# Boundary wall friction

Hello. When i create a slope model for failure simulation, the left and right wall boundaries are normally y-axis locked and x- and z- axis free. I normally use –
block gridpoint apply velocity-y 0 range group ‘left’
block gridpoint apply velocity-y 0 range group ‘right’

So I wanted to ask is there any friction present in the boundary (between block and boundary)? I want it to be zero friction.

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Yes, this command will essentially create a frictionless wall such that the gridpoints on the boundary are free to move in the x and z direction, but not in the y direction. (note that the default orientation of things is such that the left side is -x and the right side is +x, so you should be fixing the x velocities on these sides. But maybe your model is rotated 90 degrees?)

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block gridpoint apply velocity-x 0 range group ‘front’
block gridpoint apply velocity-x 0 range group ‘back’
block gridpoint apply velocity-y 0 range group ‘left’
block gridpoint apply velocity-y 0 range group ‘right’
block gridpoint apply velocity 0 0 0 range group ‘bottom’

This are my boundary conditions. Please check if correct?
And I had one other question, will the width (y-axis) of the model affect the sliding of voronoi blocks? Like if I make the width very thin like 1 unit, will it change the sliding behaviour with a model which has a width of 5 unit? This is the reason I asked about zero friction walls. If walls have zero friction I think a thinner width (y-axis) model will also give similar sliding surface related to a wide model(y-axis).

Boundary conditions are fine. Not sure what to say about the thickness. You might want to have something reasonably thick so the blocks can move around each other in the out-of-plane dimension. Probably that is not an important mechanism, but it will depend on the properties and block geometries. I would try some numerical experiments and see what you get.