Drilling Pile Construction Technology of Rotary Drilling RIGS in Strongly Developed Karst Strata

In the construction of Bridges, buildings and other engineering projects, bored pile construction is a common foundation operation. However, in strata with strong karst development, the construction difficulty will increase significantly. As an efficient drilling device, the rotary drilling rig has a series of unique technologies when working in such strata. Now let's introduce it in detail for everyone.

1. Geological investigation before construction: Comprehensive and precise geological investigation is of vital importance. Drilling and geophysical exploration methods should be comprehensively utilized to conduct meticulous detection of each pier and pile one by one. Clarify the thickness of the covering layer, the location, quantity and filling status of soil holes and karst holes to provide a reliable basis for the formulation of subsequent construction plans. For instance, in the construction of a certain high-speed railway bridge, through meticulous investigation, the complex geological conditions were clarified, ensuring the smooth progress of the construction.

2. Drilling sequence planning: Reasonable planning of the drilling sequence can effectively enhance construction efficiency and quality. For bridge piers with unequal length piles, the long piles should be constructed first, followed by the short ones. In the same pier position, in the order of the cave from deep to shallow and from many to few, the edge and corner piles are constructed first to seal the cave and block the passage, which is conducive to the subsequent pile construction.

3. Mud wall protection technology: Mud wall protection is a key link. Select clay or bentonite with good viscosity to prepare the slurry. When performing impact drilling, directly throw the clay into the hole to make the slurry. For areas with complex geology and prone to slurry leakage and hole collapse, adding an appropriate amount of cement to the slurry can enhance the wall protection effect and prevent hole collapse and slurry leakage.

4. Construction of artificial hole walls: When the borehole encounters a karst cave, according to the conditions of the cave, a mixture of clay blocks (woven bags of clay mixed with rice and wheat straw), rubble (crushed) stones, etc. is added into the hole. By means of the impact tamping of the drill bit, it and the mud are forced into the fissures of the cave to form a stable hole wall sealing ring. For instance, in the construction of bored piles for a certain extra-large bridge, this method was relied upon to successfully pass through numerous karst caves.

5. Drill bit selection skills: Select drill bits reasonably based on the characteristics of different strata. In soft soil layers, drill buckets with high excavation efficiency can be selected. When facing hard rock or cave strata, special drill bits with stronger cutting and breaking capabilities, such as cylinder drills, should be adopted to ensure the smooth progress of drilling.

6. Key points for concrete pouring: When pouring underwater concrete, it is necessary to closely monitor the elevation of the concrete surface to prevent the pipe from being suspended and causing pile breakage. Appropriately increase the height of concrete pouring, generally 1.5 to 2.0 meters above the designed elevation. Wait for the concrete surface to stabilize for 0.5 to 1.0 hours before pulling out the guide pipe to avoid the occurrence of short piles.

In karst strata with strong development, the use of rotary drilling RIGS for bored pile construction can effectively overcome the challenges brought by complex geological conditions by conducting thorough geological surveys before construction, planning a reasonable drilling sequence, applying appropriate mud wall protection and artificial hole wall technologies, selecting the right drill bits, and strictly controlling the concrete pouring process. This ensures the quality and progress of bored pile construction and lays a solid foundation for various types of engineering projects.