A new slope mass rating in mountainous terrain, Jammu and Kashmir Himalayas: application of geophysical technique in slope stability studies

The slopes of western Lesser Himalaya (at Sangaldhan Block of Udhampur near Ramban, Jammu and Kashmir India) are being severely affected by tectonic and erosional activities. These activities result in deposit of a thick cover of rock fragments and overburden just above the hard rock. The thickness of overburden cover has directly affected the stability of slope in the study area, though the traditional stability estimation techniques, rock mass rating and slope mass rating, rate this area as moderately stable which does not represent the real stability condition. In this research work, the geotechnical and geophysical surveys have been carried out to reckon the slope stability conditions more accurately as compared to traditional slope stability estimation techniques. A new rating, new slope mass rating, is developed, which gives a better picture of the stability of slopes. It incorporates a new parameter of overburden thickness profile, along with slope angle and other associated factors on the slopes of the mountainous terrains. The vertical electrical sounding surveys were conducted for the demarcation of rock–overburden interface and for determining the overburden cover. This new classification depicts an increase of 12.84 % in unstable slope areas giving a better assessment and factual picture of slope stability in our study area. This study also enumerates the importance of geophysical applications in slope stability studies. The research work is applicable in mountainous terrains such as Himalaya, and the major component of the application is the orientation of overburden or the profile of thickness in relation with slope of surface.     

Stability analysis and supporting system design of a high-steep cut soil slope on an ancient landslide during highway construction of Tehran–Chalus

The stability of both natural and cut slopes in mountainous areas is a great challenge to highway constructions and operations. This paper presents a successful case study of stability analyses and protection treatments for high-steep cut soil slopes in an ancient landslide zone which was located at Km12+700 to Km15+000 along the Tehran?CChalus highway. This report has three parts. First, geotechnical investigations of in situ direct shear test, SPT tests and laboratory tests were implemented to get the subsurface profiles and the mechanical properties of the soil mass. Second, finite difference analysis was carried out to evaluate the stability of both the natural and cut slopes. Minimum safety factors and potential failure modes of cut slopes were obtained under both static and dynamic conditions. These results indicated that the ancient landslide could not be reactivated under the present climatic and morphological conditions, but there were some potential shallow failures in some cut soil slopes (failure actually occurred during excavation). Protection treatments and reinforcements were thus necessary. Third, the stability of the cut slopes was re-assessed by simplified Bishop limit equilibrium analysis (using Slide 5.0). Some potential failure zones were designed to be protected by back-anchored concrete retaining wall at the slope toe, rock bolts and frame beams on the slope face and planting grass on the slope face. Numerical analysis indicated that these protection measures could stabilize this remedial slope. These practical experiences may be of benefit for similar highway construction projects.     

Geotechnical characterisation of lateritic soils from south-western Nigeria as materials for cost-effective and energy-efficient building bricks

Lateritic soils which have been described as highly weathered tropical or subtropical residual soils were studied with an attempt to establish its suitability or otherwise as sustainable material in building bricks and housing development that will meet the present challenge of sustaining the environment without costing too much and maintaining a high standard of strength, durability and aesthetics. Index properties of the tested lateritic soils revealed them as mostly well graded, comprising both cohesive (silt and clay) and cohesionless (sand and gravel) soil fraction. The geotechnical analyses on the studied lateritic soil revealed a strong compressive strength with a relatively sound dry density which could guarantee a good durability in resulting bricks made from these soil materials. Further test on the strength and durability of the compressed earth bricks (CEBs) made from these lateritic soils revealed a brick with compressive strength ranging between 6.33 and 15.57 MPa which is considered to be of good strength coupled with its sound durability strength established over a period of more than one year under a complete cycle of weather and seasonal conditions. In conclusion, lateritic soils from the study area were found to be suitable as materials for bricks (CEB) with good compressive and durability strength which qualifies them as sustainable and cost-effective materials for low-cost housing development.     

