study of motion characteristics of rock slopes with weak intercalation under seismic excitation

In order to investigate the effect of a weak intercalation on slope stability, a large-scale shaking table model test was conducted to study the dynamic response of rock slope models with weak intercalation. The dynamic response of the prototype slopes were studied in laboratory with the consideration of law of similitude. The initiation failure was observed in the rock slope model with a counter-tilt thin-weak intercalation firstly, not in the slope model with a horizontal thin-weak intercalation. Furthermore, it was interesting that the fracture site is shifted from crest top to the slope surface near the weak intercalation, which is different with the location of failure position in a normal layered slope. We also discussed the effect of the dip angle and the thickness of weak intercalation on the failure mechanism and instability mode of the layered rock slope. From the experimental result, it was noted that the stability of the slope with a counter-tilt weak intercalation could be worse than that of the other slopes under seismic excitation. The findings showed the difference of failure in slopes with a horizontal and counter weak intercalation, and implicated the further evaluation of failure of layered slopes caused by seismic loads.     

新铺下二台滑坡变形机制及中长期预报模型

以奉节新铺下二台滑坡为例, 基于GPS位移监测数据、裂缝数据、降雨量及库水位等多源数据, 总结分析了大型古滑坡的复活规律, 引入滑坡中长期预报模型, 实现了以季度或月份为时间单位的跨水文年滑坡位移预测, 并通过岩土体蠕变压缩模型, 验证了推移式滑坡后缘裂缝形成机理。结果表明: ①降雨是下二台滑坡变形的主导因素, 滑坡变形使得滑体产生裂缝并成为降雨入渗通道, 加剧了岩体破碎与软弱层软化, 降低了滑坡稳定性, 集中持续降雨可使滑坡失稳破坏; ②通过模型预测值与地表监测数据的比较, 将年降雨量作为滑坡中长期预报模型中的主控因素具有实际可操作性且有助于提高滑坡中长预报精度; ③推移式滑坡后缘裂缝由滑坡推移式位移和岩土体压缩形成, 引入蠕变压缩模型计算的裂缝宽度并和监测数据的比较说明, 蠕变压缩模型非常适合该类边坡, 同时应用岩土体蠕变压缩模型反推得到岩土体平均变形模量, 判断岩体破碎程度, 可以为滑坡稳定性分析及后续工程治理提供参考。      

Rock slope stability evaluation using kinematic and kinetic methods along the Kamyaran-Marivan road,west of Iran

Interest in rock slope stability in mountainous regions has increased greatly in recent years.This issue has become a topic of major interest for geoscientists and engineering professionals,as well as for private citizens and local administrators,in many parts of the world.This paper evaluates the stability of seven rock slopes along the KamyaranMarivan tourist road,Kurdistan province,Iran,using various methods.The two main reasons for performing this research were to determine whether different methods of stability analysis provide the same results,and to determine how different factors such as the presence of water,tension cracks,and seismic forces affect the stability of these rock slopes.Firstly,field investigations were performed to obtain the engineering characteristics of the rock masses,discontinuities,and intact rocks of the slopes.Secondly,laboratory tests were carried out on rock samples obtained from the slopes,to determine the engineering properties of the intact rocks.Then for each rock slope,the contour diagram of discontinuities and slope face was drawn in the Dips v.5.1 software environment,and the failure mechanism was determined based on the kinematic or stereographic method.Next,the factors of safety of the rock slopes were calculated using the limit equilibrium method,based on the failure mechanisms resulting from the kinematic method.The accuracy of the results obtained by these two methods was investigated using SWedge v.4.0 software.The results indicated that four rock slopes have a potential for plane,wedge,and toppling failure,and three others are stable.Also,it was found that the stability of the studied rock slopes decreases greatly in the presence of water,tension cracks,and seismic forces.     

冻融循环作用下砂岩单轴压缩破坏断口特征分形研究

寒区岩石的力学特征往往受到冻融循环和荷载的共同影响,冻融岩石单轴压缩破坏断口蕴含着与冻融循环和荷载有关的损伤演化信息,冻融岩石单轴压缩破坏断口研究对冻融岩石断裂破坏机理分析有重要价值。为研究冻融岩石单轴压缩破坏断口形貌特征及其与宏观力学参数之间的关联性,通过摄影观测经历不同次数冻融循环的砂岩单轴压缩破坏断口形貌,采用像素点覆盖法计算断口分维值,探究了断口分维值与宏观力学参数之间的关系。结果表明:随着冻融次数的增加,冻融砂岩的力学性能劣化,单轴抗压强度、弹性模量、断口分维值、耗散能密度逐渐减小,峰值应变增大;单轴抗压强度、弹性模量、耗散能密度均与断口分维值之间存在指数关系,断口分维值越大,对应的单轴抗压强度、弹性模量、耗散能密度越大。冻融岩石单轴压缩破坏断口分维值可作为寒区岩体断裂破坏机理分析的有效参数。      

