Optimizing thermal and strength characteristics of loess-based ceramic aggregates for sustainable buildings
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Ⅰ. RESEARCHED PROFILEIn China, the most detailed study on loess was carried out in the Heimugou loess profile located at Luochuan County, Shaanxi Province, where the loess has a thickness of 135m. According to the lithologic character, loess of this section can be divided into Pouto loess, Malan loess, Lishi loess and Wucheng loess. The layer of red clay, 15m
Lithology
Loess plateau
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Based on a great number of laboratory tests on soils and loading tests on cast-in-place piles in the loess region,the rules of the shear strength decreasing with the increasing of moisture content of the loess,the development and variation of skin resistance and the additional settlement deformation of piles with saturation of unsaturated loess were found.The emperical formulas of the skin resistance and bearing capacity of piles were set up for the loess.
Settlement (finance)
Saturation (graph theory)
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Yili area is located in the west of Xinjiang and is an intermountane basin of Tianshan, in which the loess is widespread. Only a few studies were carried out during past decades. For this reason, there are different opinions on the origin of loess. The results of grain size analysis of loess and reworked loess show that the textural features of both are same on one side and different on the other side. Firstly, the composition of grain size of loess is similar to that of the reworked loess, but the sand particles of loess is higher and the clay particles is lower than that of reworked loess. Secondly, the frequency curve of loess and reworked loess occures to be positive normal distribution. The mode of both locates in the range of 15-30μm, but the percentages are different. The amount of loess is less than 20 %, while the maxmum percentage of reworked loess reaches 50 %. Thirdly, the sorting of loess is better than that of the reworked loess, even though both are poor sorting deposits. The skewness of loess ranges from 0. 13 to 0. 43 and most of them is lower than 0. 3. Comparied with the loess, the skewness of reworked loess is higher and the mediun size moves toward coarse side. The kurtosis of loess is medium, while peak of reworked loess is steep. In summary, the loess and the reworked loess were transported and sorted by different dynamics before the dust deposited. In addition, the depositing environments were also different. The evidences from the grain size show the loess in Yili area is a typical eolian deposit.
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The stress-strain relationship of loess with different depth and water content of loess slope is studied with the reduced triaxial compress test of undisturbed loess and compared with the results of conventional triaxial compress test of undisturbed loess. It is pointed that the deformation and failure process of loess slope under excavation and unloading can be reasonably explained by the reduced triaxial compress test. The test results show that the surface unsaturated loess of loess slope with toe excavation is easy to appear strain softening or plastic flow, and strength reduction, the deep layer saturated loess appears strain softening under the condition of mid-lower confining pressure and strain hardening and strength increase under high confining pressure. Then, based on the results of reduced triaxial compress test, deformation mechanism analysis of loess cut slope is made. It is considered that the particular engineering geological conditions of loess slope leads to a disadvantageous combination of water content and confining pressure to the strength of soil. Then the disadvantageous combination causes deformation and failure of soil mass and slope. The deformation and failure mechanism of loess slope under excavation belongs to creeping slide and crack arising from pressing or retrogressive slide.
Triaxial shear test
Overburden pressure
Stress path
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Most researches related to loess mechanical properties highlight loess foundations and slopes,while little attention has been paid to loess tunnels.Several typical characteristics of loess both as a special soil and surrounding rock of loess tunnels,such as sensitivity to water content,failure at small strain,anisotropy,loess joints and its impact on stability of loess,are studied from the perspective of stability of tunnel and underground engineering.It is concluded that the existing methods and results associated with mechanical behaviours of loess can't take the actual characteristics of loess into account when the loess behaves as surrounding rock of deep-buried tunnels.The necessary tests and corresponding methods are suggested mainly aimed at the surrounding rock classification of loess tunnels.
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In this paper,collapse characteristics of intact loess from three typical loess areas under different moisture condition are studied,and the principles of loess collapsibility influenced by water content,dry density as well as pressure and behaviors of these in different loess are approached respectively.Base on the collapsibility difference existing in different loess area,a concept of rate of potential collapse is presented,and the test results show that it can be used to analyses the loess collapsibility and reflect the structure characteristics for different kinds of loess preferably.
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This paper reports the analytical results of major chemical components of 94 loess samples from the Xiashu loess profile in the middle and lower reaches of the Changjiang River, the major component contents and the weathering intensity of Xiashu loess were compared with those of Luochuan loess from Northwest China. The results show no obvious difference in the contents of major components in the different Xiashu loess profiles, but some difference in the contents of readily leaching elements of loess and the chemical weathering intensity of loess among the different Xiashu loess profiles.
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Loess is a typically structured soil. The study on loess soil structure is an important aspect of soil structure research, contributing to the broader understanding of soil structural properties. This paper draws on primary data collected from confined compression tests of unsaturated loess, including intact loess and anthropogenic modified loess, and discusses the key influences on changes in the structural properties of unsaturated loess. Research results indicate that increasing vertical pressure, increasing water content and increasing soil density promote gradual structural weakening of unsaturated loess; and the structural integrity of the loess is reinforced in some instances by the increasing of cementing agents. Other important findings are that the key influences on loess structure are not uniform across loess regions, and that achievement of higher loess structural integrity is difficult under very high and very low clay content.
Soil structure
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