12.2 Environmental and engineering geophysics

Environmental and engineering geophysics applies various methods to investigate subsurface conditions for practical applications. These techniques help explore groundwater, map contaminants, and assess geotechnical sites, providing crucial data for environmental management and construction projects.

Geophysical methods like seismic surveys, electrical resistivity, and ground-penetrating radar offer unique insights into the subsurface. By integrating these tools with geological and geotechnical data, professionals can make informed decisions about site suitability, foundation design, and environmental remediation.

Geophysical Methods for Environmental and Engineering Problems

Investigating Subsurface Conditions

Top images from around the web for Investigating Subsurface Conditions

• 

  SE - 3-D seismic travel-time tomography validation of a detailed subsurface model: a case study ... View original

  Is this image relevant?

• 

  Data — Electromagnetic Geophysics View original

  Is this image relevant?

• 

  GI - Shallow geophysical techniques to investigate the groundwater table at the Great Pyramids ... View original

  Is this image relevant?

• 

  SE - 3-D seismic travel-time tomography validation of a detailed subsurface model: a case study ... View original

  Is this image relevant?

• 

  Data — Electromagnetic Geophysics View original

  Is this image relevant?

1 of 3

Top images from around the web for Investigating Subsurface Conditions

• 

  SE - 3-D seismic travel-time tomography validation of a detailed subsurface model: a case study ... View original

  Is this image relevant?

• 

  Data — Electromagnetic Geophysics View original

  Is this image relevant?

• 

  GI - Shallow geophysical techniques to investigate the groundwater table at the Great Pyramids ... View original

  Is this image relevant?

• 

  SE - 3-D seismic travel-time tomography validation of a detailed subsurface model: a case study ... View original

  Is this image relevant?

• 

  Data — Electromagnetic Geophysics View original

  Is this image relevant?

1 of 3

• Geophysical methods investigate subsurface conditions and detect potential hazards in environmental and engineering applications
  • Groundwater exploration
  • Contaminant mapping
  • Geotechnical site characterization
• Seismic methods (reflection and refraction surveys) map subsurface geology, bedrock depth, and soil layering
  • Essential for foundation design
  • Earthquake hazard assessment
• Electrical resistivity and electromagnetic methods detect and map subsurface variations in electrical properties
  • Indicate the presence of groundwater, contaminants, or buried objects
• Ground-penetrating radar (GPR) provides high-resolution imaging of shallow subsurface features
  • Buried utilities
  • Voids
  • Archaeological sites
• Gravity and magnetic methods map subsurface density and magnetic variations
  • Indicate the presence of buried objects, geologic structures, or mineral deposits

Applying Geophysical Methods

• Geophysical methods are applied to investigate a wide range of environmental and engineering problems
  • Groundwater exploration and management
    • Mapping aquifer geometry and properties
    • Identifying recharge and discharge zones
  • Contaminant mapping and remediation
    • Delineating the extent and migration of contaminant plumes
    • Monitoring remediation progress
  • Geotechnical site characterization
    • Assessing soil and rock properties for foundation design
    • Identifying potential geohazards (sinkholes, landslides, active faults)
  • Infrastructure mapping and monitoring
    • Locating and mapping buried utilities (pipes, cables)
    • Detecting leaks and assessing the condition of underground infrastructure
  • Archaeological and forensic investigations
    • Mapping buried structures and artifacts
    • Locating unmarked graves or buried evidence

Suitability of Geophysical Techniques

Factors Influencing Method Selection

• The choice of geophysical method depends on several factors
  • Specific application and target properties
  • Target depth and required resolution
  • Site conditions (geology, topography, access)
• Seismic methods are suitable for deep investigations (tens to hundreds of meters)
  • Provide information on subsurface layering and mechanical properties
  • Require good coupling with the ground
  • May be affected by surface noise (traffic, industrial activities)
• Electrical and electromagnetic methods are suitable for mapping subsurface variations in electrical properties
  • Groundwater and contaminant mapping
  • May be affected by cultural noise (power lines, metal structures)
  • Require good electrical contact with the ground
• GPR is suitable for high-resolution imaging of shallow targets (up to tens of meters)
  • Works best in low-conductivity environments (dry sand, granite)
  • Signal attenuation in conductive soils or the presence of clay can limit penetration depth

