# Inclined Plane Reference Material

The flow of a material down an inclined plane is a common representation of a granular flow, such as a landslide, avalanche or debris flow. It consists of a pile of material resting on a planar surface. The normal to this plane can be referred to as the slope-normal direction, and the two other coordinate directions are commonly referred to as the down-slope and cross-slope directions. In this case, the inclined plane is roughened by sticking particles to it. In the down-slope and cross-slope directions we have placed periodic boundaries.

Under these conditions, we can assume that the shear and normal stresses inside the granular material are due solely to the gravitational field which is applying them, and therefore both of them increase linearly with depth. At any depth, therefore, the ratio of these two is a constant. This ratio is commonly referred to as the friction coefficient. By varying the slope angle, we can therefore vary the applied friction angle. To probe the material behaviour we can then vary the slope angle consistently and measure the shear rate and density of the material. This is the rationale behind the famous mu(I) rheology.

This simulation contains two main components, the simulation pane and the graph pane. On the right hand side is the simulation pane. Here you can see a discrete element simulation evolving. The simulation begins with a number of grains arranged on a regular grid that are not in contact. As the page loads, you will see these particles fall under the action of gravity towards the rough plane represented as a wireframe with a set of white lines. You can vary the slope angle by either clicking on the menu on the top right of the screen, or by using the W and S keys on your keyboard. You can use the dropdown menu to change the brightness of the particles to represent the velocity magnitude or rotation rate magnitude of each individual particle. They will go brightly when these values are high. You can click the "New loading path" toggle to create a new line on the graph pane with a new colour.

On the left hand side of the screen is the graph pane. Here you can see ...