Joint　spacing　is　one　of　the　most　important　geological　factors　influencing　rock　fragmentation　by　TBM　cutters　and　TBM　performance.　In　order　to　study　the　influence　of　joint　spacing,　full-scale　linear　cutting　tests　have　been　conducted　for　the　Beishan　granite　samples　with　different　joint　spacing　(i.e.　one　intact　sample,　two　jointed　samples　with　joint　spacing　of　100　mm　and　400　mm).　For　different　joint　spacing,　the　influence　of　penetration　depth　on　rock　fragmentation　was　also　explored　by　varying　the　penetration　depth　with　an　interval　of　0.5　mm.　During　the　test　process,　the　three　directional　forces　acting　on　the　TBM　cutter　were　recorded,　and　the　rock　chips　formed　by　each　cutting　pass　were　weighed,　respectively.　By　analysing　the　cutting　force,　crack　initiation/propagation　and　rock　chips,　the　influences　of　joint　spacing　on　rock　fragmentation　process　by　TBM　cutter　were　investigated.　The　test　results　showed　that　the　increase　of　penetration　depth　cannot　improve　the　TBM　breakage　efficiency　after　reaching　a　certain　value　for　the　intact　rock　sample,　and　the　normal　force　for　intruding　the　intact　rock　is　larger　than　that　for　intruding　the　rock　jointed　samples.　It　is　also　found　that　the　sample　part　below　the　joint　plane　is　intact,　thus　joint　can　restrain　the　crack　propagating　cross　the　joint　plane　and　facilitates　the　chips　formation　on　the　cutting　surface.　For　the　rock　sample　with　joint　spacing　of　100　mm,　two　rock　fragmentation　modes　were　found　during　the　cutting　process.　One　mode　is　that　the　cracks　initiate　from　the　crushed　zone　under　TBM　cutter,　and　the　cracks　propagate　to　the　joint　plane,　consequently　form　large　rock　chips.　The　other　one　is　that　the　cracks　initiate　from　the　joint　plane　and　then　propagate　to　the　rock　cutting　surface,　and　the　cracks　initiate　before　the　formation　of　the　crushed　zone　under　the　cutter.　For　the　rock　sample　with　joint　spacing　of　400　mm,　there　are　two　rock　fragmentation　stages,　i.e.,　the　normal　rock　fragmentation　stage　and　the　joint-controlled　rock　fragmentation　stage.　There　is　a　transitional　process　between　these　two　stages,　and　also　the　median　crack　can　be　promoted　to　propagate　vertically　to　joint　plane　due　to　the　joint　existence.　This　study　can　provide　useful　guidance　for　operation　optimization　and　performance　prediction　for　TBM　operating　in　jointed　rock　masses.　(C)　2016　Elsevier　Ltd.　All　rights　reserved.