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Gas Bag

An inflatable bladder used to block off a blast hole and support explosives or stemming.

gas bag


A geophone is a device that converts ground movement (velocity) into voltage.

Geophones typically comprise a spring-mounted magnetic mass moving within a wire coil to generate an electrical signal. The response of a coil/magnet geophone is proportional to ground velocity.

Geophones for recording blasting vibration should be able to record from 0.1mm/sec to 300mm/sec and over a frequency range from 4.5 Hz to 250 Hz.


Geophones require annual calibration by an approved testing station (NATA) to ensure they continue to accurately record ground vibration.

Geotechnical failure modes

There are a number of common failure modes relating to rock slope stability.

These are:


Pertaining to heat energy extracted from reservoirs in the earth’s interior.


Grams per metre. Common expression of core loading of detonating cords. (1 gm/m = 4.7 grains/foot).

grains per foot

Grains per foot is a measure of the explosives loading in detonating cord. The term is in imperial units and cord from North America is often rated in these units.

A grain is a unit of weight with 1 gram = 15.43 grains.

The conversion from grams per meter to grains per foot is:

1 gram per meter = 4.7 grains per foot.

Ground Vibration

Oscillatory movement of the ground caused by the passage of seismic waves.

Ground vibration is typically measured as a velocity of ground motion in millimeters per second using a seismograph.


A seismograph consists of a data recorder connected to a geophone. Geophones are devices that convert ground movement into voltage using a moving magnet and coil arrangement.





Skip Manage Drill and Blast Operations 5 DAY MASTERCLASS