Academic literature on the topic 'Wetting-Drying cycles'
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Journal articles on the topic "Wetting-Drying cycles"
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Du, Bin, Haibo Bai, Minglei Zhai, and Shixin He. "Experimental Study on Dynamic Compression Characteristics of Red Sandstone under Wetting-Drying Cycles." Advances in Civil Engineering 2020 (December 14, 2020): 1–10. http://dx.doi.org/10.1155/2020/6688202.
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To study the influence of wetting-drying cycles on dynamic mechanical properties of rock masses, the impact compression tests of red sandstone samples were carried out by using a split Hopkinson pressure bar (SHPB) apparatus with a diameter of 50 mm. The results showed that under the same number of wetting-drying cycles, the dynamic compressive strength of red sandstone increased exponentially with the strain rate, and the sensitivity of the strain rate decreased with the increase of wetting-drying cycles. The deterioration effect of wetting-drying cycles was significant, and the dynamic and static compressive strength decreased with the increase of wetting-drying cycles; the higher the strain rate, the stronger the sensitivity to wetting-drying cycles. Besides, the influence of wetting-drying cycles and strain rate was comprehensively studied, and the equation of dynamic compressive strength of red sandstone was obtained. After different wetting-drying cycles, the fractal characteristics of red sandstone dynamic fragmentation were obvious, and the fractal dimension was 2.02–2.80, and the fractal dimension increased logarithmically with the strain rate. Finally, the internal microstructure of red sandstone after different wetting-drying cycles was analyzed, and the degradation mechanism of the rock by the cycles was discussed.
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Wang, Jian, Dexter B. Watts, Qinqian Meng, Fan Ma, Qingfeng Zhang, Penghui Zhang, and Thomas R. Way. "Influence of Soil Wetting and Drying Cycles on Soil Detachment." AgriEngineering 4, no. 2 (June 16, 2022): 533–43. http://dx.doi.org/10.3390/agriengineering4020036.
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Agricultural soils undergo periods of saturation followed by desiccation throughout the course of a growing season. It is believed that these periods of wetting and drying influence soil structure and may affect the rate of soil detachment. Thus, an experiment was conducted to investigate the influence of a disturbed soil (soil sieved to simulate tillage) subjected to various wetting and drying cycles, on soil bulk density and the resistance to soil detachment with runoff. Seven treatments consisting of wetting and drying cycles ranging from 0 to 6 cycles were evaluated under laboratory conditions using an experimental flume apparatus. A Richards growth model proposed for predicting the influence of wetting and drying on soil detachment was also evaluated. Results showed that the soil bulk density increased as the number of wetting and drying cycles increased. The soil detachment rate decreased as the number of wetting and drying cycles increased. Moreover, initial soil detachment (occurring as soon as runoff began) rates were high for 1 to 3 wetting and drying cycles, while the rate of initial detachment decreased after the third cycle. For example, soils with two and three wetting and drying cycles took 6.5 and 7 min to reach the maximum 1 cm souring depth, respectively, while the soils subjected to four or more wetting and drying cycles did not reach the maximum 1 cm depth during the 15 min runoff experiment. In addition, the proposed S-Shaped Richards growth model was a good predictor for estimating the soil detachment of soils experiencing various wetting and drying cycles. Findings from this study suggest that more attention should be given to the influence that soil wetting and drying have on the prediction of soil detachment. Information from this study is expected to be useful for improving soil management strategies for reducing soil erosion.
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Hu, Zhi, Kai Peng, Lihua Li, Qiang Ma, Henglin Xiao, Zhichao Li, and Pinbo Ai. "Effect of Wetting-Drying Cycles on Mechanical Behaviour and Electrical Resistivity of Unsaturated Subgrade Soil." Advances in Civil Engineering 2019 (June 16, 2019): 1–10. http://dx.doi.org/10.1155/2019/3465327.
