Key Construction Technologies for Rotary Drilling Rigs in Deep-Water Soft Ground at Port Wharves

    As the load-bearing core of the entire pier structure, port pier pile foundation engineering directly determines the safety and durability of pier operations. Deep water and soft foundation are common complex conditions in port pier construction. Soft soil layers feature high water content, low shear strength, and strong compressibility, while deep water environments are significantly affected by current and tidal disturbances, posing numerous challenges for pile foundation construction. With advantages such as high drilling efficiency, minimal disturbance, and strong adaptability, rotary drilling rigs have become the preferred equipment for deep water soft foundation pile foundation construction in ports and piers. Optimizing construction techniques based on specific working conditions is key to ensuring pile foundation construction quality.

    Pre-construction preparation is the foundation for smoothly advancing the project, with the core focus on working condition adaptation and risk anticipation. It is necessary to refer to the geological survey report of the port terminal to clarify parameters such as the thickness of soft soil layers, moisture content, void ratio, flow velocity in deep-water areas, and tidal range, and select appropriate rotary drilling rigs. Priority should be given to models with high torque, superior waterproof performance, and strong stability, paired with short spiral drill bits suitable for soft soil layers, ensuring the equipment meets the requirements for deep-water soft foundation construction. Additionally, pre-treatment of the site and equipment is essential: floating or island work platforms should be constructed in deep-water areas to ensure their bearing capacity meets the drilling rig's operational requirements and resistance to water flow disturbance. In soft foundation areas, advance measures such as replacement cushion layers or drainage consolidation should be implemented to improve soil mechanical properties and reduce risks of borehole wall collapse or pile deviation during construction. Furthermore, precise design and installation of casing pipes are required, employing a double-layer steel casing structure to enhance anti-seepage and anti-impact capabilities, ensuring the casing pipe is embedded in stable soil layers with positioning deviations and tilt angles complying with regulatory standards.

        Hole formation is the core technical process, requiring strict control over three key indicators: borehole wall stability, verticality, and sediment thickness. In deep soft soil foundations, dynamic slurry wall protection technology must be employed for drilling. The slurry mix ratio should be optimized by adding external agents such as soda ash and CMC to enhance viscosity and wall protection performance, ensuring stable slurry skin formation on the borehole wall to resist water flow erosion and soft soil creep. Simultaneously, slurry circulation speed must be controlled to prevent excessive loss. During drilling, construction parameters should be adjusted based on soft soil layer characteristics, adopting low-speed, high-pump-volume drilling methods to minimize borehole wall disturbance. Drilling speed should not be excessive, with inclinometer measurements conducted at regular depths to monitor verticality and promptly adjust drilling machine position to prevent exceeding allowable deviations. Upon reaching the designed depth, air-lift reverse circulation cleaning should be performed to thoroughly remove bottom sediment, ensuring compliance with design requirements for sediment thickness. Prompt concrete pouring must follow cleaning to avoid secondary sedimentation at the borehole bottom.

    The hoisting of the steel cage and concrete pouring must be seamlessly connected, with strict control over construction details. The steel cage is fabricated in segments and lifted by two cranes, maintaining vertical alignment during hoisting to avoid collisions with the borehole wall and casing. After positioning, it should be promptly secured to prevent floating or misalignment of the steel cage. Before installing the guide pipe, a watertightness test must be conducted to ensure no leakage, and the pipe should be centered during installation, maintaining a distance from the borehole wall that complies with specifications. Concrete pouring is performed continuously using the guide pipe method, with concrete selected to have a long initial setting time and meet slump requirements. The volume of the first batch of concrete must satisfy the embedment depth requirement of the guide pipe. During pouring, the embedment depth is monitored in real time to avoid excessive shallowness, which could lead to broken piles, or excessive depth, which might reduce pouring efficiency. Additionally, the pouring speed is controlled to minimize impact on the borehole wall. The concrete pouring height must exceed the designed pile top by a certain distance to ensure the strength of the pile top concrete.

    The entire construction process must ensure quality and safety control to guarantee compliance with engineering standards. In terms of quality control, real-time monitoring of mud slurry indicators, hole-forming parameters, reinforcement cage quality, and concrete performance is required. Each process must pass inspection before proceeding to the next stage. Methods such as the low-strain reflection wave method should be employed to assess pile integrity and bearing capacity, while abnormal conditions like hole enlargement or contraction during construction must be promptly addressed. For safety control, enhanced stability monitoring of work platforms and drilling rigs is necessary, along with regular inspections of anchor chains, platform structures, and drilling equipment. All personnel must wear complete protective gear. Regarding environmental protection, construction mud slurry and waste materials must be properly managed, with dewatering treatment using filter presses to prevent water pollution.

    Conclusion: For the construction of rotary drilling rigs in deep-water soft foundations at ports and terminals, the key lies in optimizing technical solutions to adapt to working conditions. Through scientific preliminary pre-processing, refined borehole control, standardized reinforcement cage and concrete construction, combined with comprehensive quality and safety management throughout the process, technical challenges such as borehole wall collapse and pile misalignment in deep-water soft foundations can be effectively addressed. Practice has shown that the rational application of these construction techniques can fully leverage the advantages of rotary drilling rigs, ensuring the quality and efficiency of pile foundation construction. This lays a solid foundation for the safe and stable structure of ports and terminals, while also providing practical reference for pile foundation construction in similar complex working conditions.