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E-mail: [email protected] Whatsapp: +8613647327093 Tel: +86-731-8403-0163
In pile foundation construction, rotary drilling rigs have become one of the mainstream hole-forming equipment thanks to their high efficiency, safety, and excellent hole quality. Whether for foundation piles of urban high-rise buildings or large-scale foundation projects such as bridges and ports, rotary drilling rigs demonstrate strong construction capability across various strata due to their versatility and adaptability.
In actual construction, the drilling bucket and drilling auger are the two most commonly used drilling tools. The former is mainly used in loose formations such as sand and clay, facilitating hole cleaning and slag removal; the latter is suitable for rapid drilling in medium-soft formations, featuring high efficiency and easy operation.
However, when construction encounters moderately or slightly weathered rock and other complex strata, the performance of these two tools often becomes unsatisfactory — slow drilling, severe wear, unstable hole walls**, and even **hole collapse or deviation** may occur.
Therefore, in addition to the auger and clean-out bucket, a rotary drilling rig should also be equipped with one essential tool — the Core Barrel.
Specially designed for hard and complex formations, the core barrel uses bullet teeth or roller bits to efficiently crush rock, significantly improving hole quality, extending equipment life, and reducing overall construction costs.
In short, the addition of a core barrel makes rotary drilling rigs more capable and gives contractors greater confidence when dealing with challenging geological conditions.
1. The Ultimate Tool for Complex Formations
Among all challenges in pile foundation work, complex geological layers — particularly moderately and slightly weathered rock or interbedded hard–soft formations — are the most troublesome. These formations are hard, heterogeneous, and demand higher cutting force, wear resistance, and slag removal capacity from drilling tools.
Conventional auger and bucket drills perform poorly under such conditions.
The drilling auger, though fast in soft strata, tends to slip and wear excessively in rock layers, sometimes causing cutter breakage.
The drilling bucket, relying on scraping and scooping, advances very slowly in hard strata, consuming high energy and reducing efficiency.
In contrast, the core barrel has natural advantages in hard formations. By using bullet teeth or roller bits to grind the rock surface, it achieves steady, uniform cutting while its outer wall acts as a temporary casing, stabilizing the hole and minimizing wall disturbance or collapse.
Moreover, its structural design allows the core barrel to maintain high cutting efficiency even in moderately to slightly weathered rock. Whether using a roller bit core barrel or a bullet bit core barrel, it operates under high torque and low speed to achieve continuous, efficient, and controllable drilling.
For these reasons, the core barrel has become the decisive tool for rotary drilling rigs in complex geological conditions. In mixed soil–rock formations, proper use of the core barrel not only enhances efficiency but also ensures construction safety and pile quality.
2. Enhancing Hole Quality and Preventing Wall Collapse
Hole quality directly determines the bearing capacity and structural safety of the pile foundation. In soft, loose, or water-rich strata, the hole wall is prone to collapse, deformation, or spalling, which may cause serious issues such as stuck tools or complete hole failure.
Unlike augers and buckets that operate in an open-cut manner, the core barrel uses a semi-enclosed design. During drilling, the spoil is contained within the barrel instead of directly disturbing the hole wall, thus reducing lateral pressure and erosion. This design provides a natural wall-protection effect, greatly reducing collapse risks.
At the same time, the core barrel maintains steady contact and uniform force on the formation, ensuring high roundness and verticality of the hole. In contrast, augers or buckets can cause uneven hole diameters or irregular bottoms due to frequent lifting and dumping. The core barrel’s method of simultaneous cutting and cleaning produces a smoother hole bottom, creating ideal conditions for reinforcement cage placement and concrete pouring.
Therefore, especially in collapse-prone strata, the core barrel serves not only as a rock-breaking tool but also as a hole-protection expert, ensuring better safety and structural integrity.
3. Combining Efficient Rock Cutting with Core Sampling
In pile construction, it is crucial to both drill efficiently and accurately understand subsurface conditions. The core barrel uniquely achieves both goals.
Unlike conventional bits, it can retain rock core samples during drilling, allowing engineers to observe the actual formation, rock hardness, and groundwater distribution. This provides a direct geological reference for adjusting drilling parameters in real time — especially valuable in regions with variable or complex strata.
Different core barrel types serve distinct purposes:
Roller Bit Core Barrel: Utilizes multiple rolling cones to crush and grind rock continuously, maintaining stable torque and high efficiency. It excels in hard and slightly weathered formations such as granite or limestone.
Bullet Bit Core Barrel: Equipped with multiple wear-resistant bullet bits that cut through rock under high torque and low speed. It performs well in medium to hard rock such as strongly weathered granite, limestone, or sandstone, and offers easy maintenance and long service life.
