Influence of Dyke on In Situ Stress Parameters, Measured in the Vicinity of a Proposed, Underground Pump House Location

In general in situ stress parameters are controlled by major geological structures like folds, faults and intrusives. Besides this, the magnitude and distribution of in situ stresses are also governed largelyby the rock mass structure and its cumulative geological history. The role played by scale effect and the boundary conditions due to the composite nature of rocks from micro scale to the regional scale in rock masses isimportant to civil, petroleum and mining engineers. The in situ stresses in rock mass can be so intricate that local stresses may be quite different from regional stress. Consequently the stress results may vary for different techniques and with deviationat different times of experiments, which should be treated as intrinsically non uniform but not as anomalies. At many construction sites, rotation of stress orientation was as high as 90⁰ to the geological structures. Due to proximity of these perturbed stresses to the underground structures, it is expected that these stresses will have a greater impact on the overall stability of the underground structure than regional stresses. Thus, stress perturbations due to local geological structures at the site of underground projects must be clearly understood before stress values are taken as input parameters for design of any structure.

Dyke intrusion has been observed at one of the construction sites where an underground pump house is proposed to be constructed. The stress measurements have to be conducted to delineate the Maximum Principal Stress direction in order to orient the long axis of the pump house parallel to it. However, it is important to note whether there is any influence of dyke on the in situ stress parameters, or the stress direction is in compromising alignmentwith the direction of the dyke. The present paper highlights the stress direction measured by hydrofracture method and the impact of the dyke on the orientation of the stress.