粘土岩质大型滑坡滑带形成机制研究

粘土质大型滑坡在渭河中下游地区广泛分布,簸箕山大型老滑坡位于宝鸡市市中心北坡,其长期蠕变滑动致灾风险较高,是陕西省与宝鸡市国土局重点监测的大型滑坡。为判别分析滑坡变形监测数据与滑动趋势,急需理清其滑带变形样式和滑体运动过程。基于滑坡地形及地层岩性、地下水调查,结合连续取芯钻探数据,进行了滑带及原岩物质成分、水理化性质及应力应变特征的物理化学实验,通过滑带与原岩的实验数据对比分析,结论如下:(1)簸箕山滑坡滑带发育于三门组粘土岩黏粒含量较高的层位中,滑坡蠕变变形亦集中于该位置、渐进扩展;(2)滑带粘土矿物以蒙脱石为主,具有较强的膨胀性和裂隙化特征,使得粘土岩在地下水作用下发生劈理化、塑性化及泥质化,使得剪切面贯通形成滑带。     

武隆鸡尾山滑坡形成机理数值模拟研究

2009年发生的重庆武隆鸡尾山滑坡,因滑源区斜坡岩层整体缓倾山内,缺乏有效的临空面和滑移空间,因此,在滑坡孕育过程中存在前缘岩溶带压缩变形、底部剪切滑移、后缘拉裂以及最终前缘关键块体(岩溶带)侧向剪断滑出等一系列的复杂动力学行为。这一过程存在显著的连续变形向非连续变形的过渡与转化,单纯用连续介质的有限元和离散介质的离散元来分析模拟都很难取得较好的效果。为探究鸡尾山滑坡的孕育过程和失稳机理,运用将连续–非连续单元有机耦合的大型数值模拟软件CDEM,模拟鸡尾山滑坡的失稳过程和形成机制。研究表明:滑体前方岩溶发育带具有"可压缩性",为滑体运动提供了一定的变形空间;滑源区下方的采矿活动产生应力重分布,滑带抗剪强度降低,滑体沿其底部软弱带发生剪切蠕滑,并逐渐形成滑体后缘拉裂缝;滑动块体在向前滑移过程中不断挤压向前缘"易压缩带",坡体应力自组织调整,并逐渐在前部三角区形成垂直的第二破裂面,前缘抗力体(关键块体)形成,最后剪断岩溶带个别与稳定山体咬合岩块,整体失稳破坏。数值模拟结果较好地揭示了武隆鸡尾山滑坡前缘视倾向展布岩溶带"软基效应"所提供"准临空面",重现了鸡尾山滑坡"蠕滑—拉裂—压缩(压碎)—剪切滑出"的致灾机理。     

风化壳淋积型稀土矿成矿分析

风化壳淋积型稀土矿的形成,主要有内生作用及外生作用两个条件决定的。内生作用是指原岩(母岩)所含稀土元素的丰度,稀土矿物、稀土副矿物和及含稀土副矿物的易风化程度;外生作用是指自然界对原岩的改造程度和作用方式,它在稀土元素成矿作用过程中占据着重要的地位,如有利风化壳形成的构造背景、气候、有利地形环境等等。在成矿作用过程中,岩石中原生稀土矿物的风化解体,提供了稀土物质的来源;原生造岩矿物的风化提供粘土矿物的来源;原生造岩矿物的风化以及粘土矿物的形成,提供了稀土次生富集的有利条件,而亚热带的潮湿多雨气候,则提供了表生作用下稀土转移富集及分异作用进行的环境条件。     

