ABSTRACT
11.1.1 The observation of physical and structural properties and behaviour of the soil and the tunnel itself are integral parts of design and construction of underground structures. This becomes particularly important in case of tunnels which, necessarily have to pass through varying type of soils and rocks and in many cases close to or below existing structures and utilities or other underground structures. Such observations serve a number of purposes and are carried out at different stages of the work viz., (i) site investigation for help in surveying and initial planning; (ii) during construction, for collection of data for design verification and also for construction control by modifying method and rate of progress as required and (iii) for monitoring the performance of the structure in service and ensuring its stability.
