PA-24 pilot reported the landing gear collapsed upon touchdown resulting in a gear up landing.

Narrative

The sky was clear visibility at 10 mile winds were calm. Practicing pattern work before a long cross country scheduled for the following day. Second lap in the pattern: Normal approach. Gear down at midfield; Plane slowed as expected; trim; 15-degree flaps deployed abeam the threshold; trim turned base second notch of flaps. GUMPS performed all good. Turn Final GUMPS is all good. Final approach @ 85 mph as expected; 80 mph over the numbers; I felt the main gear touch down followed by an immediate slam and a moment later the prop striking and the sound of metal scratching. I knew at this moment that the gear had collapsed. I maintained directional control; switched the fuel pump off; and guided the plane on its belly down the runway notifying the Tower to know I had a gear failure and we were disabled on the runway. Master/mags off and I was exiting the aircraft waited for support. Examination of the aircraft on the runway. When lifted by a tow truck in slings; it was noted the gear doors were open; (more notably on the starboard side) by 1-2' respectively. A mechanic noted the landing gear switch was in the down position as he boarded to deploy the gear. He turned on the master and a loud mechanical grinding sound was coming from the aircraft's landing gear and the gear would not deploy mechanically through the utilization of the gear-down switch. The landing gear had to be lowered by the emergency deployment lever.The plane was towed to its hangar for storage.