Characteristics of thawed interlayer and its effect on embankment settlement along the Qinghai-Tibet Railway in permafrost regions

The formation of thawed interlayer beneath embankment can result in embankment settlement in permafrost regions. Based on the data on ground temperatures and deformations beneath the embankment, observed in-situ along the QinghaiTibet Railway in permafrost regions from 2006 to2013, characteristics of the thawed interlayer beneath the embankment and its influence on the embankment settlement are studied. The results indicate that the thawed interlayer hardly forms beneath the natural field, and beneath the embankments from the Qinghai-Tibet Railway the thawed interlayer develops widely, and it can be refrozen totally in the regions with lower mean annual ground temperature, and developed further in the regions with higher mean annual ground temperature.The thawed interlayer is closely related to the embankment settlement. The ice content of permafrost underlying the thawed interlayer influences the settlement of embankment. The higher the ice content is, the larger the settlement is, and vice versa. The increase in thickness of thawed interlayer mainly results from the decline of artificial permafrost table in high-temperature permafrost regions.

Thermal Characteristics of the Embankment with Crushed Rock Side Slope to Mitigate Thaw Settlement Hazards of the Qinghai-Tibet Railway

Permafrost （perennially frozen ground） appears widely in the Golmud-Lhasa section of the Qinghai-Tibet railway and is characterized by high ground temperature （≥1℃） and massive ground ice. Under the scenarios of global warming and human activity, the permafrost under the railway will gradually thaw and the massive ground ice will slowly melt, resulting in some thaw settlement hazards, which mainly include longitudinal and lateral cracks, and slope failure. The crushed rock layer has a thermal semiconductor effect under the periodic fluctuation of natural air. It can be used to lower the temperature of the underlying permafrost along the Qinghai-Tibet railway, and mitigate the thaw settlement hazards of the subgrade. In the present paper, the daily and annual changes in the thermal characteristics of the embankment with crushed rock side slope （ECRSS） were quantitatively simulated using the numerical method to study the cooling effect of the crushed rock layer and its mitigative ability. The results showed that the ECRSS absorbed some heat in the daytime in summer, but part of it was released at night, which accounted for approximately 20% of that absorbed. Within a year, it removed more heat from the railway subgrade in winter than that absorbed in summer. It can store approximately 20% of the ＂cold＂ energy in subgrade. Therefore, ECRSS is a better measure to mitigate thaw settlement hazards to the railway.

Characteristics of thawed interlayer and its effect on settlement beneath embankment in permafrost regions--A case study for the Qinghai-Tibet Highway

Based on ground temperatures and deformations monitored at the Xieshuihe site along the Qinghai-Tibet Highway(QTH)in permafrost regions from 2004 to 2015,variation of artificial permafrost table(APT),maximum frozen depth(MFD),thawed interlayer thickness(TIT)and ground temperature beneath embankment is analyzed,respectively.The results indicate that under the embankment,the change of APT occurred from October to December of that year and presented a deepening trend.The change of MFD occurred from April to June of that year with no obvious change trend,and TIT had an increasing trend year by year,which mainly resulted from the deepening artificial permafrost table.Mean annual ground temperature at 0.5 m depth was 3.91°C higher beneath the embankment center than that under the natural field.The rising ground temperature at shallow layer of embankment resulted in the development of thawed interlayer beneath the embankment and warming of underlying permafrost.Embankment settlement is closely associated with TIT.Greater settlement easily occurs when permafrost with higher ice content exists under the thawed interlayer,and in turn the settlement is smaller when permafrost with lower ice content exists under the thawed interlayer.

Settlement characteristics of large-diameter shield excavation below existing subway in close vicinity

A case of Qinghuayuan tunnel excavation below the existing Beijing Subway Line 10 is presented.The new Qinghuayuan tunnel,part of the Beijing-Zhangjiakou High-speed Railway,was excavated by a shield machine with an outer diameter of 12.2 m.The existing subway was excavated by shallow tunnelling method.The project layout,geological conditions,reinforcement measures,operational parameters of shield machine and monitoring results of the project are introduced.During the Qinghuayuan tunnel excavation below the existing subway,total thrust,shield driving speed,cutterhead rotation speed and torque were manually controlled below the average values obtained from the previous monitoring of this project,which could effectively reduce the disturbance of the surrounding soil induced by shield excavation.The Gaussian fitting function can appropriately fit both the ground and the existing subway settlements.The trough width is influenced not only by the excavation overburden depth,but also by the forepoling reinforcement and tail void grouting measures.

