For an industry built around blasting as its primary means of rock fragmentation, that shift changes the calculus. When explosive supply is abundant and cheap, the incentive to extract maximum value from every kilogram is weak. When it isn’t, efficiency stops being a nice-to- have and becomes operationally necessary.

The Usual Levers and Their Limits

Mining operations generally have four levers available to improve explosive efficiency:

– Higher-energy explosives and better initiation accessories — effective, but often constrained by what’s approved, available, and contracted with suppliers.

– Optimised blast design — burden, spacing, sub-drill, and stemming length — already implemented to varying degrees at most established Indian quarries, leaving diminishing room for further gains.

– Borehole liners, to improve coupling between explosive and rock.

– Stemming plugs and air-deck techniques, which modify how energy is contained and released within the hole itself.

Of these, the first two are frequently already optimised or constrained by factors outside a mine’s direct control — explosive selection is often dictated by regulatory approval and supply agreements, and design parameters have typically already been through several rounds of refinement. That leaves stemming technique as one of the few remaining levers that’s genuinely under-exploited at most sites, and one that can be adopted incrementally without disrupting existing drilling or charging infrastructure.

A Practical Illustration

A recent trial at Zuari Cement’s Sitapuram Limestone Mine in Telangana offers a useful data point. By introducing PVC stemming plugs to create a controlled air deck above the explosive column, the mine reduced ANFO consumption per hole from 83 kg to 77.5 kg — a real cut in explosive tonnage per hole — while simultaneously achieving better fragmentation and greater muckpile throw than the conventionally stemmed section of the
same blast.

That’s not a trade-off between efficiency and performance. It’s evidence that a meaningful share of explosive energy in conventional stemming was being wasted rather than converted into useful rock breakage — energy that a properly engineered air deck can help recover.

Published research backs this up at a broader scale: air-deck techniques have been reported to deliver explosive savings in the range of 15–30% across various site conditions, alongside reduced fly-rock, airblast, and ground vibration. The exact figure always depends on rock properties, hole diameter, and how the air deck is sized — which is exactly why site-specific validation trials, like the one at Sitapuram, matter more than generic industry benchmarks.

The Strategic Case

In a tightening explosive supply environment, the mines best positioned to weather volatility are the ones that use technique, not just tonnage, to extract fragmentation performance. Stemming plugs won’t insulate an operation from every price shock, but they represent a low- capital, quickly deployable way to reduce dependence on raw explosive volume per tonne of ore or rock produced — precisely the kind of resilience that becomes valuable when supply chains wobble.

For quarry and mine operators reviewing their explosive strategy this year, the question is less “should we use less ANFO” and more “how much of our current usage is actually doing useful work, versus venting away as wasted energy.” Increasingly, that’s a question worth answering with a controlled field trial rather than an assumption.

Uttam Blastech Pvt Ltd works with mining operations across India to design blast trials that reduce explosive dependency without compromising fragmentation performance. Reach out to discuss a stemming audit for your site.

The post Explosives Squeeze: Why Every Kilogram of ANFO Now Matters More first appeared on Uttam Blastech.

Fragmentation Is a Decision, Not an Accident

When a blast produces coarse, oversized rock, that cost doesn’t disappear — it moves downstream and grows. Oversized boulders need secondary breaking, which means extra drilling, extra explosive, or extra time with a hydraulic hammer. Loading equipment works harder and slower against a poorly broken pile. Haul trucks carry less effective payload per cycle when material is irregular. And at the crusher, oversized feed reduces throughput, increases wear on liners and jaws, and — for operations like cement plants — raises the grinding energy needed downstream to get the material to the fineness the process requires.

None of these costs show up on a “blasting” line item. They show up scattered across maintenance budgets, energy bills, and productivity reports, which is exactly why fragmentation quality is so easy to underinvest in: the cost of getting it wrong is real, but it’s invisible at the point where the decision gets made.

A Concrete Example

A recent field trial at Zuari Cement’s Sitapuram Limestone Mine puts numbers to this. By introducing PVC stemming plugs to create a controlled air deck above the explosive charge, the trial team achieved measurably better fragmentation and greater muckpile displacement — while simultaneously reducing the ANFO load per hole from 83 kg to 77.5 kg.