地下采动顺向缓倾构造山坡的滑移机理

采空区地表山体侧向变动,不同于一般天然山坡,也与采空区一般上覆岩层的变形破坏有异;它是二者复合机理的效应。本文在分析考察了毗邻电厂的横山顺倾构造山体、剖析了地下采空情况认为:山体侧向变动中,软弱夹层有决定性作用,变动范围、速率和规模与地下采空有关;并利用地质力学模型试验和数值模拟,探索了采动引起山体应力场及变动规律。结果表明,山体岩层的变形、位移、破坏、由直接顶板向地表发展,采空坍陷诱发了软弱夹层的蠕滑,则产生山体侧向滑移;电厂区地表隆起变形是山体侧向滑移挤压地基土的反映。通过现场实际调研、变形观测资料分析与数值模拟和模型试验的对比研究,提出了“坍落拱梁”的成生效应、挤压蠕滑效应、失稳效应;揭露了顺倾构造山体在采空影响下,具有地表、地下的“复合临空面”的“复合应力场”中“复合变动”的“复合机理”;并提出这种山体侧向变动机理的典型地质模式,借以论证山体稳定性。     

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软硬互层顺层岩质边坡破坏试验

软硬互层结构的顺层岩质边坡破坏类型复杂、难于防治, 针对此类边坡地质灾害易发、多发的问题, 从坡面角度、岩层倾向及组合形式、节理分布等方面进行了研究。边坡物理模型试验是揭示边坡变形破坏机理的重要手段, 基于相似理论, 以重庆市万州区孙家滑坡为工程依托, 根据滑坡区地质勘探报告设计了室内边坡物理模型试验; 试验通过顶升模型箱模拟重力加载来探究顺层岩质边坡发生破坏时, 前缘坡角和软弱夹层倾角之间的关系; 结合有限元分析软件Plaxis 2D对物理模型进行了多组数值模拟试验, 以验证软硬互层顺层岩质边坡破坏机制。试验结果表明: 对于顺层岩质边坡, 当软弱夹层的倾角在22°左右, 前缘开挖坡角58°左右时, 顺层岩质边坡容易发生滑动, 滑动面为后缘节理面和软弱夹层的贯通面。因此, 顺层岩质边坡稳定性受层面和节理面密度的控制, 当边坡含多层软弱层面时, 易沿层面和后缘节理贯通面发生破坏, 随着软弱面层数增加, 边坡稳定系数逐渐降低。研究成果可以为公路开挖切坡导致的顺层岩质边坡失稳机理研究及其稳定性评价提供理论依据, 为顺层岩质边坡失稳的预测预报提供支撑。      

Assessment of rock slope stability by probabilistic-based Slope Stability Probability Classification method along highway cut slopes in Adilcevaz-Bitlis (Turkey)

Rock slope stability is of great concern along highway routes as stability problems on cut slopes may cause fatal events as well as loss of property. In rock slope engineering, stability evaluations are commonly performed by means of analytical or numerical analyses, principally considering the factor of safety concept. As a matter of fact, the probabilistic assessment of slope stability is progressively getting popularity due to difficulties in assigning the most appropriate values to design parameters in analytical or numerical methods. Additionally, the effect of heterogeneities in rock masses and discontinuities on the analysis results is minimized through the probabilistic concept. In this study, slope stability of high and steep sedimentary rock cut slopes along a state highway in Adilcevaz-Bitlis (Turkey) was evaluated on the basis of probabilistic approach using the Slope Stability Probability Classification (SSPC) system. The probabilistic assessment indicates major slope stability problems because of discontinuity controlled and discontinuity orientation independent mass movements. Almost all studied cut slopes suffer from orientation-independent stability problems with very low stability probabilities. Additionally, the probability of planar and toppling failures is significantly high with respect to the SSPC system. The stability problems along the investigated rock slopes were also verified by field reconnaissance. Remedial measures such as slope re-design and reinforcement at the studied locations should be taken to prevent hazardous events along the highway. On the other hand, the probabilistic approach may be a useful tool during rock slope engineering to overcome numerous uncertainties when probabilistic and analytic results are compared.     

Slope debris flows in the Wenchuan Earthquake area

Avalanches and landslides, induced by the Wenchuan Earthquake on May 12, 2008, resulted in a lot of disaggregated, solid material on slopes that could be readily mobilized as source material for debris flows. Rainstorms triggered numerous slope debris flows with great damage to highways and rivers over the subsequent two years. Slope debris flows (as opposed to channelized debris flows) are defined as phenomena in which high-concentration mixtures of debris and water flow down slopes for short distances to highways and river banks. Based on field investigations and measurements of 19 slope debris flows, their main characteristics and potential mitigation strategies were studied. High rainfall intensity is the main triggering factor. Critical rainfall intensities for simultaneous occurrence of single, several and numerous slope debris flow events were 20 mm/day, 30mm/day, and 90 mm/day, respectively. Field investigations also revealed that slope debris flows consist of high concentrations of cobbles, boulders and gravel. They are two-phase debris flows. The liquid phase plays the role of lubrication instead of transporting medium. Solid particles collide with each other and consume a lot of energy. The velocities of slope debris flows are very low, and their transport distances are only several tens of meters. Slope debris flows may be controlled by construction of drainage systems and by reforestation.     

