Investigation of Stability of the Critical Rock Blocks that Initiated the Jiweishan Landslide in China

The objective of the paper is to investigate the initiation of the Jiweishan landslide by simulating the field geological conditions around and inside a selected critical rock block and then to study its stability through 3-D discontinuum stress analysis. The study led to the following main conclusions: (1) The mining excavations that occurred underneath the investigated block at the landslide site, the friction angle of T2 discontinuities and sliding plane and the dip angle of the sliding plane seem to be the most important factors with respect to the instability of the investigated block; (2) It seems that the friction angle of T2 discontinuities and sliding plane need to drop to a value between 5° and 10° for the investigated block to be unstable. This means that the rainfall and karstification have played important roles in reducing the said friction angle and contributed to the failure of the investigated block. (3) The northern part of the investigated block (key block) had moved out first from the top of the mountain in a direction parallel to the strike of the north boundary discontinuity plane (T2) and had undergone shear failure on the T2 surface as well as on a weak shale layer (the sliding plane) and the remaining part of the investigated block (driving block) had moved along a direction slightly east of the north direction and had undergone shear failure on the sliding plane and separation from southern and western boundary discontinuity planes (T0 and T1) to fill the empty space created by the key block to initiate the Jiweishan landslide.     

Characterization, lateral variability and lateral extent of discontinuity surfaces on a Carbonate Platform (Barremian to Lower Aptian, Oman)

Hiati of various duration in carbonates are commonly expressed as discontinuity surfaces. The understanding of processes that form and affect these surfaces leads to an improved sequence-stratigraphic interpretation, a reliable outcrop correlation, and better models for reservoir compartmentalization. Various intraformational discontinuities were analysed and interpreted in a well-exposed study window, 2·5 km in lateral length and 60 m in height comprising the Barremian-Aptian Qishn Formation (Haushi-Huqf area, central Oman). This study focuses on the lateral extent and morphology of the surfaces, the petrography of the underlying rocks, and the facies changes and geochemical trends across these discontinuities. Furthermore, the lateral variability of discontinuity surfaces was documented. Three genetic types of discontinuities are differentiated: (i) erosion surfaces; (ii) omission surfaces (hard- and firmgrounds); and (iii) composite surfaces with evidence for both subaerial exposure and submarine boring. Field observations, combined with petrographic and geochemical data, suggest that 17 surfaces are laterally extensive for at least 20 km and record relative sea-level fluctuations of regional scale. In contrast, a large number of laterally limited surfaces (<1 km) are related to locally active processes such as waves and current erosion. The lateral variability along extensive surfaces is the result of the depositional environment below the discontinuity, the sea-floor topography, waves and currents and differential erosion. The most pronounced lateral variability is present along six laterally extensive composite surfaces that record terrestrial exposure and subsequent flooding of a tidal flat environment. This variability is caused by spatial variability in the tidal flat environment, meteoric alteration and differential erosion. This study emphasizes the spatial and temporal complexity of processes that form and modify discontinuity surfaces. This variability must be kept in mind when interpretations and correlations are based on one-dimensional sections or cores.     

估算异性岩石不连续面峰值剪切强度的经验公式

长江三峡库区广泛发育着两侧岩性不同的不连续面（称为异性不连续面）,研究其峰值剪切强度可为相关岩体的稳定性分析和评价提供理论依据。采用高强石膏浇注3组不同形貌且上、下壁面强度不同的不连续面试件,并在不同常法向应力下进行剪切试验。引入不连续面壁组合系数λ来综合量化不连续面壁的抗压强度和基本摩擦角对异性不连续面峰值剪切强度的影响,λ越小,上、下不连续面壁强度差异越大。异性不连续面的峰值剪切强度随λ的增加呈非线性增加,且在高法向应力下更为显著。在Barton公式的基础上,通过多元回归分析建立了估算异性不连续面峰值剪切强度的经验公式。采用天然和人工锯齿形异性不连续面的直剪试验结果对新公式做了进一步验证,试验剪切强度与新公式预测值吻合较好。简要分析了新公式在软硬互层岩质边坡稳定性评价中的应用。最后,讨论了Wu公式的适用性以及新公式的优点和不足。     