Analyzing land use characteristics of rural settlements on the urban fringe of Liangjiang New Area, Chongqing, China

The objective of this paper is to analyze land use characteristics of rural settlements in urban fringe so as to provide references for optimizing the regional distribution of rural settlements, consolidating rural settlements, and coordinating urban-rural integrated development. The methods of spatial statistical analysis, buffer analysis, Ripley's K function, kernel density analysis based on GIS(Geographic Information System) were used to analyze the characteristics of scale, spatial differentiation and spatial patterns of the rural settlements in Liangjiang New Area in Chongqing Municipality of China. The fractal dimension formula was also developed to reflect fractal feature of the rural settlements. The results show that, the scale of rural settlements in Liangjang New Area takes on distinct characteristics of spatial differentiation along with changes in elevation, gradient, location, geohazards distribution, and the like. The fractal characteristic of rural settlements has obvious regional variations subject to the 6 factors of location in the Liangjiang New Area. Overall, the worse the terrain conditions are, the larger the fractal dimension values become. The better the locationconditions, the larger the fractal dimension values are. The spatial pattern in the township scale presents three kinds of distribution as being aggregated, uniform and random. In contract, the spatial pattern in the plaque scale displays a banding distribution from a general view with several aggregation zones centering on each town center. From the results, we can see that the characteristics of rural settlements in urban fringe are more complicated. For such kind of rural settlements in special regions, in the rural land consolidation more attention should be paid to improve the rural living environments and public services, as well as to promote the harmonious relationship between the urban and rural areas.

Simulation analysis on characteristics of land surface over western Qinghai-Xizang Plateau during freez-ing-thawing period

Using the Global Energy and Water Cycle Experiment-Asian Monsoon-Tibet Plateau Experiment (GAME-Tibet) observa-tional data-from October 2002 through September 2003-of Gaize in the western Qinghai-Xizang Plateau (QXP),the land-surface characteristics of the Qinghai-Xizang Plateau are simulated by the improved land-surface model Common Land Model (CoLM).The results show that CoLM can reproduce the land-surface characteristics of plateau areas well.In the sur-face-energy balance of the western QXP in the winter half year,the sensible heat (SH) flux constituted the dominant energy,and the latent heat (LH,here and after) flux is very small.Although the LH flux nearly equals zero in freezing season,it cannot be ig-nored during the period of freezing-thawing in QXP.In the transition season from midto late-May,the frequent phase change of soil water that is caused by the freezing-thawing process leads to the increase of LH flux and decrease of the Bowen ratio.The simulation results also indicate that the changes of surface effective heat fluxes (SH and LH flux) are associated with precipitation and the frequent change between freezing and thawing processes in soil surface.

Heterogeneous Spaces in the City: Study on Spatial Characteristics of Tibetan Settlements in Chengdu

Settlement of the minorities is a particular heterogeneous space in a metropolis,and such spaces exist as inseparable parts of the city for historical,social and geopolitical reasons.Taking Tibetan settlement in Wuhou District,Chengdu City for example,this study analyzed spatial features and evolution history of minority settlements,and explored how to respect and accept historic signifi cance and cultural value of these heterogeneous spaces during the rapid urban development,and then use them reasonably and reform creatively,so as to maintain their original spatial features and integrate the spaces into the overall urban structure.

Settlement Characteristics of Cement Fly-Ash GravelPile-Plate Composite Foundation of High-Speed Railway

Field tests on settlement characteristics were carried out on the cement fly-ash gravel （CFG） pile-plate composite foundation on Beijing-Xuzhou section of Beijing-Shanghai high-speed railway. The settlements of the piles and the soil between pries were measured and analyzed. The results show that the settlement-time dependency experienced three phases： rapid development phase, stable development phase and stable phase. Therefore, surcharge preloading was necessary to reduce the settlement after construction. The finite element software Plaxis was used to calculate the deformations of the pile top and the soil between piles at the embankment center, as well as the settlements of CFG pile reinforcement area and the underlying stratum under surcharge preloading. The calculation results and the field test results were compared and analyzed. Both the results show that the settlement of the composite foundation mainly occured in underlying stratum. The settlement characteristics of pile-plate composite foundation under high embankment are also concluded.

Spatial Protection and Development of Traditional Mountain Settlements from the Perspective of Self-organization : A Case Study of Anju Ancient Town in Tongliang District, Chongqing

Through literature research, field research and urban design analysis methods, based on the self-organization theory, the evolution characteristics of the settlement space of Anju Ancient Town with significant characteristics of traditional mountain settlements were analyzed, and then its internal and external influencing factors were summarized. Finally, appropriate protection and development strategies were proposed, such as reasonably planning functional zones, breaking through the single structure, and creating a good living cultural environment. The innovation of this study is that it integrates the self-organization theory into the cognition of traditional mountain settlement space, and discusses the connection between the mountain settlement space and the traditional regional context under the modern development concept, so as to seek the benign protection and reasonable development of traditional mountain settlement space.

