Slope instability is a common safety hazard in projects such as highways, railways, mines, and construction pits. It can lead to accidents like landslides and collapses, threatening both personnel safety and project progress. Slope anchors, as a highly effective slope reinforcement technology, have become a core solution to slope stability issues due to their unique structure and operating principles. Let's take a closer look at their functions and roles.

   I. Basic Components of a Slope Anchor

   A slope anchor is a slender member that connects to the rock and soil through an "anchor section" and transmits tension through a "free section." It typically consists of three parts:

  1. Rod: The core load-bearing component, typically constructed of high-strength steel bars, stranded wire, or fiberglass reinforced plastics. It must possess sufficient tensile strength and durability to withstand the lateral thrust of the slope rock and soil.

  2. Anchor Section: The key section where the anchor is tightly bonded to the rock and soil. Grouting (cement slurry, cement mortar, etc.) bonds the rod to the borehole wall, forming an integrated "rock-soil-grout-rod" load-bearing system to ensure effective transmission of tension.

   3. External Anchor Head: Located on the slope surface, this head consists of a backing plate, nut, and other components. It distributes the anchor tension to the slope surface, preventing localized stress concentration that could damage the surface rock and soil. It also facilitates subsequent tensioning and locking.

   II. Core Functions of Slope Anchors

   The core functions of slope anchors revolve around improving slope stress conditions and enhancing stability, and can be summarized into three categories:

  1. Active Reinforcement: Restraining Rock and Soil Deformation

   The fundamental reason why slope rock and soil are prone to instability is that their internal shear strength is insufficient to balance the shear forces generated by their own weight or external loads. Anchors actively constrain deformation in the following ways:

   ① When the slope exhibits a tendency for slight displacement, the bond between the anchored section of the anchor and the rock and soil generates a reverse tension, preventing further sliding.

   ② When multiple anchors form an "anchor cluster," they create a "reinforced zone" within the slope, effectively adding "internal support" to the rock and soil, improving overall shear resistance and delaying or preventing the formation of a sliding surface.

  2. Load Transfer: Optimizing Force Distribution

   Loads on the surface rock and soil of a slope (such as its own weight, rainwater seepage pressure, and external loads) tend to be concentrated in localized areas, causing stresses to exceed the rock and soil's bearing capacity. Anchor bolts act as "force transmission channels":

   ① They transfer loads from the surface or shallow layers of the slope through the bolts to the deeper, stable rock and soil (where the anchoring section is located);

   ② They prevent load accumulation in the shallow layers, ensuring more uniform force distribution across the entire slope and reducing the risk of localized collapse.

  3. Restoring Rock Integrity: Filling Structural Defects

   Rock slopes often contain natural defects such as cracks and joints. These defects can weaken the rock's integrity and become "breakthrough points" for landslides. Anchor bolts can repair these defects through grouting and tensioning:

   ① During the grouting process, the grout fills the cracks in the rock mass, bonding the dispersed rock blocks together and improving the rock's integrity.

   ② The pre-tensioning stress of the anchor bolts creates a "compressive stress zone" within the rock mass, closing micro-cracks, reducing erosion from rain and weathering, and extending the slope's service life.

   III. The Practical Engineering Role of Slope Anchors

   Based on the aforementioned functions, slope anchors play an irreplaceable role in various engineering scenarios, specifically in the following four areas:

   1. Anti-slip and Stability: Preventing and Controlling Landslide Disasters

   This is the primary function of anchors. On slopes prone to landslides (such as highway slopes and mine spoil dumps), anchors can directly apply force to the sliding surface:

   ① When a potential sliding surface exists on the slope, the anchor penetrates the sliding surface, connecting the unstable rock and soil above the sliding surface (the sliding mass) with the stable rock and soil below (the sliding bed);

   ② The anchor's tension balances the downward force of the sliding mass, preventing it from sliding along the sliding surface. This approach is particularly effective on slopes with clay, gravel, and weathered rock. For example, on mountain highway slopes, a combination of anchors and shotcrete is often used. This approach not only prevents slippage through the anchors, but also protects the surface rock and soil through shotcrete, thereby preventing small landslides and rockfalls.

