The unified strength theory is a new theory system which can almost describe the strength characters of most geomaterials and has been applied widely. And FLAC3D is an excellent geotechnical program. If the former can be integrated in the later

many complex problems in engineering will be settled well. So according to this problem

the numerical scheme of elastoplastic unified constitutive model in FLAC3D was studied. And the numerical format of the elastoplastic constitutive model based on the unified strength theory was derived. The corresponding UDM interface codes were programmed. Finally

a circle tunnel case is analyzed using this program. The corresponding simulated results are presented and compared with the analytic solution. The comparison expresses a good agreement with the analytic solution and verifies the validity of the numerical scheme and the codes. The merits of the unified strength theory and the FLAC3D program will be utilized well in geo-engineering after their combination.