In complex geotechnical projects such as tunnel excavation, slope reinforcement, and foundation pit support, hollow anchors have become a key support material to ensure project safety with the core advantage of integrating "anchoring + grouting". It breaks the construction limitations of the traditional separation of anchor rods and grouting pipes. It realizes the coordinated operation of drilling, grouting and anchoring through the hollow rod body. It can not only quickly provide initial support to control the deformation of surrounding rock, but also consolidate broken rock masses and block groundwater through pressure grouting. It is like implanting "bones" into the geotechnical structure. It plays an irreplaceable role in many major projects from the Sichuan-Tibet Railway to the urban comprehensive pipe gallery.
1. Core definition and working principle: the internal logic of integrated support

The hollow anchor is a slender rod structure that has both tension anchoring and grouting reinforcement functions. The core consists of a hollow fully threaded rod, an anchor head, a grout stopper, a backing plate, a nut and other components. Some types are equipped with special accessories such as drill bits and connecting sleeves. Its essence is to combine the anchor body and the grouting pipe into one. The working principle can be summarized as a four-step closed loop of "precise positioning-anchoring forming-pressure grouting-overall reinforcement": select the corresponding type of anchor according to the geological conditions, and insert the rod body into the target formation through drilling or self-drilling; use anchor head expansion, resin anchoring, etc. to fix the rod. The body quickly forms initial support force; slurry (cement slurry, composite material slurry, etc.) is injected into the hole at high pressure through the hollow rod body, and the slurry penetrates into the rock and soil fissures and pores under the pressure; after the slurry solidifies, the rod body and the surrounding rock and soil form a strong overall anchor system, achieving anti-corrosion protection and long-term stability improvement at the same time.

Compared with traditional support methods, the core advantage of hollow anchors is that "support and reinforcement are completed simultaneously" - it can not only control the deformation of rock and soil through the rod's tensile force, but also improve the properties of surrounding rock through grouting. It solves the pain points of incomplete grouting, corrosion of anchors, and low support efficiency in traditional construction, and is especially suitable for engineering needs under complex geological conditions.

2. Mainstream types and characteristics: “accurate solutions” adapted to different geology

According to the construction method, structural design and application scenarios, hollow anchors have formed a diversified product system. The five mainstream types have their own emphasis and accurately match different geological and engineering needs:

(1) Plug-in hollow grouting anchor

As a basic product, this type of anchor adopts the construction mode of pre-drilling and then inserting the rod. The rod body is mostly made of steel or fiberglass. It has a simple structure and is easy to install without the need for complicated construction equipment. Its core advantages lie in its controllable cost and wide adaptability, which can meet the needs of tunnel support, slope reinforcement and foundation pit support in ordinary rock and soil layers. It is most commonly used in projects with moderately good geological conditions. It occupies a major share of the foundation support market with its characteristics of "quick installation and easy operation".

(2) Self-drilling hollow anchor

For geological conditions prone to hole collapse such as broken rock formations and soft soil, the self-drilling hollow anchor has achieved an integrated breakthrough of "drilling-grouting-anchoring". The front end of the rod body is equipped with a special drill bit. No pre-drilling is required. The rod body is directly driven to drill to the designed depth, and grouting is simultaneously injected through the hollow channel, effectively avoiding the problem of hole collapse and stuck drilling. Its construction efficiency is more than 30% higher than that of traditional techniques, and it is suitable for tunnel face reinforcement, mine support, complex slope management and other scenarios. It is known as the "nemesis of complex geology" in geotechnical engineering.

(3) Self-propelled hollow grouting anchor

The grouting system is optimized based on the self-drilling type and is equipped with a high-efficiency grout stop device and a high-pressure grouting interface. The grouting pressure is greater, the grout is distributed more evenly, and the anchoring effect is significantly improved. Compared with the self-drilling type, it focuses more on grouting density and long-term stability. It is suitable for scenarios such as tunnel lining, deep foundation pit support, and permanent underground engineering support that have strict requirements on reinforcement quality. It can form a dense slurry curtain around the rod body through pressure grouting, which has the dual functions of reinforcement and anti-seepage.

(4) Expanding shell type prestressed hollow anchor

Prestress is applied through mechanical tensioning of the tail shell expansion device. The anchoring force is strong and adjustable, and can effectively cope with geotechnical deformation in high-stress areas. Its core feature is that it can actively control the stress distribution of the surrounding rock to avoid cracks in the rock layer due to stress concentration. It is widely used in high-risk scenarios such as high slope support, long-span tunnels, and large-scale underground projects. It is especially suitable for high-stress strata that require early application of support force.

