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Role of geophysics in investigations for pump storage projects Can it replace requirement of Drifts?

Role of geophysics in investigations for pump storage projects Can it replace requirement of Drifts?

Dr. Sanjay Rana 


Geophysics plays a crucial role in the investigations and planning of pump storage projects. Pump storage projects involve the use of water reservoirs at different elevations to generate electricity. During off-peak hours or when there is excess electricity in the grid, water is pumped from a lower reservoir to a higher one. When electricity demand is high, the stored water is released, flowing downhill and passing through turbines to generate electricity.

Geophysics provides valuable information about the subsurface conditions, geological structures, and hydrological characteristics of the project area. Here are some specific ways in which geophysics contributes to pump storage project investigations:

1. Site Selection: Geophysical surveys help in identifying suitable locations for pump storage projects. Geophysical methods, such as seismic surveys, can determine the subsurface structure and identify potential geological features, such as faults and fractures, which are important considerations for site selection.

2. Geological Mapping: Geophysical techniques, such as electrical resistivity tomography (ERT), Seismic Refraction, MASW and ground-penetrating radar (GPR), enable detailed subsurface mapping. These methods help to characterize the geological formations, identify rock types, and locate potential water-bearing zones or aquifers.

3. Reservoir Capacity Assessment: Geophysics aids in estimating the capacity and storage potential of reservoirs. By using methods like seismic refraction or electrical resistivity, the thickness and extent of suitable rock layers or sediments can be determined, helping to assess the volume of water that can be stored.

4. Hydrological Studies: Geophysical investigations provide insights into the hydrological properties of the project site. Techniques such as groundwater exploration surveys or electromagnetic surveys can identify groundwater flow patterns, determine aquifer propertsies, and assess the feasibility of using existing aquifers for water storage.

5. Stability Analysis: Geophysics assists in evaluating the stability of the reservoir and the surrounding slopes. Methods like electrical resistivity imaging, MASW, seismic refraction, or microgravity surveys can identify potential instabilities, such as subsurface faults or mass movements, which could affect the integrity of the reservoir and overall project safety. MASW can provide insights into the subsurface conditions, including the presence of potential slip planes, weak layers, or areas susceptible to liquefaction.

6. Foundation Design: The stability and load-bearing capacity of the project infrastructure, such as dams, powerhouses, or tunnel portals, depend on the properties of the foundation materials. SRT, ERI and MASW assists in designing reliable foundations by characterizing the subsurface conditions and identifying any potential weaknesses or problematic soil or rock layers that could affect the structural integrity of the project.

7. Environmental Impact Assessment: Geophysics plays a role in assessing potential environmental impacts. Surveys using geophysical techniques help to identify and map sensitive ecosystems, archaeological sites, or other important features that should be preserved or avoided during the project development phase.

8. Seismic Hazard Assessment: Pump storage projects require a thorough evaluation of seismic hazards. MASW can contribute to this assessment by providing information about the subsurface conditions that influence ground shaking during earthquakes. By determining the shear wave velocity profile, MASW helps estimate the site- specific seismic response and the potential amplification or attenuation of seismic waves.

9. Construction Planning: Geophysical data aids in the planning and design of the pump storage project infrastructure. For instance, it can assist in determining the most suitable locations for tunnels, penstocks, and powerhouse facilities by providing information on rock quality, depth to bedrock, and potential construction challenges.

Overall, geophysics provides valuable information for the comprehensive understanding of subsurface conditions and hydrological dynamics crucial for the successful planning, design, and implementation of pump storage projects. It helps in minimizing risks, optimizing resource utilization, and ensuring the long-term sustainability and efficiency of such projects.

Can geophysical methods like high resolution seismic tomography replace requirement of Drifts in pump storage projects investigations?

Geophysical methods, such as high-resolution seismic tomography, can provide valuable subsurface information in pump storage project investigations. However, it is unlikely that these methods can entirely replace the need for physical drifts or adits in such investigations. Heres why:

1. Complementary Information: Geophysical methods like seismic tomography offer indirect measurements of subsurface properties. While they can provide valuable insights into the overall subsurface structure and velocity variations, they may not capture all the detailed information required for project design and construction. Drifts or adits allow direct access to the subsurface, enabling visual inspection, geological sampling, and detailed mapping of geological features, which may be crucial for accurate engineering assessments.

