6.3m Dia. Core Barrel for Piling in Xihoumen Bridge

Xihoumen Bridge is a combined road-rail bridge located in the Zhoushan Archipelago, Zhejiang Province, China. It is 68 meters wide, 3.1 kilometers long, with a total investment of 10.75 billion RMB (1.5 billion USD). The project is renowned for its high wind-resistance requirements and the difficulty of its foundation construction.

One of the Core Challenges in Pile Foundation Construction — Ultra-Large Diameter Drilling

The pile foundations have a large diameter (up to 6.3 meters), and drilling starts on inclined exposed rock, placing extremely high demands on the drill tools.

To address this challenge, the construction team at the time adopted a combined drilling technique:
For extremely hard rock, they used the “large-diameter rock-embedded enlarged-base drill bit” and “graded hole formation” process: first drilling a small pilot hole for guidance, then gradually enlarging it while frequently changing specialized cutting teeth. Here, Drillmaster’s double-layer core barrel was employed.

Construction Steps:

Soft Soil Layer Drilling with Double-Bottom Core Barrel (Diameter 6.3 m)

After placing the casing, the upper soft soil layer was drilled directly using a 6.3-meter-diameter double-bottom core barrel.
When drilling reached the hard rock layer and could no longer proceed, a 2.0-meter-diameter, 4-meter-high roller-cone core barrel was used, along with coring tools to extract cores.
Notes:
- At this stage, a 6.3-meter-diameter guide must be installed above the 2.0-meter drill, with a height of at least 1.5 meters.
- Transporting the 6.3-meter double-bottom core barrel is difficult, requiring on-site assembly and welding.

Pilot Hole Enlargement from 2.0 m to 3.5 m

A roller-cone reaming drill with a lower guiding device was used for drilling. Since the 2.0-meter pilot hole ensured verticality, the lower guiding device could maintain a straight hole wall while drilling downward to the 2.0-meter pilot hole position, forming the required hole shape.

Progressive Reaming to Target Diameter

A 3.5-meter roller-cone drill was used to break the annular rock between 2.0 m and 3.5 m, and a debris-collecting bucket removed cuttings, enlarging the hole to 3.5 m. Reaming was then carried out successively to 4.5 m, 5.5 m, and finally 6.3 m, achieving the target diameter. The first pile was completed in just 12 days.

In this project, Drillmaster ensured smooth large-diameter drilling with its reliable product quality (up to 6.3-meter core barrels) and advanced graded design, contributing to verticality control in ultra-large-diameter drilling projects. Solving problems as they arise is the essence of Drillmaster’s spirit.