Dynamic response of a dip slope with multi-slip planes revealed by shaking table tests

This study investigated the effect of internal discontinuity on the dynamic response of a dip slope and evaluated the performance of Newmark’s theory on the sliding of a dip slope with multi-slip planes. A series of shaking table tests were performed under various geometric conditions to explore the dynamic behavior of a dip slope under different external excitations. The test results, including for deformation processes and critical accelerations, under various slope angles, slope sizes, and seismic intensities were examined and further compared with Newmark’s theory. The results of this study are summarized as follows: (1) two types of slope sliding (differential and complete) were determined. (2) Increasing the slope angle and the height of sliding mass tended to shorten the duration of slope deformation. (3) Critical acceleration of the slope increased gradually with increasing peak ground accelerations of input excitations; when the slope height and dip angle increased, the critical acceleration decreased. (4) The triggering time became earlier as the frequency of input excitation increased; the magnitude of sliding mass greatly depended on the amplitude of the input excitation. (5) By comparing critical acceleration between the experimental and theoretical results, Newmark’s theory was determined to overestimate critical acceleration during seismic-induced dip slope failure. This may cause unsafe evaluations, and sliding along existing discontinuities develops more easily in reality.     

自然与饱水条件下异性结构面的剪切特性研究

利用室内剪切试验装置,开展不同正应力、自然与饱水条件下岩体异性结构面的剪切试验,分析异性结构面的剪切变形和强度特性,利用JRC-JCS抗剪强度力学模型将试验结果与计算结果进行对比分析。结果表明,（1）异性结构面的剪切变形曲线属于弹塑性残余变形类型。相比自然状态试件,饱水试件的弹性区减小,较早进入峰值区或塑性区;（2）异性结构面的剪切刚度均随法向力的增大而增大,但同一正应力下饱水试件的剪切刚度要小于自然状态的剪切刚度,在低法向力下尤为显著;（3）水对岩体异性结构面剪切强度参数有不同程度的弱化,尤其对内摩擦角 的劣化明显;（4）只要计算参数选取得当,并考虑实际岩体的受力及水等情况,JRC-JCS计算模型可以为实际工程岩体的结构面强度提供较为准确的参数。     

Empirical Formula of Shear Strength of Rock Fractures Based on 3D Morphology Parameters

The prime objective of this work is to provide a reference to predict the peak shear strength of rock fractures. The paper studied some shear properties of rock fractures and proposed an empirical formula for the peak shear strength of rock fractures based on 3D morphology parameters. The rock fractures were induced in cylindrical sandstone and marble specimens by means of indirect tension. A rock direct shear apparatus (RDS-200) was adopted to conduct direct shear tests on five groups of rock fractures under different levels of normal load. Before the direct shear test, 3D morphology parameters of rock fracture surfaces were obtained using a 3D optical scanner. By analyses of direct shear test data, the relationships between peak shear strength, peak shear displacement, peak dilatancy angle, residual friction coefficient and peak normal stress were found. According to the evolution trends of peak shear strength and peak dilatancy angle along with the normal stress, an empirical formula was proposed to predict the peak shear strength of rock fractures in both sliding and cutting failure modes considering the 3D morphology parameters of rock fracture surfaces. The empirical formula could be commonly used for different types (sandstone and marble) and grain sizes (powder-grained, fine-grained, medium-grained and coarse-grained) of rock fractures.     

注浆材料和预制裂纹缺陷角度对类岩石试件单轴抗压强度及破坏模式的影响

选用环氧树脂和纯水泥浆作为注浆材料,对含不同角度和不同注浆材料裂隙试样进行单轴压缩试验。试验结果表明,注浆材料和裂纹缺陷角度对类岩石试件单轴抗压强度及破坏模式具有重要影响;环氧树脂加固效果优于纯水泥浆,环氧树脂可以有效地消除预制裂纹尖端的应力集中;在裂纹缺陷角度很小( <30°)和角度很大( =90°)的情况下无论裂隙是注环氧树脂还是纯水泥浆,注浆效果都不明显,当 =60°时两种注浆材料的加固效果都很好。提出滑动裂纹模型,对注浆裂隙进行力学分析发现,含注浆裂隙试样的抗压强度随着注浆材料和完整材料胶结面摩擦系数和黏聚力的增大而增大,不同注浆材料和完整材料胶结面的摩擦系数和黏聚力不同,解释了为什么不同的注浆材料对注浆试样强度提升作用不同。研究成果为分析工程中注浆材料和裂纹缺陷角度对岩体强度的影响提供了一定的理论基础。     