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Compacted soil is widely used in road and railway subgrade, while alternation of seasons can cause fluctuations in moisture content of soil (i.e., wetting-drying cycles) and influence the performance of soil. In order to research the effect of wetting-drying cycles on mechanical behaviour and electrical resistivity of compacted unsaturated subgrade soil, wetting-drying tests considering different number and cyclic amplitude were conducted on compacted unsaturated clay specimens, and the electrical resistivity and unconfined compressive strength of soil were measured in this study. The AC (alternative current) two-electrode method was applied in the resistivity measurement. The experimental results show that increasing number and cyclic amplitude of wetting-drying cycles can both reduce the strength and electrical resistivity of the compacted unsaturated specimens. After 3-4 wetting-drying cycles, the strength and electrical resistivity tend to be constant value. The change of pore structure can be the key factor leading to the reduction of electrical resistivity of soil subjected to wetting-drying cycles and consequently causing the decrease of soil strength in the present study. Thus, the electrical resistivity can be adopted to indirectly assess the mechanical behaviour of unsaturated compacted soil after wetting-drying cycles.
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Zhou, Yan-Ming, Zong-Wei Deng, Zi-Jian Fan, and Wen-Jie Liu. "Shear Strength Deterioration of Compacted Residual Soils under a Wind Turbine due to Drying-Wetting Cycles and Vibrations." Advances in Civil Engineering 2021 (December 13, 2021): 1–10. http://dx.doi.org/10.1155/2021/8628842.
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The soil beneath a wind turbine withstands not only environmental impacts but also continuous vibrations transmitted from the superstructure. This paper presents an experimental study of the deterioration characteristics of shear strengths of residual soils affected by drying-wetting cycles and continuous vibrations. A series of triaxial tests were performed on compacted residual soil specimens after various drying-wetting cycles and vibrations. The influences of drying-wetting cycles and vibrations on the shear strengths of residual soils with different compaction degrees were analyzed. The results demonstrate that the shear strength and cohesion of compacted residual soils decreased as the number of drying-wetting cycles increased, and they tended to be stable after three drying-wetting cycles. The angle of internal friction decreased linearly with the reduction of compaction degree but was generally not affected by drying-wetting cycles. The shear strength of compacted residual soils also decreased because of continuous vibrations. After 10000 vibrations, the strength was stabilized gradually. Both the cohesion and angle of internal friction showed dynamic attenuation phenomenon. Finally, a modified Mohr–Coulomb strength equation considering the effects of drying-wetting cycles and vibrations was established. This equation could be used to predict the shear strength of compacted residual soils and further estimate the embedded depth of wind turbine foundations.
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Li, Shuyi, Zhilei He, Peng Zhu, Longxi Mei, Shaojun Zeng, and Siwei Wang. "Experimental Study on the Triaxial Compression Properties of Coarse-Grained Filling Soil under Drying–Wetting Cycles." Geofluids 2022 (November 14, 2022): 1–14. http://dx.doi.org/10.1155/2022/1452916.
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To explore the mechanical properties of coarse-grained filling soil in the hydrofluctuation belt of the Baihetan reservoir, a fast drying–wetting cycle method for large-scale triaxial tests was developed and a series of large-scale triaxial compression tests of coarse-grained soil were conducted under drying–wetting cycles. The results show that the drying–wetting cycles and the confining pressure are both important factors affecting the mechanical properties of coarse-grained soil. The influences of the first and second cycles on the deviatoric stress–strain curve of the coarse-grained soil are the greatest, while the influences of the third to seventh cycles tend to be stable. The peak strain is not affected by the drying–wetting cycles but only increases with increasing confining pressure. The axial strain and volumetric strain at the volume expansion point decrease with increasing number of drying–wetting cycles but increase with increasing confining pressure. The secant modulus of the peak point decreases with increasing number of drying–wetting cycles, and the initial tangent modulus decreases slightly. The influence of the drying–wetting cycles on the cohesion of the coarse-grained soil is greater than that on the internal friction angle. The typical “bulging” phenomenon occurred after the specimens were destroyed. A damage constitutive equation was developed by introducing a damage variable into the hyperbolic model to reflect the influence of the number of drying–wetting cycles. The model parameters were obtained and the proposed model was verified by fitting the experimental results.
