| 摘要: |
| 【目的】研究冻融作用下土的物理力学性质的变化，构建一种同时考虑荷载效应和冻融循环的损伤模型，为预测冻土地基反复冻融作用下的沉降变形提供理论基础。【方法】以青藏铁路沿线常见的粉质黏土为研究对象，制备了20组同一目标含水量（16%）和干容重（1.30 g/cm3）的重塑试样，开展了3种正压力（100，200和300 kPa）下的直接剪切试验，剪切变形速率控制为0.8 mm/min。以粉质黏土的抗剪强度数据为基础，采用3种常用的分布函数（正态分布、对数正态分布和Weibull分布），分析了粉质黏土的抗剪强度分布特征。之后基于Weibull概率密度函数和Lemaitre等效应力原理,推导出三维应力条件下冻土的本构关系；采用Drucker Prager强度准则反映荷载所致土结构损伤，并选取冻融数次后弹性模量描述冻融循环所致结构损伤，最后提出了一种同时考虑冻融作用和荷载效应的损伤变量，并嵌入冻土损伤本构关系，构建了损伤模型。采用冻融试验数据和三轴剪切试验数据，验证该模型的合理性。【结果】相比于正态分布和对数正态分布，粉质黏土的强度数据更符合Weibull分布规律，曲线吻合程度和最大偏差均最小。验证试验结果表明，构建的损伤模型的计算结果与试验结果的相关系数均高于0.70，说明该模型能够较好地描述粉质黏土冻融数次后的应力应变特征。【结论】成功构建了一种同时考虑荷载效应和冻融作用的损伤模型，这为统计损伤本构关系的研究和有效的工程应用提供了参考依据。 |
| 关键词: 粉质黏土 冻融 本构关系 统计损伤 Weibull分布 |
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| 基金项目:国家自然科学基金项目（51408486,41572268）；北京市属高等学校高层次人才引进与培养计划项目（CIT&TCD20150101） |
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| Statistical damage constitutive model for silty clay after freeze-thaw cycling |
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WANG Songhe,LIU Fengyin,QI Jilin
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| Abstract: |
| 【Objective】The physical and mechanical properties of soils after freeze-thaw cycling were studied and a constitutive model was built to provide theoretical basis for better predicting settlement of permafrost foundations after cyclic freeze-thaw.【Method】This study investigated the frequently encountered silty clay along Qinghai-Tibet railway.Twenty remolded samples with identical target water content (16%) and dry unit density (1.30 g/cm3) were produced and used in direct shear tests under three normal stresses (100,200 and 300 kPa),with a shear rate of 0.8 mm/min.Based on the shear strength data of silty clay,the statistical strength characteristics were investigated by comparing three typical statistical distributions including the normal distribution,lognormal distribution and Weibull distribution.The constitutive equation for frozen soils at triaxial conditions was deduced based on a Weibull probability density function and Lemaitre equivalent stress principle.A statistical damage variable incorporating a Drucker-Prager strength criterion was suggested for load-induced structural damage of silty clay while the variation in the elastic modulus was taken as the damage variable for freeze-thaw induced damage.After coupling the two damage variables,a statistical damage constitutive model was proposed for silty clay.The reasonability of the constitutive equation was verified by a series of laboratory freeze-thaw tests and conventional triaxial tests on silty clay.【Result】The Weibull distribution was more suitable for the strength of silty clay compared with the normal and the lognormal distributions and the predicted curve fit well with test data and the maximum deviation was relatively small.The calculated stress strain curves agreed in general with test data with correlation coefficient of >0.7.【Conclusion】A damage constitutive model was proposed by considering both the loading and freeze-thaw effects to provide guidance for further study on statistical damage constitutive model and the effective application in engineering. |
| Key words: silty clay freeze-thaw constitutive model statistical damage Weibull distribution |
