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《寒旱区科学》2021年第二期——国际冻土大会专刊

已有 244 次阅读 2021-6-30 14:50 |系统分类:论文交流


0077−0086  Artificially frozen ground and related engineering technology in Japan … Satoshi Akagawa

Abstract: Since the 1970's, frozen ground has been developing near the Tokyo Bay area around liquefied natural gas (LNG) in-ground storage tanks. For disaster prevention purposes, the tanks are constructed below the ground surface. Since the temperature of the liquid stored in the tanks is −162 °C the soil surrounding the tanks freezes. Since this frozen ground has existed for almost half a century, we have permafrost near Tokyo. The development of artificial frozen ground may cause frost heaving, resulting in frost heave forces that may cause structural damage of adjacent LNG in-ground storage tanks. Therefore, the demand for frozen ground engineering increased and consequently we now have advanced technology in this area. Fortunately, we use this engineering technology and artificial ground freezing for civil engineering, especially in big and crowded cities like Tokyo. This paper provides a summary of the testing apparatus, test methods, and assessment methods for frost heaving.

 

日本人工冻土及相关工程技术  Satoshi Akagawa

二十世纪七十年代以来,东京湾附近的液化天然气(LNG)地下储罐周围一直在发育冻土。出于防灾目的,这些储罐都修建于地下。由于储存在储罐中的液体温度为−162 °C,因此储罐周围的土体处于冻结状态。由于这些冻结土层已经赋存了半个世纪之久,因此我们可以说在东京附近居然也发育出了“多年冻土”!但是,人工冻土发育所引起的冻胀力可能对邻近液化天然气地下储罐结构造成破坏。冻土工程建设的需求推动了相关领域先进技术的发展。我们也在土木工程领域应用了人工冻结技术,尤其是在东京这样拥挤的大城市中实现了成功应用。本文对冻胀相关的测试设备及测试和评估方法进行了总结。

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0087−0094  Frost susceptibility of soils―A confusing concept that can misguide geotechnical design in cold regions … DaiChao Sheng

 

Abstract: Frost susceptibility is a concept widely used in cold region geotechnical design, to quantify the capacity of a soil in generating frost heave and frost damage. The laboratory test used to verify frost susceptibility of a soil is based on the measurement of frost heave generated in the soil under specific conditions. In reality this concept is, however, more related to the soil's potential to thaw weakening than to frost heave. Recent experimental studies show that frost non-susceptible soils like clean sand and clean gavel can also generate much ice segregation and frost heave if the conditions are favourable, hence challenging the usefulness and suitability of soil classification based on frost susceptibility. It is further shown that the concept is not suitable for design scenarios where frost heave itself is a serious hazard, such as in high-speed rail embankments.

 

是时候考虑放弃使用土冻胀敏感性分类了  盛岱超

土冻胀敏感性分类在寒区岩土工程中广泛用来衡量土体产生冻胀的能力。冻胀敏感性在室内试验条件下主要基于土试样产生的冻胀量;而在野外条件下主要反映融沉弱化冻害程度,并非冻胀量大小。所谓冻胀敏感性土,其细粒含量高渗透系数低,在冻土融解时超孔隙水不易消散,进而导致融沉弱化;而含冰砾石层融解时渗透系数大,通常不会产生超孔隙水压或融沉弱化。近期试验清楚表明,非冻胀敏感性土体,如干燥纯净砂或砾石,在一定条件下同样可以产生冰富集和冻胀;这些试验结果严重挑战土冻胀敏感性分类的适用性,特别是当冻胀本身是一种冻害时。在高铁路基里,冻胀影响列车平稳运行,土冻胀敏感性分类此时已经不再适用。

0095−0106  Laboratory study and predictive modeling for thaw subsidence in deep permafrost … ZhaoHui Joey Yang, Gabriel T. Pierce

 

