R. Anbalagan

Landslide hazard evaluation and zonation mapping in mountainous terrain

Abstract Landslide hazard zonation (LHZ) maps are of great help to planners and field engineers for selecting suitable locations to implement development schemes in mountainous terrain, as well as, for adopting appropriate mitigation measures in unstable hazard-prone areas. A new quantitative approach has been evolved, based on major causative factors of slope instability. A case study of landslide hazard zonation in the Himalaya, adopting a landslide- hazard evaluation factor (LHEF) rating scheme, has been presented.

Landslide hazard and risk assessment mapping of mountainous terrains — a case study from Kumaun Himalaya, India

Landslides are studied systematically in order to evaluate the nature of hazard and the damages to the human life, land, roads, buildings and other properties. This can be expressed in terms of risk, which is a function of hazard probability and damage potential. A risk map will indicate the priorities for landslide hazard management. A new approach to risk assessment mapping using a risk assessment matrix (RAM) is presented.

Landslide susceptibility zonation in part of Tehri reservoir region using frequency ratio, fuzzy logic and GIS

A comprehensive study for the identification of landslide susceptible zones using landslide frequency ratio and fuzzy logic in GIS environment is presented for Tehri reservoir rim region (Uttarakhand, India). Temporal remote sensing data was used to prepare important landslide causative factor layers and landslide inventory. Primary and secondary topographic attributes namely slope, aspect, relative relief, profile curvature, topographic wetness index, and stream power index, were derived from digital elevation model. Landslide frequency ratio technique was adopted to correlate factors with landslides. Further, fuzzy logic method was applied for the integration of factors (causative factor) to map landslide susceptible zones. Normalized landslide frequency ratio value was used for the fuzzy membership function and different fuzzy operators were considered for the preparation of landslide susceptibility/hazard index map. The factors considered in this study were found to be carrying a wide range of information. Accordingly, a methodology was evolved to integrate the factors using combined fuzzy gamma and fuzzy OR operation. Fuzzy gamma integration was performed for six different gamma values (range: 0–1). Gamma value of 0.95 was selected for the preparation of final susceptibility map. Landslide susceptibility index map was divided into the following five hazard zones – very low, low, moderate, high, and very high – on the basis of natural break classification. Validation of the model was performed by using cumulative percentage curve technique. Area under curve value of cumulative percentage curve of proposed landslide susceptibility map (gamma = 0.95) was found to be 0.834 and it can be said that 83.4% accuracy was achieved by applying combined fuzzy logic and landslide frequency ratio method.

Landslide susceptibility mapping using analytical hierarchy process (AHP) in Tehri reservoir rim region, Uttarakhand

A comprehensive use of analytical hierarchy process (AHP) method in landslide susceptibility mapping (LSM) has been presented for rim region of Tehri reservoir. Using remote sensing data, various landslide causative factors responsible for inducing instability in the area were derived. Ancillary data such as geological map, soil map, and topographic map were also considered along with remote sensing data. Exhaustive field checks were performed to define the credibility of the random landslide conditioning factors considered in this study. Apart from universally acceptable inherent causative factors used in the susceptibility mapping, others such as impact of reservoir impoundment on terrain, topographic wetness index and stream power index were found to be important causative factors in rim region of the Tehri reservoir. The AHP method was used to acquire weights of factors and their classes respectively. Weights achieved from AHP method matched with the existing field conditions. Acceptable consistency ratio (CR) value was achieved for each AHP matrix. Weights of each factor were integrated with weighted sum technique and a landslide susceptibility index map was generated. Jenk’s natural break classifier was used to classify LSI map into very low, low, moderate, high and very high landslide susceptible classes. Validation of the susceptibility map was performed using cumulative percentage/success rate curve technique. Area under curve value of the success rate curve was converted to percentage validation accuracy and a reasonable 78.7% validation accuracy was achieved.

Plane failure analysis of rock slopes

SummaryHoek and Bray (1981) gave an analytical approach for plane failure analysis for rock slopes that is limited to those slopes in which the upper slope surface is horizontal and the tension crack is vertical. An analysis is presented here which can take these factors into account. It is found that varying the angle of the upper slope from 0° to 30° causes a significant reduction in the factor of safety. Varying the tension crack from vertical to 70° only has an effect when the upper slope angle is less than 20°.