2. Validation of Geophysical Data: Drifts can serve as ground truth information for validating geophysical data. Geophysical methods have inherent limitations and uncertainties, and physical access through drifts allows comparison and calibration of geophysical results with actual observations. It helps in refining the interpretation and reliability of the geophysical data and improves the accuracy of the subsurface models.

3. Site-Specific Challenges: Pump storage projects often face site-specific challenges that may require direct exploration through drifts. These challenges could include complex geological structures, fault zones, or localized areas of weak or unstable rock masses. Drifts allow for direct investigation and characterization of such features, which may not be accurately resolved by geophysical methods alone.

4. Detailed Engineering Design: Pump storage projects require detailed engineering design for tunnels, powerhouse structures, and underground excavations. While geophysical methods can provide a broad overview of the subsurface, drifts allow for precise geological mapping and evaluation of rock mass properties, such as rock strength, rock mass quality, and rock discontinuities. This detailed information is crucial for designing safe and efficient underground structures.

5. Construction Considerations: Drifts provide valuable information about the actual ground conditions encountered during excavation. This information helps in assessing the stability of the excavated drifts, planning support systems, and identifying potential hazards or risks during construction. Geophysical methods alone may not provide the necessary level of detail for construction planning and management.

While geophysical methods can significantly contribute to pump storage project investigations and provide valuable subsurface information, the physical access provided by drifts or adits remains essential for accurate characterization, validation, and detailed engineering design. The combination of geophysical surveys and physical drifts offers a comprehensive approach to subsurface investigations, ensuring a thorough understanding of the project site and optimizing project design and construction.

In what type of geological conditions geophysical methods like high resolution seismic tomography replace requirement of Drifts in pump storage project's investigations?

Geophysical methods like high-resolution seismic tomography can be particularly useful in certain geological conditions where they may partially or fully replace the requirement of drifts in pump storage project investigations. Here are some scenarios where geophysical methods can provide sufficient subsurface information:

1. Homogeneous and Stratified Geology: areas with relatively uniform and predictable geological conditions, geophysical methods can effectively characterize the subsurface without the need for drifts. If the geology consists of well-defined and continuous layers with minimal variations, seismic tomography can provide accurate velocity models, allowing for detailed subsurface mapping and assessment of geotechnical properties.

2. Open and Eposed Geological Formations: In situations where the geological formations of interest are exposed or accessible at the surface, the need for drifts can be reduced. Geophysical methods can be employed to collect data along surface lines or profiles, such as seismic refraction or reflection surveys, to image the subsurface without the need for direct physical access.

3. Shallow Subsurface Investigations: When the depth of interest for the pump storage project is relatively shallow, geophysical methods can be sufficient for subsurface characterization. Seismic tomography, for instance, can provide valuable information on the velocity distribution and layering in the upper tens to hundreds of meters of the subsurface, which may be adequate for design and construction purposes.

4. Non-Intrusive Investigations: In situations where minimizing ground disturbance is desired, or drilling is not feasible, geophysical methods offer a non-intrusive alternative. By deploying surface-based techniques like seismic tomography, resistivity surveys, or seismic methods (SRT, MASW), subsurface information can be obtained without the need for excavation or drifts.

5. Preliminary Assessments and Feasibility Studies: Geophysical methods are often employed in the early stages of project development to conduct preliminary assessments and feasibility studies. These methods can provide a rapid and cost- effective means of gathering initial subsurface information, helping to determine the viability of a pump storage project, and guiding further investigation needs.

It's important to note that while geophysical methods can provide valuable insights in the above scenarios, they may not completely replace the need for drifts in more complex geological conditions or situations where detailed engineering design, ground truth validation, or construction considerations are critical. The decision to rely solely on geophysical methods or incorporate drifts in pump storage project investigations should be based on a comprehensive understanding of the project's specific geological and engineering requirements.