Abstract: Oil wells on the North Slope of Alaska pass through deep deposits of permafrost. The heat transferred during their operation causes localized thawing, resulting in ground subsidence adjacent to the well casings. This subsidence has a damaging effect, causing the casings to compress, deform, and potentially fail. This paper presents the results of a laboratory study of the thaw consolidation strain of deep permafrost and its predictive modeling. Tests were performed to determine strains due to thaw and post-thaw loading, as well as soil index properties. Results, together with data from an earlier testing program, were used to produce empirical models for predicting strains and ground subsidence. Four distinct strain cases were analyzed with three models by multiple regression analyses, and the best-fitting model was selected for each case. Models were further compared in a ground subsidence prediction using a shared subsurface profile. Laboratory results indicate that strains due to thaw and post-thaw testing in deep core permafrost are insensitive to depth and are more strongly influenced by stress redistributions and the presence of ice lenses and inclusions. Modeling results show that the most statistically valid and useful models were those constructed using moisture content, porosity, and degree of saturation. The applicability of these models was validated by comparison with results from Finite Element modeling.

 

深层多年冻土融沉的试验研究和预测模型  杨朝晖,Gabriel T. Pierce

在阿拉斯加北坡建造的油井需要穿越深层多年冻土。石油生产过程的油-井热交换必然会导致井周冻土融化,进而产生井壁周边地面沉降,增加壁压应力,产生过大变形,甚至破坏。本文描述一个冻土融沉固结试验装置、参数实验结果并提出预测模型。首先利用天然多年冻土样品通过融沉固结试验获得融沉应变和土力学物理参数。然后利用实验数据以及文献中的历史数据进行多参数回归分析提出经验模型并运用于地面沉降预测。预测结果与现场观测数据及有限元模型数据吻合良好。研究表明,对于深层冻土融沉应变预测,最重要的参数包括水含量、空隙率和冰饱和度。


0107−0122  Permafrost distribution and temperature in the Elkon Horst, Russia … Mikhail Zhelezniak, QingBai Wu, Anatolii Kirillin, Zhi Wen, Aleksandr Zhirkov, Vladimir Zhizhin

 

Abstract: The Elkon Horst is a geological structure that consists of heterogeneous strata with highly variable geocryological and temperature conditions. Gaining accurate knowledge of permafrost distribution patterns within this structure is of both scientific and practical importance. In mountainous terrain, the ground thermal regime is controlled by both surface and subsurface conditions. Surface conditions include snow cover characteristics, the presence or absence of vegetation, vegetation density, etc.. In contrast, subsurface conditions involve rock lithology or petrography, density, quantity and depth of fissures, groundwater, etc.. This article examines ground thermal regimes in various geomorphological settings based on temperature measurement data from geotechnical boreholes. The occurrence and extent of permafrost were evaluated for the entire horst area using direct and indirect methods. The maximum permafrost thickness measured in the Elkon Horst is 330 m, and the estimated maximum is 450 m at higher elevations. Thermophysical properties were determined for the major rock types, and the geothermal heat flux was estimated for the study area. The thermal conductivities were found to vary from 1.47 to 4.20 W/(m·K), and the dry bulk densities to range between 2,236 kg/m3 and 3,235 kg/m3. The average geothermal heat flux was estimated to be 44 mW/m2.

0123−0132  A full-scale field experiment to study the thermal-deformation process of widening highway embankments in permafrost regions … ShuangJie Wang, Long Jin, Kun Yuan, DongGen Chen, JinPing Li, Yi Song

 

Abstract: As one of the widely used upgrading way in road engineering, the widening embankment (WE) has suffered evident differential deformation, which is even severer for highway in permafrost regions due to the temperature sensitivity of frozen soil and the heat absorption effect of the asphalt pavement. Given this issue, a full-scale experimental highway of WE was performed along the Qinghai-Tibet Highway (QTH) to investigate the differential deformation features and its developing law. The continuous three years' monitoring data taken from the experimental site, including the ground temperature and the layered deformation of WE and original embankment (OE), were used to analyze the thermal-deformation process. The results indicate that the widening part presented the remarkable thermal disturbance to the existing embankment (EE). The underlying permafrost was in a noteworthy degradation state, embodying the apparent decrease of the permafrost table and the increase of the ground temperature. Correspondingly, the heat disruption induced by widening led to a much higher deformation at the widening side compared to the original embankment, showing a periodic stepwise curve. Specifically, the deformation mainly occurred in the junction of the EE and the widening part, most of which was caused by the thawing consolidation near the original permafrost table. In contrast, the deformation of EE mainly attributed to the compression of the active layer. Furthermore, it was the deformation origination differences that resulted in the differential deformation of WE developed gradually during the monitoring period, the maximum of which reached up to 64 mm.

