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季节性温度边界条件下高含冰量冻土路基融化固结特性
杨高升, 毛海涛, 陈文轩, 陈佩佩, 兰晓玲
raybet体育在线 院报 ›› 2025, Vol. 42 ›› Issue (7) : 142-149.
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季节性温度边界条件下高含冰量冻土路基融化固结特性
Thaw Consolidation Characteristics of High-Ice-Content Frozen Soil Subgrade under Seasonal Temperature Boundary Conditions
为了研究季节性温度边界条件对冻土路基融化固结特性的影响,对三维非线性大变形融化固结理论进行修正,引入季节性温度边界条件,并采用摩尔-库伦准则描述土体融化后进入塑性阶段的沉降,建立了能够考虑季节性温度边界条件影响的三维非线性塑性融化固结理论模型。在此基础上,采用FLAC3D软件对所建理论模型进行数值实现,并以青藏公路某段高含冰量路基为例,分析了其在季节性温度边界条件下的融化固结规律,最后结合实测数据验证了所建理论模型的有效性。研究结果表明,冻土路基的沉降随着地表温度的季节性变化而呈现出周期性的变化规律,这是季节性温度边界条件下冻土路基融化固结规律的最显著特征。在路基土体自重长期作用下,其垂直有效应力的分布范围会随时间逐渐扩展。通过对固结过程中孔隙水压力分布的研究发现,路基浅层融化区域内的孔隙水在运营初期已经消散,而在之后长时间的运营过程中,冻土路基融化沉降的持续发展主要是由于融化锋面处新融化的孔隙水的消散。
[Objective] Under the influence of climate change and engineering activities, the thermodynamic stability of subgrade engineering in permafrost regions faces severe challenges. To investigate the influence of seasonal temperature boundary conditions on the thaw consolidation characteristics of frozen soil subgrade, this study modifies the three-dimensional nonlinear large-deformation melting-thaw consolidation theory. [Methods] By introducing seasonal temperature boundary conditions and using the Mohr-Coulomb criterion to describe the plastic settlement deformation of thawed soil, a three-dimensional nonlinear plastic thaw consolidation theory incorporating seasonal temperature effects was developed. The theoretical model was numerically implemented using the FLAC3D simulation platform. Taking a typical high ice-content frozen soil subgrade section of the Qinghai-Tibet Highway as the research object, the thaw consolidation evolution patterns under seasonal temperature boundary conditions were systematically analyzed. The validity of the theoretical model was verified through comparison with field-measured data. [Results] The results showed that the settlement deformation of the frozen soil subgrade exhibited a periodic variation pattern with seasonal surface temperature changes, representing the most significant characteristic of thaw consolidation under seasonal temperature boundary conditions. Due to self-weight of subgrade soil, the distribution scope of vertical effective stress expanded with time. The calculation model considering plastic deformation demonstrated higher prediction accuracy. As plastic deformation accumulated continuously during thaw consolidation, its effect could not be neglected in long-term deformation predictions for high-ice-content frozen soil engineering. Through the study of the pore water pressure distribution during the consolidation process, it was found that the pore water in the shallow thawed area of the subgrade dissipated during initial operation. In the subsequent long-term operation, the continuous development of the thaw and settlement of frozen soil subgrade primarily resulted from the dissipation of the newly thawed pore water at the thaw front. [Conclusion] The improved theoretical model proposed in this study can more reasonably describe the thaw consolidation characteristics of high-ice-content frozen soil subgrades under seasonal temperature boundary conditions, providing a critical theoretical basis for the design and maintenance of subgrade engineering in frozen soil regions.
