How to Support Tunnels in Sand Layer?


Supporting tunnels in sand layers is a critical aspect of tunnel construction, essential for ensuring the safety and stability of the structure. Sand layers present unique challenges due to their loose and unconsolidated nature, which can lead to issues such as collapse, falling debris, and decreased bearing capacity. Rock bolts serve as vital reinforcement mechanisms in such conditions, providing structural support and enhancing stability throughout the tunneling process.

Understanding Sand Layers

Sand layers, characterized by their loose, granular composition, are common geological formations encountered during tunnel construction. These layers lack cohesion, posing significant challenges for engineers and construction crews. The loose nature of sand layers increases the risk of collapse and falling debris during excavation and shotcreting phases. Additionally, the presence of groundwater can further compromise the stability of surrounding rock, necessitating robust support systems to prevent structural failure.

Rock Bolts: Fundamentals and Types

Rock bolts are structural elements used to reinforce and stabilize rock formations, including sand layers, in tunnel construction. These bolts serve the crucial purpose of redistributing load and providing additional support to the surrounding rock mass. Common types of rock bolts utilized in tunnel support include mechanical rock bolts, grouted rock bolts, and self-drilling anchor bolts. Factors such as bolt length, diameter, and anchoring mechanisms must be carefully considered to ensure optimal performance in sand layers.

rock bolt drilling in tunnel

Design Considerations for Rock Bolts in Sand Layers

Designing effective rock bolt systems for sand layers requires a comprehensive geotechnical assessment to evaluate the stability and characteristics of the surrounding rock. Engineers must determine the appropriate bolt length, diameter, and spacing based on factors such as geological conditions, anticipated loads, and project specifications. Considerations for anchoring mechanisms are crucial in sand layers to ensure secure fixation and long-term stability.

A. Clearing Site

If the surrounding sand rock of the tunnel has collapsed or the gravel has fallen, it is necessary to clean up the gravel first. At the same time, pay attention to the collapse of the tunnel vault and surrounding rock. If the collapse is small, temporary support should be carried out first, and if the collapse is large, reinforcement grouting is required.

B. Shotcrete

After the site is cleared, it is necessary to spray grout on the face of the tunnel to avoid problems such as falling gravel during operation. If spray grouting cannot solve the current tunnel problem, you can consider bolting and grouting for reinforcement.

C. Install Rock Bolts

Tunnels in sand surrounding rocks need to be supported by rock bolts. The traditional support method is pipe casing construction, which takes a long time and requires a lot of manpower. The use of self drilling anchor bolt support has high construction efficiency, and the hollow bar body does not need to be pulled out after the drill bit is driven in.

D. Grouting

The casing construction process adopts the method of drilling first and then grouting, and the construction process of self drilling anchor bolts adopts the method of grouting while drilling. When drilling, the hole diameter and the grout penetration range will be enlarged, thereby improving the pullout force of rock bolt. It has obvious advantages in terms of pullout force and bearing capacity, force value performance and construction efficiency.

Monitoring and Maintenance of Rock Bolts

Regular inspection and monitoring are imperative to ensure the ongoing effectiveness of rock bolt systems in sand layers. Techniques such as visual inspections, load testing, and non-destructive testing can be utilized to assess the integrity of rock bolts and detect any signs of deterioration or displacement. Routine maintenance practices, including grout reinforcement and bolt replacement, are essential for mitigating potential risks and prolonging the service life of rock bolt installations.


In the design of special geological tunnels, special attention needs to be paid to the safety of personnel. From design, materials to construction techniques, design requirements must be strictly followed to eliminate problematic support projects. Sinorock self-drilling rock bolts make special geological tunnel support simpler and construction more efficient.

As a leading expert in the ground support industry, the Sinorock team has many years of experience in providing complete geotechnical engineering services. If you have any needs or questions about self-drilling anchor systems and their applications, please feel free to contact us at

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