 

多年冻土公路拓宽路基热-变形特性全尺寸实体工程试验研究  汪双杰、金龙、袁堃、陈东根、李金平、宋怡

公路拓宽路基是道路工程中常见的改扩建方式。在多年冻土区,由于冻土温度的敏感性和沥青路面的强吸热作用,公路拓宽路基差异变形非常严重。针对这一问题,在青藏公路沿线开展了拓宽路基的全尺寸试验,研究多年冻土公路拓宽路基的差异变形特性和发展规律。基于连续三年的地温、分层变形等监测资料,分析了拓宽路基和普通路基的热-变形过程。结果表明,路基拓宽部分对既有路基表现出显著的热扰动效应。路基下伏冻土处于明显的退化状态,具体表现为冻土上限下降和地温上升。由路基拓宽带来的热扰动诱发了显著的变形,明显大于普通路基的变形。拓宽路基的差异变形主要发生在原路基与拓宽部分的交界处,变形主要是由原多年冻土上限附近的融化固结导致。而普通路基的变形则主要来源于季节活动层的压密变形。正是由于变形成因的差异,我们发现在监测期间,拓宽路基的差异变形在不断发展,最大可达64 mm


0133−0149  Sandstone-concrete interface transition zone (ITZ) damage and debonding micromechanisms under freeze-thaw … YanJun Shen, Huan Zhang, JinYuan Zhang, HongWei Yang, Xu Wang, Jia Pan

Abstract: The sufficient bond between concrete and rock is an important prerequisite to ensure the effect of shotcrete support. However, in cold regions engineering protection system, the bond condition of rock and concrete surface is easily affected by freeze-thaw cycles, resulting in interface damage, debonding and even supporting failure. Understanding the micromechanisms of the damage and debonding of the rock-concrete interface is essential for improving the interface protection. Therefore, the micromorphology, micromechanical properties, and microdebonding evolution of the sandstone-concrete interface transition zone (ITZ) under varying freeze-thaw cycles (0, 5, 10, 15, 20) were studied using scanning electron microscope, stereoscopic microscope, and nano-indentation. Furthermore, the distribution range and evolution process of ITZ affected by freeze-thaw cycles were defined. Major findings of this study are as follows: (1) The microdamage evolution law of the ITZ under increasing freeze-thaw cycles is clarified, and the relationship between the number of cracks in the ITZ and freeze-thaw cycles is established; (2) As the number of freeze-thaw cycles increases, the ITZ's micromechanical strength decreases, and its development width tends to increase; (3) The damage and debonding evolution mechanisms of sandstone-concrete ITZ under freeze-thaw cycles is revealed, and its micromechanical evolution model induced by freeze-thaw cycles is proposed.

 

冻融对砂岩-混凝土界面过渡区损伤及脱黏微观机制分析  申艳军,张欢, 张津源, 杨宏伟, 王旭, 潘佳

混凝土与岩石界面充分粘结是确保喷射混凝土支护效果的重要前提。然而,在寒区工程防护体系中,混凝土与岩石表面的粘结状况易受寒区冻融环境影响而产生界面损伤及脱黏,进而引起支护失效。而科学认知冻融对岩石-混凝土界面损伤及脱黏微观机制,是后期针对性改进界面防护的基础性工作。据此,本文以砂岩-混凝土二元组合体为对象,开展冻融条件下砂岩-混凝土界面过渡区(ITZ)损伤脱黏微观机制分析,通过综合采用扫描电子显微镜、体视仪显微镜及纳米压痕等试验手段,研究不同冻融次数(05101520次)下ITZ微观形貌、微观力学性能及微观脱黏演化全过程。藉此明确了ITZ的分布范围及受冻融影响的扩展演化过程。研究结论包括:明确了不同冻融参数对ITZ的微观损伤演化规律,建立了ITZ裂隙数量与冻融次数关系式;ITZ微观力学强度随着冻融次数的增加而降低,且发育宽度趋于增加;揭示砂岩-混凝土二元体ITZ冻融损伤脱黏演化机理,并提出冻融诱发砂岩-混凝土二元体ITZ微观力学演化模型。


