As the patent invention unit of the complete technology of screw piles, thread pile forming equipment and methods, and an important compiling unit of technical specifications (standards), Hainan Zhuodian High-Tech Development Co., Ltd. also expresses a few opinions.

The three technologies of screw piles, their pile-forming equipment, and pile-forming methods have distinct technical characteristics. If not clearly understood, they are easily confused with long spiral cast-in-place piles, pile-forming equipment, and pile-forming methods, falling into traps and bringing long-term hidden dangers to engineering quality. At present, the phenomenon of using long spiral cast-in-place pile equipment and methods to construct screw piles and thread piles in high-speed railways is quite common and has aroused widespread public attention.

First, it is necessary to clarify what kind of pile a screw pile is and how it differs from a long spiral cast-in-place pile.

A screw pile is a type of displacement pile with screw threads on the pile body. The pile relies on the drilling tool to squeeze the soil during drilling to form threaded holes and cylindrical holes. No soil is removed during construction, and concrete is pumped to form the pile.

Equipment characteristics: Screw piles place high demands on equipment, requiring the equipment to have both rotational power and pressure power working together. Automatic control technology is used to control the synchronization of pressure and rotational force on the drilling tool. For each rotation of the drilling tool, one pitch is drilled. This is called synchronization technology in regulations and standards. Automatic control technology is used to control the non-synchronization of pressure and rotational force. For every several rotations of the drilling tool, one pitch is drilled. This is called non-synchronization technology in regulations and standards.

To test whether a machine has the capability to implement screw pile and thread pile forming technology, the first thing is to see whether its pile machine has the following three points:

First, the pile machine equipment must have dual power of pressure and rotation, and the pressure must reach 40 to 80 tons. The standard pressure equipment uses chain pressure because the chain has little elongation and strong tensile strength, which can maintain the precision of synchronous operation of pressure and rotational force and avoid the phenomenon of disordered thread recombination. The second is wire rope pressure. How to reduce the error caused by wire rope elongation places high demands on automatic control technology. At the same time, once there is 40-80 tons of pressure, the phenomenon of being unable to drill on some sites will not occur, nor will the phenomenon of 'thread slipping' loss or disordered threads occur.

Second, the automatic control device is the core technology for controlling the synchronization and non-synchronization of dual power and quality monitoring. It is the key equipment for implementing soil displacement to form the threaded section and straight shaft section of the pile body. In addition, the automatic control device has computer and display functions, can automatically record pressure, rotational force, and pile length, and transmit data remotely.

Third, the drilling tool with toothed threads is one of the key equipment to ensure the compactness of the pile body concrete. It allows residual air in the concrete to be discharged to the ground through the toothed threads during concrete pouring, increasing the compactness and strength of the concrete.

Simple necessary summary:

1. The drilling rig must have a pressure device of no less than 40 tons.

2. The drilling rig must have an automatic control device that meets the above requirements. Whether the automatic control device can achieve synchronization of pressure and rotational power must be tested on site.

3. The thickness of the front end of the drilling tool blade with toothed threads on the pile machine shall not be less than three centimeters, and the root of the blade shall not be less than five centimeters.

4. Among them, no soil removal is allowed during the hole formation of screw piles.

5. Automatically upload information such as pressure, rotational force, and depth during hole formation and pile formation.

A typical screw pile machine is as follows:

6. Long spiral cast-in-place pile is a soil-removal pile. Its pile-forming process: the drilling tool with Archimedean spiral blades throughout freely drills down. The drilling tool has no pressure, only a single rotational power. During the rotation of the drilling tool, the soil is removed to the ground along the Archimedean spiral blades. Once the soil is removed, the lateral confinement is lost, producing a relaxation effect. The degree of exertion of the soil's bearing capacity on the pile becomes smaller, and the soil bearing capacity is weakened. In addition, because there is no pressure, when encountering high-strength soil layers, the phenomenon of being unable to rotate or advance will occur. Whether the Shandong High-Speed Railway China Construction Eighth Engineering Division used this equipment for construction, if so, it is understandable that it cannot be driven down. Because this technology and equipment are cheap, construction speed is fast, and construction cost is low, it still has a considerable market application range. However, as far as I know, screw piles in high-speed railway construction generally use long spiral cast-in-place piles to impersonate screw pile construction, often resulting in soil removal construction and inability to drill, as well as soil removal pile formation, which will have hidden dangers of post-construction settlement.

