ABSTRACT
the paper details the in-situ stress measurements in twin tunnel boring machine (TBM) of the Neelum Jhelum Hydropower project, located in the Azad Kashmir region of Pakistan in foothills of the Himalayas, with overburdens up to 1870 m and high tectonic stresses. The most significant challenge during tunnel construction was the occurrence of rockbursts which, although expected, have been a constant danger to tunnel personnel and equipment. The ability to predict the likelihood, location, severity and number of rockbursts directly impacts upon the tunnel safety and daily production rates. The in-situ tests provided actual ground stresses and their orientations an indication of location along the tunnels which experienced the rockbursts. The in-situ stress results contradicted the forecasts based on the classical empirical rules combining stress analysis and rock strength. This paper details how data was interpreted and integrated to support excavation, prevention and control of rockbursts which improved tunnel safety and productivity.
