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Study on the Deterioration of Engineering Properties of Loess under Freerzing-Thawing Cycles

Author: DongXiaoHong
Tutor: ZhangAiJun；GuoMinXia
School: Northwest University of Science and Technology
Course: Geotechnical Engineering
Keywords: Loess Freeze-thaw cycles Loess strength Deterioration BP Model Consolidation creep
CLC: TU444
Type: Master's thesis
Year: 2010
Downloads: 125
Quote: 1
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Abstract


Paper relies on the National Natural Science Foundation of China Loess Engineering Properties deterioration mechanism and structures life prediction study (N0.50779058) and Open Fund of the State Key Laboratory of Frozen Soil Engineering, Chinese Academy of Sciences \depiction of research (SKLFSE200803), summarize and absorb the results of previous studies based on laboratory test method to reveal the effects of repeated freezing and thawing deterioration of loess mechanical properties, loess safety of the works and long run certain theoretical and experimental guidance. Carry out the project of the old loess building Danger reinforcement, life prediction and formulation of the theory of \Test in Frozen Soil Engineering, State Key Laboratory of Chinese Academy of Sciences, Lanzhou, the test using the freeze-thaw test under confinement the the Yangling Dian Q of 3 loess strength deterioration, consolidation creep characteristics experimental research, key findings are as follows: (1) long-term one-way indoor freeze-thaw cycle test, loess with the increase in the number of freeze-thaw deterioration of the physical phenomena described, the results show that the loess moisture content and dry density on loess affects both surface physical deterioration, but the degree of influence of the moisture content than dry density was significantly; while its mechanism of degradation and deterioration in-depth discussions on regional projects affected by freeze-thaw some suggestions. Comparison sample analysis, the the loess surface physical deterioration of two basic modes: crack patterns and pore mode. (2) the number of freeze-thaw cycles of freezing and thawing cycle test and loess direct shear test, freeze-thaw cycles of loess dry density, cohesion, internal friction angle, the results showed that: the first freeze-thaw loess dry density maximum impact; among the density of loess dry density decreases after freezing and thawing, low dry density of loess dry density is increased somewhat; higher the moisture content, dry density is reduced more. After a few times before freeze-thaw cycles, higher dry density of the sample cohesion will have decreased significantly low dry density of the sample cohesion slightly elevated after the first freeze-thaw cohesion the most dramatic changes , but repeated freezing and thawing, the specimen cohesion will be a little slow increases; lower the moisture content, cohesion reduced more, but each moisture content of the sample cohesion to reduce the proportion is closer to. Internal friction angle through the first freeze-thaw were increased, but the long term wavy fluctuations ships within 5 °, no change can be considered. The strength of the trend like cohesion. (3) test data using mathematical methods modified linear fit, and then on this basis, BP artificial network, multiple regression analysis reflect the the loess strength (cohesion) and moisture content, degree of compaction, freeze-thaw cycles between the loess strength (cohesion) deterioration model, and then a comprehensive comparison between each model, the results show that the BP model is the solution the loess strength (cohesion) deterioration of the quantitative research more effective method. (4) the consolidation creep test by the freezing and thawing of loess, a different normal pressure, the clusters of different freeze-thaw cycles of freezing and thawing under the loess consolidation creep curves. The number of freeze-thaw on the creep properties of loess must have impact. In the same method to the pressure, the freeze-thaw loess strain with the number of freeze-thaw cycles increased, usually 3-5 times after freezing and thawing strain stabilized, the first time the impact of freezing and thawing is most obvious. Creep curve shape of the freeze-thaw loess, it is recommended that the with Burger elements model to describe the consolidation creep characteristics. Established under a different number of freeze-thaw strain, normal pressure and time creep model appropriately describes the creep characteristics of the freeze-thaw loess, and fitting the model parameters.

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CLC: > Industrial Technology > Building Science > Soil mechanics,foundation engineering > Various types of soil and foundation > Loess and foundation
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