blasting near water 3

[miningman]

Can anyone advise the relationship between peak particle velocity and the anticipated peak pressures in a body of water close to a blast?? We are presently planning a number of small blasts within 25-100 metres of a body of water and are restricted to 100kPa pressure in the water. How does this relate to explosive charge/ distance/ peak particle velocity. Can such pressure be readily measured directly or does one monitor peak particle velocity and then calculate forwards??

 

[exploengineer]

This is out of a training manual I wrote. I hope it helps. I haven't found a good way to go from PPV to pressure. We do underwater blasting and have to predict both. If the charges are not actually in the water, vibration will be very low over the distances you stated.

VIBRATION PREDICTION

PPV = K(D/W^½)^-1.6 = (SD)^-1.6 x K
PPV = Peak Particle Velocity (ins/sec or mm/sec)
SD = Scaled Distance
^-1.6 = to the -1.6 power
K = K Factor – Confinement Factor
Underconfined: 100 (metric 713)
Normal: 150 – 160 (metric1070 – 1141)
Overconfined: 205 (metric 1462)
Upper bound: 242 (metric1725)
Expected Average Vibration: 160 (metric1141)
Highly confined: 605 (metric 4314)

To calculate the “K” factor, use the following formula:
K = PPV/(D/W^½)^ 1.6

Example:
PPV = 0.75 ips, lbs. = 15, D = 100’
K = .75/(100/15^½)^-1.6
K = 136 Metric =

1. Calculate Scaled Distance = SD = Distance/Weight^½
2. Calculate SD to the –1.6 power
3. Multiply by the “K” factor. – Choose the H factor or calculate from previous blasts.
4. K x SD^-1.6 equal to your predicted PPV.
5. K factor has huge significance.
6. If this formula is used well, it can be accurate. This formula is used in regression curves, but K factor and power are calculated from the data.

WATER SHOCK

Damage is extremely localized in water. Environmental damages such as fish kills are rare.

Simple prediction methods in shallow water are not reliable. Also, nobody has developed a reasonable set of limits for water shock.

Prediction
Developed in 1948.
Water depth- 40 feet
Charges varied from .5 lbs. (.23 kg) to 55 lbs. (25 kg) of TNT.

PWS = 21,600(W^1/3/D)^1.13

PWS = Peak Water Shock at point of interest (PSI)
D = Distance to the point of interest in feet
W = Charge Weight in pounds (lbs.)

Scaled Distance for Water Shock
SDw = W^1/3/D

PWS = 21,600 (1/SDw)^1.13






Frank Lucca M.I.Exp.E.

http://www.terradinamica.com