Overview
This method statement covers the geophysical survey procedures for cavity investigation areas. It details the equipment, survey techniques, safety measures, and quality control procedures for conducting geophysical surveys in construction projects.
Scope of Work
The scope includes site preparation, equipment setup, data acquisition, processing, and reporting of geophysical survey results for cavity detection and subsurface investigation.
Survey Methods
Ground Penetrating Radar (GPR)
GPR uses electromagnetic pulses to image the subsurface. It is effective for detecting voids, cavities, and changes in soil composition.
Electrical Resistivity Tomography (ERT)
ERT measures subsurface resistivity variations to identify cavities, water-bearing zones, and geological boundaries.
Microgravity Survey
Microgravity measurements detect density variations in the subsurface, useful for locating cavities and voids.
Equipment
- GPR unit with appropriate antenna frequencies
- Electrical resistivity meter with multi-electrode system
- Microgravity meter
- GPS for positioning
- Data acquisition computer
- Safety equipment
Step-by-Step Procedure
1. Site Preparation
Clear the survey area of debris and obstructions. Mark survey grid with reference points. Conduct utility survey to identify underground services.
2. Equipment Setup
Calibrate all equipment according to manufacturer specifications. Set up data acquisition system. Verify GPS accuracy.
3. Data Acquisition
Conduct survey along predetermined grid lines. Maintain consistent speed and spacing. Record all data with position information. Monitor data quality in real-time.
4. Data Processing
Process raw data using specialized software. Apply necessary corrections and filters. Generate subsurface models and cross-sections.
5. Reporting
Prepare comprehensive survey report including methodology, results, interpretation, and recommendations.
Quality Control
Conduct repeat measurements for verification. Maintain equipment calibration records. Document all survey parameters and conditions.
Health & Safety
All personnel shall wear appropriate PPE. Be aware of traffic and equipment hazards. Follow electrical safety procedures for resistivity equipment.
