Landslides: Theory, Practice and Modelling

Mass wasting is a natural phenomenon by which rock, soil and/or debris move downwards due to the action of gravity. It describes all the processes that act continuously with varied intensity on all type of slopes to lower the ground surface. The mass wasting process is controlled by the interaction of geological agents and processes with the geo-materials. The degree and type of movements depend upon a few aspects of geology, environment, geomorphology, hydrology, and some additional environmental stress factors, including biotic factors. It is more active in hilly regions like Himalayas, Western Ghats, Alps, and some other extensive mountain chains of the world. Sometimes it becomes disastrous to lives, property and economy. This chapter gives an overview of mass wasting processes and its classification. Some widely used mass movement classification schemes have been documented.

In order to mine out the valuable minerals from the depths of the earth’s surface, huge amounts overlying material must be removed first. This overlying material, which in most cases is of no economic value to the mining operation, is called overburden (a mine waste), and has to be stored in the mine vicinity in order to keep on mining the underlying mineral effectively. Limited space available in a mining project renders it necessary for the overburden to be stored in form of dumps, which can reach huge dimensions as mining moves on to higher and higher stripping ratios. It hence becomes a necessity to ensure that these dumps are safe in all conditions and stages of mine working. Understanding of the mechanics and dynamics of the dumps and dump slopes therefore, becomes a crucial requirement for a mining engineers that will help them design safer dumps, simultaneously considering the economic aspects of mining. With this consideration, this chapter deals with a broad overview of the dumps and dump design, covering various details of the dumping methodologies, dump characterisations, and mechanics and dynamics of dump slope failure. Stress of this chapter is specifically focused on proper understanding of the various factors that affect the stability of the dump slopes.

Rocks encountered in civil and mining engineering structures are generally jointed in nature. The presence of joints renders anisotropy in rock and makes them weaker in their engineering response. Assessment of shear strength response of such jointed rocks, subject to given stress state, is a challenging task. Large size field tests are very expensive and time consuming and hence not feasible for majority projects. The best alternative available is to use indirect methods to describe the shear strength behaviour of jointed rocks.

The present articles presents some of the most widely used techniques developed during last few decades, using which the shear strength response of jointed rock can be assessed with reasonable accuracy. Relatively simple tests and observations are required for applying these techniques and hence input data can be procured without much difficulty. The shear strength response is divided into two broad categories i.e. strength behaviour of joints and strength behaviour of jointed rock mass. Shear strength models described in this article cover linear as well as non-linear strength response. Classification systems are widely used to characterize the rock masses in the field. It has been explained, how, these classification systems could be used to assess the shear strength response of the rock masses.

Rockfall is a specific case of mass wasting that occurs frequently in mountainous regions and when it occurs along transportation corridor or near populated areas it can pose significant hazards. Rockfall is a freefall type of movement generally from steep cliffs or slopes. After initiation of rockfall, type of movement or trajectories of falling blocks largely depends upon certain factors like potential falling blocks, prevailing geometry and geomechanical properties of interacting surfaces. Various other natural and anthropogenic causative and triggering factors have been briefly described here. During preliminary investigation stage, vulnerable zones can be screened out by using Rockfall Hazard Rating schemes. A comprehensive review of major existing rockfall hazard rating system is presented. The delineated hazardous zones should be evaluated in detail using comprehensive site specific studies by modeling techniques which provide much better insight of the problem. Earlier rockfall studies were conducted using in-situ tests and physical modeling which includes lot of time, money and man-power. Later, the development of software for rockfall simulation reduced ambiguity, cost, time and expenditure. Such techniques are used worldwide extensively and have achieved immense popularity among researchers working on rockfall studies. Few such software have been discussed in this chapter. A summary on remedial and protection measures has been presented.

InfraRed Thermography (IRT) is presented herein as a support methodology during the rock mass survey. Although this technique is widely used in several scientific fields, its direct application for such purposes is still pioneering. In this review paper, the outcomes of the most recent researches on the application of IRT to the rock mechanics are reported and commented, with particular reference to the study of thermograms and to the development of a Cooling Rate Index (CRI), useful for the evaluation of the jointing condition of the rock.

