JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV Year ROCK SLOPE TECHNOLOGY Previous Question Paper (October/November - 2020 - R16)

Geotechnical investigation for rock slopes involves a systematic approach to characterize the geological, structural, and hydrogeological conditions. The primary methods include:

• Geological Mapping: Detailed surface mapping to identify lithology, rock mass quality, and weathering grades.
• Structural Mapping: Identification and measurement of discontinuities (joints, faults, bedding planes) using scanline or window mapping to determine orientation, spacing, and persistence.
• Drilling and Core Logging: Boreholes are drilled to obtain rock cores for RQD (Rock Quality Designation) assessment, RMR (Rock Mass Rating) calculation, and to determine the depth of the groundwater table.
• In-situ Testing: Methods such as plate load tests, shear box tests, or borehole televiewers to measure the mechanical properties of the rock mass and discontinuities in their natural state.
• Laboratory Testing: Testing of core samples for uniaxial compressive strength (UCS), triaxial shear strength, and slake durability.
• Geophysical Methods: Non-destructive techniques like seismic refraction or electrical resistivity tomography to map subsurface stratigraphy and detect fracture zones.
• Hydrogeological Monitoring: Installation of piezometers to measure pore water pressure, which is critical for slope stability analysis.

For a rigid block of weight W resting on an inclined plane of angle β, with a potential failure plane inclined at angle ψ, the Factor of Safety (FS) is defined as the ratio of resisting forces to driving forces.

The driving force (D) acting parallel to the failure plane is given by:

The normal force (N) acting perpendicular to the failure plane is:

Assuming the Mohr-Coulomb failure criterion, the resisting force (R) provided by the shear strength of the discontinuity is:

Where c is the cohesion, A is the area of the failure plane, and φ is the angle of internal friction. The Factor of Safety is derived as:

If pore water pressure (U) acts on the failure plane, the effective normal force becomes (W cos(ψ) - U), modifying the formula to: