In the field of modern engineering construction, Zhongyan Dadi's high-speed high-pressure mixing composite pile (DMC) technology, with its outstanding performance and wide applicability, has become the preferred solution for large-scale infrastructure construction and civil building projects under complex geological conditions. This technology has been successfully applied in numerous company projects, demonstrating strong engineering value. The following provides a systematic exposition from the aspects of technical principles, process characteristics, construction procedures, and quality control, offering a reference for the industry.

1.  Principles and Advantages of DMC Pile Construction Technology

1.1  Construction Technology Principles

      DMC (super deep mixing composite pile) is a high-performance new composite pile in which a precast core pile and a cement-soil pile work together to resist superstructure loads. It is a further upgrade and breakthrough based on the cement-soil composite pipe pile, and belongs to the non-soil-extraction pile planting category. This method uses a DMC mixing drilling rig, assisted by cement slurry and a new drag-reducing agent, to rapidly drill and mix the in-situ soil to form a stable, uniform large-diameter high-speed deep mixing cement-soil pile, after which a precast core pile is concentrically implanted.

      This method combines the high efficiency and stability and high friction resistance of the high-speed deep mixing cement-soil pile with the prefabrication and high strength of the precast core pile itself. It offers advantages such as high construction efficiency, stable quality, economic and environmental friendliness, and high bearing capacity, and can effectively control superstructure settlement. It is an ideal foundation form for medium-soft soil areas.

1.2  Core Process Advantages

1.2.1  Leading Equipment Performance

      A self-developed new high-speed mixing drilling rig is adopted, featuring active downward pressure, fast pile formation, small dimensions, low energy consumption, and flexible relocation. The drilling speed can reach up to 2 m/min, the mixing speed can reach 60 r/min, and the number of mixing operations at any position is no less than 300, ensuring full mixing of soil and slurry. High-speed rail wear-resistant technology is introduced to reduce drill bit wear costs.

1.2.2  Intelligent Construction Management and Control

      Through IoT technology, construction parameters are monitored in real time and dynamically adjusted according to formation changes, achieving full-process information management and ensuring construction quality.

1.2.3  Drag Reduction Technology Innovation

      A self-developed new drag-reducing material is added during the mixing process, reducing mixing resistance and pile sinking resistance by 30%-50% under the same working conditions.

1.2.4  Bearing Performance Optimization

      Compared with cast-in-place piles, the diameter is increased, and the characteristic values of side resistance and end resistance are improved, significantly enhancing bearing capacity. This allows further optimization of the number or length of piles, thereby reducing costs.

1.2.5  Green and Efficient Construction

      Compared with cast-in-place piles, construction efficiency can be increased by more than 30%, with low on-site slurry discharge, no vibration or noise pollution, controllable precast core pile quality, and a clean on-site construction environment, actively responding to the national strategy of green construction and ecological environmental protection.

1.2.6  Expanded Formation Adaptability

      It solves the pile sinking difficulty of precast piles in medium-dense to dense sand layers, maximizes the bearing strength of pile and soil materials, and expands the applicable range of precast piles.

2.  DMC Pile Process Flow and Construction Method

2.1  DMC Pile Process Flow

2.2  DMC Construction Method

3.  Full-Cycle Quality Control System

      DMC pile construction technology achieves efficient foundation treatment through innovative processes, but because it involves the integration of multiple technical aspects such as material proportioning, equipment coordination, and intelligent control, it is more complex than traditional pile foundation construction. During actual construction, design specifications and technical standards must be strictly followed, and technical and safety briefings must be comprehensively conducted before construction to ensure that the construction team fully masters equipment operation points, parameter control standards, and quality acceptance requirements. At the same time, operators must strictly comply with the dedicated DMC pile operating procedures, precisely controlling construction details in each stage from equipment commissioning and material preparation to mixing and implantation, thereby ensuring stable and reliable DMC pile construction quality and fully leveraging its technical advantages under complex geological conditions.

3.1  Pre-construction Pre-control

      A three-dimensional pre-control system of "material-equipment-process" should be established during construction to ensure construction quality.

3.1.1  Material Control

      The strength of precast core piles must meet design requirements, with no honeycombing or exposed reinforcement in appearance, and dimensional deviation must not exceed 5 mm. Cement and admixtures must be provided with factory certificates and type test reports, and materials used on site must be sampled and sent for inspection.

3.1.2  Equipment Inspection

      Check the operating status of the drilling rig's mixing system, intelligent control system, and pile planting operation system to ensure normal equipment operation, identify potential problems, and minimize quality issues caused by equipment failures during construction. Calibrate pressure gauges, flow meters, and other metering units of relevant equipment, ensure the inner channel of the drill pipe is unobstructed, and maintain sufficient reserves of wearing parts.

3.1.3  Process Briefing

      Organize technical training for the construction team, focusing on mastering key parameter control points such as lifting speed, drilling speed, mixing rotation speed, flow rate, and water-cement ratio.

3.2  Control During Construction

3.2.1  Real-time Parameter Monitoring

      Collect data such as torque, pressure, and verticality through an intelligent system to form construction parameter cloud maps, and adjust immediately when deviations are found.

3.2.2  Process Quality Control

      Strictly implement the continuous operation of "grouting-mixing-drill lifting-pile planting-site leveling"; after interruption, the overlap length must not be less than 0.5 m.

      During mixing, ensure the verticality of the frame and drill pipe, with verticality deviation not exceeding 1%. During construction, use a total station to observe the verticality of the drill pipe in two directions and use a spirit level to measure the leveling of the frame; adjust promptly if excessive deviation is found.

      For pipe pile lifting, the two-point lifting method should preferably be used, or the hook lifting method may be used, with hooks at the end plates of the pipe pile and the angle between the rope and the horizontal axis of the pile body greater than 45°.

      During pile planting, when the pile body has just been inserted into the soil, operate the clamping cylinder to readjust the verticality of the pipe pile, and then start the pile pressing machine to slowly press the pipe pile into the soil. During pile pressing, use a total station for monitoring to ensure verticality. Before connecting the upper and lower pipe pile sections, correct the verticality, and the centerline deviation of the upper and lower pile sections must be less than 5 mm.

3.2.3  Slurry Management Standards

      Use a hydrometer to detect the water-cement ratio in real time, ensure the grouting volume is greater than the design value, and strictly prohibit lifting without grouting.

3.3  Acceptance Standards After Construction Completion

3.3.1  Vertical Bearing Capacity Testing

      Conduct static load tests 28 days after pile formation. The number of tested piles shall not be less than 1% of the total number of piles under the same conditions and shall not be less than 3; when the total number of piles is less than 50, it shall not be less than 2. The ultimate compressive value of a single pile must meet design requirements.

3.3.2  Horizontal Bearing Capacity Testing

      Pile foundations subjected to horizontal forces require single-pile horizontal static load tests, with the number of tested piles not less than 1% of the total number of piles under the same conditions and not less than 3. The characteristic value of horizontal bearing capacity shall be taken ascritical load0.6 times the value, and shall not exceed 50% of the single-pile horizontal ultimate bearing capacity.

3.3.3  Integrity Testing

      Use the low-strain method to test pile integrity. The number of tested piles shall not be less than 20% of the total number of piles and shall not be less than 10. At the same time, supplement with shallow excavation or dynamic penetration testing to verify the quality of the mixing pile.

4.  DMC Pile Construction Cases

5.  Prospects for Technology Application

     Through practical verification in numerous engineering projects, DMC high-speed high-pressure mixing composite piles have significant advantages over traditional pile foundation technology. They can be flexibly combined with special precast core piles and new reinforcing materials to form a composite bearing system combining rigidity and flexibility, significantly improving the compressive and uplift performance of single piles. With excellent adaptability to complex formations such as dense sand layers and highly plastic clay, as well as the characteristics of low slurry discharge and low-noise environmental protection throughout construction, their advantages are fully demonstrated in the construction of urban core areas. As infrastructure construction transforms toward intelligence and green development, the deep integration of DMC piles with BIM technology and IoT monitoring systems will continuously improve its supporting technical system. As long as key links such as material proportioning, equipment parameters, and construction processes are strictly controlled, construction quality and safety can be firmly guaranteed. In the field of foundation treatment for major projects such as super high-rise buildings and rail transit, DMC pile technology will surely play a greater role and embrace broader application prospects. Zhongyan Dadi will continue to deepen technological innovation and contribute core strength to the high-quality development of China's construction with more advanced and reliable geotechnical engineering solutions!