Stress perturbation near two fault zones in Himalayas-field measurements and numerical simulation
Near a fault the orientation of maximum horizontal stress (σH) seems to rotate relative to the regional stress (σR) orientation in a consistent manner. The maximum horizontal stress direction is reported to have been rotated even 90 degrees to the regional stress. In this paper, the state of stress near two fault zones located in two hydroelectric projects in North Western Himalayas is discussed. In each case the stress rotation has been noticed distinctly. To understand factors responsible for the rotations, the faults are simulated using a two dimensional Distinct Element Method incorporating Mohr-Coulomb model and a parametric study has been conducted. The parametric study has revealed that a major geological structure could considerably influence the stress setup around it. It has also been inferred that external parameters like angle (α) formed by geological structure with regional stress orientation (σR) and ratio of boundary stress magnitude (K0) are more responsible for stress rotation as compared to the internal parameters like cohesion (c), angle of internal friction (ϕ), bulk and shear moduli (K, G) and joint stiffness (Ks, Kn). Thus any major civil engineering structures falling within this perturbed stress due to the geological structure may have to be designed accordingly.