Basics of drilling 3
- 1. BASICS OF DRILLING-3 I. Satyanarayana, M.Tech,MBA,MCA Dy. Manager, Project Planning, SCCL isnindian@gmail.com, visit at www.slideshare.net/isnindian ISN
- 2. Inclined hole drilling If the strata conditions permit, inclined blastholes allow better distribution of the explosives Advantages: More fragmentation and displacement Eliminate front row toe burden and digging problem Probability of cut offs reduced More useful in higher benches Less over break New face formed is smooth and sound Less ground vibration Reduce secondary blast requirement Cost effective Disadvantages: Angled versus vertical blastholes Difficult to drill (requires sophisticated drilling equipment) and increased drilling cost. Requires close supervision Risk of bore hole collapse Difficult in charging and loading of explosives. ISN
- 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. EVALUATION OF DRILL PERFORMANCE Drill hole deviation Drills equipped with hydraulic shock wave reflex dampening system To maintain ideal feed rate, maintain verticality,achieving higher drilling rates and drill steel economy Computerised drilling control to control feed force, torque,and penetration rates ISN
- 5. • Drill machine navigation systems 1. GPS guidance system 2. The coordinates of each drill hole is sent via a radio network to the drill from the planning office 3. The data of actual drill position is sent to the planning cell for necessary computation ISN
- 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. Drill monitoring Drill monitoring system offers the ability to collect information • Drill production statistics • Ore and waste interactions • Exact collar location • Hole position and depth • Maintenance information • Consumable tracking • Blastibility index(BI) ISN
- 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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