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Shear strength of frozen clay under freezing-thawing cycles using triaxial tests

Earthquake Engineering and Engineering Vibration 2018年第4期17卷 761-769页

作者： Wang Miao Meng Shangjiu Sun Yiqiang Fu Haiqing Institute of Engineering Mechanics China Earthquake Administration Harbin 150080 China Key Laboratory of Earthquake Engineering and Engineering Vibration China Earthquake Administration College of Civil Engineering andArchitecture Harbin University of Science and Technology Harbin 150080 China Shandong Earthquake Administration Jinan 250014 China

Using a new low-temperature dynamic triaxial apparatus, the influence law of freezing-thawing cycles on clay shear strength is studied. In this research, the concept of correction coefficients of freezing-thawing cycles on clay static strength, cohesion and internal friction angles is proposed, and the change patterns, correction curves and regressive formulae of clay static strength, cohesion and internal friction angles under freezing-thawing cycles are given. The test results indicate that with increasing numbers of freezing-thawing cycles, the clay static strength and cohesion decrease exponentially but the internal friction angle increases exponentially. The performance of static strength, cohesion and internal friction angles are different with increasing numbers of freezing-thawing cycles, i.e., the static strength decreases constantly until about 30% of the initial static strength prior to the freezing-thawing cycling and then stays basically stable. After 5-7 freezing-thawing cycles, the cohesion decreases gradually to about 70% of the initial cohesion. The internal friction angle increases about 20% after the first freezing-thawing cycle, then increases gradually close to a stable value which is an increase of about 40% of the internal friction angle. The freezing-thawing process can increase the variation of the density of the soil samples; therefore, strict density discreteness standards of frozen soil sample preparation should be established to ensure the reliability of the test results.

关键词： seasonally frozen soil freezing-thawing cycles cohesion internal friction angle correction coefficient

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Potential methane and nitrous oxide production and respiration rates from penguin and seal colony tundra soils during freezing–thawing cycles under different water contents in coastal Antarctica

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Advances in Polar Science 2017年第1期28卷 61-74页

作者： LIU Yashu ZHANG Wanying ZHU Renbin XU Hua School of Environmental and Chemical Engineering Jiangsu University of Science and Technology Anhui Province Key Laboratory of Polar Environment and Global Change School of Earth and Space SciencesUniversity of Science and Technology of China State Key Laboratory of Soil and Sustainable Agriculture Institute of Soil ScienceChinese Academy of Science

In coastal Antarctica, frequent freezing-thawing cycles （FTCs） and changes to the hydrological conditions may affect methane （CH4） and nitrous oxide （N2O） production and respiration rates in tundra soils, which are difficult to observe in situ. Tundra soils including omithogenic tundra soil （OAS）, seal colony soil （SCS） and emperor penguin colony soil （EPS） were collected. In laboratory, we investigated the effects of FTCs and water addition on potential N2O and CH4 production and respiration rates in the soils. The CH4 fluxes from OAS and SCS were much less than that from EPS. Meanwhile, the N2O fluxes from OAS and EPS were much less than that from SCS. The N2O production rates from all soils were extremely low during freezing, but rapidly increased following thawing. In all cases, FTC also induced considerably enhanced soil respiration, indicating that soil respiration response was sensitive to the FTCs. The highest cumulative rates of CH4, N2O and CO2 were 59.5 mg CH4-C·kg-1 in EPS, 6268.8μg N2O-N·kg-1 in SCS and 3522.1mg CO2-C·kg-1 in OAS. Soil water addition had no significant effects on CH4 production and respiration rates, but it could reduce N2O production in OAS and EPS, and it stimulated N2O production in SCS. Overall, CH4 and N2O production rates showed a trade-off relationship during the three FTCs. Our results indicated that FTCs greatly stimulated soil N2O and CO2 production, and water increase has an important effect on soil N2O production in coastal Antarctic tundra.