The Form Characteristics and Construction of the Public Space of the Oasis Traditional Settlements in Turpan

Based on the analysis of the form characteristics and construction of the public space of oasis traditional settlements in Turpan,and from the analysis and summary of the types,elements,scales and functions of the public space of the traditional settlements,this study put forward that the public space of the oasis villages can be divided into point space,line space and plane space,and the formation and evolution rules of the public space of oasis traditional settlements in Turpan were obtained.Explore the role of public space in the construction of traditional settlements’ overall space,so as to provide reference for the development and renewal of public space of the current similar oasis settlements.

Deformation characteristics and safety assessment of a high-speed railway induced by undercutting metro tunnel excavation

Stratum deformation(settlement) is a challenging issue in tunnel engineering, especially when construction of metro tunnels has to undercut high-speed railway. For this purpose, we used the FLAC30 software to analyze the stratum settlement characteristics of high-speed railway at different crossing angles intersected by metro tunnel, in terms of ground settlement trough, stratum slip line and irregularity of ballastless tracks. According to the evolution of the stratum settlement at different angle regions, an optimized angle is proposed for the actual project design. In order to reduce the influence of stratum settlement on the safety of high-speed railway, an approach of safety assessment is proposed for the shield engineering undercutting high-speed railway, as per Chinese specifications using numerical results and on-site conditions. A case study is conducted for the shield tunnel section crossing the Wuhan-Guangzhou High-speed Railway between the Guangzhou North Railway Station and the Huacheng Road Station, which represents the first metro tunnel project passing below a high-speed railway in China. A series of measures is taken to ensure the safe excavation of the shield tunnel and the operation of the high-speed railway. The results can provide a technical support for performing a safety evaluation between high-speed railways and metro tunnels.

Study on temperature field and settlement of thawing soil under static and dynamic loading

A series of tests were conducted to analyze temperature field distribution and thawing settlement of a thawing soil under static and dynamic loading at various cooling and thawing temperatures. The results demonstrate： （1） the temperature field distribution of the thawing soil was not significantly influenced by the loading form under the tested loading conditions; similar results were obtained for samples at different dynamic loading frequencies and different dynamic loading ampli- tudes, which verified the independence of loading form and temperature field; （2） changed temperature field distributions were found in thawing soil with different cooling and thawing temperatures, and the cooling and thawing temperature of the samples were the main factors affecting their temperature distributions; （3） under the tested conditions, thawing set- tlements were little influenced by the thawing temperature and the dynamic loading frequency; and （4） a linear relation- ship existed between the thawing settlement and the cooling temperature, and a logarithmic function could be used to describe the relationship between the thawing settlement and the loading amplitude.

考虑桩土间黏滑机制的桩基沉降动态特性研究

基于桩基运动控制方程,对荷载作用下的桩基沉降动态特性进行了研究。首先,考虑桩土间黏滞与滑动两种接触状态,建立了一种考虑侧阻软化及侧阻恢复的桩土相互作用模型;然后采用该模型及修正三折线模型分别模拟桩与桩侧土以及桩端土间的相互作用,结合有限差分法建立了考虑桩土间黏滑机制的桩基沉降分析方法;最后,基于建立的桩基受荷沉降分析方法,研究了桩基沉降的黏滑动态特性以及桩身的力学特性,并讨论了桩土相互作用模型中的参数对桩基沉降动态特性的影响。结果表明:当桩顶荷载接近桩基单级加载极限值,桩基沉降表现出黏滞位移与快速滑动位移交替的动态特性;桩身力学响应表现出加载路径相关性,与单级加载相比,分级加载时桩侧摩阻力能得到更好发挥,桩基极限承载力更高;提出的分析方法能够较好地模拟桩基静载试验沉降过程。