冻土路基 / 融化固结规律 / 季节性温度边界条件 / 非线性塑性 / 应力分布 / 孔隙水压力分布
frozen soil subgrade / thaw consolidation law / seasonal temperature boundary conditions / nonlinear plasticity / stress distribution / pore water pressure distribution
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为解决融化期季冻区边坡失稳问题，针对川西高原地区混合土边坡，综合考虑粗颗粒含量及含水率影响，采用大型直剪与常规直剪相结合的试验方案，获取混合土抗剪强度参数，基于冻土水热耦合理论，通过COMSOL有限元软件对边坡融雪入渗过程进行数值模拟，分析边坡水热场时空变化规律，同时考虑冻融过程中土体强度参数动态改变建立季冻区混合土边坡稳定性计算分析模型，分析融化期混合土边坡稳定系数、滑动面发展规律，定量分析总结融化期季冻区边坡失稳机理。结果表明：相同干密度条件下，混合土饱和渗透系数与粗颗粒含量成正比，抗剪强度与粗颗粒含量成正比而与含水率成反比；融化期边坡融雪入渗作用加强，浅层土体处于富水状态，形成最大厚度0.80 m的暂态饱和区；川西季冻区混合土边坡潜在滑动面与冻融交界面位置基本一致，滑动面形式主要是折线型，为浅层滑动；融雪入渗与冻土消融作用是季冻区边坡融化期失稳破坏的主要诱因，融化期间边坡稳定性系数减小速率随融雪入渗过程逐渐加快，融化深度最大时，边坡稳定性系数最小；川西地区季节冻土边坡稳定性主要影响因素为粗颗粒含量与初始含水率，粗颗粒含量越高，初始含水率越低，融化期边坡稳定性越好。
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Slope instability is an important issue in seasonally frozen soil slopes. This study investigates mixed soil slopes in the seasonally frozen soil region of Western Sichuan to effectively address the issue of slope instability. Small and large direct shear tests were carried out to assess the effect of the percentage of coarse particles and moisture content on the shear strength parameters of the mixed soil samples. The slope snowmelt infiltration process was numerically simulated using COMSOL finite element software according to the unsaturated soil moisture-heat migration law. Simultaneously, a calculation model that considers the soil strength parameters for the stability of mixed soil slopes was established. The stability coefficient of the mixed soil slopes and sliding surface progress principle were then analyzed, and the slope instability mechanism in the seasonal freezing area during the thawing period was also quantitatively assessed and summarized. From this work, the following findings were obtained: ① under identical conditions of dry density, the permeability coefficient of mixed soil increases as the coarse particle content rises; ② shear strength is directly proportional to the coarse particle content and inversely proportional to the water content; ③ during the period of thawing, slope snowmelt infiltration increases, resulting in a sharp rise in the water content of the shallow soil and the formation of a temporary saturation zone with a thickness of approximately 0.80 m; ④ the potential sliding surface of a mixed soil slope is identical to the location of the freeze-thaw interface, corresponding to shallow slope collapse; ⑤ the main factors contributing to the shallow slope collapse during the thawing season in seasonally frozen areas are snow infiltration and the melting of frozen soil; ⑥ the rate at which the slope stability coefficient decreases during the thawing period is gradually accelerated by the snow infiltration process, and it reaches its lowest value when the thawing depth is the greatest; and ⑦ the coarse particle content and initial water content are the primary factors influencing the stability of seasonally frozen slopes. In summary, it was observed that the higher the soil coarse particle content, the lower the initial water content becomes, which is better for the overall stability of the slope during the thawing period.
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The heat-moisture exchange between atmosphere and ground is very complex. The exchange occurring the adherent layer on ground is just such a complex phenomenon. We have developed an equation which directly relates air temperature to ground temperature at the bottom of adherent layer. As a result, adherent layer should not be taken into consideration in the calculation of heat exchange, which makes easier to determine the upper heat boundary of the calculation. In this paper, we theoratically propose the approximate solutions to various basic parameters and reveal the physical meaning of the observed data obtained for a long time.
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于景飞, 张文月, 李明浩. 季节性冻土区铁路路基冻融变形规律[J]. raybet体育在线
院报, 2020, 37(5):133-138.
为探究冻融循环作用对季节性冻土区铁路路基变形特性的影响,以兰新铁路的路基填土为研究对象进行冻融循环试验和固结压缩试验,得到了冻融变形和压缩特性的变化规律,并利用正交试验对压缩特性的影响因素进行显著性分析。试验结果表明:随着冻融循环次数的增加,冻胀率和融沉系数均呈多项式函数增加;在相同冻融循环次数下,两者均与含水率呈正相关,与压实度呈负相关。压缩模量随冻融循环次数的增加先增加,最终趋于稳定,各因素及其交互作用对压缩模量的影响从高到低依次为压实度B、含水率C、冻融循环次数A、B和C的交互作用BC、A和B的交互作用AB、A和C的交互作用AC。建议选取9次冻融循环后的压缩模量作为兰新铁路路基强度设计值,该研究成果对防治冻胀融沉和控制路基变形具有一定的指导意义。
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In order to explore the influence of cyclic freezing and thawing on the deformation characteristics of railway subgrade in seasonal frozen soil region, we performed freeze-thaw cycle test and consolidation compression test on the roadbed filling of Lanzhou-Xinjiang Railway as the research object. Through the tests we obtained the regularities of railway subgrade deformation caused by freeze-thaw cycles and compression characteristics. Moreover, we analyzed the influencing factors of compression characteristics by significance test via orthogonal analysis. Results revealed that the frost heave rate and the melting subsidence coefficient both increased in a power function with the increase of the number of freeze-thaw cycles, and both were positively correlated with water content and negatively correlated with compaction degree at the same freeze-thaw cycle. The compressive modulus of subgrade soil increased at first and then stabilized with the proceedings of cyclic freezing and thawing. The compaction degree (B) had the largest influence on compressive modulus, followed by water content (C), freeze-thaw cycle (A), the interaction between B and C, the interaction between A and B, and the interaction between A and C in sequence. We recommend choosing the compression modulus after nine freeze-thaw cycles as the design value of the road strength of Lanzhou-Xinjiang Railway. The research finding is of guiding significance for the prevention and control of frost heaving and subsidence of railway subgrade.
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