defining walls of geometry which lies on different planes

I am trying to setup a CFD-DEM case which should be able to model the particle packing. the geometry is attached in the figure, you can see that lower wall is not on single plane rather on different planes.
To achieve what i wanted, 1st i have performed pure liggghts simulations which prepares the bed in the lower section of geometry. Once the lower section is filled, i prepared a another liggghts input script (which restarts from pure liggghts simulations) and openfoam setup, in which small particles are injected along with the flow from inlet (left boundary). The small particles and flow should interact with created bed with pure liggghts simulation. But the problem arises when defining walls and wall interaction for CFD-DEM part. What i understand the walls and their interaction (using fix wall/gran command) can be defined using planes in x,y and z direction. As I have the lower walls on different planes which makes it difficult to define the boundaries properly.
I tried by defining various y planes, but every plane extended through out the simulation box thus obstructs the injected particles with flow. Any ideas how can i define my boundaries which are not on the same plane.

for reference, I define boundaries (walls) something like this:

%definig upstream channel boundary
fix xwalls1_us all wall/gran model hertz tangential history primitive type 1 xplane -0.1
fix xwalls2_us all wall/gran model hertz tangential history primitive type 1 xplane 0.0
fix ywalls1_us all wall/gran model hertz tangential history primitive type 1 yplane 0.1
fix ywalls2_us all wall/gran model hertz tangential history primitive type 1 yplane 0.24

%definig bed boundary boundary
fix xwalls1_bed all wall/gran model hertz tangential history primitive type 1 xplane 0.0
fix xwalls2_bed all wall/gran model hertz tangential history primitive type 1 xplane 0.3
fix ywalls1_bed all wall/gran model hertz tangential history primitive type 1 yplane 0.0
fix ywalls2_bed all wall/gran model hertz tangential history primitive type 1 yplane 0.24

%definig downstream channel boundary
fix xwalls1_ds all wall/gran model hertz tangential history primitive type 1 xplane 0.3
fix xwalls2_ds all wall/gran model hertz tangential history primitive type 1 xplane 0.4
fix ywalls1_ds all wall/gran model hertz tangential history primitive type 1 yplane 0.1
fix ywalls2_ds all wall/gran model hertz tangential history primitive type 1 yplane 0.24

%defining wall in z-dir
fix zwalls1 all wall/gran model hertz tangential history primitive type 1 zplane -0.45
fix zwalls2 all wall/gran model hertz tangential history primitive type 1 zplane 0.45