**2. Background**

Hindustan Copper Limited (HCL), a public sector undertaking under the administrative control of the Ministry of Mines, is engaged in mining, beneficiation, smelting, refining and casting of refined copper metal. HCL maintains focused on its mission and vision which include increasing the ore production by three times over a decade and implementing continuous improvement in productivity. To continue to achieve these goals, it has geared up to tap the resources from the un-mined areas by designing stopes below the mined areas.

The present study was undertaken in Kolihan Copper Mine, an important captive under‐ ground mine of Kolihan Copper Complex of HCL and this mine is situated near the village of Khetri, in the District Jhunjhunu, Rajasthan. The mine plan to develop stope blocks at lower levels below the mined out areas to sustain and increase the productivity.

For the design of stopes, in-situ stress is one of the most important factors which dictates the size of the stopes and the size of the pillars and the sequence of extraction. The main host rocks of Kolihan mines are garnetiferous chlorite quartz schist, quartzite and amphib‐ olite quartzite. The strike length of the ore body is 600 m with a width varying from 30 m to 100 m and the ore dips steeply to almost vertical. The main mining method adopted is Large Diameter Blast Hole Stoping. The mine extends from 486 ML to 0 ML. (Hindustan Copper Limited internal notes)

A detailed stress measurement programme was undertaken before the commencement of any stoping activity (pre- mining stage) between 486 mL and 184 mL for the determination of stress around the mine openings. Three locations with different depths (different rock covers) were selected inside the mine and stress measurements were conducted inside boreholes drilled from development tunnels (cross cuts), using the hydrofracture method.

Mining up to 306 ML is complete and presently mining is active at 246 ML and 184 ML. Mine development has to commence at lower level soon, below 184 ML.(Figure 2.) Thus it was felt to undertake a stress measurement programme again below the mined out area (post mining stage) to find the impact of mining activities on the stresses. Three levels with different rock covers were selected, similar to what was done in the pre-mining stage and stress measure‐ ments were conducted inside boreholes using the hydrofrac method.
