The symmetric drilling method, also known as symmetrix drilling, is a specialized drilling technique used primarily in the construction of large-diameter boreholes in difficult geological conditions, such as hard rock formations. This method is commonly employed in various applications, including foundation drilling, anchoring, and micropile installation.
Here's how the symmetric drilling method works:
Drill Bit Design: The key feature of symmetric drilling is the design of the drill bit. The symmetric drill bit consists of a central pilot bit surrounded by multiple radial wings or cutters arranged symmetrically around the circumference of the bit.
Borehole Creation: During drilling, the central pilot bit advances into the rock formation, creating a small-diameter pilot hole. The radial wings or cutters on the symmetric drill bit then engage with the surrounding rock, progressively enlarging the borehole to the desired diameter.
Casing Advancement: As the borehole is drilled, casing or steel tubes are simultaneously installed behind the symmetric drill bit. The casing is pushed or rotated into the newly drilled section of the borehole, providing immediate support and stabilization to the surrounding rock formation.
Cuttings Removal: Cuttings produced during drilling are flushed out of the borehole through the annular space between the casing and the borehole wall. This continuous flushing action helps to maintain borehole stability and prevent blockages.
Completion: Once the desired depth and diameter of the borehole are achieved, the symmetric drill bit is removed, leaving the casing in place. Depending on the specific application, grouting or other materials may be injected into the annular space between the casing and the borehole wall to further stabilize the borehole and enhance its integrity.
The symmetric drilling method offers several advantages, including the ability to drill large-diameter boreholes in challenging geological conditions, efficient cuttings removal, and immediate casing installation for borehole stability. It is commonly used in construction projects where the integrity of the borehole is critical, such as in foundation drilling for buildings, bridges, and other structures.
