you could maybe put lines up and down in the cylinder. Then place the center of the balls on the line but tangent the balls to each other. If you want to offset the balls just put the lines closer than the ball dia. and add tangent to the balls in the other lines. You may want to play with diaganal lines too.
Feras, you can mate spheres to one-another with tangent mates to prevent them from interfering. That said, piles are more of a dynamic simulation formation than a design model formation. You need physics calculations to make a realistic pile.
How I would suggest proceding depends really on what the pile is going to be used for.
If it's job is to occupy space and mass and be displayed in an engineering drawing, then calculating a parabaloid from from the size and number of pebbels is a good way to get this done and move on. If you have a lexan flour container that's about the same diamter as your vessel, you can pour pebbels into it and take the pile height and diameter measurement directly. To provide a visual indication of what the parabaloid represents, you can take an overhead picture of the pile in the container and and project that onto the parabaloid surface as a decal. It won't look realistic, but you'll know what you're seeing in a shaded view.
If you are trying to make a realistic pile for rendering using SolidWorks, you're going to need to involve animation software that can do rigid body simulation, and export the geometry to a format that you can read into SolidWorks.
Fortunately, all of those capabilities are included in Blender (http://www.blender.org) and it's free. If you look on Youtube, you'll find lots of videos on using rigid body physics in Blender. It's not going to be obvious how to do it so if you're rushed to make a rendering, then get the help of an animation contractor.
What you're gonig to want from blender animation is a mesh output of the last frame of the animation in STL or VRML format. If the pile is smalll without many particles, you can import it as solidbodies into a single part document. You can then apply appearances to it and render it in SolidWorks.
If the pile is to large or if you need advanced rendering capabilities, then it's probably easier to export the SolidWorks assembly to STL, import that into Blender and build the scene around the pile.
Blender also has something called weight-painting that you can use to apply spheres to a surface in air-brush fashion. I used that to create an ice pile for an animation. That was pretty quick and easy and It worked OK.