Foundation Drilling Case
B47K22*28 Bullet Teeth
Test for Qingdao Subway Granite Drilling
Drillnova tested B47K22-28 bullet teeth on a 1000mm core barrel for a
Qingdao Subway bored pile project, with field records covering drilling footage,
cutter wear, tool vibration, and cleaning cycles.
Location
Qingdao
Rig
SANY 405R
Tool
1000mm Core Barrel
Cutter
B47K22*28
Record
23.85m Pile Length
Project Background
Reducing bullet tooth loss in medium to slightly weathered granite.
The Qingdao Metro site worked close to Quanzi Mountain, with clay, strongly weathered granite, medium-weathered granite, and some slightly weathered granite. Existing tools included a bullet tooth core barrel and cleanout bucket.
The contractor was satisfied with the general drilling speed of about 0.5-1.5m per hour, but cutter consumption was high. Broken tooth bodies appeared on both cleanout buckets and core barrels, with most failures observed on the cleanout bucket.
B47K22-28 bullet teeth prepared for the field test
Field Diagnosis
The test focused on real wear, not only penetration speed
The site used a 1000mm core barrel with 18 teeth. Tooth holders, spiral guide areas, and older cutters already showed wear, including normal wear and partial uneven wear.
1
Hard formation
Granite hardness varied around 30-100MPa, with most piles in medium-weathered granite.
2
High cutter loss
The original cutting tools achieved acceptable footage but showed high loss and broken tooth bodies.
3
Tool change cycles
The site alternated between core barrel cutting and cleanout bucket breaking and muck removal.
Drillnova Solution
B47K22-28 teeth installed for controlled on-site comparison
At 16:53, the prepared test teeth were installed. The cutter body was cold-forged 3050 steel, with 22x28mm straight carbide tips. The site continued drilling with recorded depth, pressure, vibration, and cutter inspection after each run.
B47K22-28 bullet teeth used in the test.
Field Results
Recorded drilling progress during the test
These figures are field records from the Qingdao Metro test log. They should be treated as site-specific results affected by geology, rig operation, tool condition, and cleaning cycles.
0.18m
First run, 7 minutes of drilling
0.56m
Second run, 17 minutes of drilling
0.97m
Third run, 26 minutes of drilling
1.08m
Fourth run, 34 minutes of drilling
Engineering Learnings
What this case shows for
bullet tooth selection
Bullet tooth performance in granite cannot be judged from hardness alone. The tool body, carbide size, tooth holder wear, barrel condition, operator parameters, and cleaning process all affect tooth life.
Track pure drilling time
Separating drilling time from cleaning time gives a more accurate view of cutter performance.
Inspect after each run
Frequent inspection helps distinguish normal wear from abnormal tooth body failure.
Watch old holders
Worn tooth holders and spirals can make new cutters perform worse than expected.
Match the whole tool
The right tooth works best when barrel structure and cleanout method are also controlled.
Follow-up inspection identified broken teeth, bearing seizure, and body wear causes.
Related Tools
Tools for similar foundation drilling projects
Bullet Teeth
Bullet teeth for rock augers, core barrels, buckets, and foundation drilling tools in medium to hard formations.
Bullet Tooth Core Barrel
Custom core barrel design with selectable tooth layout, diameter, Kelly box, and wear protection.
Cleaning Bucket
Bucket options for muck removal, broken rock cleaning, and bored pile drilling support.
Project Support
Need to reduce bullet tooth cost in
granite drilling?
Send us your pile diameter, rig model, formation hardness, current tooth photos, and drilling footage.
Drillnova can help compare tooth size, carbide shape, holder condition, and tool layout for your jobsite.