Every Hole Passed. Why Did the Quarry Process Still Drift?
A quarry can accept every individual hole and still produce a worse batch. The warning often appears first as a sequence: depth corrections rise across a row, air behaviour changes with distance, tool wear accelerates, exceptions cluster, and downstream results move away from the established baseline.
Table of Contents
Every Hole Passed, but the Process Was Moving
The first holes in the row were completed with stable cleaning and routine depth correction. Later holes required more cleaning time. Tool wear became less even, minor hose attention increased, and two replacement decisions appeared near the same geological transition.
Each hole could still be signed off under the project’s individual acceptance rule. Nothing looked severe enough to stop the shift.
After the blast, coarse material concentrated toward one end of the batch and the loader reported a less workable floor. The issue was not one dramatic outlier. It was a gradual change that became visible only when the records were read in sequence.
The real question is not only, “Did this hole pass?” It is also, “Is the process that produced this hole still behaving like the process we approved?”
Specification Limits Are Not Process-Control Limits
A specification limit defines what the project will accept. A process-control limit describes the normal variation of a stable process under comparable conditions. They answer different questions.
If a measurement remains inside its acceptance band but moves steadily in one direction, the hole may pass while the process deserves investigation. Waiting for the first rejection can mean waiting until wear, leakage, setup drift, geology, cleaning loss, or recording bias has already affected several holes.
A common mistake is to copy a generic statistical rule into the quarry procedure. Control limits and trend rules must be established from reliable site data, separated by meaningful operating context, and reviewed by qualified project personnel. They are not blast-design parameters.
Control Concept Question It Answers Quarry Example Misuse to Avoid
Specification limit Is the delivered item acceptable under the approved project rule? Hole condition, identity, geometry evidence, or completion requirement Treating every passing value as proof that the process is stable Process baseline How does a controlled process normally behave under comparable conditions? Typical range and sequence of cleaning, correction, wear, or exception observations Mixing unlike geology, rigs, tools, shifts, or measurement methods Trend signal Is variation becoming directional, clustered, or unusually persistent? Several consecutive holes show increasing correction or deteriorating cuttings return Using one unusual point to justify a quarry-wide change Reaction rule What must the team do when a defined signal appears? Hold the affected row, inspect the air path, review tools, or reconcile geology Writing “monitor closely” without owner, evidence, or release condition
Build a Baseline Before You Watch for Drift
A baseline is not the average of everything the quarry has ever drilled. It should represent a period when the process, measurement method, equipment configuration, and geological context were understood and considered controlled.
Separate data where the operating mechanism changes. A new bit condition, different hammer, altered hose route, changed rig setup, wet zone, fractured band, replacement operator, or different measurement method may require its own context rather than being blended into one chart.
In my view, a small clean baseline is more useful than a large mixed dataset. Volume does not repair poor comparability.
Baseline Element What Must Stay Comparable Evidence to Record Reason for Separation
Geological context Rock domain, visible discontinuities, water, instability, and bench condition Zone map, hole IDs, field notes, and observed transitions Natural formation change can look like equipment drift Pattern and workfront Controlled revision, hole role, access, setup direction, and free-face context Revision, collar map, row sequence, release status, and exceptions Different geometry or setup changes the operating mechanism Equipment chain Rig, compressor, air path, hammer, bit, rods, adapters, and wear state Configuration ID, component state, service event, and replacement point A mixed package can hide which interface moved Measurement method Instrument, procedure, timing, units, and recorder Method version, calibration or check status, timestamp, and operator A method change can create an artificial trend Downstream context Loading face, loader class, haulage condition, crusher state, and observation method Batch identity, shift context, interruption code, and result location Downstream variation can be wrongly assigned to drilling
Track Hole-Pattern Signals as a Sequence
A plan view shows where holes belong. A process view shows how delivery changed from one hole to the next. Both are required.
Sequence the records by row, drilling order, geological zone, or another meaningful production path. Then look for persistence, clustering, direction, or a sudden shift after a known change. The purpose is not to turn every observation into a number; categorical exceptions can also form a pattern.
The verified quarry blast hole pattern design guide explains the pattern variables, deviation, air calculation, equipment scope, and field evidence that should remain linked. Site-specific blast design and regulated execution belong to qualified local professionals.