Three application cases are commented to demonstrate the reliability of such methodology in the geomechanics, taking into account both bare-jointed rock masses and highly weathered rock slopes. Achieved results lay the foundation for future researches aiming at a refined and improved survey methodology, which would be a useful support in the geomechanical analysis of heavily fractured rock masses.

Despite of our increasing knowledge on the subject, the damage tolls due to landslides are on rise during monsoon in hilly terrain. Hence, landslide prediction on temporal scale is a viable option for risk reduction. Prediction of shallow landslides developing rainfall thresholds using information on landslide occurrences and precipitation will be a cost effective risk reduction measure and may be applicable at a regional/catchment/district/tehsil/village/road corridor level in hilly terrain. Further, the installation of a real-time monitoring system can also be an alternate effective risk mitigation measure for perennial severe landslides and will be useful for community and traffic control on roads and railway tracks in hilly terrain. A Landslide Observatory with wireless instrumentation for real time monitoring of ground deformation and hydrologic parameters has been established at Pakhi Landslide in Garhwal Himalayas, India. The measurement sensors include in-place inclinometers (IPI), piezometers, wire-line extensometers and an automatic weather station (AWS). The real time data is being monitored to establish warning thresholds. The annual cumulative rainfall during 2015 was 1388 mm with cumulative monsoon period (June to September 2015) rainfall of 825 mm. At the crown of landslide beyond main scarp, there is negligible displacement being the stable part. Within the main body of the landslide, it could be inferred that the colluvium, greatly weathered bedrock and their interface experience somehow greater extent of movement at different depths in comparison to the interface between greatly weathered bedrock and unweathered bedrock. A correlation between higher intensity rainfall events and displacement pattern across the inclinometer sensors is also witnessed. However, these inferences can only be established with further data analysis of later periods. The principal aim of this chapter is to discuss the processes involved in establishment of a ground based real time monitoring system for landslides in hilly regions, in particular Indian Himalayas. Apart from establishing a landslide observatory in one of the severe landslide, the data acquisition and analysis for one monsoon season is also discussed.

The current study is focused on landslide susceptibility mapping over a critical mountainous watershed, Chehel-Chai, located in the Golestan Province, Iran. An integrated data mining new ensemble model, comprised of random forest and frequency ratio (RFFR), was proposed and employed as a robust computational algorithm in the study area. Landslide inventory map was prepared in Geographic Information System (GIS) by using several field surveys, local information, and available organizational resources. In this study, using different literature review and data availability, 12 landslide conditioning factors including proximity from fault (PFF), proximity from stream/river (PFS), proximity from road (PFR), lithological units, soil texture, land use/land cover (LU/LC), slope degree, slope aspect, altitude, plan curvature (PlanC), profile curvature (ProfC), and topographic wetness index were chosen and the corresponding maps were produced in the ArcGIS 10.2. For modeling, the FR values were calculated and then used for implementing RF in R 3.0.2 statistical software by “randomForest” package. In order to validate the built model, the receiver operating characteristic (ROC) curve using 30% of cast-off landslide was considered. The results revealed that the RFFR new ensemble model with the AUC value of 0.831 had a good performance (AUC = 83.10%) for landslide susceptibility zonation over the study area. Based on the RFFR model, about 42.27% of the Chehel-Chai Watershed has high (24.18%) and very high (18.09%) susceptibility to landslide occurrence. Hence, the proposed new algorithm was found to be suitable for landslide susceptibility modeling in the study area and, accordingly, for land use planning and landslide hazard management.

Landslide or the landmass movement is a geomorphic hill slope physical process of mass-wasting resulting in downslope rolling of large mass of debris, regolith and soil under influence of gravity. It is caused by a combination of particular geo-factors that are region or territory specific. Landslides are generally triggered and activated by substantial precipitation and/or earthquake tremors and other anthropogenic interventions such as over the top cutting of slant for development of mountainous roads/streets and other excavations for civil structures, etc. The relatively young entire Himalayan hilly tract, mountainous steep slopes in sub-Himalayan landscape of North-east India, Western Ghats, the Nilgiris in Tamil Nadu and Konkan ranges are susceptible to landslides or debris flow.

In order to formulate strategies to minimize societal impacts of landslides, a systematic approach would entail preparation of Landslide Susceptibility Maps linked to landslide incidence inventory and making them available to the concerned stakeholders for necessary preparatory and mitigation measures. Geological Survey of India (GSI) being the nodal agency for landslides studies in India formally launched on February 05, 2014 the National Landslide Susceptibility Mapping (NLSM) programme which has been a geoscientific exercise on 1:50,000 scale on GIS platform in making both quantitative or qualitative estimates of spatial distribution of landslides which either exists or has the potential to occur in a given area. GSI has formulated a set of standard operating procedures that emphasize on geo-parametric data collection (as per standard and devised formats) for landslide inventory. These data sets are synthesized with relevant spatially-distributed causative thematic maps into susceptibility zonation which represents geospatial information indicating intensity and propensity of landslides. Such baseline data will ultimately lead to the collation and evaluation of landslide hazard and risk and mitigation plans. It will also help in disaster preparedness of the country and to indicate areas critical for landslide monitoring and developing early warning system (EWS). It is aimed to demarcate and facilitate prioritization of areas for further detailed studies (Meso- and Micro-scales) and help in Regional Land Use Planning and provide the scientific basis for framing the Land Use Zoning Regulations. Several lessons were learnt from Uttarakhand disaster of June 2013 in India that compelled re-evaluation of the existing methodology of conducting geosurveys of macro scale landslide susceptibility maps. Additional geofactors that also need to be considered include: effect of toe erosion by higher order streams; effect of long run-outs of the debris flows and drainage morphometry; nature and size of clastic components, etc.

It is intended to elaborate here a synthesis of various approaches and constraints on continuing research on such country-wide programmes on landslides related geohazards characterization and its implications on evolving EWS for the societal preparedness and resilience for mitigating impending disasters. However, any method of predicting landslide susceptibility needs validation which sometimes may be difficult in areas having no land sliding history. Besides, EWS need also to highlight mitigation efforts/remedial measures through geotechnical and engineering solutions as suited to Indian conditions on case to case basis, delineation of safe escape routes in the event of a landslide/debris flow/flash floods, and for optimum utilization of available resources.

The present chapter discusses the soil nailing technique as an effective stabilization measure for slopes, excavations, rail or road embankments, tunnels and retaining walls. Different aspects of the technique such as favorable ground conditions, advantages and limitations over other methods have been reported. Further, different installation process, failure modes of soil nailed structures, design philosophies, effects of various construction parameters on the design method has been discussed in detail. The pullout response of the soil nail is the critical parameter for the soil nail design. Analytical, numerical, field and lab testing procedures are usually used to determine the pullout capacity of the soil nail. A chronological literature review examines the influence of various parameters such as grouting pressure, overburden pressure, soil dilation, degree of saturation, roughness of the nail surface and borehole on pullout capacity of soil nail. A comparative study based on different types of experimental setup reported in the literature along with the innovative pullout system developed at CSIR-CBRI for determination of pullout capacity of soil nail has also been summarized. The last section briefly describes the recent advancements in the soil nail technique and its beneficial effects over the conventional soil nailing system.