The direct saving worked out to roughly ₹259 per hole, or ₹0.59 per tonne of limestone, after accounting for the cost of the plugs themselves. On a mine producing at scale, savings like that compound quickly across thousands of holes a year. And that figure captures only the explosive cost difference — it doesn’t yet quantify the secondary savings in reduced oversize handling, faster loading cycles, or lower crusher wear that better fragmentation typically delivers.

Why This Is an ROI Conversation, Not Just a Technical One

The appeal of an intervention like stemming plugs is that it doesn’t ask for capital expenditure, new equipment, or a change of explosive supplier. It’s a modification to existing charging practice that a blast crew can adopt within a normal shift. That makes the ROI calculation unusually clean: a small, well-defined cost per hole, weighed against explosive savings that are directly measurable and downstream productivity gains that, while harder to isolate precisely, are consistently reported across the wider body of blasting research.

For operations managers under pressure to find efficiency wherever it exists — and for finance teams increasingly asked to justify every cost line — blasting deserves a second look. It’s one of the few places in the mining value chain where a low-cost, low-disruption change can pay for itself immediately and keep paying dividends through every stage that follows.

The Real Question

The question worth asking isn’t “can we afford to trial a change to our stemming practice?” It’s “what is poor fragmentation already costing us, and how much of that is hiding in budgets we don’t associate with blasting at all?”

Sitapuram’s early results suggest that for at least some mines, the answer is: more than expected, and more recoverable than assumed.

Uttam Blastech Pvt Ltd runs data-driven blast optimisation trials that connect blasting decisions to bottom-line outcomes. If you want a clear-eyed look at what your current fragmentation practice is costing you, we’d be glad to help you find out.

The post The Hidden Cost of Poor Fragmentation: Why Blasting Is a Bottom-Line Issue, Not Just a Mining One first appeared on Uttam Blastech.

Compression Is Not the Whole Story

Rock is deceptively tough in compression. Competent limestone can resist over 80 MPa of compressive stress before it fails. But put that same rock under tension, and it gives up far more easily — often somewhere between 8 and 12 MPa. Rock, in other words, is roughly ten times weaker when you pull on it than when you push on it.

Conventional blasting relies heavily on compressive shock and gas pressure to do the breaking. It works, but it’s not using the rock’s weak point efficiently. Air-deck stemming — the technique behind stemming plugs — is built around exploiting that weak point directly.

What Actually Happens Inside the Hole

When a stemming plug is placed above the explosive column, it leaves a gap of air between the top of the charge and the stemming material above. That gap is the air deck.

At the moment of detonation, a high-pressure shock wave races up through the explosive column. When it hits the air deck, it meets a sudden, dramatic change in acoustic impedance — going from dense, tightly coupled explosive and rock into a pocket of compressible air. Physics dictates that at a boundary like this, part of the wave reflects back the way it came, but as a tensile wave rather than a compressive one.

That reflected tensile wave travels back down through the already-shocked rock and explosive column, and because rock is so much weaker in tension, it drives fracturing far more efficiently than the original compressive pulse alone. The net effect: more fracture surfaces, more uniform breakage, and less energy wasted crushing rock immediately around the borehole wall — a zone that gets pulverised in conventional blasting without contributing much to overall fragmentation.

The Second Job: Sealing the Hole

There’s a mechanical piece to this too. As detonation gases expand into the air deck, they build pressure against the underside of the plug. A well-designed plug folds outward under that pressure and wedges firmly against the borehole wall, forming a seal.

That seal matters because it stops detonation gas from venting prematurely through the collar of the hole — a common failure mode with drill-cuttings-only stemming, where loosely packed material can blow out before it’s finished doing useful work. By holding the seal longer, the plug extends the duration the pressure pulse acts on the surrounding rock, squeezing more fragmentation and displacement out of the same charge.

Why This Isn’t Just Theory

This isn’t a new or speculative idea — it’s been studied across dozens of published trials over the past three decades, from Armstrong’s foundational 1994 work on stemming quality through more recent field studies by Saharan et al. and Choudhary and Rai. Reported explosive savings from air-deck techniques generally fall in the 15–30% range, alongside documented reductions in fly-rock, airblast, and ground vibration — though the exact numbers always depend on rock mass properties, hole diameter, explosive type, and how the air deck is sized, which is why site-specific trials remain essential.

