Create rock bolts accurately in PLAXIS 3D AE

Introduction

In the PLAXIS 3D AE version it is not directly possible to intersect lines with surfaces. This is because of the parametric definition of the PLAXIS 3D AE surface objects, which is not compatible yet for line objects.

This makes the process of designing rock bolts for a tunnel project cumbersome, since the created lines might not be accurately snapped on the lining (surface) of the tunnel. Manual snapping of the end point to the tunnel lining can be done, however this might change the angle of the rockbolt slightly, which may be undesired. A manual intersection of the line and surface could solve the problem. However, this is not currently possible.

Alternative rock bolt definition

Depending on the desired geometry, different approaches are suggested. In this article the following cases are explained, related to the reference point that is given for designing the rock bolts:

• reference point is inside the tunnel geometry
• ending point of rock bolt

Reference point inside the tunnel geometry

In this case, the reference point is located inside the tunnel geometry. This point and a given angle assists in providing the direction of the rock bolt.
The following steps describe how to create a rock bolt accurately snapped on the surface of the tunnel lining:

1. create the reference point
2. find the name of the surface from which the rock bolt will be created
3. use the lineangles command to create a line starting from the reference point towards this surface
4. the newly created point is the starting point of the rock bolt
5. (optional) delete the created line as not needed
6. use the lineangles command to create the rock bolt by specifying the length (instead of a target surface)

For this example the following assumptions are taken:

• reference point is: (25 1 -20)
• angle of the rock bolt with respect to the xz-plane is: 60º for x-axis

Commands used:

point(251-20) # reference point lineanglesPoint_1060Surface_2deleteLines[-1]  # optional lineanglesPoints[-1]  0604 # same command with length embeddedbeamLines[-1] "Behaviour""Rockbolt""ConnectionPoint""First"

Ending point of rock bolt

In this case, the suggested alternatives are given below using two available commands: lineangles and the line command using "vector" parameters.

lineangles command

The following steps describe how to create a rock bolt accurately snapped on the surface of the tunnel lining:
create the reference point

• find the name of the surface towards which the rock bolt will be created
• use the command lineangles to create a line starting from the reference point towards this surface (remember to adjust the angle to find the correct value for the command)

For this example the following assumptions are taken:

• reference point is: (32 1 -7.5)
• angle of the rock bolt with respect to the xz-plane is: 60º for x-axis (240º for x-axis at the opposite direction)

Commands used

point(321-7.5) # reference point lineanglesPoint_10240Surface_2 # adjust angle 

line command with "vector" parameters

The line command can be used in different ways. One way to create a line is using a vector to define the direction of the line towards a surface. The structure of this command is the following:

line|referencepoint(x,y,z)|"vector"|direction(a,b,c)|targetobject

Example:

line250.2"vector"0-10Surface_1

Creates a line from a new point with coordinates (2, 5, 0.2) with a direction of (0, -1, 0) onto Surface_1.

For this example the following assumptions are taken:

• reference point is: (32 1 -7.5)
• angle of the rock bolt with respect to the xz-plane is: 60º for x-axis (30º for z-axis)

The following steps describe how to create a rock bolt accurately snapped on the surface of the tunnel wall:

1. find the name of the surface towards which the rock bolt will be created
2. use the line command to create a line starting from the reference point towards this surface (the vector in this case is calculated accordingly based on the angle given) 

Commands used:

line321-7.5"vector"-0.50-0.866Surface_2embeddedbeamLines[-1] "Behaviour""Rockbolt""ConnectionPoint""Second"

( vector is calculated based on the following: [-0.5, 0, -0.866] = [cos60 , cos0 , cos30] )

These commands can also be written in a single line so it can easily be used when the rock bolt generation is prepared in for instance a spreadsheet program (see example here[]link]). The command would look like this:

embeddedbeam(321-7.5)"vector"-0.50-0.866Surface_2"Behaviour""Rockbolt""ConnectionPoint""Second""Material"”RockboltBeamMaterial

For more information on the structure of the commands used, please check the Command reference, under Help menu in Input.