花岗岩类土质边坡工程特性及加固方法研究

华南、华东南地区具有厚度可达上百米的花岗岩风化残积层。高等级公路、铁路的规模建设在该地区形成了大量的花岗岩类土质高边坡。深入认识该类边坡的工程特性并提出有效的针对性边坡加固方法,对该地区公路、铁路的安全建设和正常运营具有重要意义。为了更有效指导该类边坡的稳定性分析及边坡设计,本文深入调查分析了广东和广西境内4条高等级公路沿线的44处花岗岩类土质边坡特征及其稳定性,认为控制该类边坡稳定性的因素主要有:土体的均匀性、岩脉(墙)及花岗岩球状硬核的分布情况、坡体中保留的结构面是否对坡体稳定性起控制作用。继而依据这些因素把花岗岩类土质边坡划分为岩脉(墙)隔挡型边坡、网状结构型边坡、外倾结构型边坡、浮石型边坡4种类型。深入分析了每种类型边坡的坡体结构特征、稳定特性,针对性地提出了边坡稳定性分析中应重点考虑的因素。认为花岗岩类土质边坡的土质及坡体结构特征,造成了该类边坡开挖临时自稳性较好,但具有较强的开挖卸荷效应和较弱的抗冲刷能力。最后针对每种类型的花岗岩类土质边坡,提出了相应的设计方案建议。基于花岗岩类土质边坡良好的临时自稳性,认为可进行陡开挖强支护设计,同时强调逐级开挖逐级支护、加强坡面防冲刷、边坡护脚及压顶、边坡截排水等设计建议。     

Optimization of slope angle of a lead-zinc mine

Summary The present study represents an attempt to optimize the overall slope angle of a lead-zinc mine in Rajasthan state, which could extend to a depth of 170 m during the first phase of mining. Detailed geotechnical investigations were conducted. These included geotechnical mapping, determination of the physio-mechanical properties of intact rock, determination of the rock mass rating and estimation of rock mass properties. Information was collected from mapping of benches and borehole logs. Based on these data, limit equilibrium and numerical simulation techniques were applied in order to assess the stability of the slopes and determine an optimum slope angle. From these investigations it has been inferred that the overall footwall and hangingwall slopes should be 42° and 48° respectively.     

Use of lateritic soils for road construction in North Dahomey

Due to the deterioration of the Parakou—Malanville highway, the preparation of a rehabilitation program was necessary. The related geotechnical exploration provided an excellent opportunity to study the properties of the encountered lateritic soils. The mineralogical analysis proved that the lateritic overburden originates from the local rocks. However, the analyses also indicated that the soils can only be identified as lateritic by virtue of their hematite content. The soils were classified according to the AASHO-system and their geotechnical properties were thoroughly investigated. The results revealed that the overwhelming majority of the available soils was unsuitable for highway construction due to their high plasticity. In order to improve them, cement stabilization was suggested. The laboratory tests resulted in an economically feasible solution.     

Structural,geomorphological and geomechanical aspects of the Koyulhisar landslides in the North Anatolian Fault Zone (Sivas,Turkey)

. Recently, numerous landslides occurred in the northern part of Koyulhisar. In 1998 and 2000, which were very wet years, landslides in different masses affected the geological formations which are well known for being prone to slope movements. Detailed geological, geomorphological and geotechnical surveys were carried out, and stability conditions in Koyulhisar village, located NE of Sivas (Turkey), are discussed in this paper. Kinematical analyses showed that the potential slope instabilities are in two main directions: the first direction is SE and the second is SW, these directions corresponding to the dominant slope directions of the study area. Geomechanic surveys confirmed that most of the rock slopes analysed are highly prone to instability. The SMR criterion gave results which correspond well with real stability conditions. Jointing and faulting, steep topography, water incisions, and heavy rainfall played a significant role in the occurrence of the landslides.     