颗粒大小对颗粒材料力学行为影响初探

利用一种特殊颗粒材料-玻璃珠进行了一系列室内直剪试验,研究颗粒大小对颗粒材料力学行为的影响。试验一共考虑了3条近乎平行的级配曲线和4种颗粒摩擦情况：干燥状态、水浸润状态、水淹没状态和油浸润状态。试验结果表明,颗粒大小对颗粒材料的力学行为有显著影响,剪胀性随着粒径的增大而增强。为考虑颗粒大小对剪胀性的影响,提出了一种新的剪胀关系式。在该剪胀关系式中,剪胀系数为依赖于颗粒大小和颗粒摩擦等颗粒基本性质的变量。试验研究同时表明临界状态摩擦角随着颗粒大小的增加而增加。此外,从颗粒细观运动的角度提出了颗粒滑动的功能模型,推导出了功能方程,并以此揭示了颗粒大小对临界状态摩擦角影响的细观机制。     

Variability of unconfined compressive strength in relation to number of test samples

Unconfined compressive strength is one of the most commonly used properties in rock engineering. Estimation or selection of an appropriate value of unconfined compressive strength for a given rock can be difficult as it can vary greatly within the same rock unit. Considering this large variability, unconfined compressive strength obtained by testing just a few samples is questionable. The purpose of this study was to investigate the variability of unconfined compressive strength for a given rock and, based on this information, determine the minimum number of samples required for obtaining a reliable value. Unconfined compressive strength values for approximately 50 NX-size (2.125 in./5.4 cm) core samples were determined for five different rock types. Statistical analyses were performed on subsets of cores to determine the minimum number of samples required to render a reliable estimate of the average strength of the entire set of cores. The results indicate that the minimum number of samples needed for strength determination depends on the statistical method used, the chosen confidence interval, and the acceptable deviation from the mean. For a 95% confidence interval and a 20% acceptable strength deviation from the mean, either 9 or 10 samples are needed to test for strength, depending on the statistical analysis used.     

某水电站坝基岩体结构面室内大型直剪试验研究

岩体结构面的抗剪强度是表征岩体强度的一项重要参数,但由于原位试验受场地等诸多因素影响,难以大规模的开展,本文提出在室内用结构面大型剪切试验开展结构面的剪切特性研究,以某水电站坝基砂岩岩体中的硬性结构面为研究对象,取得了较好的成果。试验表明:结构面的多组剪切变形曲线具有一定的应变硬化的特征;达到峰值剪切强度时的剪切位移普遍较大,在8.9mm～44.5mm之间;砂岩中硬性结构面光滑面的基本摩擦角为31.4,结构面平均起伏角为6.3。     

Correlation of large displacement drained shear strength of landslide soils measured by direct shear and ring shear devices

Based on a laboratory study of drained direct shear tests of remoulded, pre-cut and polished specimens and drained ring shear tests of uncut and remoulded specimens of slip surface materials of five landslide soils, significant correlations of the mobilized shear strength parameters, cohesion (c, c _r) and internal friction angle (Φ, Φ_r), are proposed. The investigated soils consisted of the slip surface material belonging to tuffaceous clay, mudstone, loess and siltstone. Most of the previous studies on residual shear strength measured by reversal direct shear and ring shear devices have obtained significantly different results using the two devices, even when pre-cut and polished specimens were used in the direct shear device. In this study, the residual shear strength values of remoulded specimens measured by a ring shear device are shown to significantly correlate with the drained large displacement shear strength values of remoulded specimens, which were measured using pre-cut and polished specimens in a direct shear device. The correlation between the cohesion measured in the two shear devices is expressed by the linear relationship, $ {c_{\text{r}}} = 0.{7394}c - {6}.{6857} $ , while the correlation between the friction angle measured in the two devices is expressed by the linear relationship, $ {\Phi_{\text{r}}} = {1}.0{852}\Phi - {6}.0{247} $ . The proposed linear correlations for effective cohesion (c′) and effective friction angle (Φ′) have yielded significant coefficients of determination within an effective normal stress range of 30–150?kN/m².     