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Xu, Xu-tang, Dao-qi Liu, Zhen-xing Xian, Feng Yang, Wen-bin Jian, Xiang Xu, and Jian-bin Huang. "Influence of Drying–Wetting Cycles on the Water Retention and Microstructure of Residual Soil." Geofluids 2022 (August 30, 2022): 1–15. http://dx.doi.org/10.1155/2022/9948658.
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Due to frequent changes in the humid and hot environment, the residual soil with a particle-size distribution (PSD) from gravel to clay experiences multiple drying–wetting cycles. The pressure plate test and nuclear magnetic resonance (NMR) spectroscopy were used to investigate the influence of drying–wetting cycles on the soil–water characteristic curve (SWCC) and pore-size distribution (POSD) of undisturbed residual soil. The results showed that the water-holding capacity of the residual soil decreased as the number of drying–wetting cycles increased and gradually stablilized, and then the van Genuchten (VG) model was found to perform well on the SWCC during the drying–wetting processes. The NMR results indicated a double-pore structure, and the porosity of the residual soil as well as the internal water content increased smoothly with more drying–wetting cycles. The obtained POSD curve of soil implied that drying–wetting cycles had a more obvious effect on small pores and macro-pores than on micro-pores and meso-pores. Theoretical calculations evinced that the product of the matric suction and relaxation time should be constant at a constant temperature. However, the experimental results did not effectively reflect such a relation between the matric suction and relaxation time. A modified VG model based on the cumulative pore volume was utilized to describe the POSD under drying–wetting cycles. Subsequently, the proposed Rational2D surface equation was used to accurately reflect the internal relationship between the SWCC and POSD curve under different numbers of drying–wetting cycles. Moreover, the fractal model for the SWCC derived from the capillary theory confirmed that the matric suction had a strong linear relationship with the relative volumetric water content in the log-log scale. Also, the fractal dimension can be approximated as a constant, because its attenuation is small with more drying–wetting cycles.
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Hao, Ruihua, Zizhao Zhang, Zezhou Guo, Xuebang Huang, Qianli Lv, Jiahao Wang, and Tianchao Liu. "Investigation of Changes to Triaxial Shear Strength Parameters and Microstructure of Yili Loess with Drying–Wetting Cycles." Materials 15, no. 1 (December 29, 2021): 255. http://dx.doi.org/10.3390/ma15010255.
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This research examined the drying–wetting cycles induced changes in undrained triaxial shear strength parameters and microstructural changes of Yili loess. The drying–wetting cycles were selected as 0, 1, 3, 5, 10, 20 and 30. Then, we collected Yili loess samples and performed unconsolidated-undrained (U-U) triaxial shearing tests to ascertain the variation in shear strength parameters with drying–wetting cycles. Additionally, we investigated the microstructural changes of Yili loess samples under drying–wetting cycles simultaneously via nuclear magnetic resonance (NMR) and scanning electron electroscopy (SEM). Finally, we established a grey correlation model between shear strength and microstructural parameters. Under U-U conditions, the prime finding was that the loess’s shear strength parameters changed overall after drying–wetting cycles; in particular, the internal friction angle φ dropped significantly while the cohesion c changed only slightly during cycles. For all the cycles, the first cycle gave the highest change. Soil morphology deterioration was evident at the initial stage of cycles. During the entire drying–wetting cyclic process, pore size distribution showed progressive variance from two-peak to a single-peak pattern, while both porosity and the fractal dimension of pores increased gradually towards stability. Soil particle morphology became slowly simple and reached the equilibrium state after 20 drying–wetting cycles. Under cyclic drying–wetting stress, the shear strength parameter changes were significantly correlated to microstructural modifications. This investigation was related to loess in the westerly region. The findings were expected to provide new insight into establishment of the connection between microstructure and macro stress–strain state of loess. To some extent, it provided a theoretical basis for the prevention and control of loess engineering geological disasters in Yili, Xinjiang and other areas with similar climate and soil types.
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Qin, Zhe, Xuxin Chen, and Houli Fu. "Damage Features of Altered Rock Subjected to Drying-Wetting Cycles." Advances in Civil Engineering 2018 (2018): 1–10. http://dx.doi.org/10.1155/2018/5170832.