However, the screw pile is a displacement pile. After the hole body is compacted, the soil's bearing capacity on the pile is exerted to a greater degree. In addition, the extruded soil and the pile body are in a threaded stress state, producing the effect that screws are better than nails. Therefore, the bearing capacity of screw piles is often more than twice that of long spiral cast-in-place piles, and the deformation is also smaller.

Because the screw pile composite foundation is widely used in high-speed railway subgrades, the pile and the soil between piles bear force together. No soil is removed during hole formation and pile formation, and the soil compactness between piles is improved. More importantly, it has a positive soil displacement effect on the composite foundation. This strengthens the overall force of the subgrade and is very suitable for use in areas with high bearing capacity requirements, small post-construction settlement deformation requirements, and high environmental protection requirements.

Long spiral cast-in-place pile is a soil-removal pile. It uses a single power rotation to drill down the soil. After soil removal and hole formation, the soil compactness between piles is weakened, the overall compactness of the subgrade is attenuated, and the coordinated force of pile and soil in the formed composite foundation is attenuated.

More importantly, under the primary condition that the pile meets the bearing capacity, controlling foundation settlement is a very important requirement. Foundation settlement mainly includes three aspects: the compression amount of the pile, the compression amount of the soil between piles, and the compression amount of the soil below the pile tip. In particular, the settlement compression deformation of the soil layer below the pile tip has the greatest impact. Therefore, merely meeting the bearing capacity is not enough. The pile length must be guaranteed. The longer the pile, the smaller the foundation settlement deformation. The final settlement of the foundation often takes up to 30 years to stabilize. The construction length of the Shandong High-Speed Railway does not meet the design requirements. Although the bearing capacity of the constructed piles may be sufficient, the final settlement requirement of the foundation is based on the design pile length as a necessary condition to ensure that the final settlement reaches stability. Or to put it this way, the final settlement of the foundation is related to the pile length. Many speakers online have not noticed such a key issue.

The screw pile technology has been designated as a national first-class construction method by the state. Its core technology surpasses existing national technical standards and reaches the world's advanced level. This kind of pile is called the best pile in the world.

At present, piles with full-thread pile bodies are called thread piles internationally and domestically. According to relevant specifications, they are classified as soil-removal type piles. Piles with threads and straight shafts are invented by the Chinese and are called half-screw piles, which are displacement piles. The above technologies have different names in national specifications, regulations of nine provinces and one city, and recommended standards at different times: thread pile, screw pile, rotary extrusion pile. The key is to look at the technical characteristics. As long as a pile has the above characteristics, it falls into the patent rights. As for what it is called, it does not matter. Just like someone who has changed their name ten times, as long as the DNA matches, it is this person. Whatever pile is designed, selecting the matching specialized equipment is the basic necessary condition for construction quality assurance.

For more than ten years, our country has widely applied screw piles in high-speed railway foundation treatment, saving a large amount of funds for national high-speed railways, and at the same time exposing some problems. Because high-speed railways adopt bidding and tendering, the winning sections are basically central enterprises, which subcontract externally. Professional subcontracting companies engage in vicious competition, using long spiral pile machine equipment that does not have the capability to construct thread piles and screw piles to impersonate thread pile and screw pile machines for construction on high-speed railways. Coupled with vicious price reduction in selecting teams, over the past decade, the subcontracting price has become lower and lower, so low that some construction units, in order to obtain meager profits, take risks. The use of long spiral pile machines for construction on high-speed railways is everywhere, bringing long-term hidden dangers to the later stage of engineering quality.

We suggest that the state formulate policies for subcontracting and not allow general contracting units to be too 'free' in lowering subcontracting prices. These incidents on high-speed railways are not accidental. If not stopped in time, there will be endless troubles. The responsibility of the general contractor is to undertake organization and management. The profit they obtain should be management profit, while the profit obtained by professional teams should be professional construction profit. There should be a policy distinction between the two, using systems to restrain extortion, achieving fairness and reasonableness, each fulfilling its responsibilities, and distribution according to work. At the same time, selecting matching specialized equipment is the basic necessary condition for construction quality assurance.