I shall agree with Crab on this one....yes I know.....mark it on the calendar as it is somewhat rare.
In my past I flew the Hughes 269/TH-55, a very limited exposure to the H-19 (Whirlwind to our British friends), the H-34/S58T, and the Alouette III which all were candidates for the Fastest Self Destruction Competition.
Starting in primary flight school we were exposed to the dangers of Ground Resonance....those of us who were flying the TH-55 and not the H-13 or H-23 had to know about.
Recognizing the onset of Ground Resonance is the most important issue....knowing what it feels like (we had demonstrations of it in our training) and then immediately doing as Crab said....Pick up to a Hover or shut down the engine(s) and decrease the Rotor RPM as quickly as possible are the two options.
It is not the shut down of the engine that makes the real difference....it is the Rotor RPM and the Angular out of balance of the Rotor system.....changing the resonance and reducing the forces generating the resonance is key.
In the video....the second Hughes 269/300 clip shows how the quickly the resonance dissipates after lifting off the ground as the aircraft is free of the surface and the feedback from contact with the surface
The chinook clip shows the aircraft was tied securely to the ground and the aircraft landing gear struts were unable to function as designed......and despite the Test Engineers shutting the engines off.....there was no way to slow the blades quickly as the aircraft did not have a Rotor Brake.