JNTU B.Tech IV STRATA CONTROL TECHNOLOGY Previous Question Paper (September - 2021 - R16)

Geological site characterization for support design involves gathering comprehensive data to understand the rock mass behavior under mining-induced stresses. Key components include:

1. Lithological Mapping: Identifying rock types, sequence, and thickness of strata, particularly the immediate roof and floor conditions.
2. Structural Analysis: Mapping discontinuities such as joints, faults, bedding planes, and cleats, including their orientation, spacing, persistence, and infilling material.
3. In-situ Stress Measurement: Determining the virgin stress field (vertical and horizontal components) to predict loading conditions on supports.
4. Hydrogeological Assessment: Identifying groundwater conditions and pore water pressure, which significantly influence rock mass stability.
5. Rock Mass Classification: Utilizing systems like RMR (Rock Mass Rating) or Q-system to quantify the quality of the rock mass based on the collected geological data, which directly dictates the support requirements.

i) Strength of rock material: This is typically determined through laboratory testing of intact rock cores. The Uniaxial Compressive Strength (UCS) test is the standard method, where a cylindrical core sample with a length-to-diameter ratio of 2:1 is subjected to an axial load until failure. The strength is calculated as the maximum load divided by the cross-sectional area. Alternatively, the Point Load Strength Index (Is) test is used for field estimation, where a rock specimen is loaded between two conical platens until failure, and the result is converted to an equivalent UCS value.

ii) Rock Quality Designation (RQD): RQD is a quantitative index used to assess the quality of rock mass based on core recovery. It is calculated as the percentage of the total length of core pieces greater than 10 cm in length relative to the total length of the borehole run:

Only sound, hard rock pieces are included in the calculation; pieces that are broken due to handling or drilling process are excluded. The resulting percentage categorizes the rock mass quality from 'Very Poor' (RQD < 25%) to 'Excellent' (RQD > 90%).