Soil-bioengineering is a cost-effective and eco-friendly alternative to the conventional methods of soil slope stabilization and erosion control. Numerous techniques such as fascines, bush layering, vegetated gabions etc. have been developed to enhance the soil slope stability, arrest soil erosion and improve the aesthetic aspect of a project, using plants as well as inert materials. Nevertheless, a limited control on the properties of the plants and the complex interaction of plant roots with the soil and other materials poses a challenge for the accurate design of soil-bioengineering techniques. The design of bioengineering techniques involves accurate evaluation of the root and root-soil properties. Different methods have been developed for the analysis of root and soil-root system that can aid in a better understanding of the complex phenomenon. The Present study provides a review on different aspects of bioengineering techniques for soil slope stabilization measures, especially, the existing techniques of physical modeling, laboratory scale testing and numerical techniques for evaluating the effect of root system on the strength properties of soil-root matrix. The different failure modes of the soil-root system i.e. adhesion failure, tension failure and progressive failure are briefly discussed. The present review will be useful for the design of bioengineering measures for soil slope stabilization or erosion control.

The estimation of factor of safety (FoS) or design reliability of slopes is a pre-requisite for an efficient and safe application of landslide mitigation measures for ensuring long-term slope stability. The evaluation of stability of slopes, especially in a hilly region with wide variations in its geological formation is an upfront challenging task for geologists as well as for geotechnical engineers and till date, has been tackled using several optimization algorithms and slope stability analysis methods. The purpose of this book chapter is to present an up-to-date along with an overall review of the slope stability analysis methods which have used different optimization algorithms for deterministic and probabilistic or stochastic evaluation of FoS or reliability index, respectively, including some case studies from published literatures. This review shows that the FoS or reliability of slopes obtained by applying the commonly established analysis methods coupled with optimization algorithms, using both the deterministic and the probabilistic approaches, may vary in their values as well as in their computational effort and errors encountered.

In Italy, landslide phenomena and mass movements are very common, particularly along the Alps, the principal mountainous chains in the northern part of the country. In this study, we used a terrestrial laser scanner (TLS) to collect a multi-temporal dataset during 3 years (2012–2014) of observation, with the aim of accurately evaluating these phenomena in the Mont de la Saxe area (Aosta Valley region, Italy). Starting from the point clouds acquired with the TLS, we derived the digital surface models and we performed a multitemporal analysis in geographical information system (GIS) to identify the morphological features of the landslide and to delineate the displacement of the phenomena. The analysis allows quantifying the major elevation change occurred in the middle and the bottom side of landslide body during 2012–2014 with a high precision. The volume displaced in the second year (2013–2014) increased by 66% than the previous year (2012–2013), showing a progressive acceleration of the landslide phenomena. This result indicates that the volume estimation is crucial for planning future landslide emergency situations and to calibrate the early warning system, based on occurred phenomena.

Machine learning techniques have been increasingly employed for solving many scientific and engineering problems. These data driven methods have been lately utilized with great success to produce landslide susceptibility maps. They give promising results particularly for mapping large landslide prone areas with limited geotechnical data. This chapter surveys their use in landslide susceptibility analysis and presents a case study investigating their effectiveness with regard to a conventional statistical method, namely logistic regression. It starts with the importance of spatial prediction of future landslides from past and present ones and discusses the requirement of advanced techniques for landslide susceptibility mapping. A critical literature survey is given under five main categories including core algorithms and their ensembles together with their hybrid forms. An application is presented for machine learning application using bagging, random forest, rotation forest and support vector machines with their optimal settings.

Recently the intensification of cryogenic processes at high rate is widespread in Russian cryolithozone. Landslides in permafrost area are characterised by frozen bottom of sliding and known as thaw slumps or mudslides. Landslide body consists of frozen soils, which thaws and forms thermo cirques and depressions. Long warm summers and snowy winters of last decade trigger cryogenic landslides over Siberia. The situation with existing linear infrastructure (roads, railways and pipelines) is changing due to permafrost thawing that has not been taken into account during design 5–30 years ago. Apart from deformations to infrastructure cryogenic landslides provoke gas release from permafrost, change of water content in lakes and rivers, and disturbance of lands (tundra and taiga) for rendering. Diversity of landslides in permafrost area and nine study cases are presented in this paper. The mitigation measures are not applicable for cryogenic landslides at high rates. There is a call for innovative solutions in this area.