To　gain　a　deeper　understanding　regarding　the　intrinsic　properties　and　correlations　of　macro　mechanical　responses,　including　critical　states　and　large　flow　deformations　under　monotonic　and　cyclic　loading　conditions,　with　a　view　to　revealing　the　fundamental　characteristics　of　internal　forces　and　deformations　in　granular　materials.　A　series　of　undrained　triaxial　compression,　triaxial　extension　and　cyclic　triaxial　numerical　tests　are　performed　using　discrete　element　method　(DEM)　software　PFC3D.　Under　both　monotonic　and　cyclic　loading　conditions,　a　comparable　deformation　mechanism　of　strain　softening　and　strain　hardening　is　observed,　and　the　effective　stress　skeleton　curves　are　in　good　agreement.　As　the　progression　from　high　stress　ratio　to　the　critical　stress　ratio,　flow　deformation　and　strain　hardening　are　observed　in　saturated　sand,　where　the　mechanical　coordination　number　gradually　increases　and　the　sliding　ratio,　suspended　particle　ratio　decrease.　The　fabric　anisotropy　tends　to　increase　in　the　flow　deformation　stage,　decreases　slightly　in　the　strain　hardening　stage　but　remains　highly　anisotropic,　and　decreases　rapidly　in　the　stress　decay　(unloading)　stage.　As　the　cycle　number　increases　after　liquefaction　of　the　sample,　the　percentage　of　deviatoric　strain　in　the　flow　deformation　stage　to　the　total　unidirectional　shear　strain　increases,　while　the　percentage　in　stress　decay　(unloading)/hardening　stages　decreases,　which　means　that　the　strain　development　of　samples　is　more　fully　developed　in　the　flow　deformation　stage.　The　results　serve　as　a　reference　for　studying　soil　dilatancy　and　modifying　constitutive　models.