统一黏塑性理论假设材料的应变仅由弹性应变和黏塑性应变组成。包含应力的黏塑性应变率表达方式，可以清晰地体现岩石材料应力增长率随应变加载速率相关的特性、在持续的偏压下的蠕变特性以及在恒定的应变下的松弛特性，但微分方程表示的本构模型在实际运用中存在计算上的困难。将无损伤Lemaitre统一黏塑性模型转换成关于应力的积分形式，并运用一致渐进展开算法得到其近似解，最后建立了基于近似解的牛顿迭代格式。开展了不同围压条件下泥质粉砂岩的三轴松弛试验，并将试验数据用于黏塑性模型的参数反分析，结果表明模型能够较好地反映泥质粉砂岩在长期作用下的力学行为特征。

Unified viscoplastic model hypothesizes material strain is divided into elastic part and viscoplastic part. Including stress part in its strain rate expression，that reflects the rock material characteristic of dependency of strength to loading rate, the characteristic of strain creep under continuous load and the characteristic of stress relaxation when with constant displacement. But showed the constitutive model of differential equations also result in difficulties in computation. Transformed the differential equations of constitutive model into integrated form, approximated the integrated form expressions by uniformly valid asymptotic expressions, and then the Newton-Raphson iteration pattern is established based on the approximate solution. A series of triaxial relaxation experiments is carrie out under different confining pressures, then based on the experiment data, a back analysis is made to get the parameters of the module. The results indicate that this model is able to describe the mechanical behavior characteristics of argillaceous siltstone under long-term loading.