That’s the underlying mechanism behind results like those recently observed at Zuari Cement’s Sitapuram Limestone Mine, where a stemming plug trial produced visibly finer fragmentation and greater muckpile throw compared to conventional stemming — a real-world confirmation of what the physics predicts.

The Takeaway

Stemming isn’t just a passive plug at the top of a hole — it’s an active part of the blast design, with its own physics to exploit. Understanding the air-deck mechanism is the first step toward using it deliberately, rather than treating stemming as an afterthought once the “real” blast design is finished.

Uttam Blastech Pvt Ltd helps mining operations apply blast physics like this to real sites — turning published research into measurable, site-validated results. Talk to us about auditing your current stemming practice.

The post Air Decks Explained: The Physics Behind Better Rock Fragmentation first appeared on Uttam Blastech.

At Zuari Cement Limited’s Sitapuram Limestone Mine in Telangana, a recent trial set out to test a simple question: could a low-cost plastic device, inserted above the explosive charge, reliably tip a blast toward that second outcome — and save money while doing it?

The Setup

The trial team, led by Uttam Blastech Pvt Ltd, split a 29-hole staggered blast face into two matched halves. Both sides were drilled to the same 150 mm diameter, 8.5 m depth, 4 m burden, and 5.5 m spacing, and both were loaded with the same explosive, ANFO. The only variable that changed was the stemming.

One half was stemmed the conventional way, with drill cuttings packed above the explosive column. The other half got a PVC stemming plug inserted directly above the charge before the cuttings went in — creating a controlled air gap, or “air deck,” of about 0.8 metres between the explosive and the stemming material above it.

Everything else — delay timing, face geometry but for explosives charge — was held constant, so any difference in outcome could be attributed to the plug itself.

What Happened

The results were visible before anyone ran a single calculation. The plug-assisted side of the face broke up more evenly, with noticeably less oversized, blocky material sitting in the muckpile. Rock that would normally need secondary breaking before it could go to the crusher was already sized right.

The plug side also threw the broken rock further forward — a strong sign that more of the detonation’s energy was doing useful work on the rock instead of venting away or dissipating as ground vibration and airblast.

And the Numbers

Here’s where it got interesting for the finance team. Because the air deck let the crew load less explosive per hole — 77.5 kg of ANFO instead of 83 kg — while still achieving better fragmentation, the plug side cost less overall, even after paying for the plug itself:

That works out to a saving of roughly ₹259 per hole, or about ₹0.59 per tonne of limestone produced — on top of the fragmentation and throw improvements, which carry their own downstream savings in loading, hauling, and crushing that weren’t even fully captured in this cost model.

Why It Matters

None of this required new drilling equipment, a change in explosive supplier, or retraining the blast crew. The plug slots into the existing charging sequence. That’s precisely what makes it worth paying attention to: it’s a rare case in blasting optimisation where you can improve output quality and reduce cost at the same time, without disrupting operations to get there.

The trial team has recommended Sitapuram move toward routine adoption, pending confirmation across a larger number of blasts, and is already planning follow-up trials with a reduced ANFO column and extended air deck to see how much further the savings can go.

For a limestone mine feeding a cement plant, where fragmentation quality ripples all the way through to grinding energy at the mill, that’s a result worth watching closely.

Uttam Blastech Pvt Ltd designs and validates blast optimisation trials for mining operations across the Globe. If your site is looking to benchmark stemming performance or reduce explosive cost per tonne, get in touch.

The post How Stemming Plug Cut Blasting Costs at Zuari Cement’s Sitapuram Mine. first appeared on Uttam Blastech.

Use of stemming Plugs

Stemming is the most critical part of blast geometry; inadequate stemming results in Flyrock, and too small a portion produces boulders needing secondary blasting.

The solution lies in better utilisation of explosives energy before it reaches the top portion of the hole and containing the explosives energy a little longer. This also ensures that material is thrown in the forward direction thus giving good quality of muck pile.

The solution is the use of stemming plugs.

Working Principle

Stemming plugs are forced to fit into the blast hole at the predetermined location. The location of the placement should be such that it results in an air deck of enough height.

When explosives are initiated at the bottom, the air deck gets compressed, stemming plug being flexible resists this pressure for a few milliseconds diverting the energy towards the free face, resulting in better fragmentation and throw.