冻融作用下断续节理岩体损伤与力学特性研究

寒区断续节理岩体受冻融作用影响易发生失稳破坏。为探究冻融作用下节理特征对岩体损伤与力学特性的影响,使用相似材料制备不同节理倾角、岩桥长度的断续节理试样,并开展冻融循环试验。通过对冻融试样进行损伤分析与单轴压缩试验,得到了各类试样的劣化损伤特性及其对抗压强度与破坏模式的影响规律。研究表明:冻融作用下,断续节理类岩石试样的劣化模式以片落模式为主,裂纹模式为辅,且不同节理特征试样间存在冻融损伤差异;节理特征与片落损伤的关联较小,但对裂纹扩展的影响显著,节理倾角越大,裂纹发育越不明显,岩桥长度越短,裂纹贯通越迅速,裂纹扩展程度不同是造成试样间冻融损伤差异的主要原因;在差异性冻融损伤的影响下,各类试样的抗压强度普遍降低,并随节理特征的变化表现出不同的强度损失规律;试样破坏过程中延性增强,节理尖端的拉伸裂纹减少、剪切裂纹增多,部分类型试样的破坏模式与岩桥贯通模式发生改变。

黄河包头段冻融期水体荧蒽残留及光降解行为

作者分别于流凌期、封河期及开河期,采集黄河包头段干流水体样品,分析该河段荧蒽(Fla)的残留水平及时空变异特性,通过光降解实验探究Fla的降解过程及光敏化剂对降解行为的影响。结果表明,冻融过程中8个采样断面均有Fla检出,且未超过标准值。大部分采样点Fla含量在稳定封河期及开河期较高,各个采样点Fla含量在0.05水平上具有显著性差异,S2、S5断面浓度相对较高,S4、S6和S7点浓度较低。水中Fla可以发生直接光降解,且符合一级反应动力学方程,72 h后降解率几乎达到90%。在避光进行暗反应时,Fla浓度基本不发生变化。添加丙酮、泥沙及低浓度H2O2均可抑制Fla的降解,反应仍符合一级反应动力学方程,而较高浓度的H2O2会促进Fla的光降解,且降解反应不再符合一级反应动力学方程。

北方寒冷地区温度场作用下公路路表形变规律分析

为了更加具体、深入地理解寒区道路,研究其病害发生、发展规律,提高对道路结构在时间和空间上的认知,开展了北方寒冷地区路表形变规律的研究。通过选取典型公路路段,建立10个监测段落,对路基的冻胀、融沉变形持续进行现场高程监测。分析温度场作用下路表形变特征和响应机制,分析公路在自然条件下的时域形变特点、动态形变特征及差异性。分析周期监测数据,构建竖向相对形变、竖向相对形变速率、横断面间形变速率最大倍数等参数,比较不同段落、不同横断面和监测点间的形变及其差异。研究北方寒冷地区路表形变与温度场协调规律,结果表明:北方寒冷地区基于温度场的路表形变具有典型的周期特性。对比分析填、挖方路段纵横方向形变的差异特征,形变极值分布规律,以及结合热胀、冻胀、融沉阶段的相对形变规律及形变速率差异特点,结果发现:挖方路段形变速率是填方路段的10余倍;8月份至10月份的热胀速率大于10月份至11月份的热胀速率;融沉主要发生在3月份至5月份;而冻胀速率较为稳定,对于填方路段,11月份至次年1月份的冻胀大于1月份至2月份的冻胀,而挖方路段则相反。给出了寒冷地区路表形变的温度场时域响应规律、特点,为开展寒区路基、路面结构和材料研究,以及道路病害等研究提供了依据。

寒区炭质千枚岩冻-动联合损伤特性

由于寒区隧道围岩在冻融及动载的作用下会产生严重的损伤和性能退化,因此研究两者耦合作用下岩石的劣化特征具有重要意义。利用MTS815加载系统对炭质千枚岩试样开展了0、30、60次不同冻融循环次数下的三轴多级循环加卸载试验,研究了冻融及循环荷载对炭质千枚岩力学参数及变形的影响,基于能量计算分析了不同冻融次数岩石在动载下的能量演化规律,从宏观和微观角度进行对比,分析岩石在静载与冻-动耦合下的破坏形态,揭示了相应的破坏模式。试验研究表明:(1)与静载压缩强度相比,在冻融和循环荷载共同作用下岩石的强度有明显的降低,并且表现出明显的塑性,同时冻融循环次数越多,该现象也越显著;(2)随着冻融循环次数的增加,弹性模量会逐渐减小而泊松比却逐渐增大;(3)在循环过程中,轴向和环向不可逆应变均逐渐增加,两者的应变增量均在每一级应力的初始循环内最大而后逐渐减小,而不可逆体积应变先增大后减小,即体积先以压实为主后逐渐转变为以膨胀为主;(4)岩石内部主要以弹性能为主,耗散能占比在第1个循环周期内迅速降低,在之后的循环周期内呈现阶梯式增加而后趋于稳定;(5)从宏观与微观角度分析,单调加载与循环加载作用下两者的破坏机理不同,但均为斜截面的剪切破坏,但循环加卸载破碎程度更大。