乌蒙山区红层软岩滑坡地质演化及灾变过程离心机模型试验研究

乌蒙山区由砂岩、泥岩、页岩等组成的缓倾角红层软岩分布广泛,软质岩石与硬质岩石形成的互层状结构体易形成滑坡。针对该类滑坡,以花生地滑坡为例,采用地质分析与离心机模型试验相结合的方法,对降雨作用下滑坡地质演化和灾变过程进行研究。研究表明,红层软岩具有易软化蠕滑,风化崩解等地质力学特性。岩体损伤与水软化效应耦合作用是影响红层软岩斜坡稳定性主要因素,斜坡岩体受地震、河谷下切等地质作用产生深部裂隙,同时裂隙的贯通促进降雨入渗,导致滑带饱水软化、加速蠕变变形至失稳。最终在暴雨形成水动力失稳破坏。滑坡地质演化和灾变过程可分为原始斜坡→岩体损伤劣化→水软化蠕滑→降雨诱发失稳破坏4个阶段。研究成果为降雨型红层软岩斜坡稳定性机制分析及工程治理提供参考。     

矿物学与烧结砖瓦生产（四）

3层状硅酸盐矿物的结构特征(粘土矿物)硅酸盐矿物中包括对烧结砖瓦产品起决定性作用的层状结构粘土矿物。第一次发现粘土矿物晶体结构是在19世纪20年代引入X-射线衍射测量技术后。由于“粘土物质”很小的粒子尺寸,在此以前认为是无定形体物质。其实粘土矿物中的原子和离子如同晶格中元素一样,它们之间仅以保持尽可能小的空间方式存在。因为这类矿物最先在粘土中发现,或因粘土及粘土岩主要由这类矿物组成,故称为粘土矿物。粘土矿物本身具有高度的分散性,但有其结晶结构,可利用结晶化学原理对它们进行研究。关于粘土矿物晶体结构的概念还是在…     

中部“砥柱”锁固平面旋转切向层状岩质滑坡启动力学机理与稳定性判据

中部“砥柱”锁固平面旋转滑坡,是切向层状岩质斜坡在特殊的边界条件控制下,发生渐进性变形而形成的。其主要特征是：在平面上,滑体中部的潜在滑床面部位,岩层抗剪强度较高,出现坡体变形的相对锁固段：而由滑体中部向周围边界,坡体变形逐渐增大。且变形岩体围绕着滑体的中部呈现出平面旋转变形之趋势。引起滑坡平面旋转的根本原因是滑体在变形时,其所受诸力的合力不通过滑体重心,从而产生了使滑体发生旋转的力矩。其变形与破坏模式可以概化为：在自重力、滑床摩擦力、滑床锁固段阻力和滑体周围边界处围岩切层阻力的共同作用下,圆环状岩块(岩板)所发生的平面旋转变形以及临界状态下“锁固段”的旋转破坏问题。基于弹性力学的平面应力问题,分析了圆环状岩块的旋转应力场：并应用极限平衡方法,分析了旋转滑坡下滑失稳的启动条件和旋转滑动的力学机理,建立了滑坡稳定性的判据。     

贵州地区大塘阶黑色软岩的工程病害特性原因分析

在贵州地区的工程建设中,遇到石炭系大塘阶黑色软岩产生特殊的工程病害:边坡开挖后岩石风化迅速、短时间内崩解破碎,发生边坡失稳;其风化残坡积土在缓坡地带遇水形成特殊的“坡麓相斜坡软土”。本文通过分析研究,认为岩石中含有的特殊矿物是其发生工程病害的根本原因,提出了针对性工程措施。病害过程为:岩石暴露后发生一系列氧化反应及聚合反应,导致边坡破坏;岩石风化物堆积在缓坡地带,在水的作用下形成的斜坡软土。     

土—岩界面滑坡变形及成因分析—以陕西南部某滑坡为例

以陕西南部山区土—岩界面滑坡为研究对象,采用野外调查和地质分析的方法,总结出该滑坡变形特点及其成因,得出结论如下:(1)该滑坡为土—岩界面滑坡,滑面上部为土岩界面,下部为含碎石粉质粘土层内错动带;(2)滑坡的形成是受地形地貌、地层岩性、地下水及人类工程活动多种因素的影响;(3)土—岩界面为此类堆积层滑坡主控滑动面。     

矿物学与烧结砖瓦生产（七）

5.2 粘土矿物的起源与粘土矿床的成因 前文中叙述了粘土矿物的分类、性质及在烧结砖瓦生产中的一些重要性,那么,粘土矿物是怎样形成的呢?粘土矿床是由粘土矿物在一定环境中堆积而成.其中粘土的物质来源、矿化(生成)方式和富集条件是构成粘土矿床的三个主要因素.在谈到粘土矿物时,必然要提及粘土.粘土是与人类生活关系最为密切的硅酸盐矿物原材料之一.     

牵引式滑坡后缘破裂面形成机制试验研究

由于河谷下切或者坡脚开挖,常会造成自然斜坡牵引式滑动,形成多级后缘拉裂面。后缘面的形成机制对牵引式滑坡的稳定性分析有重要影响,因此开展试验测试和理论分析。开发能够同时模拟地下水对滑带软化作用和滑坡渐近破坏过程的试验装置,由若干渗透盒构成分段式滑面,可以模拟各种几何形态的滑动面,通过对不同渗透盒注水,可模拟滑带分阶段饱和软化,从而实现对各种滑坡破坏模式的模拟。设计4种试验方案,模拟圆弧型、折线型和直线型滑动面,以及三段线和两段线坡面线。分三阶段设计滑坡工况,测试滑体后缘面破裂倾角。试验表明,后缘面倾角试验值受滑体厚度和失稳滑段位置影响明显。假定牵引式滑坡的后缘面可能形成机制为整体滑动式、滑动拉裂式和滑动剪切变形式,计算后缘面倾角。比较表明,滑动拉裂机制计算值与试验值最接近,在试验值上下浮动,相对误差小于10%。据此认为牵引式滑坡的后缘面形成机制为:底滑面失稳下滑,在失稳滑面末端对应的滑体部位出现了拉破坏区,拉应力由最小主应力控制,拉破坏面方向与最大主应力方向基本一致。     

Correlation between natural slope angle and rock mass strength rating in the Betic Cordillera,Granada, Spain

This study proposes a method to determine zones gentler or steeper than the equilibrium slope angle based on rock mass strength (RMS) and to regionalize the parameters. The method was developed using GIS and applied to rock masses of the Alpujarride Complex (Granada, Spain). 41% of the natural slopes studied have angles lower than the equilibrium due to dissolution processes and the presence of alluvial or colluvial deposits, while 28% of those slopes have angles higher than the equilibrium due to rapid erosion in tectonically active zones. Cross correlation analysis between maps showing degrees of slope equilibrium and landslide inventories suggest that long-term geomorphic changes have induced slope angles higher than the equilibrium which are associated with rock falls and rock slides.      

地质灾害形成的内外动力耦合作用机制

 以三峡水电工程库区大型山体滑坡为研究对象,从三个方面研究地质灾害形成的内外动力耦合作用机制：(1) 通过对大量古滑坡的空间分布特征和发育时间的研究,寻求滑坡时空分布的控制因素,揭示滑坡发育演化与地球内外动力耦合作用的关系;(2) 通过对大型基岩滑坡滑带发育演化过程的研究,提出滑带形成演化的典型四阶段模式及其内外动力耦合作用机制;(3) 以三峡库区千将坪滑坡为例,通过对泥化夹层和滑带结构的精细地质分析和测试,重建滑带形成演化过程,研究千将坪滑坡发育及滑带形成的内外动力耦合作用机制。研究结果表明,新构造运动和第四纪气候变化的耦合作用是三峡库区发育多期大型古滑坡的主要动因;层间剪切作用和水岩相互作用的耦合是基岩滑坡滑带形成演化的主控因素;应重视三峡库区新生滑坡的研究,特别是对重点地层的层间剪切带地质力学特性的研究,将是发现和预测新滑坡的重要途径之一。     