Limitations and Constraints

• Gravity and magnetic methods are suitable for mapping large-scale subsurface variations
  • Density and magnetic properties
  • Lower resolution compared to other methods
  • May be affected by nearby sources of noise (buildings, vehicles)
• Each geophysical method has its own limitations and constraints
  • Depth of investigation
    • Seismic and electromagnetic methods can reach greater depths than GPR
    • Gravity and magnetic methods have the greatest depth of investigation but lowest resolution
  • Resolution and target size
    • GPR provides the highest resolution but is limited to shallow depths
    • Seismic methods have intermediate resolution and depth of investigation
  • Signal-to-noise ratio
    • All methods are affected by various sources of noise (natural and anthropogenic)
    • Proper survey design and data processing are essential to enhance signal-to-noise ratio
  • Site accessibility and logistics
    • Some methods require extensive field setup (seismic, electrical resistivity)
    • Others are more portable and adaptable to different terrains (GPR, magnetic)

Interpretation of Geophysical Data

Data Processing and Analysis

• Geophysical data are processed and interpreted to create 2D or 3D models of subsurface properties
  • Seismic velocity
  • Electrical resistivity
  • Radar reflectivity
• Interpretation requires knowledge of
  • Underlying physical principles
  • Characteristics of the target and surrounding geology
  • Limitations of the method
• Seismic data interpretation
  • Identify subsurface layers, velocities, and discontinuities
  • Indicate changes in lithology, porosity, or the presence of faults or fractures
• Electrical and electromagnetic data interpretation
  • Map variations in subsurface resistivity or conductivity
  • Indicate the presence of groundwater, contaminants, or changes in lithology

Identifying Potential Hazards

• GPR data interpretation
  • Identify subsurface reflectors and discontinuities
  • Indicate the presence of buried objects, voids, or changes in soil properties
• Geophysical data can be used to identify potential hazards
  • Subsurface voids (karst, mining, or construction-related)
  • Faults and seismically active zones
  • Contamination (leaks, spills, or migration of pollutants)
• Interpretation of potential hazards guides further investigations or remediation efforts
  • Targeted drilling or sampling
  • Monitoring of hazard evolution over time
  • Design of mitigation or remediation strategies

Integration of Geophysical Data

Comprehensive Site Characterization

• Geophysical data provide valuable information on subsurface conditions
  • Should be integrated with other geological and geotechnical data for a comprehensive understanding of the site
• Geological data provide context for interpreting geophysical data and constraining subsurface models
  • Borehole logs
  • Surface mapping
  • Regional geologic models
• Geotechnical data are used to calibrate geophysical models and assess the engineering implications of subsurface conditions
  • Soil and rock properties
  • Groundwater levels
  • In-situ tests (standard penetration test, cone penetration test)
• Integration of multiple geophysical methods (joint inversion or cooperative inversion) can improve the resolution and reliability of subsurface models
  • Combining complementary data sets (seismic and electrical, GPR and magnetic)
  • Reducing uncertainty and non-uniqueness in interpretation

Informed Decision-Making

• Integrated site characterization is essential for informed decision-making in environmental and engineering projects
  • Site selection and suitability assessment
    • Identifying favorable conditions for construction or waste disposal
    • Avoiding potential hazards or environmentally sensitive areas
  • Foundation design and geotechnical engineering
    • Determining the depth and properties of load-bearing layers
    • Assessing the potential for soil liquefaction or ground deformation
  • Remediation planning and monitoring
    • Delineating the extent of contamination and identifying preferential pathways
    • Designing and optimizing remediation strategies (extraction wells, barrier walls)
• Geophysical data, when properly integrated with other site information, contribute to
  • Reduced uncertainty and risk in project planning and execution
  • Optimized use of resources and improved cost-effectiveness
  • Enhanced safety and environmental protection throughout the project lifecycle