Anchor Bolts

Definition:

Anchor bolts are threaded steel rods or bars that are inserted into pre-drilled holes in rock or concrete. They are then secured with grout or resin to provide a reliable anchor point for attaching and stabilizing structural elements in tunneling and underground structures.

Uses/benefits:

Anchor bolts have several uses and benefits in tunneling and underground structures, including:

Structural Stability: Anchor bolts are crucial for ensuring the stability and integrity of tunnel linings, support systems, and other structural components. They help withstand external forces, such as ground movement or equipment loads, preventing displacement or failure.
Load Transfer: Anchor bolts transfer applied loads from the supported structures to the surrounding rock or concrete, effectively distributing the forces and reducing stress concentrations.
Safety Enhancement: By securely anchoring tunnel linings and support systems, anchor bolts enhance safety by minimizing the risk of structural collapse, loosening, or shifting during operation or in the event of unforeseen conditions.
Versatility: Anchor bolts can be used in a wide range of tunneling and underground applications, including securing tunnel linings, rock bolting, attaching equipment or fixtures, and reinforcing structural connections.
Long-Term Durability: When properly installed and maintained, anchor bolts provide long-lasting stability and performance, ensuring the long-term integrity of the tunnel or underground structure.

Specifications:

Specifications for anchor bolts in tunneling and underground structures can vary depending on the specific project requirements, design considerations, and load conditions. Some common specifications include:

Diameter and Length: Anchor bolts come in various diameters and lengths, which are determined based on the design requirements and the thickness of the structural element being anchored.
Material Grade: Anchor bolts are typically made of high-strength steel, with specific material grades specified to meet the required tensile strength, yield strength, and corrosion resistance.
Thread Type: Anchor bolts may have different thread types, such as fully threaded or partially threaded, depending on the intended application and the need for adjustment during installation.
Embedment Depth: The specified embedment depth of the anchor bolt determines the depth at which the bolt is inserted into the rock or concrete, ensuring sufficient anchorage and load-bearing capacity.
Load Capacity: Anchor bolts have defined load capacities, specified in terms of their allowable working load or ultimate tensile strength, which should be suitable for the anticipated loads in the application.

Types:

There are several types of anchor bolts commonly used in tunneling and underground structures, including:

Expansion Anchor Bolts: Expansion anchors use mechanical expansion to secure the bolt in place, creating a tight fit within the drilled hole.
Resin Anchor Bolts: Resin anchors utilize epoxy resin to bond the bolt to the surrounding rock or concrete, providing reliable anchorage and load transfer.
Grouted Anchor Bolts: Grouted anchors are embedded in drilled holes and secured by injecting grout, typically cementitious or resin-based, into the hole to provide anchorage and load-bearing capacity.
Mechanical Anchor Bolts: Mechanical anchors use mechanical devices, such as wedges or bolts, to secure the anchor in place and provide load transfer.
Swellex Anchor Bolts: Swellex anchors consist of an expandable shell that expands against the drilled hole when pressurized, providing anchorage in unstable or fractured rock conditions. A minimum 150 kN yield load of Swellex Bolts are utilized in tunnels as a temporary kind of support.
SN-Anchors (Store-Norfors-Anchors): These are made of deformed reinforcing steel with a corrugated surface, Of which one end shall be fitted with a suitable thread to fix anchor plate with nut. SN Anchors are mostly utilized as temporary supports (minm diameter of 25 mm with yield load=200kN (min) for Fe 415 & 245kN (min) for Fe 500) for rock stabilization, ground support, and anchorage in rocks.
Self-Drilling Anchors: These are the composite form of the drill rod and rock bolt. In situations where drill holes swiftly collapse during drilling, such as in loose ground or fractured rock, SDA bolts provide immediate stabilization of the aperture (minm diameter of bolt is 32 mm with yield load=200kN).

Some standards, including EN 1997-1 (Geotechnical Design, Part 1: General Rules), DIN 1054:2005-01 (Ground Verification of the Safety of Earthworks and Foundations), and BS EN 1537-2000 (Execution of Special Geotechnical Work-Ground Anchors), may be used for the installation and geotechnical design of ground anchors. For the mechanical qualities of high-strength deformed bars, Indian Standard Code IS 1786: High-Strength Deformed Steel Bars and Wires for Concrete Reinforcement-Specification may be used with the inclusion of several tests (tensile, bend, rebend, etc.).

The selection of anchor bolts in tunneling and underground structures depends on factors such as the design requirements, geological conditions, anticipated loads, and project specifications