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An abandoned open pit was used as a tailing pond for a concentrating mill, with the height of the water surface subject to cyclic fluctuation. The effects of drying and wetting cycles on the mechanical parameters of pit rock were tested. Interactions of the hydrochemical environment, due to the dissolution of tailings, and drying and wetting cycles caused degradation of mechanical properties in the rock. It was found that uniaxial compressive strength and elastic modulus decreased as the number of dry/wet cycles increased. The quantitative relationship between the mechanical parameters and the number of dry/wet cycles was indicated by an exponential function. In addition to uniaxial testing, cohesion and the internal friction angle were determined through triaxial testing. The shear strength index deteriorated under the drying and wetting cycles. The hydrochemical environment also negatively affected the mechanical parameters. Potential effects between drying and wetting cycles and slope displacement were analyzed by on-site monitoring. The results show that the displacement increased because of the drying and wetting cycles, which may lead to sudden failure of the slope.
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Mao, Yun Cheng, Guo Yu Li, Jun Xia Lei, Li Ru Zhang, and Zhao Yu Chen. "Experimental Study on the Effects of Wetting-Drying Cycles of Compacted Loess." Advanced Materials Research 831 (December 2013): 326–30. http://dx.doi.org/10.4028/www.scientific.net/amr.831.326.
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It rains more concentrated in the summer with high temperature and strong evaporation in Gansu province, wetting-drying cycles usually occur in the embankment. Different collapse and uneven settlement appeared on the embankment in loess areas. Based on those engineering disease, through wetting-drying cycles tests of compacted loess, results show that void ratio increased, dry density decreased and cohesion significantly reduced with violent wetting-drying cycles. This illustrates that wetting-drying cycle has a significant impact on compacted loess and makes well-compacted loess with collapsibility again, it is the important reason of uneven settlement of embankment in northwest loess areas.
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Kong, Lingwei, Hossain Md Sayem, and Huihui Tian. "Influence of drying–wetting cycles on soil-water characteristic curve of undisturbed granite residual soils and microstructure mechanism by nuclear magnetic resonance (NMR) spin-spin relaxation time (T2) relaxometry." Canadian Geotechnical Journal 55, no. 2 (February 2018): 208–16. http://dx.doi.org/10.1139/cgj-2016-0614.
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Due to the formational environment and climatic variability, granite residual soils with grain-size distribution ranging from gravel to clay undergo multiple drying–wetting cycles. The influences of multiple drying–wetting cycles on the soil-water characteristic curve (SWCC) and pore-size distribution (POSD) of undisturbed granite residual soils are investigated using the pressure plate test and nuclear magnetic resonance (NMR) spin-spin relaxation time (T2) distribution measurement, respectively. Results show that the water-retention capacity and air-entry value decrease and pores become more uniform with increasing drying–wetting cycles. After four drying–wetting cycles, the soil reaches a nearly constant state. The POSD change of multiple drying–wetting cycle samples is consistent with the SWCC of the soils. Furthermore, a modified van Genuchten model in terms of cumulative pore volume is used to obtain the best-fit POSD of the drying–wetting cycle samples. The shape and changing tendency of both curves of SWCC and POSD are quite similar and achieved a better correlation. It can be concluded that the SWCC is strongly dependent on the POSD of the soil and NMR T2 relaxometry can be used as an alternative to the assessment of microstructural variation of residual soils subjected to the periodic drying and wetting process.
Dissertations / Theses on the topic "Wetting-Drying cycles"
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Abualgasem, Jumma. "The effect of wetting and drying cycles and carbonation on thaumasite formation." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/6899/.