The geological strength index: applications and limitations

The geological strength index (GSI) is a system of rock-mass characterization that has been developed in engineering rock mechanics to meet the need for reliable input data, particularly those related to rock-mass properties required as inputs into numerical analysis or closed form solutions for designing tunnels, slopes or foundations in rocks. The geological character of rock material, together with the visual assessment of the mass it forms, is used as a direct input to the selection of parameters relevant for the prediction of rock-mass strength and deformability. This approach enables a rock mass to be considered as a mechanical continuum without losing the influence geology has on its mechanical properties. It also provides a field method for characterizing difficult-to-describe rock masses. After a decade of application of the GSI and its variations in quantitative characterization of rock mass, this paper attempts to answer questions that have been raised by the users about the appropriate selection of the index for a range of rock masses under various conditions. Recommendations on the use of GSI are given and, in addition, cases where the GSI is not applicable are discussed. More particularly, a discussion and suggestions are presented on issues such as the size of the rock mass to be considered, its anisotropy, the influence of great depth, the presence of ground water, the aperture and the infilling of discontinuities and the properties of weathered rock masses and soft rocks.     

Numerical evaluation of strength and deformability of fractured rocks

Knowledge of the strength and deformability of fractured rocks is important for design, construction and stability evaluation of slopes, foundations and underground excavations in civil and mining engineering. However, laboratory tests of intact rock samples cannot provide information about the strength and deformation behaviors of fractured rock masses that include many fractures of varying sizes, orientations and locations. On the other hand, large-scale in situ tests of fractured rock masses are economically costly and often not practical in reality at present. Therefore, numerical modeling becomes necessary. Numerical predicting using discrete element methods(DEM) is a suitable approach for such modeling because of their advantages of explicit representations of both fractures system geometry and their constitutive behaviors of fractures, besides that of intact rock matrix. In this study, to generically determine the compressive strength of fractured rock masses, a series of numerical experiments were performed on two-dimensional discrete fracture network models based on the realistic geometrical and mechanical data of fracture systems from feld mapping. We used the UDEC code and a numerical servo-controlled program for controlling the progressive compressive loading process to avoid sudden violent failure of the models. The two loading conditions applied are similar to the standard laboratory testing for intact rock samples in order to check possible differences caused by such loading conditions. Numerical results show that the strength of fractured rocks increases with the increasing confning pressure, and that deformation behavior of fractured rocks follows elasto-plastic model with a trend of strain hardening. The stresses and strains obtained from these numerical experiments were used to ft the well-known Mohr-Coulomb(MC) and Hoek-Brown(H-B) failure criteria, represented by equivalent material properties defning these two criteria. The results show that both criteria can provide fair estimates of the co     

Impact of weathering on slope stability in soft rock mass

Weathering of soft rocks is usually considered as an important factor in various fields such as geology, engineering geology, mineralogy, soil and rock mechanics, and geomorphology. The problem of stability over time should be considered for slopes excavated in soft rocks, in case they are not protected against weathering processes. In addition to disintegration of material on slope surface, the weathering also results in shear strength reduction in the interior of the slope. Principal processes in association with weatherinz are discussed with the examnles of marl hosted on flvsch formations near Solit. Croatia.     

Traitement d’image appliqué aux matériaux: Exemple d’une analyse quantitative des feldspaths dans les roches

Mechanical properties of Neogene sedimentary soft rocks and their discontinuities are deteriorated by environmental changes, such as wetting and stress release. In addition, the reliable estimation of shear strength of weakness planes in these rocks is a common problem. This paper aims to characterize the engineering properties of weak, stratified, clay-bearing coal measures encountered in surface coal mining in southwest Turkey with special reference to the shear strength of their discontinuities and weak zones which are of particular significance in determining slope stability. The results obtained from a series of laboratory shear tests carried out on specially prepared bulk samples containing natural discontinuities and weak zones were compared with values, which resulted from tests on similar weakness planes in another pit and back-analyses of instabilities experienced in two mines, for further design considerations.     