Finite element modelling of landslide prone slopes around Rudraprayag and Agastyamuni in Uttarakhand Himalayan terrain

Himalayan mountain chains are neo-tectonically active and significantly susceptible to frequent geohazards like landslides, earthquakes, cloudburst and flash floods, etc. Himalayan slopes are characterized by highly fractured, jointed and sheared rock mass. This affects the strength of the rocks and thus largely influences the stability characteristic of slopes which have been aggravated by human intervention. The ongoing developmental activities, particularly in the last two decades, are responsible for large-scale destabilization of slopes. In rugged terrain, safer designs along hill-cut roads must be ensured. Despite extensive geotechnical works for slope stabilization done in the Himalayan range, slope sections evolve due to various natural and man-made factors are need to be understood in greater details. Proper evaluation and treatment were done on the cut slopes that are severely affected during Kedarnath disaster of June 2013. One of such roads is national highway from Rudraprayag to Gaurikund near Kedarnath. In this study, the stability of vulnerable road cut slopes from Rudraprayag to Agastmuni was investigated. Three key road cut slopes were considered. Finite element analysis was conducted using PLAXIS simulator. Factors of safety, stress, strain, horizontal and vertical displacement have been determined for each slope. The most unstable slope had a factor of safety (FoS) equal to 0.935, while the most stable slope had FoS equal to 2.56. Outcomes from simulation are in good agreement with the prevailing field conditions. Slope stability evaluation must be performed to ensure better safety and to achieve disaster mitigated design.     

含软弱夹层岩质边坡稳定性研究现状及发展趋势

含软弱夹层岩质边坡在自然环境和工程实践中都比较常见，稳定性差，边坡失稳产生了大量的滑坡灾害，造成大量人员伤亡和经济损失。因此，含软弱夹层岩质边坡稳定性研究一直是工程地质和岩土工程领域的研究重点之一。在收集整理国内外相关资料的基础上，从自重工况、开挖工况、暴雨和蓄水工况、地震工况方面总结了目前含软弱夹层岩质边坡稳定性的研究现状及进展，取得如下主要认识:(1)软弱夹层对岩质边坡稳定性有显著不利影响，含软弱夹层岩质边坡的稳定性比均质岩质边坡、不含软弱夹层的层状岩质边坡都差；(2)含软弱夹层岩质边坡的稳定性系数、变形特征和破坏模式与软弱夹层的含水状态、抗剪强度、倾角、厚度、间距、层数和边坡坡度有关；(3)开挖容易诱发坡体沿软弱夹层滑坡，含软弱夹层岩质边坡开挖后需要及时支护；(4)爆破层裂效应改变了软弱夹层与围岩的接触状态，减小了它们之间的凝聚力和摩擦力，导致边坡稳定性降低；(5)暴雨和蓄水都不利于含软弱夹层岩质边坡稳定；(6)岩质边坡地震动力响应和变形破坏特征受软弱夹层参数(厚度、倾角、含水状态)、地震波特性(地震波的类型、幅值、频率、激振方向)和边坡结构(顺层或反倾)共同影响；(7)在软弱夹层对水平向动力响应的放大或减弱作用及厚层软弱夹层的消能减震作用方面仍然存在不同观点。在此基础上，分析了研究方法的优缺点，指出当前含软弱夹层岩质边坡稳定性研究存在的问题。最后，针对该领域的研究现状，提出了未来的研究重点和方向，主要包括:含多层软弱夹层岩质边坡的渐进性变形破坏过程和稳定性；全面深入研究单因素作用(开挖卸荷、爆破、地震、暴雨、库水位变化、地下水等)对含软弱夹层岩质边坡稳定性的影响机制；多因素耦合作用下含软弱夹层岩质边坡稳定性；支挡结构体系对含多层软弱夹层高陡岩质边坡的加固机制。     

