【作者】 张侠；

【导师】 徐存东； 毕贵权；

【作者基本信息】 兰州理工大学 ， 水利水电工程， 2010， 硕士

【摘要】 我国北方地区分布有面大域广的黄土。黄土是第四纪堆积的以粉土颗粒为主、富含碳酸盐、具有大孔隙、黄色的土状沉积物。而季节冻土分布于北方地区,包括贺兰山至哀牢山一线以西的广大地区,以及北线以东、秦岭-淮河以北地区。随着西部大开发战略的实施,黄土地区高速铁路、公路等基础建设取得了长足的发展,大大地推动了地方经济建设的可持续发展,由于黄土(包括黄土状土)分布范围广,厚度大,因此是各种建筑、道路等工程建设的主要承载土体。但是在寒冬季节负气温影响下,一方面地表土层中孔隙水冻结成冰,体积膨胀(膨胀系数为9%)；而另一方面更主要的是,在负温度梯度作用下,下部未冻土层中的水分源源不断地向上部冻结区迁移、聚集,并冻结成冰透镜体,出现大幅度隆胀,其总冻胀变形量变化在10-30cm不等,甚者可超过40cm。如此大的冻胀变形,几乎没有任何建筑物可以承受。它是发生季节冻土灾害的主要原因。并且黄土是一种典型的非饱和结构性土,它对水的特殊敏感性使得黄土普遍具有湿陷性,黄土的湿陷性是湿陷性黄土特有的工程地质性质,它在一定压力下受水浸湿后结构会发生变化而产生显著附加下沉现象,黄土的这一特征常威胁与破坏工程建筑的正常运营和使用。本文拟从冻融过程与黄土路基湿陷变形关系的角度出发,研究G30连霍高速古永段冻融循环对黄土路基湿陷变形机理的影响。采取该路段典型黄土样,通过冻融循环作用前后压实黄土的密度、水分分布以及变形等试验,开展冻融循环与黄土的密度、水分迁移、变形关系研究,并得出以下主要结论：1、反复冻融循环作用使得补水条件下的土样含水量增加,从底板到顶板土样含水量逐渐递增,且随着冻融循环次数越的增加,含水量增加幅度越大。2、土体经过反复冻融过程以后,土体的结构发生了变化,而且越接近顶板,变化越剧烈。土体结构的变化主要是因为水分迁移和土颗粒的重排列,使得土体的渗透性和持水性增强,更易于水分的输运。3、小密度土样含水量增加速率明显比大密度土样大,但随着冻融次数的增加,土样含水量趋于某一稳定值。这一稳定值取决于冻融循环温度变化及其周期。4、冻融循环使得大密度土样孔隙增大,干密度变小,使小密度土样干密度变大。最终维持在某一稳定范围,这也进一步论证了冻融循环过程是土体从不稳定态向动态稳定态的发展过程,反复的冻融循环改变了原来土体的性状,使得土体向新的动态稳定平衡状态发展。5、土样在冻结稳定时有一稳定冻结锋面,也是土样的冻融交界面,这一地带可能是冻融循环对土样影响的临界点,冻融交界面附近土体温度变化缓慢,主要是因为这里含冰量(水)较大,相变剧烈,所以冻融交界面是水分、温度发生剧烈反应的地区,是冻土水分迁移、成冰机理等研究的重点区域。6、土样在冻结开始时发生明显的冻胀,变形急剧增加,融化时融沉变形较小,冻胀量大于融沉量,土样表现为增高；在冻融次数8次到15次期间,冻胀量等于融沉量,土样高度稳定；随着冻融次数的增加,土样表现为略微沉降。7、冻融循环后土样的孔隙度比冻前增加,随着冻融循环次数的增加,土样湿陷变形呈线性增加,并且在压实黄土的密度变小的双重影响下,其湿陷变形更加明显。所以,多年冻融区、季节冻土区的工程建设,压实黄土路基的湿陷变形将更加突出。更多还原

【Abstract】 In north China region distribution of a large domain of loess. In loess accumulation is quaternary soil particles, powder is rich in carbonate, big pore, yellow soil. And in northern tundra season, including the helan shan to a vast area of ailao shan west and north qinling-uptown huaihe river region,. With the implementation of the western development strategy, the loess region high-speed railway, highway construction has achieved great development, has greatly promoted the sustainable development of the local economic construction, because of the loess (including the loess shape soil) distribution range in thickness, therefore, all sorts of buildings, roads are the main bearing soil engineering construction.But in the winter season and, on the other hand, under the influence of the negative temperature and topsoil pore water in the frozen ice, volume expansion (9%) expansion coefficient, On the other hand, is more important role in the negative temperature gradient, the moisture in the permafrost not flowing of freezing area migration, gathered together, and frozen ice lens, appear drastically lung expansion, the frost heave deformation changes in 10-30cm, what can exceed 40cm. So frost heaving deformation, almost no buildings can withstand. It is the season is the main reason for the disaster permafrost. And the loess is a typical kind of unsaturated soil water, its structural special sensitivity collapsible loess generally has made sex, sex is the collapsible loess collapsible loess engineering geological properties of peculiar, it under certain pressure after soaking water changes and structure of significant additional sink phenomenon, the characteristics of loess engineering construction and often threat to the normal operation and use.This paper from the freeze-thaw processes and loess embankment collapsible deformation of the relationship G30 study Angle, highway and freeze-thaw cycle period of ancient collapsible loess embankment of deformation mechanism. Take this section typical loess samples, through the freeze-thaw cycles and compaction effect of moisture distribution density, and the deformation and test, the density of the loess freeze-thaw cycle and migration, deformation, research, and relationships are as follows:1, repeated freeze-thaw cycle function under the condition that the soil water content, from the bottom to increase soil moisture roof gradually, and with the increase of freeze-thaw cycle times, increasing the content.2, the soil after repeated freeze-thaw processes, the soil structure has changed, and more close to the roof, change. The changes in the structure of the soil moisture, mainly because of the heavy soil particles and migration, make the permeability of soil and water, water transport more easily.3, small soil moisture content increase rate density than big density, but with the soil sample frequency increases, freeze-thaw soils tend to be a stable content. This is a stable value depends on natural freeze-thaw cycle changes in temperature and cycle.4 and freeze-thaw cycles that soil porosity density increases, dry density decreases, density of dry density soil samples. Maintain a stable in the end, it also further demonstrates the process of freeze-thaw cycle is to never stable state soil dynamic stability of development process, repeated freeze-thaw cycle changes, the properties of soil was to new dynamic stability of soil balance development.5, and in the frozen soil samples from stable, frozen soil samples of frontal interface, this thawing zone may be of freeze-thaw cycle of critical influence, freeze-thaw interface soil temperature changes slowly near here, mainly because the ice quantity (water), phase interface, so the freezing-thawing is vigorous moisture content, temperature, reaction is frozen water transfer mechanism of ice, the focus of research area.6, in frozen soil samples, the beginning of the frost heave significantly increased dramatically, deformation, melting thaw deformation is lesser, frost heaving and thaw quantity index increased performance for the soil sample, In the number of freeze-thaw eight times to 15 times during freezing expansion, equal to thaw is highly stable; soil samples, Along with the increase of number of freeze-thaw soils, is slightly settlement.7, and freeze-thaw cycles of porosity ratio would increase, with the former frost thawing cycle times, collapsible soil deformation in linear increase, and the density of compacted loess, the smaller dual influences the collapsible deformation is more apparent. Therefore, the seasonal frozen thawing, engineering construction, the roadbed compaction of collapsible loess deformation will become more prominent.更多还原