Sequential Signal Possible Meaning Evidence to Compare Required Caution
Increasing depth correction along a row Setup, floor reference, cleaning, blockage, geology, or measurement may be moving Survey basis, final-hole method, cuttings return, geology, and rig setup Do not assume drilling error before checking the reference and formation Exceptions cluster near one boundary A geological or workfront transition may need separate control Zone map, water, fractures, hole condition, replacement reasons, and result map Do not average the cluster into the full bench Hole behaviour changes after a tool event Wear, compatibility, connection, or handling may have changed energy transfer Component ID, wear state, replacement timestamp, penetration response, and hole IDs Separate tool condition from a coincident geological change Replacement holes rise across consecutive batches A recurring mechanism is not being contained Original IDs, reasons, approvals, final positions, equipment state, and geology Do not treat every replacement as the same failure mode Records become unusually uniform Rounding, copied nominal values, weak measurement, or reporting pressure may hide variation Raw records, timestamps, method, recorder, and physical recheck Low variation is not automatically good data
Use the Equipment List to Explain the Trend
Statistical signals do not identify the cause by themselves. They tell the team where and when the process changed. The equipment list provides the physical interfaces to investigate.
Link every configuration or maintenance event to hole IDs and time. If air behaviour moved after a hose-route change, or wear accelerated after a component replacement, the event record creates a testable hypothesis. Without this link, the team sees correlation but cannot locate the mechanism.
More importantly, the package must be observable. Pressure and flow basis, connection condition, tool identity, wear criteria, service status, measuring tools, recovery tools, and critical spares are part of control—not optional documentation.
The verified customized drilling solution matches rigs, compressors, bits, rods, hammers, adapters, accessories, and support to the site duty.
Equipment Record Trend It Can Help Explain Minimum Linkage Weak Practice
Rig setup and operating state Directional change, repeated correction, unstable feed, or shift effect Rig ID, workfront, row, hole sequence, setup check, and operator context Recording only total metres per shift Compressor and air path Cleaning loss, depth-related deterioration, heat, leakage, or unstable drilling response Duty basis, hose route, connection status, service event, timestamp, and hole IDs Using compressor nameplate data as delivered-hole evidence Hammer, bit, rods, and adapters Wear acceleration, vibration, connection damage, or changing energy transfer Component ID, start point, wear observations, replacement point, and affected holes Discarding worn components without recording where they worked Service and consumables Temperature, lubrication, contamination, recurring minor fault, or maintenance effect Service type, consumable, condition, owner, time, and post-service comparison Closing maintenance work without checking process response Critical spares and substitutes Performance shift after an emergency replacement or uncontrolled substitute Part identity, compatibility approval, installation time, reason, and result window Treating every physically fitting part as functionally equivalent
Define a Reaction Plan for Trend Signals
A chart without a reaction plan is decoration. Before production pressure appears, define which signal requires observation, local inspection, row hold, workfront hold, equipment-chain isolation, or qualified technical review.
Reaction rules should match the strength of evidence. A single unusual point may trigger verification. A persistent direction, cluster, or step change after a known event may justify containment. The site should establish its own rules from validated data rather than borrow generic constants without context.
The response must also protect the evidence. Do not change the bit, hose route, operating method, measurement method, and pattern at the same time unless safety or regulation requires it. Multiple simultaneous changes may restore production but destroy the project’s ability to learn which mechanism mattered.
Signal Level Typical Situation Proportionate Response Release Evidence
Verify One unusual observation with uncertain measurement or context Check identity, method, instrument, timestamp, and physical condition Signal confirmed as valid or measurement issue corrected Inspect locally A short cluster appears within one row, tool period, or geological zone Inspect setup, air path, tool state, geology, and nearby holes Mechanism contained and affected extent defined Hold the affected sequence Trend persists or repeats across consecutive holes or batches Stop expansion, preserve records, and review the connected equipment and pattern evidence Corrective action implemented and comparable confirmation obtained Escalate for qualified review Trend may affect regulated blast assumptions, safety, or accepted geometry Refer the evidence to the authorised site professionals Documented decision and updated controlled basis Re-baseline A verified permanent change creates a new stable operating condition Collect a clean comparable window under the new condition New baseline reviewed, approved, and version controlled
Connect Drilling Drift to Blast-Efficiency KPIs
Blast and downstream KPIs should confirm or challenge the drilling signal. They should not be used to assign cause automatically.
