While working in a raise, employees had scaled & installed bolts with wire. During process of drilling round, the ground popped, loosening a 9' x 4' wide x 1"" thick into the wire. In doing so, the wire ripped from one of the corner bolts causing some pieces of rock to fall thru, striking EE on rt shoulder. He fell, landed on rt knee causing a laceration needing 5 stitches.