This document discusses measuring burden velocity, which is the average velocity of rock mass after detonation. Burden velocity depends on explosive strength and confinement. It is measured to evaluate blasting performance and compare explosive efficiencies. High-speed video cameras capturing 500+ frames per second are used to record blasts and analyze the motion in software. Frames are calibrated and markers track face movement to calculate real-time velocities, allowing evaluation of outcomes like fragmentation.
2. What is Burden Velocity?
Burden velocity (vb), measured in m/s, is the average
velocity of the burden rock mass after detachment from
the solid rock mass.
The velocity depends on -
1. The strength of the rock and explosive
2. The confinement provided
Burden
Burden
detached
after blasting
3. Why do we measure burden velocity?
1. To evaluate blasting performance.
2. For comparing explosives efficiencies in relation to burden velocity.
3. To estimate optimum delay times to provide adequate forward relief.
4. For evaluating the physical feasibility of overburden casting.
4. How do we measure Burden Velocity?
The assessment of many crucial outcomes of a blast (except ground vibration and air
overpressure) viz. face movement, bench face analysis, fragmentation, muck pile geometry,
after-blast high wall and floor condition, rock projectiles etc., largely depend on visual analysis.
On the other hand, blasting is a millisecond event which happens too fast to see and to
characterize the whole blasting process, it is crucial to really understand that what is happening
between the start of the blast to final muck pile generation.
Use of High speed video camera helps in capturing the initiation process and motion of the
blasted material in a series of very rapid photographs which otherwise would not be cognizable
by naked human eyes.
5. Blast monitoring using High-Speed Video
Camera
A modern High Speed Video Camera for
recording bench blasts
Monitoring bench blast in an opencast coal mine
High-speed video cameras are the devices capable
of capturing moving images with exposure of less
than 1/1000 second or frame rates in excess of 250
fps (Usually 500 to 1000 fps). After recording, the
images stored in the medium can be played-back in
slow motion for analysis.
6. Frames obtained from HSVC
When we use a camera of 500 fps, the number
of such frames generated are 500 in one second
of recording
7. Instrument set-up and controls
Position of the camera for recording
the blast event. The camera is usually
kept beyond 500 m from the blast site
to ensure safety
Markers of suitable size and preferably of fluorescent colour are
lowered with the help of a wire/rope for identification of face
movement
Blasthole
Bench top
Markers
attached to the
lowered rope
8. Analysing the blast video in MAS
Calibration of
the video
frames
Markers attached
to the face and
identified for
tracking the
movement
These values show the real-time
velocity in the video during analysis
10. Calculation of heave energy in the blast
(Chiapetta,1991)
𝐸𝑘 =
𝑚𝑣𝑏
2
2
After getting the value of burden velocity, the kinetic energy (heave energy in the
blast) can be calculated from the following empirical formula
