The northern stretch of the Arun watershed in East Nepal is dominated by steep slopes and rugged topography and experiences extensive landslides each year. Reliable landslide susceptibility assessment can potentially be an important tool for risk evaluation and mitigation in the Himalayas. The present study explores two GIS-based bivariate statistical methods, the weight of evidence method and the frequency ratio method to assess the landslide susceptibility of the study area. Seven major variables including slope angle, slope aspect, slope shape, geology, stream proximity, stream power index and land use were examined as the major contributing factors to landslide occurrences in the assessment. The landslide susceptibility map produced from these two methods are characterized by four zones of very low, low, moderate and high susceptibility. The landslide percentage of each zone turns out to be consistent with the order of its susceptibility. The results suggest that the weight of evidence method is more sensitive to the spatial variation of relevant factors; both methods produced fairly reliable results, as confirmed by a success rate of 75% for the weight of evidence method and 71% for the frequency ratio method. The present study demonstrates that the quantitative assessment methods explored may have a promising potential for landslide assessment and prediction in the Himalayas.

The geology of the Himalayas is intricated and intriguing. It features numerous tectonic bodies and structures too complex to interpret. Along with such mysteries it has too many common geohazards, such as landslides. In this study, a detailed geological investigation is carried out to overcome the discrepancies in structural interpretation, the nature of two crystalline bodies, and non-uniformity in geological mapping in the central Himalayan arc, in the Jajarkot district of Nepal. Along with the geological exploration and landslide characterization of the area, consequent landslide susceptibility mapping is performed considering 13 causative factors related to geology, topography, land use, hydrology, and the anthropogenic factor, using two bivariate statistical models. This study concludes that the two metamorphic crystalline bodies in the study area are most probably the klippen, due to the absence or erosion of the root zone. The field study revealed that haphazard road excavation without the consideration of geological and geotechnical features has caused shallow landslides. The results obtained from the susceptibility maps, with a varying range of susceptibility zones, are in good agreement with the spatial distribution of pre-historic landslides. The results of the susceptibility modeling are validated by calculating landslide density and plotting area under curves (AUC). The AUC value for the WOE, and the FR method, revealed an overall success rate of 79.42% and 77.62%, respectively.

The Himalayas are one of the most unstable regions in the world. Underground excavations are very challenging in this region due to the fragile geology, tectonic activities and complex geological structures. In the present study, three hydropower head race tunnel projects from Nepal, as well as six additional tunnel projects from Bhutan, India and Pakistan located at different parts of the Himalayas, are reviewed with a focus on the common problems encountered during the tunneling and their possible causes and remedies. It is found that rock bursts often occurred around the overburden of 1000 m or higher, while tunnel squeezing problems were commonly observed in a wide range of overburden. Most of the rock failures occurred in sheared zones, thrusts and heavily weathered rock mass. The geological conditions around these projects are often characterized by significant presence of folds, faults, joints and interbedding of different types of rock strata; they are so complex and diverse that it is often difficult to accurately predict the field condition from conventional geotechnical site investigation. In many cases, the presence of shear zones, thrusts and tectonic activities has a strong influence on the in situ stress. Review of these prominent projects suggests that the complicated dynamics between a wide range of geological and geotechnical factors play a critical role in the tunneling in the Himalayas.

No abstract