在研究建立三维应力空间土的本构关系数学模型过程中，作者给出了反映第三个应力独立变量洛德角θ影响的流动规则；再用承德中密砂进行了真三轴（σ1≠σ2≠σ3）试验；阐明了在π平面上屈服轨迹与破坏轨迹是相似的；从而提出：在常规三轴压缩试验所测定的本构关系的基础上，只要加做一个测定强度的三轴伸长试验就可建立土的三维弹塑性模型，不必另做其它复杂应力组合的试验了。作者又设计和进行了旁压仪模型试验；编制了轴对称有限元计算程序；将结果与用本文所建议的弹塑性模型和其它四种本构模型计算的结果比较；也用平面应变的试验成果对上述各种模型进行了比较验证；从这些比较研究得到一些有意义的结论，也显示了本文所建议的模型的一些特点。

In the course of study of the constitutive relationship of soils in three-dimensional stress space, a new expression of flow rule, with consideration of the influence of the third independent variable of stress, the Lode Angle θ, has been developed. Using medium dense “chengde” sand, a series of true triaxial tests withσ1≠σ2≠σ3 has been performed. Both test results and theoretical study have shown that on the π plane the yield loci and the failure locus are similar in shape. The above study leads to the conclusion that together with the constitutional relationship determined from the conventional triaxial test only an additional triaxial tension test to determine the strength of the soil needs to be performed the three-dimensional elastoplastic constitutive relationship of soils can be established, thus eliminating the necessity of using the complicated expensive true triaxial compression device for testing. The writer has prepared an axially symmetric Finite Element calculation program. By using the experimental data obtained from a model pressure meter testing device, comparative studies were mare made with the numerical results obtained from the elasto-plastic constitutional model suggested by the writer together with those from 4 other models suggested by various different writers. Similar studies with these 5 models were also made by using the plane strain test data thus far available. The above examination leads to significant conclusions on the relative merits of various models, and particularly on some merits of the model proposed by the writer.