Map oversize, toe, floor condition, fragmentation band, loading difficulty, secondary breaking, and crusher interruption back to the batch, zone, hole sequence, equipment state, and exception window. A quarry-wide monthly average can hide the exact location where drift began.
The verified guide to quarry blast efficiency evaluation covers repeatable review of fragmentation, oversize, toe, muckpile, compliance evidence, and downstream effects.
Downstream KPI Useful Trend View Drilling Evidence to Compare Interpretation Boundary
Toe or high floor Location and recurrence by batch, row, and geological zone Depth method, final condition, hole path evidence, exceptions, and sequence Geology and regulated blast inputs must also be reviewed Localized oversize Cluster position rather than one quarry-wide percentage Final pattern, blocked or replacement holes, tool and air state, and zone map One cluster does not justify changing every workfront Fragmentation consistency Distribution band and spatial movement across comparable batches Hole sequence, geometry evidence, equipment events, and geological context Average size alone can hide a widening distribution Loading difficulty Cycle interruption and location under comparable loader and access conditions Floor, pile geometry, oversize map, batch identity, and workfront context Loader, access, and operating method can change the result Crusher interruption Cause code and batch-linked recurrence rather than total lost time alone Feed observation, oversize location, dispatch sequence, and production buffer state Plant and haulage conditions must be separated from blast effects
Run a Batch Review Without Chasing Noise
Not every variation deserves correction. Quarry conditions are variable, and over-adjustment can create more instability than the original signal.
Use a fixed review rhythm. Confirm data quality first. Separate unlike conditions. Examine the sequence and event markers. Test the most credible physical mechanisms. Contain only the affected scope. Then verify the response on a comparable batch.
Close the review when the evidence supports one of three outcomes: normal common variation, a special cause that has been contained, or a verified permanent change that requires a new baseline. Keep unresolved items visible rather than forcing a premature conclusion.
That is process control in a quarry: not more charts, but earlier and better decisions.
Why Welldone Mining
Welldone Mining reviews the drilling package as a connected process. Formation, hole diameter, depth, access, rig duty, compressor demand, air path, hammer, bit, rods, adapters, measuring needs, service items, and critical spares are considered together.
Comparable configuration: Equipment identity and interface changes can be linked to the holes they affected.Observable condition: Wear, air-path condition, service events, exceptions, and recovery actions support trend interpretation.Evidence-led support: Drilling-side records can be reviewed with batch-linked field outcomes instead of assumptions.
Review the verified quarry drilling solution for quarry applications, drilling methods, equipment categories, and operating constraints.
Conclusion
Individual acceptance protects each delivered hole. Process control protects the sequence that produces the batch.
Build a clean baseline. Preserve operating context. Link equipment and maintenance events to hole IDs. Define reaction rules before a trend appears. Then compare downstream results by batch and location, not only by monthly average.
If every hole in tomorrow’s row passes, what evidence will tell you whether the process is becoming more stable—or merely drifting toward the edge together?
Frequently Asked Questions
What is SPC in quarry drilling? Statistical process control uses ordered, comparable process evidence to identify stable variation, directional drift, clusters, or step changes before they become widespread defects.
Are process-control limits the same as hole-acceptance limits? No. Acceptance limits come from the approved project basis. Process-control limits describe normal variation under validated comparable conditions and support investigation.
Can a quarry use one baseline for all benches? Only when geology, workfront, equipment, measurement, and operating context are sufficiently comparable. Otherwise, separate baselines are more defensible.
Does one unusual hole prove the process is out of control? Not automatically. First verify the measurement and context. Stronger evidence comes from persistence, clustering, direction, or a step change linked to a physical event.
Can Welldone Mining set our blast-control limits? Welldone Mining can support drilling-side configuration and evidence planning. Site-specific blast design, limits, approvals, and regulated execution remain with qualified local professionals.
Written by: Welldone Mining Engineering TeamTechnical review: Mostafa Ansary, Technical Sales Manager — mechanical design and production-management background with 15 years in machinery and production fieldsMarket context: Welldone Mining Project Support Team — quarry equipment matching , process evidence, and operating-control requirements
Find the Drift Before the Batch Fails
Send the formation, hole diameter and depth, approved pattern basis, workfront sequence, equipment configuration, air requirement, measurement method, recurring exceptions, and batch-linked downstream results. Welldone Mining can help review the drilling-side package and evidence chain.
Website: www.welldonemining.com
Email: info@welldonemining.com
