Continuous Coring Drilling Method
Concept of the Test
Continuous coring is a subsurface exploration method used in geotechnical engineering and geology to obtain continuous cylindrical samples of soil or rock from the ground. This technique provides detailed information about the subsurface stratigraphy, geological formations, and material properties. The primary goal of continuous coring is to retrieve an intact, continuous core sample that can be analyzed for various properties, such as composition, structure, strength, and other geological or engineering characteristics. Continuous coring is essential for site investigations, foundation design, environmental assessments, and resource exploration. Standards for continuous coring include ASTM D2113 for rock core drilling and sampling.
Figure 1: Continuous Coring Drilling.
Figure 2: Different Types of Drilling Equipment’s of BKP Group.
Descriptions and Procedure
Apparatus Required
- Drill rig capable of continuous coring
- Core barrel assembly (double or triple tube core barrels)
- Diamond or tungsten carbide drill bit
- Drill rods
- Water or drilling fluid circulation system
- Core recovery and handling tools
- Core boxes for storing and transporting core samples
- Logging equipment for recording core characteristics
Procedure
1.Site Preparation
- Selecting Test Location: Choose a representative location for subsurface exploration.
- Setting Up Equipment: Position the drill rig over the test location and secure it. Ensure all equipment is calibrated and in working order.
2.Drilling and Coring
- Initiating the Borehole: Start by drilling a pilot hole to the desired depth using conventional drilling techniques. This helps to stabilize the borehole and guide the core barrel.
- Assembling the Core Barrel: Attach the core barrel assembly to the drill rods. The core barrel consists of an outer barrel and an inner barrel that holds the core sample.
- Drilling Process: Lower the core barrel into the borehole and begin drilling. Rotate the drill bit and apply downward pressure to cut through the soil or rock. Use water or drilling fluid to cool the drill bit and remove cuttings from the borehole.
3.Core Recovery
- Extracting the Core: Once the core barrel is filled with the core sample, lift the core barrel assembly to the surface. Carefully disassemble the core barrel to retrieve the core sample.
- Handling the Core: Handle the core sample gently to avoid breakage or contamination. Place the core sample in core boxes, aligning the core sections to maintain their original orientation.
- Logging the Core: Record detailed observations about the core sample, including depth, length, lithology, color, texture, and any other notable features.
4.Re-inserting the Core Barrel
- Continuing the Process: After logging and storing the core sample, reassemble the core barrel and lower it back into the borehole. Repeat the drilling and coring process to obtain continuous core samples at different depths.
5.Completion of Drilling
- Reaching Target Depth: Continue the coring process until the desired depth is reached or until the borehole conditions make further coring impractical.
- Sealing the Borehole: After completing the coring, seal the borehole according to local regulations to prevent contamination and ensure safety.
Data Interpretation
1.Core Analysis
- Visual Examination: Conduct a detailed visual examination of the core samples. Identify and describe different soil or rock layers, noting any changes in material properties or geological features.
- Laboratory Testing: Perform laboratory tests on the core samples to determine properties such as grain size, mineral composition, strength, porosity, permeability, and other relevant parameters.
- Geotechnical Properties: Analyze the geotechnical properties of the core samples, such as compressive strength, shear strength, and modulus of elasticity.
2.Stratigraphic Logging
- Creating Core Logs: Develop detailed core logs that summarize the findings, including descriptions of each core section, depths, and any significant observations. Use standardized logging formats to ensure consistency and accuracy.
3.Geological Interpretation
- Geological Profile: Use the core logs to construct a geological profile of the subsurface. Identify and correlate different stratigraphic units, fault zones, and other geological features.
- Engineering Analysis: Apply the geological and geotechnical data to assess the suitability of the site for construction, foundation design, slope stability, and other engineering applications.
Summary Table
Description
Select location, set up drill rig, ensure equipment calibration.
Description
Drill pilot hole, assemble core barrel, drill and cut core sample.
Description
Extract core, handle and store carefully, log detailed observations.
Step
Re-inserting Core Barrel
Description
Reassemble and lower core barrel, continue coring process.
Step
Completion of Drilling
Description
Reach target depth, seal borehole, complete coring process.
Description
Visual examination, laboratory testing, analyze geotechnical properties.
Step
Stratigraphic Logging
Description
Create core logs, summarize findings, use standardized logging formats.
Step
Geological Interpretation
Description
Construct geological profile, assess site suitability for engineering applications.
Key Points to Remember
- Purpose: Obtain continuous core samples for detailed subsurface analysis.
- Apparatus: Drill rig, core barrel, drill rods, drill bit, water/drilling fluid system.
- Procedure: Prepare site, drill and core, recover and log core samples, analyze data.
- Data Interpretation: Examine core visually and through laboratory tests, create core logs, construct geological profile.
- Standards: ASTM D2113.
Final Summary
Continuous coring is a crucial method for detailed subsurface exploration, providing valuable information about soil and rock properties. Proper execution and interpretation of the test ensure accurate assessment of geological conditions, aiding in the design and analysis of geotechnical and engineering projects.