川西林盘8种典型树种凋落物的蓄积量及其持水特性

凋落物在维持林地的土壤水分、肥力和养分平衡等方面发挥着重要的作用。但迄今为止,川西林盘的凋落物对雨水的吸持和拦截效应还未见报道。采用室外调查和室内浸泡相结合的方法,在分别生长有8种典型林盘树种的纯林地中设置样方,收集并测试其凋落物的蓄积量及其持水特性。结果显示,8种树种的地表凋落物年总蓄积量均值为(7935.52±6042.96)kg·hm^(-2),土壤中凋落物年总蓄积量均值为(2765.70±2206.40)kg·hm^(-2)。8种树种的凋落物年蓄积量差异显著,落叶树种的年凋落物蓄积总量是常绿树种的1.29倍,具体表现为:枫杨>慈竹>构树>香樟>雷竹>银杏>水杉>黑壳楠。土壤中凋落物的自然持水率(4.54%—20.39%)高于其地表凋落物的自然持水率(4.97%—10.01%)。地表和土壤凋落物的吸水速率均在浸泡5分钟后达到峰值,12小时后达到饱和,其吸水速率和浸泡时间极显著相关。地表凋落物的有效持水量、有效持水率和凋落物径流拦蓄量均高于土壤中的凋落物。凋落物径流拦蓄量与蓄积量呈极显著相关,枫杨(66.02 t·hm^(-2))和慈竹(60.06 t·hm^(-2))凋落物的径流拦蓄总量显著地高于其他树种。此外,地表凋落物和土壤中凋落物的径流拦蓄量还分别与凋落物的有效持水率和最大持水量显著相关。广泛栽植径流拦蓄能力最强的枫杨、慈竹和构树,有利于川西平原的水源涵养和水土保持。

冻融和盐作用对糯米粉的结构和糊化特性的影响

糯米浆是我国古代应用最广泛的建筑胶凝材料,可显著提高三合土和灰浆的强度特性、抗渗特性和粘结特性.挖掘糯米浆的科学价值,对于传统技术的科学利用,特别是对古建筑的修复具有十分重要的意义.文中用石油醚对糯米粉进行脱脂,采用双波长法对糯米粉中的直链淀粉和支链淀粉进行测定,用FT-IR,XRD,TG/DTG和SEM分析了糯米粉脱脂前后的结构和形貌,同时用XRD和SEM分析了冻融循环、Na 2SO 4加入对糯米淀粉结构、晶型和形貌的改变,用Brabender粘度仪研究了不同条件下的糊化特性.结果表明,糯米粉中直链淀粉和支链淀粉的含量分别为9.16%和78.56%,糯米粉和脱脂糯米粉的糊化温度基本相同,但峰值粘度、崩解值和回升值下降.冻融循环不会改变糯米粉中淀粉颗粒的结构和晶型,但峰值粘度、谷值粘度、终值粘度、崩解值和回升值均有降低趋势;加入4%的Na 2SO 4后,会使糊化温度升高,崩解值升高,回升值下降.本研究对糯米粉的科学认知具有重要的意义,期望为针对性地提高糯米浆的胶凝品质提供理论参考.

冻融循环下沥青混合料损伤特性研究

目的 探究季节冻土地区温差和冻融循环等气候特点对沥青混合料使用性能的影响,为我国不同地区的沥青路面设计、养护、寿命评估和冻融损伤评估提供依据。方法 采用室内冻融循环模拟试验,根据不同温度配置和不同循环次数下沥青混合料的弯拉强度、疲劳寿命和单轴压缩动态模量的衰减,研究冻融循环作用前后沥青混合料的损伤特征,明确冻融循环下沥青混合料的性能衰变特征,最终提出沥青混合料冻融损伤温度等效效应。结果 冻融循环对沥青混合料低温抗裂性能造成严重破坏,冻融循环30次后性能的衰减幅度总体上超过50%。融化温度和冻结温度对沥青混合料损伤的影响存在差异,且归因于结冰过程、经典热力学和膨胀力三个方面。在仅冻融循环作用下,沥青混合料的性能衰减表现出先快速下降,后缓慢下降的特征。结论 冻融循环对沥青混合料性能的影响程度受循环次数和温度条件影响,其中融化温度较冻结温度对性能的影响更为显著。不同温度配置下冻融30次后的沥青混合料性能表现出相似的分布规律,明确了温度等效效应。建立了混合料冻融循环后的残余抗裂性能的等效模型,将损伤程度简化为三个等级。