基于模糊因素的岩质边坡地震稳定性多模型组合评价

岩质边坡地震稳定性评价是岩土边坡地震失稳防治的基础工作,针对评价过程中评价因素的多源模糊性,借鉴工程可变模糊集理论,将模糊可变评价模型应用于岩质边坡地震稳定性评价中。综合考虑岩质边坡内在结构和外部自然条件,选取岩土体特性、新构造运动特征、坡高、坡角、年均降雨量和场地地震烈度6个指标作为评价指标体系并建立等级标准;将改进熵权算法引入该模型中,利用指标实际数据离散性求权重;通过改变模糊可变评价模型参数对岩质边坡地震稳定性进行线性与非线性组合评价,并将均值作为最终评价结果。将该方法应用于天然边坡与路堑边坡实例中,结果表明,模糊可变评价模型评价结果合理、客观,具有更高的可靠性与稳定性,为岩质边坡地震稳定性评价工作提供了一种新的研究方法与思路     

侵入岩脉风化壳对中林村残积土滑坡渗流场和稳定性的影响

岩脉侵入是一种普遍的地质现象,侵入岩脉及其风化壳对斜坡的渗流场和稳定性具有重要影响,但目前国内外在该方面的研究鲜见报道。我国东南沿海约50×104 km2的白垩系火山岩地层中广泛分布侵入岩脉及其风化壳,改变了该地区残积土斜坡的失稳机制。以浙江省文成县中林滑坡为对象,研究花岗岩脉风化壳对其渗流场和稳定性的影响。中林滑坡主要由凝灰岩及其残积土组成,后部有侵入的花岗岩脉及其残积土,利用室内土柱试验获取降雨作用下两种残积土渗透性质的差异,利用不同含水率下的直剪试验获取非饱和抗剪强度参数;利用Geo-studio软件中的Seep/W模块反演土柱降雨试验,获取两种土体的非饱和渗透参数;接着将上述参数应用于中林滑坡的渗流场模拟,获取降雨入渗下坡体的渗流场;将渗流场耦合到坡体稳定性计算中,获取了坡体的稳定性变化曲线及最危险滑面。结果表明,降雨通过侵入岩脉风化壳快速入渗,并顺着基覆面向凝灰岩残积土区侧向渗流,导致侵入区与原始斜坡的交界处以及基覆面附近的地下水位快速升高,孔隙水压力迅速增大,斜坡在该位置最易变形破坏,且失稳深度远大于普通的浅层残积土斜坡,可达6～10 m。该研究成果可为东南沿海地区有岩脉侵入的残积土斜坡的稳定性评价与防治设计提供理论依据。     

Early weathering of palladium gold under lateritic conditions,Maquiné Mine,Minas Gerais,Brazil

Since the 80's, studies have shown that Au is mobile in supergene lateritic surficial conditions. They are based either on petrological, thermodynamic studies, or experimental works. In contrast, few studies have been done on the mobility of the Pt group elements (PGE). Moreover, at the present time, no study has addressed the differential mobility of Au, Ag and Pd from natural alloys in the supergene environment. The aim of this study is to understand the supergene behavior, in lateritic conditions, of Au–Ag–Pd alloys of the Au ore locally called Jacutinga at the Maquiné Mine, Iron Quadrangle, Minas Gerais state, Brazil.The field work shows that the host rock is a “Lake Superior type” banded iron formation (BIF) and that the Au mineralization originates from sulfide-barren hydrothermal processes. Primary Ag–Pd-bearing Au has developed as xenomorphous particles between hematite and quartz grains. The petrological study indicates that the most weathered primary Au particles with rounded shapes and pitted surfaces were found, under the duricrust, within the upper friable saprolite. This layer, however is not the most weathered part of the lateritic mantle, but it is where the quartz dissolution resulting porosity is the most developed. The distribution of Au contents in the weathered rocks are controlled by the initial hydrothermal primary pattern. No physical dispersion has been found. Most of the particles are residual and very weakly weathered. This characterizes early stages of Au particle weathering in agreement with the relatively low weathering gradient of the host itabiritic formations that leads essentially to the development of isostructural saprolite lateritic mantle. Limited dissolution of primary Au particles issued from the friable saprolite induces Pd–Ag depleted rims compared to primary Au particle Pd–Ag contents.In addition, limited very short distance in situ dissolution/reprecipitation processes have been found at depth within the primary mineralization, as illustrated by tiny supergene, almost pure, Au particles. The supergene mobility order Pd>Ag>Au as reflecting early weathering stages of Au–Ag–Pd alloys under lateritic conditions is proposed.     