Case study

A Mine Near Hyderabad

How to use

Operating Procedure:

1. Storage: Store boxes in a dry area to prevent premature deterioration of the packaging.

2. Transport and Handling: The stemming plug is not classified as a dangerous good for transport, storage, and handling and can be shipped and stored as general cargo. It is made of Resilient, Flexible material such as PVC Urethane, Rubber or similar material moulded and has a virtually infinite shelf life if stored correctly with intact packaging. 

3. Shape Maintenance: If the plug has distorted during shipping and/or storage, stretch the plug back into shape.

4. Loading with Emulsion Explosive: If an emulsion explosive has been loaded, wait for at least 30-45 minutes for the emulsion to gas before loading the stemming plug. Loading prematurely can cause ‘dead pressing’ of the explosive, preventing it from achieving the correct detonation characteristics or preventing detonation altogether.

5. Deployment: Use a stemming rod long enough to push the plug into position. The correct stemming height generally ranges from the bottom charge height + 0.7 to 1m airdeck, depending on the quality of the stemming material, presence of water in the top portion of the hole, powder factor, rock strength in the upper flitch, and burden. The depth should be clearly indicated on the pole for the operator’s benefit, ensuring consistency from hole to hole across the shot.

5. Positioning: 

• In a dry hole, push the plug to the desired depth with the stemming rod. In a wet hole, pushing into position may be slower as the water needs to pass the geared profile of the plug.
• The geared profile of the plug is designed not to damage down lines and cords. Note any added tension on the down lines when pushing the plug.
• After using the stemming rod to push the plug to the desired depth, manually put enough stemming material in the hole to fill the plug cup, tamping the material to lock the plug in position.

6. Wet Ground: In wet ground, water will be displaced by the stemming material. When tamping the stemming material, especially if it consists of drill cuttings or a significant percentage of drill cuttings, take extreme care not to cause any damage to down lines and cords in the stemming area. Only trained and experienced operators should perform this task.

7. Using Liners: If liners are used in wet and/or badly cracked ground, push the liner to one side before placing the plug in the collar. Carefully push the plug into position and ensure the stemming is well-tamped to increase ejection resistance when using liners.

8. Final Inspection: After stemming has been loaded and during final inspection prior to firing the shot, ensure all holes are stemmed to surface level at least, and no holes show signs of subsidence of the stemming material. Subsidence can occur when drill cuttings are used as stemming in wet ground or if the stemming plug has moved. Any change to the downlines (such as increased tension or evidence of movement) should be carefully remedied or at least recorded in case it is relevant to any post-blast analysis.

Technical Specifications

Contact crm@uttamblastech.com to get commercial details of the above.
Check www.uttamblastech.com/resources for more information

The post Stemming Plugs first appeared on Uttam Blastech.

What is a Flexible Liner

Flexible liners are HDPE (High-Density Polyethylene) tubes that are flexible and can be easily inserted into the hole.

When to use?

1. A Blast hole may be full of cracks and crevices. When Explosives are loaded into these holes, Explosives tend to occupy these cracks and crevices, thus resulting in wastage of explosives and Fly Rock and Bad Blasts due to improper energy Distribution.
2. Explosives needed to be charged in the hole are controlled by the diameter of the drilling. A situation may demand charging a lesser quantity of explosives, the only options available are either to use a deck charge or use a lesser diameter of holes.

Deck charging results in uneven distribution of explosives and will result in uneven distribution of fragmentation and may produce boulders from the decked portion.

The diameter of the Drilling is decided by the Drilling Machine purchased and is difficult to change.

Solution, use a flexible liner. Liners can be manufactured to suit your required diameter.

Result: Even distribution of Explosives throughout the holes, resulting in Even Fragmentation and saving of explosives

Calculate Explosives Savings through reduction of Diameter

Download the brochure of Flexible Liners.

Contact crm@uttamblastech.com to get commercial details of the above.

Check www.uttamblastech.com/resources for more information

Rigid Liners:

Disadvantages with the flexible liners are they can’t be used in holes that are collapsing after drilling or vertically drilled holes such as for sublevel caving.

The solution is Rigid liners that, once inserted, prevent the collapsing of holes.

These liners can be waterproof.

Calculate Explosives Savings through reduction of Diameter

Download the brochure of Rigid Liners

Contact crm@uttamblastech.com to get commercial details of the above.

