Basics of drilling 3


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Basics of drilling 3

  1. 1. BASICS OF DRILLING-3 I. Satyanarayana, M.Tech,MBA,MCADy. Manager, Project Planning, SCCL, visit ISN
  2. 2. Inclined hole drilling If the strata conditions permit, inclined blastholes allow better distribution of the explosivesAdvantages:More fragmentation and displacementEliminate front row toe burden and digging problemProbability of cut offs reducedMore useful in higher benchesLess over breakNew face formed is smooth and soundLess ground vibrationReduce secondary blast requirementCost effectiveDisadvantages: Angled versus vertical blastholesDifficult to drill (requires sophisticated drilling equipment) and increased drilling cost.Requires close supervisionRisk of bore hole collapseDifficult in charging and loading of explosives. ISN
  3. 3. DRILLING PARAMETERS• Blasthole diameter (D): Generally, the cost of drilling and blasting decreases as hole diameter increases. The relationbetween blasthole diameter and face height is approximately: D = 0.001 to 0.02 H• Burden (B) : This is the distance in metres from a blasthole to the nearest free face and has the following approximate relation: B = 25D to 40D Or B = 25D to 30D for hard rock B = 30D to 35D for medium rock B = 35D to 40D for soft rock• Spacing (S) : This is the distance in meters between adjacent blastholes and is measured perpendicular to the burden. Usually the relation between drilled burden and spacing is: S = 1 to 1.8B• Charge length (L): This is the explosive column in a blasthole and should be at least 20D in order to utilize fully the explosion-generated strain in the rock.• Stemming (T): This is the inert material filled between the explosive charge and the collar of the blasthole to confine the explosion gases. The stemming material could be water, drill cutting, sand, mud or crushed rock. The best is the dry angular crushed rock (<30mm) as it tends to form a compaction arch, which locks into the blasthole wall, increasing its resistance to ejection. A stemming length shorter than 20D usually causes flyrock, cut-offs and overbreak problems. It is also suggested that the stemming length should not be less than the effective burden B.• Powder factor or specific charge or blasting ratio: This is the ratio between the mass of explosives required to break a given uantity of rock and is normally expressed in kg/m3 or kg/t3. ISN
  4. 4. EVALUATION OF DRILL PERFORMANCEDrill hole deviationDrills equipped with hydraulic shock wave reflex dampening systemTo maintain ideal feed rate, maintain verticality,achieving higher drilling rates and drill steel economyComputerised drilling control to control feed force, torque,and penetration rates ISN
  5. 5. • Drill machine navigation systems1. GPS guidance system2. The coordinates of each drill hole is sent via a radio network to the drill from the planning office3. The data of actual drill position is sent to the planning cell for necessary computation ISN
  6. 6. Benefits of monitoring drill performance• Higher rate of penetration• Reduced over drilling• location of weak and strong strata• Optimum blasting• Adequate fragmentation• Higher bit life• Lower maintenance cost &• Higher accuracy of data and reports ISN
  7. 7. Drill monitoringDrill monitoring system offers the ability tocollect information• Drill production statistics• Ore and waste interactions• Exact collar location• Hole position and depth• Maintenance information• Consumable tracking• Blastibility index(BI) ISN
  8. 8. DRILLABILITY• Rock drillability is defined as the penetration of a drill bit into the rock expressed in metres per minute. ISN
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