Cultural heritage and geological hazards: the case of the Calomini hermitage in Tuscany (Italy)

The Calomini hermitage is located on a steep slope, below an 80- to 130-m-high hanging rock wall. The hermitage, a significant example of religious architecture, has been a pilgrimage place since the Middle Ages. The monastery, completed by the tenth century, is built into the rock mass for more than half of its length. The stability and safety of the complex are threatened by stability problems in the rock slope. Structural and geotechnical investigations were carried out, showing the potential for rock blocks slides, particularly under dynamic conditions, with the fall of middle size blocks. Recently, some remedial works have been carried out, and wire meshes have been hung on the rock wall. Nevertheless, a significant portion of the Calomini hermitage area may be still dangerous and exposed to severe landslide hazard. Therefore, further research and countermeasures are necessary to protect a very important item of Italian cultural and architectural heritage.     

A resilience framework for safety management of fossil fuel power plant

In the present study, cut slope stability assessment along ghat road section of Kolli hills was carried out by using various geotechnical parameters of rock and soil slope sections and structural kinematics of major discontinuities is presented. The rock slope (RS) stability assessment was carried out using Rock Mass Rating basic (RMR_basic) and Slope Mass Rating (SMR) classification systems. The type of failure and their Factor of Safety (FOS) for individual RS was calculated using Hoek and Bray method. In the case of soil slopes (SS), the FOS was calculated using Circular Failure Chart (CFC) and Limit Equilibrium (LE) methods. The input data for the slope stability analyses were collected through extensive field work followed by stereonet plotting and laboratory test. There are six rock slope sections, and five soil slope sections were taken into consideration for the cut slope stability analyses. The area depicts class II (RS-1, 2, & 6) and class III (RS-3, 4, & 5) of RMR classes. The SMR result depicts for RS-1, RS-2, and RS-6 are 64.40, 60.02, and 60.70, respectively, and falls in class II stable condition. The SMR values of RS-3 and RS-5 were 44.33 and 57, respectively, and come under the class III partially stable condition. The RS-4 with SMR value of 17.33 falls under the class I completely unstable condition. The FOS of planar failure case indicates that RS-3 (FOS = 0.22) is more unstable, while all other sections are having greater than 1 FOS. The calculated FOS values using CFC method reveals that the FOS is very close to 1 for all the SS sections that fall under completely saturated condition which indicates that these slope sections may fail during heavy rainfall. In LE method, the sections SS-3 and SS-4 are unsafe under partially and completely saturated (natural slope) condition. In average slope condition, all the SS sections are unsafe under partially or completely saturated conditions. The facets 2, 3, 4, and 5 required mitigation measures, to improve the stability of slopes. Site-specific mitigation measures were suggested for partially or completely unstable rock and soil cut slopes.     

降雨入渗下强风化软岩高填方路堤边坡稳定性研究

降雨入渗是影响边坡稳定性、导致边坡失稳的最主要和最普遍的环境因素。强风化软岩用于高填方路堤填土边坡时,填土的压实度直接影响路堤土的渗透性和强度。利用饱和与非饱和渗流有限元模拟降雨入渗时高填方路堤的暂态渗流场,将计算得到的暂态孔隙水压力分布用于边坡的极限平衡分析,并考虑基质吸力对非饱和土抗剪强度的影响。探讨降雨强度、持时和压实度对边坡稳定性的影响。研究表明,强风化软岩用于高填方路堤压实度不能低于90 %;当暴雨强度为200 mm/d时,边坡就会失稳。其成果将为高填方路堤边坡防护设计提供科学依据。     

