Create rock bolts accurately in PLAXIS 3D


ApplicationPLAXIS 3D
VersionPLAXIS 3D 2013
Date created17 February 2016
Date modified17 February 2016
Note: Since PLAXIS 3D 2018, the introduction of the reinforcements/rockbolts in the Tunnel Designer (i.e., creating rock bolts perpendicular to the tunnel lining or creating forepoling/umbrella arches) is now straightforward (see related pages).

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. The manual snapping of the endpoint to the tunnel lining can be done, however, this might change the angle of the rock bolt 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 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:

Commands used:

point (25 1 -20)                       # reference point 
lineangles  Point_1  0 60 Surface_2    # line under 60 degree angle extended to Surface_2
delete Lines[-1]                       # optional 
lineangles  Points[-1]  0 60 4         # same command with length 
embeddedbeam Lines[-1] "Behaviour" "Rockbolt" "ConnectionPoint" "First"

End-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

For this example the following assumptions are taken:

Commands used

point (32 1 -7.5)                      # reference point 
lineangles  Point_1  0 240 Surface_2   # adjust angle

line command with "vector" parameters

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

line | reference point (x,y,z) | "vector" | direction (a,b,c) | target object

Example:

line   2 5 0.2   "vector"   0 -1 0   Surface_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:

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:

line  32 1 -7.5  "vector"  -0.5 0 -0.866  Surface_2
embeddedbeam Lines[-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 (single line) command would look like this:

embeddedbeam (32 1 -7.5) "vector" -0.5 0 -0.866 Surface_2 "Behaviour" "Rockbolt" "ConnectionPoint" "Second" "Material" RockboltBeamMaterial

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

See also