Bolt Implementation

Some important assumptions when modeling Bolts in RocTunnel3:

• For a bolt to have any effect on the block, the start of the bolt must intersect the free face (i.e., excavation face) and the end of the bolt must intersect the joint face and extend through the block.
• The embedded length of the bolt inside the block is calculated as the distance between the intersection point of the bolt at the free surface to the intersection point of the bolt at the joint surface.
• The imbedded length of the bolt outside the block is calculated as the distance between the intersection point of the bolt at the joint surface to the end of the bolt.
• Bolts can fail in one of six Bolt Failure Modes depending on which capacities are exceeded first. The limiting capacity controls the mode of failure.
• In a Successive Failure analysis, the bolt is removed with any excavation surface facing blocks which fail if the start of the bolt intersects the free face (assume that the bolt no longer provides any capacity).

Bolt Deformation Mode

The bolt support force which is ultimately applied to a block, and the orientation of the applied force (tension, compression, or shear), depends on the following factors:

The Bolt Deformation Mode denotes the mode in which a bolt intersects a block failure plane. The deformation mode depends on whether the failure plane is a shear (sliding) plane or a dilating (opening) plane, and also on the orientation of the bolt with respect to the plane and the sliding direction.

There are six possibilities considered, as illustrated in the figure below.

Capacity

Whichever capacity gets exceeded first will control the Bolt Failure Mode and the Bolt Force provided:

• Plate Capacity + Bond Strength (and Bond Length inside block)
• Tensile Capacity (or Compression Capacity)
• Bond Strength (and Bond Length outside block)
• Shear Strength

Bolt Support Force

The Tensile Force provided by a bolt is the minimum of:

• Plate Capacity + Bond Strength (and Bond Length inside block)
  
• Tensile Capacity
  
• Bond Strength (and Bond Length outside block)
  

The Compression Force provided by a bolt is simply the Compression Capacity. The Shear Force provided by a bolt is simply the Shear Capacity. For any given bolt, only one support force will ultimately be applied, Shear, or Tensile (or Compression). Both modes cannot operate simultaneously.

The Bolt Force is computed depending on the Bolt Deformation Mode and whether Bolt Orientation Efficiency, Use Shear Capacity, and Use Compression Capacity are ON/OFF.

• Modes A, B, C: Bolt is in tension as block moves away from joint (shear is ignored)
  • Zero Shear Force
  • If Bolt Orientation Efficiency is ON then Tensile Force is reduced to Tensile Force x Bolt Orientation Efficiency Factor
    
  • If Bolt Orientation Efficiency is OFF then Tensile Force is as is
• Mode D: Bolt is shearing as blocks shears along sliding joint, and also in tension
  • If Use Shear Capacity is ON then failure is in Shear:
    • Zero Tensile Force
    • Shear Force is the bolt's Shear Capacity
  • If Use Shear Capacity is OFF:
    
    • Zero Shear Force
      
    • If Bolt Orientation Efficiency is ON then Tensile Force is reduced to Tensile Force x Bolt Orientation Efficiency Factor
      
    • If Bolt Orientation Efficiency is OFF then Tensile Force is as is
      
• Mode E: Bolt is shearing as blocks shears along sliding joint, and is neither in tension nor compression
  • If Use Shear Capacity is ON then failure is in Shear
    
    • Zero Tensile Force
    • Shear Force is the bolt's Shear Capacity
  • If Use Shear Capacity is OFF:
    • Zero Shear Force
      
    • If Bolt Orientation Efficiency is ON then zero Tensile Force
      
    • If Bolt Orientation Efficiency is OFF then Tensile Capacity is the bolt's Tensile Capacity
• Mode F: Bolt is shearing as blocks shears along sliding joint, and is in compression
  • If Use Shear Capacity is ON then failure is in Shear
    
    • Zero Compression Force
    • Shear Force is the bolt's Shear Capacity
      
  • If Use Shear Capacity is OFF:
    • Zero Shear Capacity
      
    • If Bolt Orientation Efficiency is ON then Compression Force is reduced to Compression Force x Bolt Orientation Efficiency Factor (if Use Compression Capacity is ON, else zero Compression Force)
      
    • If Bolt Orientation Efficiency is OFF then Compression Force is the bolt's Compression Capacity (if Use Compression Capacity is ON, else zero Compression Force)

Direction of Bolt Support Force

• Tensile Force: Bolt force is applied in the same direction of the bolt installation. Only applies if block is moving in the opposite direction to the bolt installation.
• Compression Force: Bolt force is applied in the opposite direction of the bolt installation. Only applies if block is moving in the direction to the bolt installation and Use Compression Capacity is ON.
• Shear Force: Bolt force is applied in the opposite direction of the block sliding direction. Only applies if bolt intersects a sliding joint of the block (i.e., sheared) and Use Shear Capacity is ON.

Location of Applied Support Force

Like all other forces in the RocTunnel3 analysis, all bolt support forces are applied through the centroid of the block. Therefore, once the magnitude and orientation of the bolt force is determined, the force doesn't really have a "location" on the block. Since moment equilibrium is not considered in the RocTunnel3 analysis, all forces are assumed to pass through the same point, the 3-dimensional centroid of the block.