(5) Combined hollow grouting anchor

Integrating the advantages of various anchor rod structures, it is flexibly combined with modules such as hollow rod bodies, grouting pipes, grout stop plugs, and shell expansion devices. The anchoring method and grouting mode can be switched according to engineering needs. It is extremely adaptable and can cope with complex geology such as faults and groundwater development. It performs well in cross-regional infrastructure construction, emergency rescue and other scenarios, realizing the customized support needs of "one pole for multiple purposes".

3. Core application areas: throughout the entire scenario of infrastructure projects

The application of hollow anchors has covered core infrastructure fields such as transportation, water conservancy, mining, and urban underground space, and has become a "rigorously needed material" to ensure project safety. In railway and highway tunnel projects, its demand accounts for 38.5%. It is the core support material for cross-border projects such as the Sichuan-Tibet Railway and the Jakarta-Bandung High-speed Railway. Through the combination of self-drilling and shell-expanding anchors, it can effectively cope with extreme geology such as high ground stress and broken surrounding rocks. In slope projects, it can achieve functions such as slope stability, rockfall protection, and cutting reinforcement. Glass fiber hollow anchors With its corrosion-resistant and cuttable properties, it has become the first choice for permanent support; in water conservancy and hydropower projects, it is used to reinforce dam foundations and construct anti-seepage curtains to block groundwater seepage channels; in the field of urban underground space development, with the acceleration of the construction of comprehensive pipe corridors and underground parking lots, the relevant demand accounted for 17.3% in 2025, doubling compared with 2021.

Data shows that projects using hollow anchor support reduce the risk of surrounding rock collapse by more than 80%, shorten the construction period by 15-25 days, and increase the safety factor by more than 2 times compared with traditional support methods in complex geological projects, becoming the core support for efficient construction of modern geotechnical engineering.

4. Technological innovation and industry development trends

Driven by policies, infrastructure upgrades and the "dual carbon" strategy, the hollow anchor industry is moving towards the four major transformation directions of "high reinforcement, intelligence, greenness and internationalization", with technological iteration and market structure continuing to optimize:

(1) Upgrading of materials and processes, continuous breakthroughs in performance

The penetration rate of high-strength alloy steel (such as HRB500E) has increased from 35% in 2021 to 58% in 2025. The tensile strength of products generally reaches more than 658MPa. At the same time, the yield rate has been increased to 96.8% through intelligent manufacturing, and unit energy consumption has dropped by 12.6%. The application of green materials such as glass fiber and bio-based composite materials has expanded. Glass fiber anchors, with their lightweight, high-strength and corrosion-resistant properties, have seen rapid growth in demand for permanent support and corrosive environments. Pilot applications of recyclable modular products have increased, which is in line with the concept of green construction.

(2) Intelligent transformation is accelerated and monitoring capabilities are upgraded.

Intelligent sensing hollow anchors have become a research and development hotspot. By embedding fiber gratings, DAS sensing units and 5G IoT modules, millimeter-level real-time monitoring and cloud early warning of grouting density, rod stress, and surrounding rock deformation are achieved, and the grouting density compliance rate has been increased to 94%. In the future, the deep integration of BIM systems and smart anchors will achieve the precise configuration of "one hole, one strategy" and promote the transformation of support projects from "passive protection" to "active early warning". It has been applied on a large scale in high-risk projects such as Wudongde Hydropower Station.

(3) The market size is growing steadily and the structure continues to be optimized.

From 2021 to 2025, domestic hollow anchor production will increase from 486,000 tons to 673,000 tons, with an average annual compound growth rate of 8.5%. Export volume will reach 58,000 tons in 2025, mainly going to countries along the "Belt and Road". The regional market shows a leading trend in the central and western regions, with Sichuan, Yunnan, and Guizhou provinces accounting for nearly 30% of the total demand. Industry concentration continues to increase, with CR5 reaching 43.2%. The implementation of the national standard "Hollow Grouting Anchors" (GB/T 35153-2024) has raised the entry threshold, and leading companies have transformed into "product + monitoring + operation and maintenance" full life cycle service providers. Looking forward to 2026-2030, benefiting from national water network construction, urban renewal and other strategies, the industry's average annual growth rate is expected to maintain 9.8%, and the penetration rate of smart anchors will jump from 5.2% to more than 18%.

5. Conclusion

From traditional steel rods to intelligent sensing equipment, from hollow single function to modular combined support, the technological evolution of hollow anchors embodies modern geotechnical engineering's demands for safety, efficiency, and greenness. As a "support all-rounder" that goes deep into the geotechnical field, it not only provides the basic guarantee for controlling surrounding rock deformation and preventing engineering risks, but also becomes an important carrier for promoting the digital and low-carbon transformation of infrastructure projects. With the expansion of overseas infrastructure and the internationalization of technical standards, the hollow anchor industry will usher in greater room for development and provide more reliable and accurate support solutions for complex geological projects around the world.