using konya’s method to identify blast design problems an overview of the havablast 4 spreadsheet

Using Konya’s Method to Identify Blast Design Problems

An overview of the Havablast 4 Spreadsheet

The Burden Field

Burden is the distance from a hole to the nearest intended free face. Konya’s method uses information on yourexplosive energy, rock density, hole size, and special rock conditions indicated by your input to determine theamount of burden that would be expected under ordinary conditions. Firing with too little burden can be expectedto cause casting, fly rock out of the face, blowout, and noise problems. Firing with too much burden can beexpected to cause ground vibration, backbreak, poor fragmentation, and cratering.

Hole VOD Burden Stiffness Stem Subgrade Spacing Stiff Check2 10000 3.2834 12.18238442 2.298401 0.98502884 6.5668589 Excessive3 11000 4.9251 8.121589611 3.447601 1.47754326 9.8502884 Excessive4 16000 6.5669 6.091192208 4.596801 1.97005768 13.133718 Excessive

4.5 12300 7.3877 5.414393074 5.171401 2.21631489 14.775433 Excessive5 16000 8.2086 4.872953767 5.746002 2.4625721 16.417147 Excessive


6.5 13600 10.671 3.748425974 7.469802 3.20134373 20.447431 Ok7 14000 11.492 3.480681262 8.044402 3.44760094 20.994669 Ok8 14000 13.134 3.045596104 9.193603 3.94011536 22.089145 Ok9 14000 14.775 2.707196537 10.3428 4.43262978 23.183622 Ok

Bench Height 40 feetP wave vel 12000 feet/secRock Factor 10

Rel Weight St 100Burden Adjust 0.744Rock Sp Grav 2.7Stem Factor 0.7Interhole Delay 2 1 = YesExp Sp Grav 1.4Crusher Gap 27 inchesPercent 2ndary 25 %Min Size 0.25 inches% Fines 10 %Min D50 5 inchesMax D50 25 inchesDistance to Mon 1500 feetScaled Dist 40

Special Rock Conditions are

Handled by a Burden Adjustment. The Class notes indicate how things such as massiverock a dipping fractures should be handled. Burden adjustment should be based on thecondition of the rock which is a feature of the site geology - not engineering design.

The Stemming Field

Hole VOD Burden Stiffness Stem Subgrade Spacing Stiff Check2 10000 3.283429 12.18238442 2.298 0.98502884 6.5668589 Excessive3 11000 4.925144 8.121589611 3.448 1.47754326 9.8502884 Excessive4 16000 6.566859 6.091192208 4.597 1.97005768 13.133718 Excessive



6.5 13600 10.67115 3.748425974 7.47 3.20134373 20.447431 Ok7 14000 11.492 3.480681262 8.044 3.44760094 20.994669 Ok8 14000 13.13372 3.045596104 9.194 3.94011536 22.089145 Ok9 14000 14.77543 2.707196537 10.34 4.43262978 23.183622 Ok

Bench Height 40 feetP wave vel 12000 feet/secRock Factor 10Rel Weight St 100Burden Adjust 0.744Rock Sp Grav 2.7

Stem Factor 0.7Interhole Delay 2 1 = YesExp Sp Grav 1.4Crusher Gap 27 inchesPercent 2ndary 25 %Min Size 0.25 inches% Fines 10 %Min D50 5 inchesMax D50 25 inchesDistance to Mon 1500 feetScaled Dist 40

Stemming is the inert material put into the top of the hole above theexplosive column. Its function is to contain the throw of materialand reduce noise. Stemming is most frequently made of drill cuttingsor stream gravel. Konya’s method recommends the minimum amountof stemming needed to avoid ejection from the hole (assuming the restof the blast was well designed). Stemming is a function of the burdenand thus indirectly all variables influencing burden. The ratio of thestemming length to the burden is determined by a stemming factorwhich was one of your inputs. The appropriate stemming factordepends on the type of material used for the stemming. Too muchstemming will usually adversely effect fragmentation at the top of thebench. Too little can be expected to eject (although poor burden, cratering, and bad shot timing can also cause stemming ejection).

