In cold regions, the strength and deformation characteristics of frozen soil change over time, displaying different mechanical properties than those of conventional soils. This often results in issues such as ground settlement and deformation. To analyze the rheological characteristics of frozen soil in cold regions, this study conducted triaxial creep tests under various creep deviatoric stresses and established a corresponding Discrete Element Method (DEM) model to examine the micromechanical properties during the creep process of frozen clay. Additionally, the Burgers creep constitutive model was used to theoretically validate the creep deformation test curves. The research findings indicated that frozen clay primarily exhibited attenuated creep behavior. Under low confining pressure and relatively high creep deviatoric stress, non-attenuated creep was more likely to occur. The theoretical model demonstrated good fitting performance, indicating that the Burgers model could effectively describe and predict the creep deformation characteristics of frozen clay. Through discrete element numerical simulations, it was observed that with the increase in axial displacement, particle displacement mainly occurs at both ends of the specimen. Additionally, with the increase in creep deviatoric stress, the specimen exhibits different deformation characteristics, transitioning from volumetric contraction to expansion. At the same time, the vertical contact force chains gradually increase, the trend of particle sliding becomes more pronounced, and internal damage in the specimen progresses from the ends toward the middle.

Upon completing large-area layered filling, the foundation soil exhibits transverse isotropy and is predominantly. unsaturated, making post-construction settlement prediction challenging. Additionally, the creep model considering transverse isotropy and unsaturated characteristics has not been proposed. Therefore, the true triaxial apparatus for unsaturated soil was enhanced, and transversely isotropic unsaturated loess samples were prepared. The relationship between matrix suction and moisture content at various depths in transversely isotropic unsaturated loess was determined using soil-water characteristic curve tests. The creep characteristics of loess fill under varying moisture content, degree of compaction, deviatoric stress, and net confining pressure were examined using a consolidation drainage test system. According to the creep curve, the expressions for six parameters in the modified Burgers element model were determined, establishing a post-construction settlement prediction method for transversely isotropic unsaturated loess fill foundations. The results show that the transversely isotropic unsaturated loess exhibits distinet creep characteristics, primarily nonlinear attenuation creep. The degree of compaction, moisture content, deviatoric stress and net confining pressure significantly affect its creep characteristics. Creep stability strain is linearly related to the degree of compaction. Enhancing soil compaction can effectively reduce post-construction settlement of the fill foundation. A prediction algorithm based on the modified Burgers model, which reflects the influence of degree of compaction, moisture content, and stress level, and accurately describes the post-construction settlement behavior of transversely isotropic unsaturated loess fill foundations, is established. Actual engineering monitoring results demonstrate that the proposed settlement prediction algorithm is simple, practical, and effective. The research results can enrich and advance the creep model of unsaturated soil, and provide a scientific basis for solving the problem of deformation calculation of high fill foundation.

Numerous incidents and failures of bank slopes are caused by the creep behavior of sliding zone soil. During reservoir regulation, the pore water pressure in the sliding zone undergoes cyclic changes. Under such complex cyclic hydraulic conditions, the creep behavior may differ from that under the monotonic seepage condition, which is still poorly understood. In this paper, the Majiagou landslide in the Three Gorges Reservoir area is taken as a case study. Triaxial creep tests were first carried out to study the creep behavior of the sliding zone soil specimen under cyclic seepage pressure. Then, the nonlinear Burgers creep model was proposed to characterize the observed creep behavior of the sliding zone soil specimen, and the secondary development was performed based on FLAC3D software. Finally, the proposed model was applied to the Majiagou landslide to simulate its deformation under fluctuating reservoir water levels. The following results were obtained: (1) Under low deviatoric stress levels, cyclic seepage pressure causes the creep strain curve to fluctuate significantly. The decrease of seepage pressure leads to a reduction in pore pressure, resulting in a sharp increase in the strain rate of sliding zone soil. (2) The proposed model can well reflect the creep characteristics of sliding zone soil under cyclic seepage pressure. (3) During reservoir operation, the landslide deformation exhibits a step-like growth, and the proposed creep model can effectively simulate the retrogressive deformation characteristics of the Majiagou landslide. The research results provide the theoretical basis for the long-term stability of reservoir landslides under fluctuating water levels.

为探究人工冻结黏土的单轴蠕变试验及其蠕变本构模型，对人工冻结黏土进行室内试验，对不同冻结温度下的试验结果进行对比分析。基于分析结果，在常规模型的基础上进行改良，推导得出弹性模量、黏滞系数等参数值，建立有关时间、应力与温度的冻土蠕变本构方程。根据结果分析可见，随冻结温度降低，抗压强度越高，冻土蠕变变形越小；对于改良的本构模型，通过对比理论值与实际值可知，蠕变发生至最终阶段时，模型计算值大于试验值，这对于实际工程是偏安全的，故所建立的本构模型具有一定物理意义，且在实际工程中具有可行性。

