Presentation on theme: "ISMR BLASTER RETRAINING Workshop"— Presentation transcript:
1ISMR BLASTER RETRAINING Workshop Jasper, IndianaDecember 07, 2009Jasper Inn & Convention Center
2FLYROCK & “ PREVENTION” Dennis Clark, PE Mining Engineer OSMRE – KFO
3Number One Rule of Blasting ALL BLASTING SHALL be CONDUCTED to PREVENT: Injury to PersonsDamage to Public or Private PropertyThrow off the Permit/Blasting Site
4Adverse Effects of Fly-rock Increases the Area of Disturbance On & Off the PermitEndangers Employees and EquipmentPhysical Damage to Private PropertyEndangers Humans and LivestockCan Result in Death – Flyrock Kills!
5Tools to Assist in Fly-rock Investigations Blast Hole Drill Logs for each HoleBlast Report or Log: ) with Diagrams of how Holes are Loaded ) the Site Specific Drill & Blast PatternOn Site InvestigationEye-Witness AccountsInstrumentation & Monitoring Data
6Before “Blasting” You Drill the Holes What is Going on Here?
7Drill Log – Example A Requirement Prior to Loading Also log any rock type changes HOLENumberDepthLOOSEMaterialin feetDepth to SOLIDContactSEAMS&CRACKSCAVITIESLocationLocation of Soft FormationIn feetDepth toWATER142'0-23'--38'244'22-24343'0-45'20-2536'441'33'50-12'40'
8BLAST REPORT or LOG Location of Blast Date & Time Drill & Blast PatternExplosives & Delays usedMax. Pounds/8ms DelayLocation of Closest “House”Distance & Direction to “”Compliance Method DataAssure Accuracy Of Blast Log InformationAny Blast Log Discrepancies will require additional in-depth investigationsEvery Blank Space of the REPORT should be FilledDigital reproduction of log, & what to look for in response to complaint. Note: this reproduction is from a digital camera
9Flyrock per 816.67(c) Rock cast from blasting site via the air or along the ground Rock traveled > ½ distance to nearest dwellingBeyond the area of controlBeyond the permit boundary
10PROJECTED ROCK-CAST RANGES Blaster projects expected rock-cast range & determines security zone (area of control)Flyrock is any throw outside the security zone, within the permit and always outside the permitted site.
11Throw Distances for Varying Size Rock (Spherical in Meters) for a Given Hole Diameter 1.08 yards = 1 meter = 3.25 feet
12Swedish Rule-of Thumb Blasting of Dense Rock Maximum Fly-rock Range meter distance for every centimeter of Bore-Hole-DiameterExample in English System 5 inch Blast-Hole-Diameter Maximum Throw = 4,128 feetNote: Less Dense Rocks will not Travel as Far!!!
13Common Optimum Fly-rock Distances For a 8 Inch Diameter Blast Hole Sandstone: 6,000 ft. Sandstone/Shale 5,000 ft. Limestone: 6,200 ft. Shale: 4,100 ft. Decomposed Rock: 6,700 ft. Bedded Clay: 2,100 ft.
14Examples of Flyrock Travel Distances State of Virginia/Pit & Quarry 1991 Rock Distance PF LS ,063 ft LS ,159 ft LS ft. ~ LS ,050 ft LS ,057 ft LS ,292 ft Trap Rock ft Taconite 11,360 ft Porphyry ,119 ft Sandstone ,987 ft
15Material Displacement via Air Ground Primary Cause due to “Blast Confinement”Conventional throw from within the permitMaterial propelled by “Explosive Energy”Primary Cause due to “Blast Site Location”Common along permit boundariesMaterial propelled by “Gravity”
16Points to Consider when Blasting Adjacent to Permit Boundaries Displaced material has tendency to “roll” downhill &/or bounce off the permitAny & all “throw” has the opportunity to land or roll off the permitOccurrence can result even if all “Rules-of-Thumb” are observedPrevention requires pre-planning & thoughtfulness prior to drilling & Loading
17Primary Reasons for Material Off the Permit Material displaced by design – the movement toward the ‘vertical free face’ by the intended use of explosive energyMaterial displaced by the adverse reaction of explosive energy - back break & swell, vibration plus unintended movement toward a natural slope or vertical outcrop
18Corrective Actions When Blasting Adjacent to Permit Boundaries By Blast Design @ Drilling & Loading Orient ‘Blast Pattern’ to ensure multi-free-face movementReduce ‘Loading Densities’ in front rows of holesDecrease # of rows so throw from rear is lessenedModify ‘Drill Hole Pattern’ to facilitate a proper ‘Blast Pattern’Ensure proper TimingDecrease # of rows of holes to be loadedReduce ‘Loading Densities’ in rear rows
19Conventional FlyrockResults from available ‘Explosive Energy’ far exceeding the competency and inherit strength of overburden material being blastedFlyrock is not from the Hole-Collar or Stemming ejectionFlyrock is from material adjacent to the explosiveTherefore You Require Confinement in terms of Burden & Confinement via the Stemming
20Examples of the Effects of Confinement Based on Military Cratering Usage Blasting is done to break rocks. When the explosive is properly confined the explosive energy is focused on the burden. Bury a charge deeply – mostly ground vibrations.Bury a charge shallow – airblast and flyrock. The goal is to be somewhere in between.