   2. Seepage Control Assistance: Reducing the Risk of Water-Induced Instability

   Rainwater infiltration is a major contributor to slope instability. Water increases the deadweight of rock and soil, reducing cohesion and the internal friction angle (especially in clayey soils). While anchor bolts do not directly prevent seepage, they can enhance their effectiveness in the following ways:

   ① During the anchor grouting process, the grout can partially block pores in the rock and soil, reducing the path for rainwater to infiltrate.

   ② "Anchor lattice beams" (reinforced concrete beams combined with anchor bolts) used in conjunction with anchor bolts can form a "grid-like protective layer" on the slope surface. Combined with anti-seepage materials such as geomembranes, they further block rainwater infiltration and reduce the risk of water-induced landslides.

   3. Space Saving: Adaptable to Complex Sites

   In narrow sites such as urban construction foundation pits and tunnel entrances, traditional "slope excavation" or "retaining wall" techniques are often limited by space (e.g., surrounding buildings or roads). The advantages of anchor bolts are their deep penetration and minimal footprint:

   ① Anchor bolts are installed by drilling vertically or obliquely along the slope, eliminating the need for significant external space.

   ② Compared to gravity retaining walls (which require heavy walls to balance the thrust), anchor bolt reinforcement solutions are more portable, reducing excavation and construction costs, making them particularly suitable for slope protection in densely populated urban areas.

   4. Dynamic Adjustment: Responding to Load Changes

   Slope loads in some projects (such as mining and loading sites) vary over time. Anchor bolts can achieve dynamic reinforcement through "pre-tensioning" and "re-tensioning":

   ① Pre-tensioning applies stress to the anchor bolt during construction, actively compacting the rock and soil and improving initial stability.

   ② If the load increases later (such as increased loading in a mine), re-tensioning can be applied via the nut on the external anchor head to supplement the anchor bolt's tension and ensure a stable slope.

   IV. Slope Anchor Construction Process

   Anchor construction must strictly adhere to the "Survey - Design - Construction - Testing" process. The core steps are as follows:

   ① Geological Survey: Through drilling and in-situ testing, determine the slope rock and soil type, strength, crack distribution, and groundwater level, and determine the anchor length, spacing, and anchoring section location.

   ② Drilling: Based on design requirements, use down-the-hole drills, rotary drills, or other equipment to drill holes. Maintain a controlled drilling angle (usually 15°-45° with the slope surface) and hole diameter (slightly larger than the rod diameter). After drilling, clean the hole of rock debris and accumulated water to avoid affecting the grouting effect.

   ③ Anchor Installation: Slowly lower the prepared rod (with anchor bars if using stranded steel wire) into the hole, ensuring the rod is centered and avoiding direct contact with the hole wall.

   ④ Grouting: Using a pressure grouting machine, inject cement slurry (usually with a water-cement ratio of 1/4) into the hole. 0.4-0.5) Grout from the bottom of the hole upwards, ensuring the grout completely fills the voids within the hole until it overflows from the hole mouth. Grouting requires curing for 7-14 days (adjusted according to the temperature).

  ⑤ Tensioning and Locking: After the grout strength reaches at least 70% of the design value, install the backing plate and nut. Pre-tension is applied using tensioning equipment. Once the design value is reached, lock the nut to complete the anchor bolt installation.

   ⑥ Quality Inspection: Pullout tests (randomly sampling 5%-10% of the anchor bolts) are performed to test the anchor bolt's pullout resistance to ensure it meets the design requirements. Grouting density is also checked (e.g., using ultrasonic testing) to avoid voids.

   Slope anchor bolts, as an active reinforcement technology, play a key role in anti-sliding stability, anti-seepage assistance, and space conservation through their core functions of "restraining deformation, transferring loads, and repairing rock mass." They have become a core means of slope protection in highways, mining, construction, and other sectors. Its construction requires strict adherence to a rigorous process of geological survey, precise construction, and quality inspection. Furthermore, careful material selection and post-production monitoring, tailored to the project's specific needs, are crucial to ensuring effective reinforcement. With the development of new materials (such as carbon fiber anchors) and intelligent monitoring technologies, slope anchors will more efficiently and accurately address complex slope stability issues, providing a more reliable guarantee for project safety.