Both types not only deliver efficient rock breaking but also preserve intact core samples for analysis. This enables the construction team to fine-tune parameters such as torque, feed pressure, and slurry weight — ensuring precision drilling and informed decision-making.
In short, the core barrel is both a rock-cutting tool and a geological sensor, helping teams “see underground” while maintaining drilling efficiency and safety.
4. Extending Equipment Life and Reducing Construction Costs
For contractors, equipment durability and maintenance cost are crucial. Rotary drilling rigs operate under high loads, and improper tool selection can cause uneven force distribution, accelerated wear, and increased downtime.
Compared with auger or bucket drills, the core barrel’s structural design distributes load more scientifically. Cutting forces are concentrated on the roller bits or bullet teeth at the bottom, ensuring smoother torque transfer and less vibration. This reduces mechanical fatigue and extends the life of key components such as the kelly bar, rotary drive, and winch.
Higher efficiency and improved hole stability also mean shorter drilling cycles, fewer tool changes, and less idle time — directly translating into cost savings and faster project delivery.
Long-term advantages include:
1) Longer tool life thanks to wear-resistant alloy cutters.
2) Better hole geometry, reducing the need for rework.
3) Lower energy consumption due to stable torque and efficient penetration.
Thus, choosing the right core barrel is not just about performance — it’s a strategic investment in equipment longevity and total project economy.
5. Compatibility with Multiple Drilling Methods and Systems
Modern foundation projects demand flexibility. Geological conditions, construction methods, and hole precision requirements vary widely. The core barrel stands out for its broad process adaptability.
It can be used in combination with various methods, including:
1) Crowd Drilling: Applying axial pressure via the rig’s crowd system for efficient rock penetration.
2) Casing Drive Method: Paired with casing systems in loose or collapse-prone strata, allowing the core barrel to cut inside while the casing supports the wall.
It is also suitable for:
1) Dry Drilling — in stable, non-water-bearing layers.
2) Slurry Drilling — in soft or sandy formations for better wall stability and debris removal.
3) Casing Drilling — for complex strata with high collapse risk.
This multi-process adaptability allows a single rig to handle diverse geological conditions, maximizing equipment utilization and minimizing downtime. Whether for high-rise buildings, bridge piles, port foundations, or wind power bases, contractors can flexibly switch between tools to achieve*multi-function, high-efficiency operation.
Although all core barrels serve similar purposes, their structures and cutting elements differ, leading to variations in performance and application. Selecting the right type can significantly improve drilling efficiency, extend cutter life, and reduce equipment wear.
1) Bullet Bit Core Barrel
Structure: Fitted with replaceable tungsten carbide bullet bits arranged at optimized angles.
Suitable Formations: Medium-hard rock, strongly weathered rock, and interbedded formations.
Advantages: Strong cutting force, high efficiency, wide adaptability.
Applications: Bridge piles, wind power foundations, metro piles requiring precise hole geometry.
2) Roller Bit Core Barrel
Structure: Multiple roller cones that crush rock through rolling and grinding.
Suitable Formations: Hard to slightly weathered rock (e.g., granite, limestone).
Advantages: Excellent penetration stability, impact resistance, and hole quality.
Applications: Port piles, mountain highway piles, high-rise building foundations.
3) Double-Layer Core Barrel
Structure: Dual-layer design with an inner core barrel for sampling and an outer casing for wall stability.
Suitable Formations: Large-diameter piles, complex and variable strata.
Advantages: High hole quality, complete core retention, superior safety.
Applications: Deep foundations, geological exploration holes, large-diameter bored piles.
In practice:
Use bullet bit core barrels for medium-hard formations.
Use roller bit core barrels for very hard rock.
Use double-layer core barrels for large-diameter or variable formations.
A well-matched combination ensures wider adaptability, “one rig, multiple functions”, and better overall project performance.
Totally, in modern rotary drilling construction, the core barrel is not optional — it’s essential. Whether facing hard rock or mixed formations, it enhances rock-cutting efficiency, hole quality, and safety, ensuring smoother project execution.
Contractors should select drilling tools based on formation type, pile diameter, and construction method, combining auger, bucket, and core barrel appropriately. Choosing the right core barrel type ensures efficient drilling, stable hole walls, and smooth concrete placement.
In short:
One more core barrel means higher efficiency.
One more core barrel means greater safety.
In today’s foundation engineering, the core barrel is not just a tool — it is a strategic asset that empowers contractors to work smarter, safer, and more competitively across diverse geological challenges.
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