# yade-users team mailing list archive

## Re: How do I create a tunnel/slope?

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```Hi,

One important rule : you cannot remove particles in a simulation.
For creating a complex geometry, one workaround is this :

```
A- first generate a packing (using e.g. the triaxial routines) , then save the simulation B- reload the simulation, using a python script or a different preprocessor, and filter bodies based on coordinates, so that only bodies in/out of a circular arc will be actually loaded and kept into the new problem.
```
```
We did that before for boreholes and slopes (perhaps Emanuele can give some details and code concerning the creation of the slope?) and it worked quite well. The only tricky part is you need to adjust the confining stress in stage A so that you will not generate an explosion when you suddendly create a free surface in a confined material. Typically, you have to balance the confinment of stage A with the gravitational effects of stage B.
```
```
You have an exemple of this from HydraulicTest below. Note that there should be far more elegant ways to do that with python.
```
Bruno

HydraulicTest.cpp, l.156 :

for ( ; bi!=biEnd ; ++bi )
{
if ( ( *bi )->geometricalModel->getClassName() == "Sphere" )
{
if ( inside ( ( *bi )->physicalParameters->se3.position ) )
{
cerr << "insert sphere" << endl;
shared_ptr<Body> b = *bi;
//b->id = idSphere++;
rootBody->bodies->insert ( b, idSphere++ );
nbSpheres++;
}
}
if ( ( *bi )->geometricalModel->getClassName() == "Box" )
{
//if(  inside((*bi)->physicalParameters->se3.position)  )
{
cerr << "insert box" << endl;
shared_ptr<Body> b = *bi;
rootBody->bodies->insert ( b );

}
}
}

boon chiaweng a écrit :
```
Hi, I am a new user. I have sufficiently understood the general purpose of Engines/Preprocessors and where to find the Contact Laws. My intention is to explore the possibility of using YADE to create a slope or a tunnel (separate problems). I understand that 'boxes' are used to surround the particles to contain them in a 3D space, when isDynamic != 0. However, I would like the face of the slope to be 'free', and would also want the tunnel perimeter/arc to be 'free'. How do I arrange the particles to make a slope? How do I remove particles to make a tunnel? Of course, there could be other techniques. Please help. Yours faithfully, Boon
```
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```

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