Design and Planning of Excavation Sequence and Blasting Techniques for large UG Caverns

The cavern construction technology governs many important aspects of design and design processes continue to the end of construction phase. The choice of reasonable excava-tion sequence and control blasting is one of the key techniques for construction of large under-ground powerhouse. 26.2m wide,57.3m high and 202.9m long cavern of 1000MW Tehri pumped storage project is under construction with top heading & benching method to accommodate 04 reversible turbines of 250MW each. Geology encountered was very poor and lot of large openings where there, so excavation of cavern was very challenging, and special excavation techniques were used. Due to vicinity of underground cavern close to under operation cavern of 1000 MW Tehri HPP, control blasting techniques adopted to maintained design PPV and minimize over excavation of cavern with heading & benching. This paper presents selection of excavation se-quence, control blasting techniques with heading & benching of powerhouse cavern for different ground condition, and continuous monitoring blasting performance and optimize blasting design to maintain designed PPV and retain designed Geometry of cavern, paper will also discuss per-formance monitoring of cavern during excavation and adopt construction techniques to minimize blasting damage of surrounding rock mass. Project is in advance stage of construction and powerhouse excavation is now complete and concreting of all four units is in progress with a target to commission of the Project by end Dec’2023.