The pilot reported that, he performed an orbit of his intended off-field landing site prior to starting the approach. As he made his final approach to the site, he realized the helicopter was fast and determined that he needed to abort the landing and perform a go-around. However, the helicopter settled, and the low rotor rpm light illuminated, which was accompanied by the low rotor rpm horn. The pilot attempted to add power but could not lower the collective due to his shallow approach and low altitude. As the helicopter touched down on a slope the pilot applied right cyclic, and the helicopter impacted the ground and came to rest on its right side. The fuselage was substantially damaged. The pilot reported that there were no preaccident mechanical failures or malfunctions with the helicopter that would have precluded normal operation.