混凝土渠道冻胀破坏机制与抗冻技术研究进展

在我国寒冷地区混凝土渠道破坏主要表现为冻胀破坏,如何防治混凝土渠道冻胀破坏成为一个非常现实的工程问题.随着混凝土渠道抗冻技术的发展,对这一问题的研究愈加深入.从土体冻胀机制、水分冻移机制及混凝土衬砌体冻胀破坏机制等方面较深入地分析了混凝土渠道冻胀破坏的机制,总结了我国近年来混凝土渠道冻胀力学模型和抗冻技术的前沿研究成果,并对目前研究工作中存在的不足进行了一定的评价,讨论了今后应进一步开展研究的若干问题,为我国寒区混凝土渠道的加固改造建设提供一定的参考价值.     

Snow and frost: implications for spatiotemporal infiltration patterns – a review

Vast regions of the northern hemisphere are exposed to snowfall and seasonal frost. This has large effects on spatiotemporal distribution of infiltration and groundwater recharge processes as well as on the fate of pollutants. Therefore, snow and frost need to be central inherent elements of risk assessment and management schemes. However, snow and frost are often neglected or treated summarily or in a simplistic way by groundwater modellers. Snow deposition is uneven, and the snow is likely to sublimate, be redistributed and partly melt during the winter influencing the mass and spatial distribution of snow storage available for infiltration, the presence of ice layers within and under the snowpack and, therefore, also the spatial distribution of depths and permeability of the soil frost. In steep terrain, snowmelt may travel downhill tens of metres in hours along snow layers. The permeability of frozen soil is mainly influenced by soil type, its water and organic matter content, and the timing of the first snow in relation to the timing of sub‐zero temperatures. The aim with this paper is to review the literature on snow and frost processes, modelling approaches with the purpose to visualize and emphasize the need to include these processes when modelling, managing and predicting groundwater recharge for areas exposed to seasonal snow and frost. Copyright © 2015 John Wiley & Sons, Ltd.     

冻土温度场的参数辨识

从冻土温度场的实际背景、物理现实及温度场的数值计算现状出发,阐述了参数辨识的重要性和必要性.以冬季开放的渠道为例,在原有温度场的基础上,利用参数之间的关系,给出了耦合温度场的数学模型.在此基础上首次建立方程中一些参数的分布控制模型,应用这些参量的连续性与变化的缓慢性,将问题分解,把在无穷维空间的辨识转化为有限维空间的辨识.论述了各子系统的解与参量的关系及优化辨识问题最优解的存在性,即可辨识性.     

一个基于行波解的冻结缘水流模型

在次级冻胀现象中,对处于已冻土和未冻土之间的冻结缘地带,研究其中的水分迁移是一个重要的课题.在已建立的次级冻胀数学模型的基础上,通过假设有行波解的存在,建立了一组新的方程和边界条件,就冰分凝和冻渗两种情况进行了讨论,并以试验数据为例,模拟了开放系统饱水土的入流量历时曲线.     

地基土冻胀的宏观分析

通过野外原位观测发现,在北半球自然气温条件下,地表裸露、原状均质、冻胀性地基土的冻结过程中,冻结速率越大越有利于土的冻胀,即冻结速率与冻胀速率呈单值升函数规律.     

季节冻土区公路路基细粒土冻胀敏感性研究

通过4种不同塑性细粒土料的室内闭式冻胀模拟试验,阐述了土的含水量、塑性、饱和度和密实度等因素对冻胀性的影响.在分别建立粘性土和粉土的η~(W-Wp)关系的基础上,综合分析并给出了细粒土的η~(W-Wp)关系.提供了典型土料的η~(W-Wp)~K_d~S_r关系图,提出了细粒土的η~(W-Wp)~K_d/S_r多元线性回归方程式.通过因子贡献率大小分析,指出超塑含水量(W-Wp)大小是影响细粒土冻胀敏感性的主导因素.     

Incident analyses of frost heaving failure of municipal underground gas pipelines in cold regions of northern China

In the cold regions of northern China, incidents of municipal underground gas pipeline rupture and leakage occur quite frequently, most often in winter. To prevent harm to citizen safety and property, analysis of the causes of such cracking and leakage is therefore valuable. Two incident analyses are discussed here and the reasons why most of these types of cases occur during winter are clarified. The effects of vehicle loadings above buried pipelines are calculated and compared with the effects and calculations of frost heaving forces. We demonstrate that when the soil layer above a pipeline freezes rapidly, the soil generates repeated frost heaving, which exerts heaving forces on the pipeline that can result in fatigue crack propagation and ultimate pipeline failure. Therefore, the incident induced by frost heaving is one of the primary reasons of gas pipeline failure. Based on these analyses, we present some recommendations pertaining to the proper design, construction, and management of gas pipelines.     

Frost heave modelling using porosity rate function

Frost‐susceptible soils are characterized by their sensitivity to freezing that is manifested in heaving of the ground surface. While significant contributions to explaining the nature of frost heave in soils were published in late 1920s, modelling efforts did not start until decades later. Several models describing the heaving process have been developed in the past, but none of them has been generally accepted as a tool in engineering applications. The approach explored in this paper is based on the concept of the porosity rate function dependent on two primary material parameters: the maximum rate, and the temperature at which the maximum rate occurs. The porosity rate is indicative of ice growth, and this growth is also dependent on the temperature gradient and the stress state in the freezing soil. The advantage of this approach over earlier models stems from a formulation consistent with continuum mechanics that makes it possible to generalize the model to arbitrary three‐dimensional processes, and use the standard numerical techniques in solving boundary value problems. The physical premise for the model is discussed first, and the development of the constitutive model is outlined. The model is implemented in a 2‐D finite element code, and the porosity rate function is calibrated and validated. Effectiveness of the model is then illustrated in an example of freezing of a vertical cut in frost‐susceptible soil. Copyright © 2006 John Wiley & Sons, Ltd.     

南极亚极地冰缘环境中分选环形成机制的观测与研究

南极亚极地冰缘环境中分选环边缘砾石砾径与其斜度坡度呈正相关,可用y=-5.0606+1.42828x表示。若砾径小于15厘米时符合y=-6.15778+1.56273x方程,大于15厘米时则符合v=-17.1913+1.97643x,说明当分选环边缘砾石砾径大于15厘米时摩擦阻力和砾石间结合力迅速增大。分选环中心表面小砾石运动具有周期性,总的位移是向边缘。中心表层冻胀力比深层大,中心冻胀强,向四周逐渐减小。体积较大的物体受冻胀力影响大。     

2018年春霜冻对江西省北部茶叶生产影响的定量评估

为探究江西省北部茶区春霜冻发生特点,深入开展茶叶春霜冻灾害定量评估工作,采用实地调查方式,获取江西省北部12个茶场2018年4月7—9日春霜冻的灾情资料和同期气象观测资料,采用加权求和法构建茶叶春霜冻灾害损失定量评估模型,对春霜冻灾害县进行灾害定量评估和检验。结果表明：婺源、浮梁等江西省北部茶叶主产县达到轻—重度春霜冻气象灾害等级,灾害指标等级计算结果与实地灾情调查结果较一致;轻度、中度、重度气象灾害等级的茶场减产率依次为10%—30%、30%—50%和50%以上;根据不同气象灾害等级的受灾面积及其减产率构建江西省北部茶叶春霜冻灾害损失定量评估模型,计算得到此次春霜冻灾害过程造成婺源县春茶直接经济损失为1.23亿元,模型评估结果和实际灾情相一致,模型能较为客观、准确的评估春霜冻灾害对茶叶生产造成的损失。