考虑D-P边界退化的冻风积土蠕变损伤规律研究

Study on Creep Damage Rule of Frozen Aeolian Soil Considering D-P Boundary Degradation

为研究季冻区冻风积土的蠕变变形规律及损伤演化规律,采用冻土GDS三轴测试分析系统开展了不同负温条件下三轴蠕变试验,分析了不同负温对冻风积土蠕变损伤特性的影响。根据典型蠕变曲线的三阶段特征提出了蠕变损伤时间阈值及屈服时间阈值确定方法。根据Kachanov对混凝土材料蠕变损伤的假设,对冻风积土的弹性模量及抗剪强度参数进行弱化,分析了不同负温条件下,不同蠕变损伤阶段冻风积土蠕变损伤规律。将西原模型中塑性元件改进成了具有损伤特征的非线性黏塑性体,并假设其服从于Drucker-Prager屈服准则,建立了冻风积土分阶段的蠕变损伤模型,将模型计算值与实测值进行比较,验证模型的合理性。研究结果表明:温度对冻风积土蠕变特征影响显著,温度低于-15℃时仅出现蠕变第I、II阶段,温度高于-10℃时会出现第III阶段,分阶段蠕变损伤模型可以较好地描述冻风积土在不同蠕变阶段损伤特征;屈服边界退化是导致冻风积土发生蠕变损伤的主要原因,发生蠕变损伤后会导致屈服边界不断缩小以及有效应力不断增加,塑性区的范围不断扩大,发生蠕变损伤后有效应力状态点会落在损伤后的屈服边界附近。

In order to study the rules of creep deformation and damage evolution of frozen aeolian soil in seasonal frozen area,the triaxial creep test under different negative temperature conditions is carried out by frozen soil GDS triaxial test and analysis system,and the influence of different negative temperatures on the creep damage characteristics of frozen aeolian soil is analyzed. A method for determining the creep damage time threshold and the yield time threshold is proposed according to the 3-stage characteristics of typical creep curve. Based on Kachanov’s hypothesis of creep damage to concrete materials,the elastic modulus and the shear strength parameters of frozen aeolian soil are weakened. The creep damage rules of frozen aeolian soil in different creep damage stages under different negative temperature conditions are analyzed. The plastic element in the Nishhara model is improved to a nonlinear viscoplastic body with damage characteristics,andit is assumed that it obeys the Drucker-Prager yield criterion,a staged creep damage model of frozen aeolian soil is established,and the model calculated value is compared with the measured value,thus the rationality of the model is verified. The result shows that( 1) temperature has significant effect on the creep characteristics of frozen aeolian soil,the Ⅰ and Ⅱ stages of creep will occur only when the temperature is lower than-15 ℃,the Ⅲ phase will occur when temperature is higher than-10 ℃,the staged model can describe the damage characteristics of frozen aeolian soil in different creep stages;( 2) the degradation of yield boundary is the main reason for creep damage of frozen aeolian soil,creep damage will cause the yield boundary shrinking,effective stress increasing,and the continues expansion of plastic zone range,the effective stress point will fall on the position near the damaged yield boundary.