S. P. Pradhan

Study of Slopes Along River Teesta in Darjeeling Himalayan Region

Landslides of different magnitudes are frequent in different regions of the morpho-dynamically active Himalayan regions. Geologically, the presence of young active fold mountains, some rejuvenated faults along with the anthropogenic factors such as unplanned urbanization in risk areas, widening of roads along cut slopes, environmental degradation and population expansion play a significant role in the occurrence of such geohazards. The landslide zones have been identified for Indian scenario to demarcate the locales susceptible to landslides and various studies are being carried out in the high risk areas to mitigate the probability of occurrence of hazards. Assessment of stability of such areas by developing models can act as early warning systems and help to implement preventive and mitigative measures to minimize the damage level. The present work focuses a similar study in a landslide prone area with evidences of recent and paleo landslides in Darjeeling—Himalayan area of India. The Birrik fault cuts across the River Teesta in the foothills of the Darjeeling Himalayan fold and thrust belt and in the close vicinity lies the National Highway No. 31A. This area has a hilly topography and some high angle slopes are further aggravated by the presence of active thrust. Evidences of landslides were observed in the field and samples were collected from the adjoining areas of slide for determination of their geomechanical properties. There are many methods to analyze the slope conditions like Slope Mass Rating, limit equilibrium method, kinematic tools, numerical simulations etc. These approaches are good to see the disturbances within the rock mass due to change in its dynamics. In this study, slope mass rating was used to evaluate the health of slopes based on various rock parameters, as determined in the laboratory. This study will be helpful to monitor the slope conditions in this area and to design the preventive measures to minimize the chances of failure, which is required for smooth transportation through highway NH 31A. It can also be set an example for regions with similar geological and geotechnical conditions, especially in the Lower Himalayan regions.

Stability assessment of Himalayan road cut slopes along National Highway 58, India

Himalaya is one of the most tectonically and seismically active mountain chains in the world having complex geological and geotechnical conditions. The Himalayan region experiences frequent slope failure posed due to various natural and anthropogenic causes. Slope instability issues have consequent effects on the socio-economic development of the people and the region in a large scale. In the present study, stability analysis of vulnerable road cut slopes along NH-58 from Rishikesh to Devprayag in the Lesser Himalayas has been conducted. Critical slopes were identified by considering the geological and the geotechnical complexities within the region. Rock mass characterisation techniques have been employed for slope stability assessment. Rock mass rating (RMR), slope mass rating (SMR) and continuous slope mass rating (CSMR) methods have been applied to evaluate different stability levels of rock mass along the highway. Spatial variation of stability classes using RMR, SMR and CSMR techniques has been analysed on geographic information system (GIS) tool. Kinematic analysis technique was also employed to identify the different modes of structurally controlled failures in jointed rock mass. Accordingly remedial measures have been suggested to improve slope stability.

Analysis of Stability of Slopes in Himalayan Terrane Along National Highway: 109, India

Morpho-dynamic terrane of Himalaya is continually facing challenges in stability of rock cut slopes, aggravated due to increased disturbance levels in rock/soil mass due to human intervention. Increased civil constructions, exploitation of resources, deforestation, changing pattern of river-flows and increase in population are among the key reasons for such disturbances leading to increased susceptibility of these slopes. Huge loss of property and lives has been reported every year from the Himalayan regions and therefore, must be attended on a priority basis. The lithological and structural variations, orientation and pattern of different water bodies and vegetation are varied along the slopes indicate site-specific studies of landslide prone areas for assessing the health of slopes and providing early warning, wherever necessary. Highly jointed rock mass along the slopes between Rudraprayag and Agasthyamuni along NH109, which connects to Indo-China border, the hilly population to the plains and runs parallel to River Alakananda, were studied. A detailed field study was carried out in the landslide area and the relevant geological data were recorded. The area constituted of mainly weak phyllitic and schistose rock at most of the places with some jointed and weathered quartzitic rock mass at a few locations. Stability of slope was investigated using two dimensional finite element methods. Slope geometry and rock parameters were incorporated in the models that were analysed for factor of safety. The changes in geomorphology as a consequence of surface and sub-surface deformations were also premeditated. At places, formation of weak tensile zones towards the rear end of the slopes as well as coalescence of schistose rock due to loading, indicate possible subsidence in weak areas, and may lead to changes in landforms. It is indicated that a stable slope in dry season may become hazardous in the wet season and remedial measures may be applied in advance to prevent any major damage to the ongoing traffic and other operations.

A Review Summary on Multiple Aspects of Coal Seam Sequestration

Presence of natural gas in adsorbed form in coal seams is the primary reason for scientists to attempt CO2 sequestration in the same. The economic analysis states that the additional methane in case of coupled enhanced coalbed methane recovery (ECBMR) with sequestration partly offsets the cost of the operation. Injected CO2 reduces the partial pressure of methane and enhances its desorption from the matrix. Furthermore, CO2 is preferentially adsorbed onto the porous surface of the coal thereby displacing methane from adsorption sites. Apart from estimation of coal gas reserves, several technical parameters related to the adsorption capacity of coals and suitable trapping/sealing mechanism must be ensured before utilizing coal as a CO2 sink.

Rockfall: A Specific Case of Landslide

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.

Mass Wasting: An Overview

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.

Formation Damage in Coalbed Methane Recovery

Abstract Coal is an unconventional hydrocarbon reservoir which is both the source and reservoir for the formed methane. Extraction of methane involves altering the existing conditions and these changes can lead to damage of the reservoir. For sustained production of coalbed methane (CBM), damage of coal needs to be minimized. Formation damage refers to the changes in the producing formation that leads to decline in coal permeability which eventually leads to the decline in production. This chapter discusses the various mechanisms in the reservoir that lead to formation damage. It describes and discusses the major types of formation damage that commonly occur when drilling CBM reservoirs. The emphasis is on the most common types of formation damage, that are those associated with drilling, completion, and specifically hydraulic fracturing. Further, damage due to volumetric deformation of coal matrix and production-related reservoir failure are also discussed.