Sand castle collapse 3D animation VFX

A sand castle collapsing with Houdini. Just testing Houdini grain sim and mantra BPR rendering. I used 2 animated spheres to wake up the particles. Render was only between 2 to 5 minutes a frame with mantra BPR for 5.2 million particles. It took around 3 minutes a frame for simulation (5 hours total).