The　peak　shear　strength　rules　of　transversely　isotropic　soils　are　stress　state　dependent　and　dependent　on　relative　orientation　between　bedding　plane　and　principal　stress.　Accordingly,　the　shear　strength　of　transversely　isotropic　soils　exhibits　two　primary　characteristics:　(a)　the　strength　curve　on　the　deviatoric　plane　is　asymmetrical　with　respect　to　three　principal　stress　axes;　(b)　the　shear　strength　changes　with　the　direction　angle　of　the　bedding　plane　when　the　intermediate　principal　stress　coefficient　is　a　constant.　In　this　paper,　the　mobilised　plane　is　introduced　and　used　to　reveal　the　failure　mechanism　of　soils.　By　projecting　the　microstructure　tensor　of　transversely　isotropic　soils　onto　the　normal　of　the　mobilised　plane,　the　directionality　of　the　transversely　isotropic　soils　is　introduced　into　the　friction　rules　on　the　mobilised　plane,　and　a　transversely　isotropic　strength　parameter　is　proposed.　The　proposed　strength　parameter　can　extend　isotropic　strength　criteria　into　transversely　isotropic　strength　criteria.　This　mobilised　plane　approach　is　used　to　establish　a　novel　transversely　isotropic　non-linear　unified　strength　criterion　(TI-NUSC).　The　difficulty　in　establishing　a　unified　description　of　the　asymmetrical　strength　curve　and　its　evolution　with　direction　angle　is　overcome　by　the　established　criterion.　Comparisons　between　available　test　results　and　the　TI-NUSC　show　that　the　TI-NUSC　can　successfully　describe　these　two　primary　peak　strength　characteristics.