Tunnel Support

Definition:

Tunnel support encompasses the methods employed to reinforce the excavation and maintain the stability of the tunnel. It involves the use of structural elements and support systems to resist ground pressure, prevent collapse, control deformations, and ensure the safety of the tunnel structure.

Uses/benefits:

The primary uses and benefits of tunnel support include:

Safety of Personnel: Tunnel support systems provide a safe working environment for construction workers by preventing potential collapses and mitigating the risk of accidents or injuries.
Structural Integrity: Tunnel support helps maintain the integrity of the tunnel structure, ensuring its long-term stability and preventing damage or deterioration due to ground movement or external forces.
Ground Control: Tunnel support systems control and stabilize the surrounding ground, preventing excessive deformations, settlements, or heave, which can affect the stability of the tunnel and adjacent structures.
Protection of Infrastructure: Tunnel support protects critical infrastructure such as utilities, pipelines, or transportation systems passing through or adjacent to the tunnel, minimizing the risk of damage or disruption.
Maintenance and Durability: Proper tunnel support ensures the long-term maintenance and durability of the tunnel, reducing the need for frequent repairs and costly maintenance operations.
Mitigation of Ground Hazards: Tunnel support systems help mitigate ground hazards such as rockfall, ground instability, or water ingress, enhancing the overall safety of the tunnel environment.

Specifications:

The specifications for tunnel support systems depend on various factors, including the geotechnical conditions, tunnel size and shape, anticipated loads, and the specific requirements of the project. Some common specifications include:

Support Elements: Specifications may include the type, size, and spacing of support elements, such as rock bolts, anchors, shotcrete, steel sets, or tunnel linings.
Load-Bearing Capacity: Specifications define the load-bearing capacity of the support elements, ensuring they can withstand the expected loads and forces exerted by the surrounding ground.
Deformation Control: Specifications may include limits on allowable deformations or settlement criteria to ensure that the tunnel remains within acceptable limits of movement.
Material Properties: Specifications may include requirements for the properties of support materials, such as strength, durability, corrosion resistance, fire resistance, or chemical resistance.
Construction Methods: Specifications may define the installation techniques and procedures for the support elements, ensuring proper installation and quality control during construction.

Types:

There are various types of tunnel support systems used based on the specific project requirements and geological conditions. Some common types include:

Rock Bolts: Rock bolts are installed to reinforce the rock mass and prevent potential rockfalls or ground instability. They are typically made of steel and provide additional support to the tunnel walls. Wedge and slot bolt. Wedge and sleeve, Perfo bolts, Swellex bolts, Cable bolts. Self-drilling rockbolts (SDA), etc. are some of the bolts used as tunnel support system as according the requirement of rock mass (IS 15026: 2002). These are the active type of supports which improve the inherent strength of rockmass and it act as reinforced rock arch.
Shotcrete: Shotcrete is a sprayed concrete mix that is applied to the tunnel surfaces to provide immediate support and reinforcement. It forms a strong, durable lining that can resist ground pressure and protect against water ingress.
Steel Sets: Steel sets consist of steel beams and supports that are installed to provide structural support to the tunnel. They are commonly used in soft ground or unstable geological conditions. Steel ribs supports are the passive supports and supports the lossened rockmass externally.
Tunnel Linings: Tunnel linings can be constructed using various materials such as cast-in-place concrete, precast concrete segments, or tunnel boring machine (TBM) rings. They provide structural support, prevent water ingress, and protect against ground movements.
Ground Anchors: Ground anchors are tensioned elements that are installed into the ground and connected to the structure to provide additional stability and prevent ground movement. They are often used in situations where the tunnel is subjected to high horizontal forces or in weak or unstable ground conditions.
Fiber Reinforcement: Fiber reinforcement materials, such as steel or synthetic fibers, can be added to concrete or shotcrete to enhance its tensile strength and control cracking.
Grouting: Grouting involves injecting a fluid material, such as cementitious grout or resin, into the surrounding ground to fill voids, improve ground stability, and strengthen the soil or rock mass.
Ground Improvement Techniques: In some cases, ground improvement techniques such as soil nailing, soil stabilization, or ground freezing may be employed to enhance the stability and strength of the surrounding ground.