On March 16, accompanied by the roaring operation of rotary drilling rigs, the first bored cast-in-place pile with a diameter of 3.1 meters for Pier 63 of the main navigation span bridge in Section 2 of the CSCEC Changhai Bridge Project officially began drilling. This pile foundation, with a designed length of 90 meters, serves as the first "anchoring pin" embedded in the seabed of the Yellow Sea for the longest cross-sea bridge in Northeast China. Its successful drilling marks the project's construction officially transitioning from the offshore steel platform erection stage.

Penetrating Multiple Overburden Layers, Anchoring into Moderately Weathered Rock

In the main pier pile foundation construction area of Section 2 of the CSCEC Changhai Bridge Project, the seabed geological conditions far exceed conventional working conditions, and the construction challenges are highly specific. According to geological survey data, the construction area features a nearly 50-meter-thick marine sedimentary layer beneath the seabed, consisting of alternating layers of silt, silty clay, and medium sand, resembling a layered "thousand-layer cake" with extremely poor geological stability. More challenging is the presence of a 10.7-meter-thick cobble layer at the bottom of the sedimentary layer, with variable lithology and uneven hardness. For every meter the rotary drilling rig advances, it must address construction risks brought by different geological conditions.

The pile foundation hole for Pier 63 under construction reaches a depth of 99.6 meters. The drilling rig must penetrate through more than 40 meters of complex soft overburden layers throughout the entire process and continue drilling into the underlying bedrock to ensure the pile tip is precisely embedded in the moderately weathered mudstone bearing layer, thereby guaranteeing the bearing capacity and structural stability of the pile foundation. Achieving large-diameter drilling in ultra-deep strata without hole collapse or deviation, and ensuring the precise lowering and positioning of the ultra-long reinforcement cage, has become the first core technical challenge to be overcome after the project's commencement.

Millimeter-Level Precision Control, Solidifying the Foundation for Pile Construction

The XR580HD rotary drilling rig undertaking the first pile construction task has a body height of 33 meters and is a large-tonnage heavy construction equipment. A single rotary excavation can bring out several tons of rock debris, providing robust equipment support for ultra-deep, large-diameter pile foundation drilling. However, pile foundation construction for a cross-sea bridge requires not only the tackling capability of heavy equipment but also refined "embroidery-like" precision. Millimeter-level precision control is the core of ensuring project quality.

For the ultra-long and overweight reinforcement cage with a total length of 95.1 meters and a total weight of nearly 70 tons, the project department adopted a factory jig pre-assembly process, strictly controlling the splicing precision of each reinforcement cage section and keeping the splicing error at the millimeter level to prevent deformation and disintegration of the reinforcement cage during lifting. For on-site lifting, a 150-ton crawler crane is planned to implement a standardized operation process of sectional lifting, aerial turning, precise alignment, and rapid connection of the reinforcement cage, ensuring precise lowering to the designed hole position.

As the "core wall-protection medium" for drilling construction, the project department has activated a professional mud separation and purification system to monitor key parameters such as mud viscosity, sand content, and specific gravity in real time, dynamically adjusting mud performance. This not only ensures hole wall stability and prevents collapse but also effectively suspends drill cuttings and improves hole cleaning efficiency. Drill cutting sampling follows a "test every 2 meters" system, and samples are repeatedly compared and verified against geological survey reports to accurately determine whether the designed bearing layer has been reached, ensuring pile foundation construction quality from the source.

Subsequent Construction of 39 Remaining Piles of the Same Type

The smooth commencement of drilling for the first large-diameter ultra-long pile foundation has greatly boosted the construction confidence of all builders and provided practical verification for the feasibility of the construction scheme for large-diameter ultra-long bored cast-in-place piles under complex marine geological conditions. Subsequently, the project department will steadily advance the construction of the remaining 39 piles of the same type, embedding all pile foundations deeply into the seabed rock layers to jointly bear the main bridge loads and fully open up the key links in the substructure construction of the Changhai Bridge.

Source: Peninsula Morning Post