**1. Introduction**

Knowing the post mining stress condition is always of interest to the mine designer ahead of designing a mining method in the non-mined areas. This knowledge helps them in the design of stopes, mining sequence and rock reinforcement for the extraction of ores economically and safely. Previous work has examined the impact of mining on stresses as revealed by actual

© 2013 Sengupta et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

measurements at the site and included the use of 3D numerical methods to understand the impact vis a vis mining to help in the designing of openings below mined out areas (Whyatt-JK, Williams-TJ, Blake. W (1995).

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

Estimation of the Impact of Mining on Stresses by Actual Measurements in Pre and Post Mining Stages…

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‐

The rock formations of the area belong to the Alwar and Ajabgarh series of the Delhi system and are younger than the Aravalli system. Both rock formations are highly deformed and metamorphosed. Rocks occurring at Kolihan mines are Amphibolite quartzite/garnet chloride

**Kolihan Mines (Study Area)**

Structurally the thick prism of metasediments comprising rocks of Alwar and Ajabgarh series has been deformed into northeast –southwesterly trending longitudinal folds of large areal

Amphibolite & Quartzite

E - S 300

N

http://dx.doi.org/10.5772/56017

917

W,

with principal economic mineral is chalcopyrite. Strike of the formation is N 300

from development tunnels (cross cuts), using the hydrofracture method.

ments were conducted inside boreholes using the hydrofrac method.

**3. Geology and tectonics**


westerly (Fig 1)

**Figure 1.** Geological and tectonic map of the project area

**3.1. Geology**

dipping 500

**3.2. Tectonics**

In this study, in a deep underground copper mine, stress measurements using the hydrofrac‐ ture method were carried out in two stages. At the pre-mining stage, when only few devel‐ opments were available and at the post mining stage from the developments between the mined out area and the non-mined out area.

Stress data generated from the stress measurements produced a value for the mining induced stress gradient (post mining) which was found to be totally different from the stress gradients of the area measured in the pre mining stage. The orientation of the Maximum Horizontal principal Stress was found to be perturbed and lying perpendicular to the strike of the orebody as against parallel orientation found during pre -mining stage. To understand the impact of the mining on the stresses a 3-D numerical modeling study was carried out using a boundary element method. The initial stress ratio from the pre mining stage measurement was used with gravity loading to account for the surface topography, which is hilly. Three observation points were monitored for stress change in mining, resulting from excavation effects and this data was found to be in agreement the measured induced stresses. The study results helped in the design of stopes, mining sequences and rock reinforcement.
