Geophysics and geotechnique are complementary disciplines that provide critical insights into subsurface conditions for environmental and civil
engineering applications. These techniques are particularly valuable for landfill engineering, contaminated site assessment, and infrastructure development where understanding subsurface characteristics is essential.
1. Core Principles and Differences
Geophysics
- Non-invasive subsurface investigation using physical properties
- Measures contrasts in:
- Electrical resistivity/conductivity
- Seismic wave velocity
- Magnetic susceptibility
- Density
- Provides lateral continuity of subsurface features
Geotechnique
- In-situ testing and laboratory analysis of soil/rock samples
- Measures:
- Strength parameters
- Compressibility
- Permeability
- Density
- Provides quantitative engineering properties
2. Integrated Investigation Approach
A comprehensive site investigation typically follows this sequence:
1. Desktop Study (historical records, aerial photos)
2. Geophysical Survey (identify anomalies and key features)
3. Targeted Geotechnical Sampling (based on geophysical results)
4. Laboratory Testing (verify and quantify properties)
5. Data Integration (create 3D ground model)
3. Advanced Applications in Waste Management
Landfill Liner Integrity Assessment
- ERT (Electrical Resistivity Tomography): Detects leaks in geomembranes
- GPR (Ground Penetrating Radar): Maps liner wrinkles or defects
- Seismic Methods: Assesses clay liner compaction
Leachate Plume Monitoring
- Time-lapse ERT: Tracks plume migration over time
- Self-potential Method: Detects contaminant flow paths
- Borehole Geophysics: Provides vertical profiling
Landfill Stability Analysis
- MASW (Multichannel Analysis of Surface Waves): Measures waste stiffness
- Inclinometers: Monitors slope movement
- Piezometers: Tracks pore pressure changes
4. Emerging Technologies
| Technology | Application | Advantage |
|------------|-------------|-----------|
| AI-assisted CPT interpretation | Automated soil classification | Reduces subjectivity |
| Distributed Acoustic Sensing (DAS) | Continuous seismic monitoring | High spatial resolution |
| Hyperspectral Core Scanning | Rapid contaminant detection | Non-destructive |
| Quantum Gravity Gradiometry | Void detection | Ultra-high sensitivity |
5. Case Study: Old Landfill Rehabilitation
Project: Assessment of a 1970s-era landfill for solar farm development
Approach:
1. Geophysical Survey:
- ERT identified leachate accumulation zones
- GPR mapped waste thickness variations
- Magnetometry located buried metal objects
2. Geotechnical Investigation:
- CPT with piezocone verified waste composition
- Laboratory tests determined consolidation properties
3. Remediation Design:
- Targeted gas venting system based on methane mapping
- Engineered cap design using geophysical stiffness data
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6. Best Practices for Effective Investigations
1. Always combine methods - No single technique provides complete information
2. Calibrate geophysics with borehole data - Essential for accurate interpretation
3. Consider anisotropic conditions - Waste and natural soils often have directional properties
4. Plan for long-term monitoring - Especially important for landfill aftercare