Check www.uttamblastech.com/resources for more information

The post Liners first appeared on Uttam Blastech.

Inaccuracy in delay timing will increase the Vibrations attract complaints, increase boulder generation, and send entire Blast planning haywire.

Quality Parameters of Explosives

The Main Quality Parameters of Explosives are 

STRENGTH 

• weight Strength
• Bulk strength
• VOD

Others

• Density
• COD
• Accuracy of Delays

How to check :

Strength: Weight of strength and Bulk Strength of Explosives need elaborate and costly arrangements to check, and its not possible to check them in the field. Very few Explosives manufacturers have this arrangement.

VoD: Velocity of Detonation can be checked by VoD meter. These VoD meters have a built-in processing timer. One needs to feed the distance between the probes. Up on blasting from one end of the cartridge, VoD of Explosives is displayed in the tab. Data can be stored at this stage in a CSV file.

Data can also  be transferred to the VoD Tool supplied free for further analysis

Uttam’s VoD meter doesn’t need any costly probes, any used lead wires can be used as probes.

Download brochure

Contact crm@uttamblastech.com to get commercial details of the above.

Check www.uttamblastech.com/resources for more information

Density: This can be measured by simple laboratory equipment.

COD: Continuity of Detonation can be verified by placing 2 cartridges 10 centimetres apart. On blasting the first cartridge, the 2^nd cartridge should blast.

Accuracy of Delays: Accuracy of delay is a tricky issue as any inaccuracy in Delays can result in a bad blast, and the user won’t even know the cause. 

Hence, it’s advisable to get all the delays checked periodically.

Uttam’s VoD Meter and delay time checks delay in the field and is accurate up to a Microsecond.

Download brochure

Contact crm@uttamblastech.com to get commercial details of the above.
Check www.uttamblastech.com/resources for more information

The post Quality Testing of Explosives And Accessories first appeared on Uttam Blastech.

A seismograph is an instrument that measures ground Vibrations irrespective of the source of vibrations. The source could be Rock Blasting, Pile Driving, Traffic or even an Earthquake.

Seismographs used by Civil and Mining Engineers measure the Particle Velocity of the medium on which the sensors are put in 3 directions, i.e. Horizontal, Radial and Vertical (X, Y, Z) and the Air Overhead Pressure (AOP). Air Overhead Pressure is the pressure produced by the displacement of air and is measured in Pascals, or Decibels (Db).

It also measures the frequency of the waveform.

Seismograph Standards

International Society of Explosives Engineers (ISEE) specifications for seismographs are widely accepted as standard in many countries. 

Download ISEE specifications.

Units of Measurement :

Units of measurement are 

Particle Velocity: mm/sec ( Millimeter per Second)

Frequency: Hertz ( Hz), meaning Cycles Per Second

Air Over Pressure: Pascals or Decibels ( dB)

WHICH SEISMOGRAPH TO BUY :

A simple checklist for buying a seismograph is 

1. Is it ISEE-compliant?
2. Does it have a good calibration and repair facility in my area?
3. How is their service?
4. Do they stock enough spares?
5. Can they provide additions that I need, such as 

1. GPS
2. Underwater Measurement
3. Remote Transfer
4. Extra Cable length for sensors
5. Does it serve my special needs such as 

1. Automatic Trigger
2. External Trigger
3. Master Slave Arrangement
4. Configure in Daisywheel arrangement

Download Seismograph Brochure

Contact crm@uttamblastech.com to get commercial details of the seismograph.

Check resources for more information

CALIBRATION 

Calibration is essential to ensure that your seismograph is showing the right readings and working well.

The sensor picks up the electrical signal, which is then converted into a waveform. Hence accuracy of processing is important. Minor damage to settings and/or parts may change the accuracy, though your seismograph may be working well. Working and accuracy are two different things.

All the measuring instruments must be calibrated at least once a year or earlier. ISEE (International Society of Explosives Engineers), ISO (International Standards Organization), Weights and Measurement Act mandates calibration once a year.

Readings from uncalibrated instruments may not be legally sustainable as they are not reliable and may not be accurate.

Contact crm@uttamblastech.com to get commercial details of the above.
Check resources for more information

The post HOW TO SELECT A SEISMOGRAPH? first appeared on Uttam Blastech.