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Thaumasite form of sulfate attack is having great attention since its discovering in series of foundations supporting motorway bridges in the UK in the late nineties of the last century. This is mainly due to its destructive effect on concrete structures, and the lack of information about its formation mechanisms. This research conducted a study on the effect of wetting and drying, carbonation and the effect of water to cement ratio on the thaumasite formation, and whether these effects are linked with other parameters such as cement type and sulfate concentration or not. 10 different mixes were produced based on four binder types in this study namely 100% CEM I, 90% CEM I + 10% Limestone filler, 50% CEM I + 50 %PFA and 30% CEM I +70%GGBS. A series of mortar samples of two types were prepared 50 mm cubes and 40 × 40 × 160 mm prisms. The samples were kept in three different solutions contain BRE DS3,DS4 based on magnesium sulfate MgSO4.7H2O in addition to deionised water. Two different temperatures 5°C and 20°C were also used to confirm the formation of thaumasite at ambient temperatures (20°C) and to accelerate its formation at 5°C. The effect of wetting and drying cycles on thaumasite formation was studied and compared with samples immersed continuously in the same solutions for 12 months. Powder-sulfate interaction and its effect on thaumasite formation was studied by grinding mortar samples to a fine powder, thus eliminating the permeability effect and enabling physical factors that affect the rate at which solutions can be transferred through the mortar to be separated from chemical factors that affect the rate at which the chemical reactions take place. Visual observations, mass and length changes were used to assess the mortar deterioration, along with X-ray diffraction, infra-red spectroscopy and SEM that were used to determine the mineralogy of deterioration products. For the cyclic wetting and drying exposure regime the results showed that wetting and drying cycles significantly delayed thaumasite formation compared with control specimens. For powder samples, it is found that thaumasite is readily formed in these powders after 3 months of exposure to sulfate solutions including GGBS and PFA samples, on the other hand cubes and prisms, exposed to the same solutions for 24 months showed no signs of deterioration. Thermodynamic modelling was used to predict the deterioration products for powders samples and good agreement between predicted and observed results was found.
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Hindle, Kristi Marie. "The influence of wetting and drying cycles on the biogeochemical dynamics of mercury in sediments." Thesis, University of Ottawa (Canada), 2005. http://hdl.handle.net/10393/26924.
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Decommissioning hydro-dams increases sediment exposure to air, altering biogeochemical cycling of metals. Hg and MeHg mobility was studied in reservoir sediments from two Eastern Ontario lakes (Stump (SL) and Black Donald (BDL)) submitted to wet/dry cycles with artificial rainwater (pH∼4.5) every two weeks. Leachate pH, sulphate, sulphide and MeHg, and sulphate-reducing bacteria (SRB) populations were monitored over 6 months. The sediments did buffer the rainwater at the start of the experiment, but leachate pH decreased over time for both lakes. MeHg release occurred during the first draining event (2-4 ppt), and decreased thereafter, with no relationship with pH, sulphide and sulphate. SRB populations remained constant over time. Over 70% of Hg was in the non-labile refractory organic and residual phases, where Hg moved to semi-mobile phases in SL, but shifted to more immobile phases in BDL over time. Decommissioning hydro-dam reservoirs may increase acid production and alter Hg partitioning in sediments, while MeHg release will be low.
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Nugent, Michelle V. "Biogeochemical dynamics of iron and sulfur in sediments from hydro-electric dams submitted to wetting and drying cycles." Thesis, University of Ottawa (Canada), 2005. http://hdl.handle.net/10393/26996.
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Water level changes due to the decommissioning of hydro-electric dams can result in sediment exposure to air. Oxidation of sediments can decrease the pH as a result of iron sulfides changing into iron oxides. The present study was designed to simulate drying and wetting cycles of shallow lake sediments from two lakes (Stump and Black Donald Lakes in Ontario), in order to assess the mineralogical changes of Fe-rich minerals. Our results indicate that the total reactive iron fraction of the sediment increased after the wetting and drying cycles. This increase was caused by the weathering of pyrite and Fe-silicates and their subsequent transformation into more Fe-reactive mineral species. The pH of the surface sediments also decreased following the addition of simulated rainwater and the oxidation of iron sulfides in the sediments. This preliminary study shows that the decommissioning of hydro-electric dams will have an effect on the biogeochemical cycles of iron and sulfur.
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Vieira, Juliana Matos. "Contribution of low crystalline compounds and wetting and drying cycles in the genesis of the cohesive character in Cearà soils." Universidade Federal do CearÃ, 2013. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=10865.
