Ground vibration in blasting refers to the seismic waves or oscillating motion of the ground caused by the detonation of explosives. These vibrations are the result of dynamic stresses and strain waves that travel through the rock and soil, potentially affecting pit slopes, man-made structures, and surrounding environments. Ground vibration is measured by its Peak particle velocity (PPV), typically in millimeters per second (mm/s), to ensure it remains within regulated limits to prevent damage.
Ground vibrations caused by blasting or mining activities can be controlled and managed using several techniques to protect nearby structures and communities.
Methods to Control Ground Vibrations
Blast design optimization
- Reduce the explosive charge weight per delay shot by using smaller hole sizes or bench heights, decking charges, or reducing the number of blastholes.
- Adjust burden and spacing of blast holes to lower confinement of the explosion.
- Use one or two free faces to relieve internal pressure and optimize delay timing.
- Modify the direction of initiation or blasting sequence to control vibration propagation.
- Use electronic delay detonators for precise timing control to reduce vibration amplitude.
Protective barriers and isolation techniques
- Use rows of solid piles, gas mattresses, or open/infilled trenches near vibration sources or the structures to isolate vibrations.
- Newer techniques include geocells placed under vibration sources to diffract and dissipate vibration energy laterally, preventing direct transmission to structures.
Monitoring and compliance with vibration limits
- Employ geophones and accelerometers to monitor blast vibrations, measuring peak particle velocity (PPV) to ensure compliance with regulatory limits designed to prevent structural damage.
- Limits vary by location and structure sensitivity but are generally set to avoid crack formation or foundation damage.
Protection for nearby structures and communities
- Consider site-specific geological conditions as they influence vibration transmission.
- Maintain safe buffer distances from blasting sites based on vibration scaling laws and empirical data.
- Implement communication and notification plans for communities prior to blasting events.
- Use vibration isolation near structures where possible and ensure compliance with local regulations on vibration limits.
In summary, controlling ground vibrations involves optimizing blast parameters, using vibration isolation and barriers, continuous monitoring, and adhering to established vibration limits to protect structures and nearby communities from damage or disturbance.