A micromechanical study of rolling and sliding contacts in assemblies of oval granules

The evolution of the microstructure of an assembly of cohesionless granular materials with associated pores, which carry the overall applied stresses through frictional contacts is a complex phenomenon. The macroscopic flow of such materials take place by the virtue of the relative rolling and sliding of the grains on the micro‐scale. A new discrete element method for biaxial compression simulations of random assemblies of oval particles with mixed sizes is introduced. During the course of deformation, the new positions of the grains are determined by employing the static equilibrium equations. A key aspect of the method is that, it is formulated for ellipse cross‐sectional particles, hence desirable inherent anisotropies are possible. A robust algorithm for the determination of the contact points between neighbouring grains is given. Employing the present methodology, many aspects of the behaviour of two‐dimensional assemblies of oval cross‐sectional rods have been successfully addressed. The effects of initial void ratio, interparticle friction angle, aspect ratio, and bedding angle on the rolling and sliding contacts are examined. The distribution of normals to the rolling and sliding contacts have different patterns and are concentrated along directions, which are approximately perpendicular to one another. On the other hand, the distribution of all contact normals (combined rolling and sliding) are close to that of rolling contacts, which confirm that rolling is the dominant mechanism. This phenomenon becomes more pronounced for higher intergranular friction angle. Characteristics of the rolling and sliding contacts are also discussed in the context of the force angle, which is the inclination of contact force with respect to the contact normal. Copyright © 2003 John Wiley & Sons, Ltd.     

煤矿井下3 000 m顺煤层定向钻孔钻进关键技术

保德煤矿大盘区工作面采前瓦斯超前治理模式要求井下定向长钻孔能够沿煤层钻进3 000 m以上,针对现有技术装备在超长定向钻孔施工中存在滑动钻进困难、进水水路压耗大、有线随钻测量信号传输距离受限、冲洗液无法循环利用等问题,开发了煤矿井下基于螺杆马达水力加压和超长钻具正反扭转给进的滑动钻进减阻工艺、基于回转钻进倾角控制和侧钻分支的复合钻进轨迹控制技术,设计了低压耗进水水路系统、泥浆脉冲无线随钻测量系统和冲洗液净化循环系统,结合保德煤矿生产需要,完成了主孔深度3 353 m、孔径120 mm的顺煤层超长贯通定向孔。钻进效果表明:滑动钻进减阻工艺有效降低了给进力,显著提高了深孔滑动定向钻进能力;基于复合钻进的轨迹控制技术,保证了钻孔轨迹沿煤层定向延伸,并提高了钻进能力和钻进效率;泥浆脉冲无线随钻测量信号长距离传输稳定可靠,克服了有线随钻测量信号传输的局限性;井下冲洗液净化循环系统净化效果良好,实现了井下定向钻进冲洗液循环利用。研究成果对支撑煤矿大区域瓦斯超前治理、以孔代巷工程、水害防治及地质勘探等技术进步具有重要意义。      

