基于应变空间硅藻质软岩的软化本构模型

三轴试验结果表明，软岩具有显著的应变软化特征。正常固结软岩表现为峰值后较缓的软化特征，而超固结软岩峰值强度后的应力-应变曲线呈陡降软化特征。应变空间表述的弹塑性理论在解决大应变和软化问题时比应力空间表述的弹塑性理论更具有优越性。基于应变空间的基本的弹塑性本构方程式，采用Mises剪切屈服准则及相关联流动法则，导出固结不排水三轴条件下的应力-应变本构关系式，并采用不同的硬化函数表达式对软岩在不同围压下的应力-应变曲线进行数值模拟。结果表明，应变空间的弹塑性理论能较好地模拟软岩应变软化特征，其中硬化函数的确定是关键问题之一。通过研究，提出了用于固结不排水状态下正常固结软岩的硬化函数形式。

Study on softening constitutive model of diatomaceous soft rock based on strain space

The result of triaxial test shows that soft rock has notable strain softening characteristic, and the stress-strain curves present different types in the normally consolidated field and over-consolidated field, in normal consolidated field the softening degree of soft rock is slight relatively; but in over consolidated field, when axial stress corhes to peak value, the softening speed increases rapidly with the increasing of strain. In order to simulate the stress-strain curves of this soft rock, the constitutive equation of consolidated undrained triaxial stress state expressed in strain space is deduced. This constitutive equation is used to simulate the stress-strain curves of soft rock, and in simulation different hardening functions, including a new proposed one, are applied. The simulation result shows good agreement with test result. It demonstrates that constitutive model established in strain space has good ability to describe the strain softening; and the new hardening function shows good applicability for normal consolidated Soft rock under consolidated undrained state.