Challenges and Solutions for Rotary Drilling Rigs in Karst Cave Formations

The Reality of Karst Caves in Construction

When we think of karst caves, images of stunning, illuminated caverns often come to mind. However, without artificial lighting, these caves may appear far less impressive. For rotary drilling rigs, the reality is even harsher—many encountered caves are not large or beautiful enough to be tourist attractions but can still severely disrupt construction, leading to equipment failures and operational delays.

Formation of Karst Caves

Karst caves are underground spaces formed in soluble rocks due to karst processes, which involve the dissolution and precipitation of rock by carbon dioxide-rich water. Limestone-rich regions are most prone to cave formation. Calcite, the primary component of limestone, reacts with water and carbon dioxide to form soluble calcium bicarbonate. When heated or subjected to pressure changes, this solution decomposes back into calcium carbonate, leading to the formation of stalactites and stalagmites. Variations in limestone composition and erosion rates create caves of different sizes and shapes.

Distribution of Karst Caves

Rotary drilling rigs frequently encounter karst caves in regions such as Guizhou, Guangxi, and Sichuan. Based on size, these caves can be categorized into three types:

1. Small caves (less than 1 meter in height)
2. Medium caves (1 to 4 meters in height)
3. Large caves (over 4 meters in height)

Common Problems and Solutions in Karst Cave Construction

Due to the unpredictable nature of karst formations, rotary drilling rigs face various challenges. Based on extensive field experience, we summarize the most common issues and their solutions:

1. Sloped or Half-Cut Rock Leading to Deviated Holes

• Problem: Uneven rock surfaces cause the drill to deviate.
• Solution:
  • Use a barrel drill to create a guide hole, followed by a rock drill bucket for debris removal.
  • Extend the barrel drill height for better guidance.
  • Apply light or floating pressure until the drill fully penetrates the rock layer.

2. Drill Bucket Jamming When Penetrating Cave Roofs

• Problem: Drill tool deformation due to impact with irregular cave roofs.
• Solution:
  • Weld guide plates to the square head for smoother transitions.
  • For stronger structures, install cutting picks to break obstructing rocks and widen the passage.

3. Collapse in Cave Roof or Unstable Fill Layers

• Problem: Soft clay or sludge collapses into the borehole.
• Solution:
  • Repeatedly remove debris until the hole stabilizes.
  • For persistent collapses, backfill with crushed stone + packed clay/block mud (0.5m–1.0m above the collapse zone), then compact before re-drilling.

4. Excessive Concrete Overflow Due to Caves

• Solution by Cave Type:
  • Small caves: Directly fill with concrete (minor overflow expected).
  • Medium caves: Backfill with crushed stone + clay/mud before re-drilling.
  • Large or interconnected caves: Use cement mortar/low-grade concrete, wait for initial setting, then resume drilling.
  • For connected cave groups: Drill all holes in the group to the cave base, backfill collectively, and compact to minimize concrete waste.

5. Severe Wear on Drill Teeth

• Problem: Fractured, compacted rock causes uneven stress and impact damage.
• Solution:
  • Reinforce tooth welding and regularly inspect for cracks.
  • Follow “low speed, variable pressure” drilling to prevent tooth breakage.

Conclusion

Karst cave formations present unique challenges for rotary drilling rigs, but with proper techniques, such as guided drilling, strategic backfilling, and reinforced equipment, construction efficiency can be maintained. Understanding cave types and applying targeted solutions ensures smoother operations and cost-effective project completion.