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CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel SuperiorThe Coastal Plains exhibit cohesive soils, which can cause physical impediments to root penetration and water dynamics. However, in the genesis of these horizons are not completely understood. Thus, the aim of the present study was to evaluate the influence of amorphous compounds in the genesis of cohesive horizons in soils of different textures of the Coastal Plains of CearÃ, as well as verify, through physical behavior of these soils in the presence and absence of these compounds. This study also aimed to evaluate the influence of wetting and drying cycles in the density of these soils. To evaluate the effect of amorphous compounds in soil cohesion, we used samples from the air-dried cohesive horizons 9 soil profiles of the state of CearÃ, these being subjected to two treatments: with and without extraction of amorphous compounds. The samples (with and without extraction) were subjected to 3 cycles of wetting and drying, and subsequently, the penetration resistance (PR), hydraulic conductivity and bulk density were determined. To assess the influence of wetting and drying cycles in the density of these soils were performed 3 different levels of wetting and drying cycles (3, 6, 9 cycles). After these cycles, penetration resistance resistance and density were evaluated. The additions of silica and aluminum low crystalline (amorphous) in cohesive soils show that these compounds contribute jointly in the genesis of these horizons. Regardless of texture, soil that passed through the extraction process of amorphous compounds showed a significant reduction in soil resistance to penetration and density. It was found that these soils, the hydraulic conductivity was higher than that observed in soil without extraction of amorphous compounds. Thus, it is clear the contribution of these compounds in the hardening in cohesive soils. With regard to the effects of wetting and drying cycles assessed characteristics of the soil (RP and density), it was observed that in general, increasing the number of cycles caused a subtle increase in bulk density. Soils that have gone by 9 cycles of wetting and drying showed a remarkable increase in RP in relation to soils soils that have undergone 3and 6 cycles.
Os Tabuleiros Costeiros apresentam solos com carÃter coeso, os quais podem ocasionar impedimento fÃsico à penetraÃÃo das raÃzes e à dinÃmica da Ãgua. No entanto, a gÃnese desses horizontes nÃo està completamente esclarecida. Dessa forma, objetivou-se com o presente trabalho avaliar a influÃncia de compostos amorfos na gÃnese de horizontes com carÃter coeso em solos de diferentes texturas dos Tabuleiros Costeiros do CearÃ, bem como verificar, atravÃs de anÃlises fÃsicas o comportamento desses solos na presenÃa e na ausÃncia desses compostos. Objetivou-se tambÃm, avaliar a influÃncia de ciclos de umedecimento e secagem no adensamento desses solos. Para avaliaÃÃo do efeito dos compostos amorfos na coesÃo dos solos, foram utilizadas amostras de TFSA de horizontes com carÃter coeso de 9 perfis de solo do estado do CearÃ, sendo estas, submetidas a 2 tratamentos: com e sem extraÃÃo de compostos amorfos. As amostras (com e sem extraÃÃo) foram submetidas a 3 ciclos de umedecimento e secagem e, posteriormente, a resistÃncia à penetraÃÃo (RP), condutividade hidrÃulica e densidade do solo foram determinadas. Para avaliaÃÃo da influÃncia dos ciclos de umedecimento e secagem no adensamento desses solos, foram aplicados 3 diferentes nÃmeros de ciclos de umedecimento e secagem (3, 6, 9 ciclos). ApÃs esses ciclos, a resistÃncia do solo à penetraÃÃo e densidade foram avaliadas. Os acrÃscimos de sÃlica e de alumÃnio de baixa cristalinidade (amorfos) nos horizontes coesos evidenciam que esses compostos contribuem conjuntamente na gÃnese destes horizontes. Independente da textura, os solos que passaram pelo processo de extraÃÃo de compostos amorfos apresentaram uma reduÃÃo significativa na resistÃncia do solo à penetraÃÃo e na densidade. Verificou-se que nesses solos, a condutividade hidrÃulica foi superior Ãquela observada nos solos sem a extraÃÃo dos compostos amorfos. Desse modo, fica clara a contribuiÃÃo desses compostos no endurecimento dos solos coesos. No que se refere aos efeitos dos ciclos de umedecimento e secagem nas caracterÃsticas avaliadas do solo (RP e densidade), observou-se que de um modo geral, o aumento do nÃmero de ciclos provocou um sutil aumento na densidade do solo. Os solos que passaram pelos 9 ciclos de umedecimento e secagem apresentaram um aumento significativo na RP em relaÃÃo aos solos que solos que passaram por 3 e 6 ciclos.