基于物质点法的土体流动大变形过程数值模拟

土体滑坡作为一种自然地质灾害,受自然因素和人类活动的影响在我国时有发生,给周围居民的生命和财产安全带来了很大威胁,日益受到人们的广泛关注。滑坡防治也逐渐成为工程研究的热点之一。土体本质上是一种具有复杂组成结构的颗粒材料堆积体,通过对颗粒流动的模拟可以深入理解自然界中的土体流动现象,如滑坡、泥石流等,进而预测灾害破坏范围及改进相应工程防护措施。但由于土体流动是一个涉及大变形及大位移的复杂流动过程,传统的基于网格的有限元法（FEM）由于网格畸变,并不适合这类问题的研究。本文采用物质点法（MPM）模拟土体流动大变形问题。作为一种源于particle-in-cell（PIC）法的无网格法,兼具欧拉法和拉格朗日法的优点,因而,物质点法在处理大变形问题上具有独特的优势。目前,国内外利用物质点法模拟边坡滑动问题已有不少研究,但对相关参数进行敏感性分析的较少。本文基于物质点法模拟了黏性土体及无黏性土体流动大变形问题,并进行了参数敏感性分析,包括土体材料的内摩擦角、黏聚力、高宽比、底面坡度对土体滑动距离的影响规律。本文计算中采用Drucker-Prager（DP）弹塑性本构模型描述土的非线性特性。研究结果表明:（1）基于物质点法得到的土体的流动形态、滑动距离以及自然休止角等数值模拟结果均与文献中的实验结果基本吻合,验证了物质点法模拟土体大变形力学行为的精度及有效性;（2）随着内摩擦角、黏聚力的增大,滑动距离相应减小;（3）坡度对边坡稳定的影响是显著的,随着底面坡度的增大,滑动距离相应增大;（4）当土柱高宽比较小时,与滑动距离呈线性增长关系。其中,内摩擦角和黏聚力反映了土体的抗剪切性能,因此通过工程措施提高土体的抗剪能力可以降低土体滑坡带来的危害。研究结果为探索土体滑动破坏规律,降低滑动破坏范围提供了可靠的参考。     

Three-dimensional slope stability analysis of South Peak, Crowsnest Pass, Alberta, Canada

South Peak is a 7-Mm³ potentially unstable rock mass located adjacent to the 1903 Frank Slide on Turtle Mountain, Alberta. This paper presents three-dimensional numerical rock slope stability models and compares them with a previous conceptual slope instability model based on discontinuity surfaces identified using an airborne LiDAR digital elevation model (DEM). Rock mass conditions at South Peak are described using the Geological Strength Index and point load tests, whilst the mean discontinuity set orientations and characteristics are based on approximately 500 field measurements. A kinematic analysis was first conducted to evaluate probable simple discontinuity-controlled failure modes. The potential for wedge failure was further assessed by considering the orientation of wedge intersections over the airborne LiDAR DEM and through a limit equilibrium combination analysis. Block theory was used to evaluate the finiteness and removability of blocks in the rock mass. Finally, the complex interaction between discontinuity sets and the topography within South Peak was investigated through three-dimensional distinct element models using the code 3DEC. The influence of individual discontinuity sets, scale effects, friction angle and the persistence along the discontinuity surfaces on the slope stability conditions were all investigated using this code.     

A large triaxial investigation of the stress-path-dependent behavior of compacted rockfill

Realistic prediction of the deformation of rockfill structures becomes increasingly important, which requires improved knowledge about the mechanical properties of rockfill materials. However, previous large triaxial tests were usually carried out with a constant cell pressure, and there is uncertainty about the behavior of rockfill along other stress paths. This paper presents the results of a series of large triaxial tests conducted on limestone rockfill specimens along different loading paths. The effect of previous loading history and moisture content has also been investigated. The results show that the stress?Cstrain and volumetric behavior of rockfill are significantly influenced by the loading directions as well as the confining pressures. However, the stress path appears to have only minor influence on the shear strength of rockfill, while the strength envelope exhibits pronounced curvature at low confining pressures and the peak friction angle decreases approximately linearly with the logarithm of the corresponding confining pressure. The previous loading history is revealed to have considerable effect on the stress?Cstrain behavior but small influence on the peak strength of rockfill. In contrast, the moisture content of rockfill has marked influence on both the deformation and the strength characteristics. The implications of the test results are discussed.     