21CONFINEMENT = PERFORMANCE All Results in Blasting Performance are Due to the Degree of Confinement, Based on the Columns of the Blasting Product being Utilized for a Given Overburden Material
22Bell Curve Showing Efficiency of Explosive Yield & Blast Confinement
23BURDEN is the DETERMINING FACTOR for all OTHER BLAST DIMENSIONS BURDEN & STEMMING DEFINE CONFINEMENT
24Seismographs Provide Data on Ground Motion Over Pressure Real Blast Detonation Time a check on Total Delay TimePPV depends on Max. Lbs per Delay & Distance, a check on # Holes/Delay IntervalOver-Confinement yields Higher than Normal PPVUnder-Confinement results in Lower than Normal PPVAssist in Determining Distance to SeismographHigher than expected dBs? Confinement ConcernsOver-Confinement results in Rifling, Cratering & Throw from Back RowsUnder-Confinement results in Flyrock well beyond the Area of Control
25TWO PRINCIPLES MUST BE KEPT IN MIND DURING THE DESIGN PROCESS Explosives Function Best When There is a Free Face Approximately Parallel to the Explosives Column at the Times of DetonationsThere Must be Adequate Space into Which the Broken Rock can Move and Expand
26THE USBM (IC-8550 & 8925) Presented Principles by Dr THE USBM (IC-8550 & 8925) Presented Principles by Dr. Richard Ash of “Mo. School of Mines” “Rules of Thumb Based on Two Major Points” 1: Rock Density is the Basis for the Amount of Explosives Required to Break a Given Volume of Rock 2: Blast Designs for Harder Rock Require Closer Control & Tighter Tolerance Than Those for Softer Rock
27General Causes of Flyrock Blasthole OverloadingInadequate FaceExcessive FaceLoose Material in Front of Free FaceExcessive Burden Between Rows‘Multiple’ Row Blasts (> 5 Rows)Inadequate Timing Between RowsExcessive Powder FactorAdverse Geology
28For a Solution to the Flyrock Problem! The Following is a MUST Anticipated Blast Designs & Blasting Plans Certified Blaster in Charge Prior to Loading - Review Drill Logs Explosives & Stemming Placed in Competent Rock Prior to Loading check & Double check Best Management Practices for all Blasting Scenarios must be Used
29What is COMPETENT ROCKCompetent Rock is rock that is of sufficient hardness and integrity that it Requires Explosive Energy to break into fragments to muckTherefore: One places not only the Explosive in Competent Rock, but also the Stemming that retains the energyIf not, Cratering & Throw is Guaranteed !
30Use When Non-Competent Rock is at the Collar of the Blast Hole Adjust for Rock Type & Explosives Use with drill logs to determine correct stemming lengths
31Low Density Blasting Agents & Typical Rock: Summary: Rule-of-Thumb for Burden For First Approximations Typical OverburdenLow Density Blasting Agents & Typical Rock:Burden in ft. = 2.5 x Hole Diameter20 ft. of Burden for a 8 inch HoleEmulsions & Typical Rock:Burden in ft. = 3 x Hole Diameter24 ft. of Burden for a 8 inch Hole
32Rule-of-Thumb for Burden Continued Low Density Blasting Agents inWeak Shale: Burden = ≥ 2.5 Hole Diameters22 ft. to 24 ft. of Burden for a 8 inch HoleCap Rock: Burden = ≤ 2.5 Hole Diameters16 ft. to 18 ft. of Burden for a 8 inch Hole
33Rule-of Thumb for Burden Continued Emulsions inWeak Shale: Burden = ≥ 3 Hole Diameters26 ft. to 28 ft. of Burden for a 8 inch HoleCap Rock: Burden = ≤ 3 Hole Diameters20 ft. to 22 ft. of Burden for a 8 inch Hole
34Summary: Rules-of-Thumb for Stemming In Competent Rock Where Flyrock Must be Prevented To prevent Violence stemming should vary from 14 to 28 times the B.H.D. Example: for a 10″ dia. hole the range by the ‘blast design rules-of-thumb’ is between 0.5 to 1.0 the B. Typically 0.7 x 25 ft. = 18 feet Using the ratios above: stemming = 14' to 28′ Additional stemming is required in competent rock when the rock sonic velocity exceeds detonation velocities or where rock is fractured or a less dense material like a shale overburden
35SHORT CASE HISTORY When Things Go Wrong – Every Thing Goes Wrong One Innocent VictimWrong the Wrong TimeOne Blaster Not Following Good PracticeNot PresentNot CommunicativeNot ObservantNot Performing per Regulations
40SUMMARY of ERRORSDid not Observe Changes in Geology Visible in High-wall FacesDid not have Drill-Logs AvailableDid not Know that Each & Every Hole Encountered a Varying Thickness of or Type of OverburdenDid not Vary Loading Parameters Based on Varying MaterialDid not Change Stemming Lengths to Compensate for Overburden StrengthsDid not Change Timing Between Rows to Ensure Movement to a Free-Face (‘Rock’ Reaction Time)