Comparative analysis in GIS-based landslide hazard zonation—a case study in Bodi-Bodimettu Ghat section, Theni District, Tamil Nadu, India

The aim of this research article is to assess and compare the reliability of spatial-based different landslide hazard zonation mapping methods in the Bodi-Bodimettu Ghat section, Theni District as a case study. In favor of this intention, the three methods like the Bureau of Indian Standard (BIS), multi-criteria analysis (MCA), and frequency ratio (FR) model have been applied to find out three different landslide hazard zonation maps. The results of the three methods were compared using parameters such as landslide density, success rate curve, and spatially agreed area. Approximately the same variation is seen in the final results of BIS in comparison to the other methods, namely MCA and FR. But if we go actually into the detail, low hazard and moderate hazard seem to merge to indicate one single zone made as moderate hazard. Moreover, the nature of weightages used in different techniques may have the same influence on the outcome of the result.

HALF TUNNELS ALONG HILL ROADS OF HIMALAYA - AN INNOVATIVE APPROACH

Abstract ‘Half tunnels,’ which are excavated as overhangs within steep slopes of hard rocks, have an advantage over conventional full tunnels or open excavations in that they involve less cost and time. However, due to a lack of interest and their uncommon occurrence, the design and analysis of half tunnels have remained by and large unexplored. In the present paper, an effort has been made to study some of the half tunnels in the Middle and the Higher Himalaya in India. In addition to studying the geology of half tunnels, rock mass properties pertaining to Q and RMR for the rocks exposed around the half tunnel have been evaluated. The Markland test has been carried out to assess the probability of plane or wedge failures along the slopes in the half tunnel area. The results obtained have been again confirmed by analyzing the data with the help of a computer program uwedge . Both analyses suggest that the wedges are stable and that all the half tunnels analyzed are safe. Finite element analyses for different slopes and spans of half tunnels have been carried out to study the distribution of stresses around half tunnels. The range of maximum tensile stress concentration in the roof of half tunnels for different slopes is suggested.

Landslide Hazard Analysis and Management: A Case Study from Nainital, India

Among the physiographic divisions of India, the Himalayan terrain is the most prone to natural hazards like landslides. Fragile nature of the mountain ecosystem coupled with unplanned construction activities renders this terrain vulnerable to mass wasting processes. In this context, tackling landslide problems in Himalayan terrain had always appeared as a major challenge to engineers and town planners while implementing development schemes. This problem turned acute when disproportionate urbanization in hill stations aggravates existing condition of slope stability and posed major threat to human establishment. Hence, the need of the hour is to go for an effective landslide hazard management program by which appropriate remedial measures can be sought for hazard prone slopes and thus avoiding future disasters. In this regard, a detailed slope stability study was carried out at landslide ravaged Kailakhan area, situated at the SE corner of Nainital town, Uttarakhand, India. After identifying the type of instability and assessing slope characters, suitable remedial measures had accordingly been indicated for restoration of geo-environmental equilibrium of the area, as a long term measure for landslide hazard mitigation and management.

Remote sensing and GIS based artificial neural network system for landslide suceptibility mapping

Landslide susceptibility mapping is necessary in order to facilitate rational, systematic and efficient decisions concerning planning of development in mountainous regions and also for the mitigation and management of landslide disasters. Radial Basis Function Link Networks (RBFLN) was used as a landslide inventory-driven method for the identification of landslide susceptibility. Generation of input data for RBFLN involved the landslide causal factor (evidential theme) maps comprising geology, photo-lineament, land use land cover (LULC), soil, slope angle, aspect, relative relief, profile curvature, distance to drainage and distance to reservoir boundary. 116 landslide incidence and 116 no incidences were used to train the network. A unique condition grid map was prepared by the combination of each evidential theme. For each input training vector, weights in the form of fuzzy membership function were assigned. Based on fuzzy membership values, weights of each pixel of unique condition grid map were computed on the basis of RBFLN. The RBFLN weights were linked to the unique condition grid and a continuous landslide prediction map was created which was further classified into five relative susceptible zones.

Geotechnical Evaluation of Lakhwar Underground Powerhouse, Uttrakhand Himalaya, India

The stability of underground excavations is dependent on the conditions of rock mass, in situ stress and distribution pattern of structural discontinuities of the area. This chapter discusses the stability status of the Lakhwar underground powerhouse in Himalaya using RMR and Q System to predict rock load and support requirements. Boundary Element Method (BEM) has been used to examine the stress distribution around the machine hall cavity to estimate the stability. In addition, the stability of the powerhouse has also been studied. Based on these analyses, suggestions on suitable support system for the power house are made.