With the advancement of science and technology, humans endeavoured to build massive caverns underground taking the advantage of physico-mechanical properties of the rockmass. The rockmass has inherent discontinuities in it whose properties vary greatly from the host rock aiding in the development of potential failure zones during and after execution of such projects. The change in rockmass behaviour observed in such zones calls for safety controls to alarm the working personnel inside the caverns. There arises the need for placing geotechnical and geodetic instrumentation inside rockmass to capture changes in its behaviour and promptly take up the remedial measures to prevent failures. To acquire correct data for right interpretation, there must be a right procedure to be adopted for planning the type of sensors and its specifications, location inside caverns, mode and frequency of data acquisition, data communication and data analysis.
Similar planning was carried out for the caverns of an underground powerhouse complex of Punatsangchhu-II Hydroelectric Project, Bhutan by the authors. The intrinsic complexities and the problems tackled during planning and execution of such mega project are explained in detail in this paper.
Excavations of underground caverns for storing crude oil, construction of powerhouse, nuclear repositories and mining minerals in recent days have increased tremendously throughout the world, thereby maximizing the utilization of underground space. But since, rock is a discontinuous, inhomogeneous and anisotropic material, the reliability of structural integrity remains uncertain. The act of excavation against nature destabilizes the surrounding rockmass which leads to development of potentially unstable zones which deforms with time and if not properly treated or supported, leads to progressive failure of the structure itself. Based on the scale of excavations, the risk associated with the project to lives and property is assessed. In order to prevent any mishap, underground projects call for geotechnical and geodetic instrumentation, that helps in early detection of such unstable zones and any abnormal behavior of the rockmass. Generally, instrumentation in underground rockmass is implemented to accomplish the needs of diagnosis, prediction, legislation and research i.e. verification of design parameters, suitability of any new construction technique, diagnosing cause of an adverse event or verification of continued satisfaction behavior of the rockmass to different operations (Dunnicliff, 1998).