The soil's creep characteristics significantly impact both the effectiveness of the support system and the enduring stability of the engineering structure. During construction, dewatering is often carried out, which results in seepage within highly permeable soils. To scrutinize the creep behavior of silty fine sand under seepage conditions, triaxial compression tests and triaxial creep tests were conducted on the silty fine sand, subject to three distinct seepage flow rates: 0.5 ml/min, 1.0 ml/min, and 1.5 ml/min. The test results indicate that seepage reduces the maximum stress capacity of the soil and increases its creep deformation. Particularly under relatively high deviatoric stress and seepage flow rates, the specimens exhibit three stages: transient creep, stationary creep, and acceleration creep. Notably, the axial creep deformation rate shows a positive correlation with both seepage flow rates and deviatoric stress. Concurrently influenced by seepage and creep, fine particles within the specimen accumulate in the central and upper regions, whereas the lower is characterized by larger particles. The progressive increase in pore water pressure, intricately linked to the impeding effect of fine particles on permeation pathways, catalyzes the creep-induced deformation of the specimen. Based on the experimental results, a modified Burgers model has been established. This model takes into account seepage, sliding damage, and particle fragmentation. A comparative analysis, contrasting the modified Burgers model against calculated values derived from the traditional Burgers and Kelvin-Voigt models, underscores the effectiveness of the proposed model. Specifically, the modified Burgers model adeptly captures the transient creep, stationary creep, and acceleration creep stages of silty fine sand, especially under varying seepage flow rates.

Freeze-thaw cycles (FTC) cause significant changes in the physical and mechanical properties of soil, leading to structural alterations that can seriously threaten the safety and longevity of engineering structures. To investigate the consolidation characteristics of soils subjected to FTC, 18 sets of consolidation compression tests were carried out with saturated clay. Using a modified consolidation apparatus, the changes in pore-water pressure (PWP) and strain during consolidation were measured, with a focus on the effects of dry density and the number of FTC. The results show that although the overall patterns of PWP and strain during consolidation are similar before and after FTC, variations in dry density and the number of FTC lead to significant differences in the measured values. Specifically, PWP decreases while soil deformation increases with an increasing number of FTC cycles, even across different dry density conditions. The most pronounced changes in PWP and strain occur during the first 1-3 FTC cycles, with some samples showing continued significant changes up to 3-5 cycles. However, beyond five FTC, the increments in PWP and strain become considerably smaller. Meanwhile, an approximate linear relationship was observed between the peak PWP and steady-state strain values during graded loading, with this linearity decreasing as dry density increases. In addition, the Burgers model was modified based on the measured dissipation pattern of PWP to overcome the shortcomings of the traditional Burgers model. The modified Burgers model provides a more accurate representation of the soil's deformation process following FTC compared to the traditional model. This study can provide theoretical guidance for predicting the deformation of soils after freeze-thaw cycles.

Establishment of a creep model is an important method to analyze the relationship between soil creep deformation and time, and the element model is widely used for studying soil creep. However, the element creep model is employed for fitting saturated soil, and the mechanical element model is generally linear, which cannot well fit the nonlinear deformation of the soil with time in practice. The creep process of the soil is not only time-dependent, but also related to the deviatoric stress level. Therefore, the fractional calculus theory and a parameter n reflecting the effect of deviatoric stress level on the creep properties of the soil were introduced into the element model, and the fractional qBurgers creep model was established by using the fractional Koeller dashpot and Caputo fractional calculus. The proposed model was used to fit the triaxial test data of reticulated red clay under different net confining pressures and matric suctions by unsaturated triaxial apparatus. The proposed model can well describe the nonlinearity of unsaturated reticulated red clay, has memory and global correlation to the creep development process of unsaturated reticulated red clay, and has clear physical meaning. The functional relationships of the model parameters with the matric suction, net confining pressure and deviatoric stress level were deduced, so that the creep curves of unsaturated reticulated red clay can be obtained for any conditions, which is of great value for the study of unsaturated soils. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

为了研究高温冻土蠕变变形特征以及各影响因素对蠕变的作用,分别在含水量15%、25%及35%,荷载100kPa、200kPa及300kPa,温度-1.5℃、-0.7℃及-0.3℃的条件下开展了室内单轴蠕变试验,分析在无侧限条件下高温冻土在不同温度、荷载及含冰量条件下的蠕变变形特性。结果表明:在当前试验条件下,冻土蠕变变形非常可观,且蠕变曲线都没有出现渐进流阶段;温度是影响冻土蠕变的最重要的外在因素,而含冰量是影响冻土蠕变的关键内在因素;在高含冰量条件下温度及荷载的改变对蠕变速率的影响非常显著,甚至引起量级上的差别。在现有试验条件下,高温冻土蠕变过程可利用Burgers黏弹性模型来较好地描述。

应用连续介质的混合物理论研究了饱和正冻土中的水热迁移问题。主要结果有：①提出了正冻土中层冰形成的一个判别法则；②将水热迁移问题化为含可动边界的非线性Ｂｕｒｇｅｒｓ方程，为研究冻土水热迁移的非线性效应提供了一个理论上的出发点。

在连续统力学的混合物理论框架下研究了冻土的力学 热学性质 ,建立了相应的本构关系 .以此为基础 ,首先给出了层冰形成的一个判别准则 ,研究了孔隙率对冻胀量的影响 ,所得规律能很好地解释已有试验结果 .其次 ,推导出控制冻土水热迁移过程的场方程为具有可动边界的非线性Burgers型方程 ,这一发现为研究土体冻结过程中的非线性效应提供了理论基础 .