In　this　article,　the　effects　of　tunnel　boring　machine　(TBM)　disk　cutter　penetrations　on　rock　fragmentation　are　experimentally　investigated.　In　these　tests,　the　tested　sample　is　composed　of　Beishan　granite　and　Chongqing　sandstone.　The　effects　of　five　sets　of　TBM　disk　cutter　penetrations　are　investigated　under　confining　pressure　of　10　MPa,　and　3-D　forces　acting　on　the　rolling　cutter　and　the　forming　rock　chips　are　analyzed.　It　is　found　from　the　experimental　results　that　in　the　mixed-faced　ground,　for　granite,　the　boreability　of　the　TBM　disk　cutter　increases　slowly　with　increasing　penetration,　while　for　sandstone,　the　boreability　of　the　TBM　disk　cutter　almost　linearly　decreases.　At　the　same　penetration,　the　average　normal　force　and　rolling　force　in　granite　are　larger　than　those　in　sandstone,　and　cutter　vibration　becomes　obvious　when　the　disk　cutter　rolls　through　the　interface　of　the　composite　rocks.　Moreover,　the　optimizing　penetration,　which　is　equal　to　2　mm　in　the　mixed-faced　ground　composed　of　granite　and　sandstone　under　confining　stress　of　10　MPa,　is　provided　to　guide　the　TBM　operation　and　to　predict　rock　fragmentation　in　TBM　tunneling.