The pilot landed a high-skid, turbine-powered helicopter at a remote construction site, which contained several bags of cement that were covered by a plastic tarp. The plastic tarp was secured by a nylon strap that was wrapped around the bags. The pilot reported that after landing near the bags of cement, he retarded the engine throttle to flight idle to begin the mandatory 2-minute engine cool down procedure. During the engine cool down, the pilot felt an abrupt airframe vibration, so he immediately closed the engine throttle and performed an emergency engine shutdown. A postflight inspection revealed that the plastic tarp had dislodged from the nylon strap, and it subsequently became entangled in the tail rotor hub and blade assembly. As a result, the helicopter sustained substantial damage to the tail rotor drive system and tailboom. The pilot said there were no preaccident mechanical anomalies with the helicopter that would have precluded normal operation.