The　mixed-face　ground　has　been　being　a　topic　for　a　long　time　because　of　its　significant　influence　on　TBM　performance.　For　example,　the　mixed-face　ground　tunnelling　usually　makes　the　high　frequency　and　great　magnitude　of　variations　in　cutter　force,　thereby　causing　heavy　dynamic　impacts　on　the　cutters　and　cutterhead　together　with　their　bearings,　which　will　incur　cutterhead　vibrations.　Therefore,　the　cutter　wear　increases,　especially　the　cutter　bearing　failure　and　abnormal　cutter　ring　wear.　However,　little　study　has　been　focused　on　mixed　face　ground.　This　paper　classifies　the　mixed　face　ground　into　three　classes,　including　layered　mixed　face　ground,　two-portion　mixed　face　ground　and　locked-corestone　or　blocky　mixed　face　ground.　Based　on　the　rock　mass　breakage　mechanism,　the　possible　influence　of　each　mixed　face　ground　on　TBM　performance　is　described.　A　case　history　of　the　two-portion　mixed　face　ground　in　DTSS　project,　Singapore　is　studied.