Performance Monitoring of Underground Structure by Extensometer - A Case Study

R K Prasad, Mahabir Dixit

Instrumentation, Geotechnical, Underground Powerhouse, Crown, MPBX, SPBX, Deformation

Each and Every type of Dam has its distinctive requirements of monitoring parameters and distinctive variety of instrumentations. Instrumentation is used to measure the response (deformation, stress etc.) of soil or rock to changes in loading or support arrangements, and from the measurements taken, the need for modifications to the loading or support arrangements is determined such that process is controlled. However instrumentation is additionally indispensable for site investigation, design verification, long term monitoring of the soundness of the structure and in particular, its safety. Geotechnical instruments are our eyes and ears inside the structure and supply valuable data for taking applicable corrective actions before it’s too late.

Disturbances in rock and soil masses is also caused by geological or structural factors beyond the periphery of a tunnel that are subjected to stresses from all the directions. Excavation of any cavity like an underground power house or boring of a tunnel, ends up in the release and readjustment of three dimensional stresses around the cavity. This results in movement within the surface reckoning on time. In such instance, instruments like Extensometer installed in boreholes can be used to check ground movement/disturbance of a section of rock/soil mass and adjacent encompassing strata with the help of anchors fully at completely different depths. It provides good sample distribution and data redundancy even under conditions of site accessibility. The depth of anchor varies with the kind of rock strata and the location of the fixed point with respect to which the deformations are to be measured.