Jawaharlal Nehru Technological University Hyderabad B.Tech II ENGINEERING GEOLOGY Previous Question Paper (September - 2021 - R18)

Physical Geology and Petrology are fundamental components of civil engineering that ensure the stability, safety, and longevity of infrastructure projects. Their importance is summarized below:

• Physical Geology: This branch deals with the internal and external processes shaping the Earth's surface. In civil engineering, it is crucial for:
  • Site Selection: Understanding geomorphological processes like landslides, erosion, and sedimentation helps in selecting stable sites for dams, bridges, and highways.
  • Hazard Mitigation: Knowledge of seismic activity and faulting patterns is essential for designing earthquake-resistant structures.
  • Groundwater Studies: It helps in identifying aquifers and managing water tables, which is vital for foundation excavation and dewatering operations.
• Petrology: The study of rocks is vital for determining the suitability of materials for construction:
  • Construction Materials: Petrology classifies rocks based on their origin (igneous, sedimentary, metamorphic), helping engineers choose durable stones for aggregate, building blocks, and road metal.
  • Foundation Stability: Evaluating the mineralogical composition and texture of bedrock helps in calculating the load-bearing capacity and potential for settlement.
  • Tunneling and Excavation: Understanding rock hardness, jointing, and cleavage assists in selecting appropriate drilling and blasting techniques.

Rock weathering is the process of physical disintegration and chemical decomposition of rocks at or near the Earth's surface. Its impact on reservoirs is significant and can lead to severe engineering failures:

• Loss of Water Tightness: Weathering increases the porosity and permeability of rocks. If the reservoir floor or abutments consist of deeply weathered rock, it can lead to excessive seepage or leakage, rendering the reservoir ineffective.
• Slope Instability: Weathering weakens the rock mass by breaking down mineral bonds. This reduces the shear strength of the slopes surrounding the reservoir, significantly increasing the risk of landslides, which can cause catastrophic dam failure or sudden displacement of water (seiches).
• Sedimentation: Weathered rock materials are easily transported by runoff into the reservoir. This leads to rapid siltation, which reduces the effective storage capacity of the reservoir over time and can clog outlet works and turbines.
• Foundation Settlement: If the dam foundation is constructed on a weathered zone (saprolite or residual soil), it may undergo differential settlement under the weight of the structure and the hydrostatic pressure of the stored water, leading to cracks in the dam body.

Engineers must perform detailed geotechnical investigations, such as core drilling and permeability tests, to assess the depth of the weathered profile and implement measures like grouting or concrete lining to mitigate these risks.