In　the　Tunnel　Boring　Machines　(TBMs)　construction　of　soft　rock　tunnels,　adverse　geological　conditions,　such　as　water-rich　and　wet　strata　are　often　encountered.　Water　in　strata　can　change　the　stress　state　and　weaken　the　mechanical　performance　of　rock　mass,　further　affecting　the　tunneling　process　and　rock　breaking　efficiency.　To　study　the　effect　of　water　content　on　mudstone　fragmentation　characteristics　and　cutter　force　during　TBM　cutter　indentation,　the　water　softening　effect　is　considered　in　the　moisture　diffusion-fracture　coupling　model　based　on　the　finite-discrete　element　method　(FDEM).　Then,　the　micro　parameters　(fracture　energy　release　rate,　swelling　coefficient　and　moisture　diffusion　coefficient)　of　mudstone　are　calibrated　by　uniaxial,　triaxial　compression　and　swelling　tests.　Subsequently,　the　water　content　and　swelling　deformation　evolution　of　mudstone　samples　during　water　migration　are　revealed.　Finally,　the　coupling　model　is　utilized　to　investigate　the　fragmentation　characteristics　and　cutter　force　of　mudstone　samples　with　different　water　contents　under　various　confining　pressures　during　TBM　cutter　indentation.　The　fragmentation　zone,　cutter　force,　acoustic　emission　(AE),　and　crack　number　during　cutter　indentation　are　quantitatively　analyzed.　Results　indicate　that　the　vertical　extent　of　fragmentation　range　(Ev)　decreases　with　the　increase　of　water　content,　while　the　horizontal　extent　of　fragmentation　zone　(Eh)　does　not　decrease　obviously　until　the　water　content　reaches　3%.　The　increase　of　confining　pressure　reduces　the　effect　of　water　content　on　Ev,　and　the　increase　of　water　content　also　reduces　the　effect　of　confining　pressure　on　Ev,　indicating　that　confining　pressure　and　water　content　have　a　mutual　inhibition　effect　on　Ev.　Besides,　both　the　peak　value　of　normal　force　and　the　fluctuation　range　of　tangential　force　for　the　TBM　cutter　decrease　with　the　increase　of　the　water　content.　The　AE　counts　show　that　the　failure　pattern　of　mudstone　is　mainly　shear　failure　during　TBM　cutter　indentation.　Specifically,　many　shear　cracks　are　generated　in　the　compression　zone　under　the　cutter,　while　few　tensile　cracks　propagate　in　mudstone　on　both　sides　and　deeper　below　the　cutter.　For　mudstone　under　different　confining　pressures,　the　proportion　of　shear　cracks　increases　with　the　increase　of　water　content.　Moreover,　the　effect　of　cutter　penetration　velocity　on　mudstone　fragmentation　characteristics　and　cutter　force　is　discussed.　The　results　in　this　paper　have　theoretical　guidance　for　TBM　construction　of　soft　rock　tunnels　in　water-rich　and　wet　strata.　©　2024,　The　Author(s),　under　exclusive　licence　to　Springer-Verlag　GmbH　Austria,　part　of　Springer　Nature.