An engineering geological approach to road cutting slope design in Ghana

Summary Road cutting slope design in tropical terrains often tends to be conservative when based on the methods of classical slope stability analysis. This could be attributed to the difficulties encountered in the accurate characterization of tropically weathered rocks and soils, and the time-dependent improvement in soil properties resulting from haematite-hardening of the slope faces. A field-orientated approach, based on a slope performance survey of both natural and existing cutting slopes in similar geo-environmental settings, often tends to provide a more reliable alternative for the design of cutting slopes along new roads. This paper presents the results of slope performance studies carried out at selected locations in Ghana as a guide to designing cutting slopes along two proposed road projects in the southwestern sector of the country. It is recommended that slopes in competent lithologies along the proposed roads should be cut at steep inclinations of 72° and 80° while slopes in the less competent lithologies should be cut at flatter inclinations of 45°.     

Characterisation of a volcanic residual soil and its implications for large landslide phenomena: application to Tenerife,Canary Islands

Large landslides are common processes during the evolution of volcanoes and individual events can exceed several cubic kilometres in volume. Volcanic slope failures are a significant risk for the neighbouring population due to their huge volumes and great runout distances. Around the Canary archipelago, a total of seventeen deposits of large landslides have been found, and on Tenerife, seven large landslides have affected the subaerial and submarine morphology during the last ∼6 Ma. However, the causes of such mass movements are still poorly understood. This work analyses the events around the Canary Islands and focuses on the ones that occurred on Tenerife in order to obtain new insights into the mechanisms of large volcanic landslides. The study is divided into a first part that includes site investigations examining the general features favouring large-scale failures at volcanoes. The second part describes the laboratory tests used to analyse a residual soil that may be the potential slip surface of the slides on Tenerife. The site investigation revealed that regional tectonics and the climate have a significant influence on the spatial distribution of the landslides. Moreover, morphological and geological features such as deep fluvial canyons, a high coastal cliff and persistent dike intrusion may favour the initiation of slope failure. A typical residual soil sample from the lateral scarp of the La Orotava amphitheatre on Tenerife was studied by carrying out standard laboratory tests. The microstructure was analysed using environmental scanning electron microscopy and a particular bonding was found. This bonding was also detected by the geotechnical tests. Consolidation tests and direct shear tests revealed that the mechanical behaviour of the residual soil changes greatly if the bonding of the soil is broken. The bonded structure generally fails when the effective normal stress surpasses the yield strength of the bonding. In the case of large volcanic landslides with thicknesses up to several hundred meters, the high overburden easily exceeds this yield strength and generates a broken bonding. Therefore, volcanic residual soils, such as the one analysed in this study, are perfect candidates for the potential failure surfaces of large volcanic landslides. Referring to the La Orotava events, we assume that residual soil layers and morphological, geological and climatic features reduced the slope stability to critical conditions, whereas a strong earthquake associated with a caldera collapse episode may have finally triggered the landslide. The results obtained indicate that the residual soils play an important role in affecting the stability of volcano slopes and their destabilising influence significantly favours large-scale sliding. We suggest that the results obtained from this study can be applied to other locations since volcanic residual soils are common in volcanic areas.     

高陡岩质料场边坡稳定性与支护设计研究

水电站料场高边坡具有高度大、坡度陡、卸荷速度快等特点,因多按临时边坡进行设计,故施工期变形破坏事例频发。基于这一现状,依托瀑布沟水电站两岩质料场边坡,通过两年多跟踪施工过程的支护设计工作,总结出一套操作性强的料场高边坡稳定性及支护设计方法。针对料场边坡存在的受软弱结构面控制的边坡整体稳定性、浅表层块体稳定性、碎裂岩体稳定性三种工程地质问题,在跟踪施工过程开展岩体结构调查的基础上,按照先整体后局部的稳定性评价思路,开展高边坡稳定性评价。施工期动态支护设计按照保证整体稳定,控制局部变形,顾全潜在失稳区域的理念,通过定性评价确定不稳定区域并优先设计提交施工;针对施工中最易出现的块体变形和碎裂岩体变形,建立了合理的支护设计原则和严格的施工规定;对稳定性差、施工风险高、支护造价大的潜在不稳定区域,应及时地调整开挖方案,减少工程造价。实践表明,这套方法保证了料场高边坡的快速施工安全,减少了工程投资。     