Subgrade

Hole VOD Burden Stiffness Stem SubgradeSpacing Stiff Check2 10000 3.283429 12.18238442 2.298401 0.98503 6.5668589 Excessive3 11000 4.925144 8.121589611 3.447601 1.47754 9.8502884 Excessive4 16000 6.566859 6.091192208 4.596801 1.97006 13.133718 Excessive



6.5 13600 10.67115 3.748425974 7.469802 3.20134 20.447431 Ok7 14000 11.492 3.480681262 8.044402 3.4476 20.994669 Ok8 14000 13.13372 3.045596104 9.193603 3.94012 22.089145 Ok9 14000 14.77543 2.707196537 10.3428 4.43263 23.183622 Ok

Subgrade is the distance that a hole is drilled and charged below the bottom of the bench to be extracted. Konya’smethod of determining subgrade is as a simple function of the burden. Thus, subgrade is indirectly effected byall variables that influence burden. Konya’s method assumes that benches are blasted in an essentially continuousrock mass such as that in a metal, industrial minerals, or quarry operation. In coal where there is often a drasticchange in density between the overburden and coal one may not have subgrade. The extra charge in the subgradehelps to pull the toe of the bench and keep the pit floor level. (In coal the natural change in density and materialcauses the bench to break out along the interface without subgrade). Too much subgrade will cause large amountsof powder to detonate without a free face causing ground vibrations, back break, and in extreme cases evencratering. Too little subgrade will often cause the pit floor to rise in the direction of advance or will allow humpsof rock to remain after blasting, in addition to causing difficulties pulling the toe.

Stiffness Ratio

Hole VOD Burden StiffnessStem Subgrade Spacing Stiff Check2 10000 3.283429 12.18238 2.298401 0.98502884 6.5668589 Excessive3 11000 4.925144 8.12159 3.447601 1.47754326 9.8502884 Excessive4 16000 6.566859 6.091192 4.596801 1.97005768 13.133718 Excessive



6.5 13600 10.67115 3.748426 7.469802 3.20134373 20.447431 Ok7 14000 11.492 3.480681 8.044402 3.44760094 20.994669 Ok8 14000 13.13372 3.045596 9.193603 3.94011536 22.089145 Ok9 14000 14.77543 2.707197 10.3428 4.43262978 23.183622 Ok

Stiffness Ratio is the ratio of the bench height to the burden. As the stiffness ratioapproaches 2, the risk of cratering becomes greater. At two the shot can beexpected to crater. Stiffness ratios above 4 tend to do little for fragmentation butthey imply that a larger hole size might have been selected with savings in drillingand blasting costs likely. Stiffnesses above 4 do not immediately become atechnical design problem, but should be examined if optimized economics are afactor. Stiffnesses over 6 can be associated with an increase risk of cut-offs.Because burden is a function of hole size, there is a relationship between a goodselection for bench height and a good selection for hole size. The spreadsheetcontains a stiffness check field. The field reports “Redesign” if the hole size willlikely crater, “ok” if there are no expected technical or economic problems with thematch of bench height and hole size, or “excessive” if the stiffness is high enough tocreate either economic optimum or cut-off risk concerns for the hole size.

Bench Height 40 feet

P wave vel 12000 feet/secRock Factor 10Rel Weight St 100Burden Adjust 0.744Rock Sp Grav 2.7Stem Factor 0.7Interhole Delay 2 1 = YesExp Sp Grav 1.4Crusher Gap 27 inchesPercent 2ndary 25 %Min Size 0.25 inches% Fines 10 %Min D50 5 inchesMax D50 25 inchesDistance to Mon 1500 feetScaled Dist 40

using konya’s method to identify blast design problems an overview of the havablast 4 spreadsheet

Documents