关键词： Antarctica CH4 N2O soil respiration freezing-thawing cycles tundra

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Effect of Preparation Methods on Mechanical Properties of PVA/HA Composite Hydrogel

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Journal of Bionic Engineering 2010年第3期7卷 235-243页

作者： Dekun Zhang~1, Junjie Duan~1, Dagang Wang~2, Shirong Ge~2 1. School of Materials Science and Engineering, China University of Mining and Technology Xuzhou 221116, P. R. China 2. School of Mechanical and Electrical Engineering, China University of Mining and Technology, Xuzhou 221116, P. R. China School of Materials Science and Engineering China University of Mining and Technology Xuzhou P. R. China School of Mechanical and Electrical Engineering China University of Mining and Technology Xuzhou P. R. China

Poly(vinyl alcohol) (PVA)/hydroxyapatite (HA) composite hydrogel specimens were prepared with 15% PVA and 1%,2%, 3%, 4% and 5% HA by repeated freezing-thawing. The tests of static and dynamic mechanical properties were carried out todiscuss the influence of different contents of HA and freezing-thawing cycles on the mechanical properties of PVA/HA compositehydrogel. The results of static mechanical tests showed that the PVA/HA composite hydrogel with 3% HA and ninefreezing-thawing cycles had excellent stress relaxation properties, higher relaxation ratio, lower stress equilibrium value andpresented better properties of creep and recovery. The results of dynamic mechanical test showed that the PVA/HA compositehydrogel with nine freezing-thawing cycles had higher storage modulus and loss modulus, so was the PVA/HA compositehydrogel with 3% HA.

关键词： composite hydrogel HA contents freezing-thawing cycles static properties dynamic properties

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Study on the long-term stability of Cr-contaminated soil in electroplating plant stabilized by calcium polysulfide

Study on the long-term stability of Cr-contaminated soil in ...

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中国土壤学会土壤环境专业委员会第二十次会议暨农田土壤污染与修复研讨会

作者： RAN Yuling LUO Qishi LU Xin WANG Manli LIN Kuangfei CUI Changzheng State Environmental Protection Key Laboratory of Environmental Risk Assessment and Control on Chemical Process School of Resources and Environmental Engineering East China University of Science and Technology Branch of Shanghai Yonker Environmental Protection Co. Ltd

In order to explore the long-term stability of chromium-contaminated soils in electroplating plants after stabilization, we conducted a study to evaluates the effect of calcium polysulfide(CPS) on Cr stabilization in soil, under acid rain leaching, freezing-thawing cycle, and alternate wetting and drying, providing methods and data support for long-term stability assessment of Cr-contaminated soil stabilization in electroplating plants. The results demonstrated that the high stabilization effect at molar ratio of CPS/Cr(Ⅵ) was 3, with the stable efficiencies of total chromium(TCr) and Cr(Ⅵ) of 99.6% and 99.9%, respectively. The release of TCr and Cr(Ⅵ) in CPS stabilized soil under acid rain can be well fitted to the cumulative release in the fast release phase and the release equilibrium phase using the modified Elovich equation and the first-order kinetic equation, respectively. Although the release concentration of TCr and Cr(Ⅵ) in CPS stabilized soil during releasing equilibrium phase were maintained in the range of 0.78 2.33 mg L and 0.125 0.243 mg L respectively, but the cumulative release content of TCr and Cr(Ⅵ) were 92 mg kg and 11 mg kg under 102 d acid rain environment by column test respectively. freezing-thawing cycle reduce the leaching of TCr in the soil. After 15 times of wetting and drying alternates, the CPS-stabilized soil leaching TCr concentration was decreased by 0.01 mg L from 2.55 mg L. Acid rain leaching can be used as a sensitive indicator to evaluate the long-term stability of Cr-contaminated soil after stabilization.

关键词： Calcium polysulfide(CPS) Long-term stability Chromium-contaminated soil Simulated acid rain leaching freezing-thawing cycles Wetting and drying alternating

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