In projects such as foundation project, slope stabilization project, and underground project , self-drilling anchor bolts integrate drilling, grouting and anchoring, becoming the core equipment for stabilizing rock mass and ensuring construction safety.In these projects, a certain number of self-drilling anchor bolts with a certain drilling depth are usually installed to anchor the rock mass. The drilling depth of self-drilling anchor bolts varies in different projects – some go as deep as 18 meters underground, while others only need 12 meters to meet the requirements. So how exactly is this depth determined? What are the factors that affect the drilling depth? Today, we will introduce them to you.
To know how to determine the drilling depth of self-drilling anchor bolts, it is essential to understand their underlying working principle. Therefore, before introducing the drilling depth, let’s first introduce the working principle of self-drilling rock bolts in geotechnical engineering.
Working Principle of Self – drilling Anchor Bolts
Self-drilling anchor bolt technology involves embedding a self-drilling hollow anchor bar into the ground. It is then wrapped with grout to form an anchor body, which is connected with the surrounding rock and soil mass to create an anchoring structure, thus reinforcing the building. Therefore, during the construction process, self-drilling anchor bolts have strict requirements for the drilling depth. Firstly, the drilling depth should penetrate through the overburden layer on the surface of the rock mass. Then, during the drilling process, it needs to penetrate through the broken rock layer or pebble layer. Finally, the self-drilling hollow anchor bar may drill into the stable rock formation. However, due to different project types and geological conditions, the requirements for depth are also different. It is worth noting that the drilling depth must precisely match the stratum structure, and this process is affected by various factors. Next, let’s look at what these influencing factors are.
What are the Factors Affecting the Drilling Depth of Self-drilling Anchor Bolts?
Generally, the drilling depth of self-drilling anchor bolts is determined by geological conditions, drilling equipment, and construction techniques.
Geological Conditions
Geological conditions, as a decisive factor, profoundly affect the feasibility and efficiency of drilling. In soft soil and sandy soil layers, although the drilling resistance is small, the low soil strength makes it prone to hole shrinkage and collapse. Therefore, the depth needs to be controlled according to the design requirements to avoid anchorage failure. When facing medium-hard rock and broken rock layers, the compressive strength and fracture development degree of the rock will significantly increase the drilling resistance. When the rock hardness exceeds the cutting capacity of the drill bit or the fractures cause drill jamming, the construction is forced to stop, severely limiting the drilling depth.
Drilling Equipment
The performance of drilling equipment also plays a crucial role. The torque, thrust, and rotational speed of the drilling rig all affect the drilling depth. High-torque equipment can effectively break hard rocks, and a large-thrust design can handle the resistance of deep-layer drilling. A reasonable rotational speed can ensure drilling efficiency while reducing drill bit wear. If the power of the equipment does not match the geological conditions, it will be difficult to break through the depth bottleneck even if the stratum is suitable.
Construction Techniques
The influence of construction techniques cannot be ignored. The grouting pressure needs to be adjusted synchronously with the drilling depth to avoid the failure of the borehole wall protection due to insufficient pressure. Excessive drilling speed may cause the collapse of the borehole wall. All these details directly affect the final drilling depth.
Now that we understand the factors affecting the drilling depth, let’s see how to determine the drilling depth of self-drilling anchor bolts.
How to Determine the Drilling Depth of Self-drilling Anchor Bolts?
The drilling depth of self-drilling anchor bolts should be scientifically determined through rigorous calculation and design, taking into account engineering requirements and geological characteristics.
In foundation project, the designers controlled the depth between 12 and 18 meters according to the building load and the mechanical properties of the foundation soil, and the maximum depth did not exceed 24 meters.This range not only provides sufficient anchoring force but also avoids construction risks and cost waste caused by excessive depth.
In slope stabilization project, the design of the drilling depth focuses on the stability of the rock mass. It is necessary to clarify the specific location of the internal stable rock formation through geological surveys, slope stability analysis, and other means. The self-drilling hollow anchor bar needs to penetrate through the unstable rock mass and reach the internal stable rock formation to form a reliable anchorage section. At the same time, the drilling angle should be precisely controlled according to factors such as the slope angle and lithology to avoid weakening the anchoring effect due to angle deviation.
In tunnel engineering, the purpose of the self-drilling anchor bolts directly determines the drilling depth. When used for advanced support perpendicular to the tunneling direction, the depth refers to that in slope protection engineering, generally 12 – 18 meters, aiming to reinforce the surrounding rock in advance. For support self-drilling anchor bolts along the tunneling direction, considering the dynamic changes in the surrounding rock stress during tunnel excavation, the depth is usually set at 15 – 30 meters.
In different engineering projects such as foundation, slope, and tunnel projects, the determination of the drilling depth of self-drilling anchor bolts needs to balance safety and benefits. Only by taking comprehensive consideration based on actual conditions can we give full play to the role of self-drilling anchor bolts and provide reliable protection for engineering construction.
Conclusion
During the construction process, the drilling depth of self-drilling anchor bolts should be determined in combination with actual engineering requirements and geological conditions. Sinorock’s self-drilling anchor bolts are highly flexible and can be cut or lengthened with a coupler according to actual engineering needs. This product has been widely used in various engineering projects, such as foundation construction, slope protection, and tunnel excavation. If you have any questions about drilling depth planning in your project, please feel free to contact us at any time. Our professional team will tailor an ideal solution for you based on the actual engineering situation.
