Background: Sikkim Himalaya is under consistent distress due to landslides. Abrupt thrust on infrastructure development in the valley regions of Sikkim Himalaya has led to a need for a prior planning to face landslide hazard. A comprehensive study for the identification of landslide hazard zones using landslide frequency ratio and fuzzy logic in GIS environment has been presented for the Lachung valley, Sikkim, India, where a number of hydroelectric projects are proposed.Temporal remote sensing data was used to generate significant landslide causative factors in addition to landslide inventory. Primary topographic attributes namely slope, aspect and relative relief were derived from digital elevation model. Landslide frequency ratio approach was adopted to correlate landslide causal factors with landslide incidences. Further, fuzzy logic method was used for the integration of landslide causative factors in order to delineate the landslide hazard zones. Fuzzy memberships were derived from the landslide frequency ratio values. Different gamma values were used in fuzzy gamma integration process, which resulted different landslide hazard index maps. Receiver operating characteristic curves were prepared to analyze consistency of the resulting landslide hazard index maps.

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. IntroductionThe underground space technology has gained greater importance in the recent times to overcome the problems of space and to accommodate strategically important projects. Designing and constructing large underground openings such as powerhouse cavities are always difficult in the seismically active Himalayan terrain which is characterized by high in situ stresses. The overall stability of the underground openings is dependent on a number of factors including, but not limited to, the conditions of rock mass, in situ stresses, stiffness of support, size and shape of cavity, method of construction and sequence of construction. Rock mass condition and its possible behavior during excavation help in calculating the stability of the cavity and the rock load. The in situ stresses also play an important role in the stability of an underground opening. The main factor in the design of underground openings is to help the rock mass to support itself.