Instability assessment of slopes in heavily jointed limestone rock

This paper presents the results of geotechnical investigations regarding the assessments of instability problems in the high wall slope faces of the heavily jointed limestone rock mass in Marulan Quarry in NSW, Australia. Generally, instability of hard rock slopes is mainly controlled by the presence of the structural geology and rock mass discontinuities through the slope faces of the open pit excavations. Stability analysis of slope faces in an open pit mine requires the laboratory assessment of the engineering properties of rock, shear strength of the discontinuities and also field investigations of the rock mass discontinuities. To achieve the above objectives, a laboratory testing program was carried out on the intact rock samples and also a three-dimensional scanline survey was carried out to consider the physical and mechanical properties of the rock mass discontinuities. The results of the discontinuity data collected during joint surveys were interpreted with the application of stereographic projection techniques for assessing the potential unstable zones and also for defining the modes of failure in different parts of the limestone quarry.      

Determination of fracture depth of rock blocks from P-wave velocity

The quality of large rock blocks produced from quarries depends significantly on the fractures and the extent to which they penetrate into the rock. The paper reports a laboratory study to evaluate the possibility of the determining fracture depth in rock blocks from P-wave velocity. Three igneous, three sedimentary and three metamorphic rocks were studied. Inverse linear relations were found between the fracture depths and the P-wave velocities. Although, the slope of the regression lines is approximately the same for the rocks belonging to one rock class, different trends are seen for the different rock types. In addition, some correlation was found between the slopes of the regression lines and the physical properties of the rocks.      

Weathering indices and their applicability for crystalline rocks

In the recent past, several weathering indices have been proposed to characterize the extent of weathering and weatherability depending upon the nature and requirement of the study. The weathering index provides a quantitative measure of the extent of weathering of rock; hence it can provide input to the prediction models to assess the strength and deformational properties of rocks and classifications of weathered rock material. In the present study some of the important weathering indices, broadly categorized as chemical, (micro) petrographical and engineering weathering indices, are reviewed and studied experimentally for three common rocks of India, namely granite of Malanjkhand, basalt of Nagpur and quartzite of Delhi, along with results of other rocks reported by other researchers. The study reveals that none of the existing chemical weathering indices is valid for genetically different common rock types and useful for engineering purposes. However, loss on ignition (LOI) may provide an approximate estimation of altered minerals (clays and hydroxides) in tested rocks. It has also shown good correlation with petrographic indices and engineering index properties. Among the petrographic indices, crack density (ρ_cr) and unsound constituent (an input to the micropetrographic index) indices provide good correlation with engineering index properties. To quantify the extent of weathering in terms of strength degradation due to weathering in rock, an index is suggested – strength ratio (R_s) – which is the percentage of uniaxial compressive strength (σ_c) of weathered rock with respect to σ_c of fresh rock. Its significance is shown statistically through the relationships with other indices for several rock types including sedimentary and metamorphic rocks. Electronic Publication     

Engineering geological properties of weathered swelling mudstones and their effects on the landslides occurrence in the Yanji section of the Jilin-Hunchun high-speed railway

To identify the mechanisms that caused landslides during the construction of the Jilin-Hunchun high-speed railway line in Yanji, China, the engineering properties of weathered swelling mudstones extracted from a representative landslide site were investigated. The experimental results indicate that both yellow-brown and magenta mudstones exhibit significant swelling and shrinkage behaviour due to significant amounts of swelling clay minerals. The yellow-brown mudstone has an obvious schistose structure with stacked flaky plates interconnected with a face-to-face pattern, while the magenta mudstone has an aggregated structure cemented by iron oxides. Both mudstones are prone to disintegration when soaked in water. The shear strengths of swollen samples decrease dramatically compared with those of unsaturated samples, and the lower the initial water content is, the smaller the shear strength of a sample after swelling. By repeatedly increasing the repeated drying-wetting-freezing-thawing cycles, the shear strength decreases. According to the experimental findings, the effects of the engineering properties of mudstones on the landslides occurrence in the Yanji section are discussed. Heavy rainfall and the weathering of mudstones induced by fluctuating climatic conditions are regarded as the principal factors that triggered the landslides. Given the high landslide incidence on south-facing slopes, the influence of slope orientation on the stability of mudstone slopes is studied and discussed.