岩体抗剪强度参数现场测试新方法及工程应用

岩体抗剪强度参数的确定是进行岩体工程稳定性分析中最基本和最重要的,也是最困难的一项工作。由于室内和现场试验方法的局限性以及经验准则的人为性,快速、简易和较可靠确定岩体抗剪强度参数的原位测试手段一直是岩石工程界关注的热点。采用引进美国生产的岩石钻孔剪切仪,在实验室混凝土空心圆柱体和向家坝水电站坝基岩体中进行了尝试,取得了有益的试验成果。将主要从钻孔剪切仪的工作原理、数值模拟分析和工程应用等几方面对其进行全面的阐述和总结。试验成果和数值分析结果显示,岩石钻孔剪切仪是一种适用于软岩~中硬岩的原位试验设备,其试验成果总体钻孔剪切试验得到的c、 小于传统三轴和直剪试验成果,但钻孔剪切试验的 值在 <40?的范围内略低于传统三轴和直剪试验成,而钻孔剪切试验的c值较传统三轴和直剪试验的c 值降低较多,一般为25%～50%。     

Mechanisms of shear failure in artificial fractures of sandstone and their implication for models of hydromechanical coupling

Summary Direct shear tests, in which the behaviour of the rock surfaces during shear could be continuously observed, were used to study the shear failure of a profiled and clean discontinuity artificially prepared from natural sandstone. Displacement transducers were used to measure the normal and shear displacements. A series of strain gauges glued on the sides of the upper block provided information on the change of the stress field occurring close to the discontinuities whilst shear displacement increased, and these changes were then compared with the behaviour of the profiled surface. The results of the laboratory tests, the sequence of photographs taken for most of them, and the results conducted with a sample of similar shape made from the same rock material and tested in a rotary shear machine, allowed several stages and mechanisms of failure to be defined: static friction and mobilization of initial shear stiffness; mobilization of sliding; mobilization of brittle fracture; post-peak failure of the teeth; descent of the teeth; gliding and ploughing; commencement of second cycle of shearing. In many respects these stages are similar to those occurring between sliding surfaces of metal and suggest that the analyses developed in tribology may be relevant to the development of constitutive models for predicting the hydromechanical coupled behaviour of a discontinuity with shear displacement. Such models will have to consider these different stages of shear, because the original discontinuity changes its geometry with displacement and is filled with gouge which changes its grain size with displacement.     

垃圾填埋场斜坡上土工合成材料受力分析

为了评价垃圾填埋场防渗系统材料界面之间的摩擦特性以及土工合成材料端部的应力,进行了模拟试验和有限元分析。采用直接剪切试验,获得了土与短纤维无纺布、短纤维无纺布与HDPE土工膜以及短纤维无纺布与TPO（PE）界面的摩擦角和黏聚力;采用离心模拟试验,得到了伴随土压缩引起的短纤维无纺布和土工膜端部拉应力。试验结果表明：材料界面之间的摩擦角较大,但黏聚力不大;伴随填埋高度的增加,短纤维无纺布和土工膜端部的拉应力也随之增大。运用有限元对土压缩引起的短纤维无纺布和土工膜端部拉应力以及界面的摩擦应力分布进行了分析,并与试验结果进行了对比,分析结果表明：两者基本一致,碾压机械下方土工膜界面之间摩擦应力比较大。     

碎石土滑坡的因素敏感性计算分析

通过资料搜集整理和分析、现场工程地质调查与勘探和室内外的物理力学试验,采用弹塑性接触有限元强度折减法、不平衡推力法和数理统计分析法,结合工程实例,分析了影响碎石土滑坡各因素的敏感性,结果表明,按因素敏感度从大到小排列,主要影响碎石土滑坡稳定性的因素依次为滑面岩土体内摩擦角、地形坡度、滑体饱水面积比和滑面岩土体的内聚力。地形坡度大、具有低内摩擦角滑面的碎石土滑坡的整体稳定性较差,而连续降雨、强降雨会抬高地下水位增大滑体饱水面积比,降低滑面带岩土体抗剪强度,增加下滑力,对碎石土滑坡的稳定性将产生最不利的影响。同时,在对碎石土滑坡进行加固处理时,必须优先考虑采取提高滑面等效内摩擦角、降低地形坡度结合降低地下水位措施,其次考虑采取提高滑面岩土体内聚力的措施。