The Discrete Element Method (DEM) based on spheres can provide acceptable approximations to many complex physical phenomena both in micro and macro scale. Normally a DEM simulation starts with an arrangement of spherical particles pack inside a given container. For general domains the creation of the sphere pack may be complex and time consuming, especially if the pack must comply with accuracy and stability requirements of the simulation. The objective of this work is to extend a 2D disk packing solution to generate random assemblies composed by non-overlapping spherical particles. The constructive algorithm, presented here, uses the advancing front strategy where spheres are inserted one-by-one in the pack, according to a greed strategy based on the previously inserted particles. Advance front strategy requires the existence of an initial set of spheres that defines the boundary of the pack region. Another important extension presented here is the generalization of algorithm to deal with arbitrary objects defined by a triangular boundary mesh. This work presents also some results that allow for some conclusions and suggestions of further work.