Weathering characterization for landslides modeling in granitoid rock masses of the Capo Vaticano promontory (Calabria,Italy)

This work focuses on developing multidisciplinary researches concerning weathering profiles related to landscape evolution of the Capo Vaticano promontory on the Calabria Tyrrhenian side (southern Italy). In this area, the tectonic uplift, occurred at least since Pleistocene, together with the Mediterranean climatic conditions, is the main cause of deep weathering and denudation processes. The latter occurred on the outcropping rocks of the crystalline-metamorphic basement, made up of weathered granitoids, in turn belonging to the Monte Poro granitoid complex (intermediate to felsic plutonic rocks covered by Cenozoic sedimentary successions). Field observations coupled to borehole explorations, geophysical surveys, and minero-petrographical analyses allowed the characterization of the granitoid outcrops typical of the studied area in terms of kind and degree of slope instability. This characterization was based on suitable correlations verified between several factors as weathering degree, elastic properties of rocks, and discontinuity features. Weathering profiles are mainly composed by rock masses varying from completely weathered rock with corestones of highly weathered rock (classes IV–V) to slightly weathered rocks (class II). The weathered rocks are involved in several landslide typologies such as debris flow (frequency 48.5%), translational slide (frequency 33.3%), and minor rock fall and rotational slide (frequency 9%). The achieved data allowed the establishment of a general correlation between weathering degree and type of slope instability. Debris flow-type instabilities are predominant on the steeper slopes, involving very poor rock masses ascribed to the shallowest portions of the weathering class IV. Translational slides are less widespread than the previous ones and often involve a mixture of soil and highly weathered rocks. Rotational slides are more frequently close to the top of the slopes, where the thicknesses of more weathered rocks increase, and involve mainly rock masses belonging to the weathering classes IV and V. Rock falls mostly occur on the vertical escarpments of the road cuts and are controlled by the characteristics of the main discontinuities. The assessment of rock mass rating and slope mass rating, based on the application of the discontinuity data, allowed respectively an evaluation of the quality of rock masses and of the susceptibility of rock slopes to failure. The comparison between the last one and the real stability conditions along the cut slopes shows a good correspondence. Finally, the geological strength index system was also applied for the estimation of rock mass properties. The achieved results give a worthy support for a better understanding of the relationship between the distribution of landslides and the geological features related to different weathering degrees. Therefore, they can provide a reliable tool to evaluate the potential stability conditions of the rock slopes in the studied area and a general reference framework for the study of weathering processes in other regions with similar geological features.     

A deep-seated slow movement controlled by structural setting in marly formations of Central Italy

The site investigation of low-gradient slopes composed by marly rocks usually focuses on shallow slides in weathered mantling material as it is assumed that the underlying bedrock has higher strength, but deeper investigations may reveal larger, active, deep-seated movements. A typical example of this is found in Montemartano (Perugia, Central Italy). Here aerial photo interpretation and field observations indicate that active movements involve the shallower portion of the slope, formed by a very old and large landslide body extending over an area of about 0.5 km². Borehole core logging and probe inclinometer monitoring reveal that the area corresponding to the deep-seated landslide is moving at a maximum rate of 70 mm/year down to a maximum depth of 40 m. A comparison of inclinometer and piezometer data indicates that the movement seasonally reactivates even when rainfall and piezometer levels are below average values and suggests that structural setting of the whole slope influences both groundwater flow and movement kinematics. This hypothesis is reinforced by seepage analyses and stability analyses yielding a mobilized shear strength close to residual strength of the clayey interbeds of the marly limestone formations. This implies that instability occurs along bedding over a large part of the slide. The importance of these phenomena in land management policy is discussed and the critical aspects of their investigation and monitoring are addressed. The reconstruction of landslide geometry/stratigraphy and geotechnical characterization of the materials is closely considered, particularly as these are complicated by the limited representativeness of field and laboratory investigations in this type of material.