Modelling the flexural buckling failure of stratified rock slopes based on the multilayer beam model

The buckling failure of stratified rock slopes intersected by a set of steep discontinuities that are approximately parallel to the slope surface is frequently encountered while constructing railways and roadways in mountainous areas. In this study, an analytical approach based on the energy equilibrium principle is presented to solve the flexural buckling stability of stratified rock slopes within the framework of multilayer beam theory. The generalized HoekBrown failure criterion is introduced to reflect the influences of slope size(scale effects) on the buckling stability. Subsequently, numerical and physical modellings from previous literatures are employed to validate the proposed approach. Furthermore, a practical case of Bawang Mountain landslide is also used for the comparative analysis. The study shows that the present analytical approach is capable to provide a more reasonable assessment for the buckling failure of stratified rock slopes, compared with several existing analytical approaches. Finally, a detailed parametric study is implemented, and the results indicate that the effects of rock strength, rock deformation modulus, geological strength index, layer thickness and disturbance degree of rock mass on the buckling failure of stratified rock slopes are more significant than that of rock type and slope angle.     

胶东邓格庄金矿床矿化富集规律及深部预测

邓格庄金矿床位于胶东牟平－乳山金矿带的北段，含金石英脉受NNE向断裂控制。工业矿体由矿化石英脉的富金段组成。富金矿体在走向上一般分布于NNE向断裂的转折地段，倾向上分布于断裂产状由陡变缓的过渡部位。控矿构造经历了压剪性到张剪性的演化过程，主要成矿作用发生于断裂的张剪性活动阶段。深部地质地球化学研究表明，Ⅱ号矿体深部还有隐伏矿体存在。     

基于逻辑回归模型和3S技术的思南县滑坡易发性评价

区域滑坡易发性评价对滑坡灾害防治具有重要意义，贵州省思南县由于其特殊的自然地理和地质条件，受滑坡地质灾害的影响非常严重，因此，非常有必要对思南县的滑坡易发性进行评价。在滑坡编录的基础上，采用由RS、GIS和GPS组成的3S技术，获取了思南县的数字高程模型、坡度、坡向、剖面曲率、坡长、岩土类型、地表湿度指数、距离水系的距离、植被覆盖度和地表建筑物指数10个滑坡影响因子；再在频率比和相关性分析的基础上，利用逻辑回归模型对思南县的滑坡易发性进行了评价并绘制了易发性分布图。结果表明:利用逻辑回归模型预测思南县滑坡易发性的准确率(AUC值)达到0.797，较为准确地预测出了思南县滑坡分布规律；极高和高滑坡易发区主要分布在高程低于600 m、地表坡度较大且以软质岩类为主的区域；而极低和低滑坡易发区主要分布在高程较高、地表坡度较小且以硬质岩类为主的区域。      

Slope reinforcement for housing in Three Gorges reservoir area

The Three Gorges Project of the Yangtze River is the largest hydropower-complex project under construction in the world. Under the largescale relocation projects, 2874 engineered slopes are formed along with the construction of new towns. In this paper, the cutting slopes are mainly soil slopes and rock slopes. Soil slopes include residual soil slopes, colluvial accumulation slopes, swelling soil slopes, and artificial earth fill slopes, etc. Rock slopes include blocky structure rock slopes, layer structure rock slopes, and clastic structure rock slopes, etc. Varied protection measures have been used for slope protection in the reservoir area including shotcrete concrete-anchor bars, frame beams, retaining walls, slope stabilizing piles, sheet-pile walls, anchorage anti-shear tunnels, flexible protection grids, and drainage, etc. Besides, slope deformation monitoring systems have been set up to monitor deformation failure and the stability state of slopes. The protection measures have guaranteed slope safety and maintained a harmony with the urban environment and surrounding landscape.     

三峡库区大型-特大型层状岩质滑坡成因模式及地质特征分析

三峡库区大型-特大型滑坡发育，尤以层状岩质滑坡的危害性大。因库区各段地质条件差异使得滑坡成因模式各不相同，这影响了滑坡的运动形式和岩土体解体程度。在收集三峡库区51处典型的大型-特大型层状岩质滑坡调查资料基础上，根据堆积岩体结构和区段地质条件反推该段滑坡破坏成因模式，而不同成因模式下的滑坡坡体渗透性不同，分析已有滑坡对库水位变动存在的复活响应差异，据此得出以下结论:①在成因模式上，除顺层滑移型滑坡在库区中均有分布外，从库首至库尾随着岩层倾角的逐渐减缓，滑坡成因模式从崩塌型、反倾弯曲型逐渐过渡到平推式；②在坡体渗透性上，成因模式造成的岩体结构变化与坡体中的泥质含量共同作用，导致顺层滑移型滑坡前后缘渗透性存在较大差异；反倾型滑坡渗透性则整体变化较小；③在库水位变动影响下，不同坡体渗透性与滑面形态共同决定了滑坡的复活变形差异。