—A Real Case from Central Asian Mining Areas
Mastering DTH Inspection Drilling: Tools, Skills & Techniques
In Central Asian mines, DTH inspection drilling is not a routine operation, but a truly technical skill.
In October 2024, at a copper mine project in Karaganda, Kazakhstan, we participated in a typical inspection drilling task: confirming the location of an old goaf at a depth of 42 meters and assessing the stability of the surrounding rock structure to prevent the risk of collapse during subsequent blasting.
Background
Region: Karaganda, Kazakhstan
Section: Upper loose sand layer + lower fractured basalt
Drilling Rig: DTH high-pressure down-the-hole drill (17 bar)
Drill Bit: φ115mm high-pressure down-the-hole flaw detection bit (ball teeth + reinforced outer shoulder)
Mission Objectives:
Detect whether the old tunnel is below the predetermined direction
Assess the density of the rock layer and the development of fractures
Provide safety assessment data for the blasting design team
Key Technical Factors in the Drilling Operation**
1. Low-speed entry, stable sampling, and acoustic feedback
Before entering the basalt layer, we reduced the air volume to 60% and maintained a low-speed impact.
When the drill bit slightly “bounces,” it indicates that the rock layer is beginning to harden and the fractures are decreasing.
This is crucial for flaw detection operations—the sound and vibration response is like a doctor’s auscultation.
2. Control drilling pressure at 2.8–3.2 kN to improve feedback sensitivity.
To accurately determine if a goaf is approaching, we deliberately avoided using full-pressure drilling.
As the drill bit approached the cavity, vibration significantly decreased, and the amount of cuttings discharged suddenly reduced.
This phenomenon occurred at 38.7 meters, and the team immediately stopped drilling.
Subsequently, a probe was used to confirm the presence of an old tunnel 2.4 meters high below.
3. Use a dual technique of “sound + pressure rebound” to identify cavities.
In local mining teams, this method is called:
“Dual Feedback Method”
Lower sound → Possibly approaching a cavity
Increased pressure rebound → Large void present
Sudden reduction in cuttings → Directly points to a goaf
This technique is more reliable than instruments in hard rock areas, especially suitable for old mining areas in Central Asia.
Key to tool selection: Why choose a reinforced high-pressure down-the-hole drill bit?
Why We Used a Reinforced High-Pressure DTH Bit?**
✔ Reinforced outer shoulder resists severe abrasion from basalt.
✔ Impact-resistant ball teeth withstand the repeated impacts of flaw detection.
✔ Larger slag removal channel suitable for slag removal during low-airflow detection.
In this mission, a φ115mm reinforced drill bit completed 72 meters of drilling while maintaining good tooth shape.
Final Result
Successfully located the old goaf with an accuracy of +0.5m.
Completely recorded changes in rock density.
Provided critical safety data for the blasting team.
Protected the stability of future mining areas.