0150−0166  A nonlinear interface structural damage model between ice crystal and frozen clay soil … Sheng Shi, Feng Zhang, KangWei Tang, DeCheng Feng, XuFeng Lu     

Abstract: The shear properties of ice-frozen soil interface are important when studying the constitutive model of frozen soil and slope stability in cold regions. In this research, a series of cryogenic direct shear tests for ice-frozen clay soil interface were conducted. Based on experimental results, a nonlinear interface structural damage model is proposed to describe the shear properties of ice-frozen clay soil interface. Firstly, the cementation and friction structural properties of frozen soil materials were analyzed, and a structural parameter of the ice-frozen clay soil interface is proposed based on the cryogenic direct shear test results. Secondly, a structural coefficient ratio is proposed to describe the structural development degree of ice-frozen clay soil interface under load, which is able to normalize the shear stress of ice-frozen clay soil interface, and the normalized data can be described by the Duncan-Chang model. Finally, the tangent stiffness of ice-frozen clay soil interface is calculated, which can be applied to the mechanics analysis of frozen soil. Also, the shear stress of ice-frozen clay soil interface calculated by the proposed model is compared with test results.

 

-冻结粘土界面结构的非线性损伤模型  史盛, 张锋, 唐康为, 冯德成, 陆许峰

-冻土界面的剪切特性研究对于分析寒区多年冻土本构模型和边坡稳定性具有重要意义。本文针对冰-冻结粘土界面进行了一系列低温直剪试验,并基于试验结果提出了描述冰-冻结粘土界面结构剪切特性的非线性损伤模型。首先,分析了冰-冻结粘土界面的胶结特性和摩擦特性,根据低温直剪试验结果,提出了冰-冻结粘土界面的结构系数比。其次,基于提出的结构系数比来描述冰-冻结粘土界面在荷载作用下的损伤程度,并采用结构系数比对冰-冻结粘土界面的剪应力进行归一化处理,归一化后的界面剪应力可用邓肯-张模型来描述。最后,计算了冰-冻结粘土界面的剪切切线刚度,并将本文模型计算的冰-冻结粘土界面剪应力与试验结果进行了比较,二者吻合较好,说明了模型的合理性。本文提出的模型可进一步用于冻土力学的研究。


0167−0176  Possible controlling factors in the development of seasonal sand wedges on the Ordos Plateau, North China … Hugh M. French, Jef Vandenberghe, HuiJun Jin, RuiXia He

Abstract: Wedge-like structures filled with silty sand penetrate Quaternary fluvial and aeolian sediments and, in places, Tertiary bedrock on the Ordos Plateau, North China. The wedges reflect thermal contraction cracking of either permafrost or seasonal frost during the Late Pleistocene and early Holocene. Wedges of about 1 m in depth form polygonal nets of 23 m in diameter (type B). They contrast with wedges of 34 m in depth that form polygons of 10-15 m in diameter (type A). This review focuses upon the highly variable size of the inferred polygon nets and discusses the problem of differentiating between seasonally and perennially frozen ground, or between seasonal frost and permafrost.

 

华北鄂尔多斯高原季节性砂楔发育的可能控制因子  Hugh M FrenchJef Vandenberghe,金会军,何瑞霞

华北鄂尔多斯高原粉砂土中的楔状构造穿透了第四纪的河流堆积和风积层,甚至有的地方达到了第三纪的基岩。这些楔体反映了晚更新世和早全新世的多年冻土或季节冻结作用环境下的热收缩开裂。深度约1 m的楔体形成了2~3 m直径的多边形网(B类楔体)。他们与深度在3~4 m、形成直径10~15 m的多边形网的A类楔体形成了鲜明的对照。本文聚焦于所推断的变化很大的多边形网的尺寸,并讨论了如何区分季节或多年冻结的岩土,或重建多年冻土与季节冻土的问题。  

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