# 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

- Zero Shear Force

- If
**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

- Zero Shear Force

- If
**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)

- Zero Shear Capacity

- If

## 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.