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Yemadje, Pierrot Lionel. "Influence des cycles humectation-dessiccation sur la minéralisation du carbone : cas de la zone cotonnière du Nord Cameroun." Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS209/document.
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Le sol est un compartiment majeur de stockage du carbone (C) organique de l’écosystème terrestre. Il joue un rôle important dans la régulation du climat. Toute variation des flux de carbone entre l’atmosphère et l’écosystème terrestre pourrait avoir un impact important sur l’augmentation de CO2 dans l’atmosphère, mais aussi sur la diminution des teneurs en matière organique du sol et donc sur la fertilité des sols. Au Nord Cameroun, les sols sont exposés à de longues périodes sèches (5 à 6 mois par an) qui alternent avec une saison humide. La période de transition entre ces deux saisons, peut durer de mi-avril à fin juin et est caractérisée par des pluies très irrégulières. Ces cycles d’humectation-dessiccation pourraient selon la littérature accentuer la minéralisation du carbone organique du sol et le cycle des éléments nutritifs. L’objectif de cette étude est de quantifier l’impact des cycles humectation-dessiccation sur la minéralisation du carbone dans un contexte soudano-sahélien. Pour faire des mesures représentatives sur le terrain, il est nécessaire d’étudier la variation sur 24 heures de la respiration du sol après humectation suite à une période sèche. Cette mise au point méthodologique a montré que la respiration du sol présente une courbe quadratique au cours de la journée, devenant presque linéaire au cours de la nuit. La température et l’humidité du sol ont permis d’expliquer au moins 73% des variations sur 24 heures. Ces observations ont été utilisées pour proposer une méthode pour estimer la respiration moyenne diurne et nocturne après humectation des sols. La méthode proposée dans cette étude a l’avantage d’être basée sur un nombre réduit de mesures et est par conséquent plus facile à mettre en œuvre pour suivre la respiration du sol sur 24 heures après les premières pluies. Une première étude expérimentale de terrain a permis de montrer que la ré-humectation des sols et le mode de gestion des pailles ont augmenté la minéralisation du carbone de ces sols. En revanche, la fréquence des cycles humectation-dessiccation des sols sur une période de 50 jours n’a pas augmenté la minéralisation cumulée du carbone des sols. Au Nord Cameroun, la minéralisation rapide des pailles rend difficile l’augmentation des stocks de carbone du sol par conservation des pailles des cultures précédentes à la surface du sol. Dans une seconde expérimentation de laboratoire, en conditions contrôlées, les cycles humectation-dessiccation n’ont pas augmenté la minéralisation du carbone organique du sol et de l’azote (N) par rapport aux sols maintenus humides. Cependant, les émissions de CO2 ont augmenté avec l’addition de paille enrichie en carbone-13. Cette addition de la paille marquée a augmenté la minéralisation de la matière organique du sol (priming effect). La minéralisation de la paille a diminué avec les cycles humectation-dessiccation et la quantité de paille restante était de 102 µg Cg-1 sol sur les sols ré-humectés contre 48 µg Cg-1 sol sur les sols maintenus humides. L’absence de cette réponse de la minéralisation du carbone et d’azote du sol aux cycles humectation-dessiccation pourrait être liée à une baisse de l’activité microbienne durant les périodes de dessèchement et l’absence d’une augmentation soutenue des taux de minéralisation du carbone avec les cycles ultérieurs d’humectation-dessiccationSoil as a major storage component for terrestrial ecosystem’s organic carbon plays an important role in regulating climate and agricultural production. Any variation of carbon fluxes between the atmosphere and the terrestrial ecosystem can have a significant impact on the increase of carbon dioxide in the atmosphere but also the decrease in soil organic matter and thus accelarate soil fertility degradation. In northern Cameroon, the transition period between long dry periods with a wet season is characterized by very irregular rainfall that can last several weeks. These wetting-drying cycles can accentuate the mineralization of soil organic carbon and nutrient cycling. The objective of this study is to assess the impact of wet-dry cycles on carbon mineralization in a sudano-sahelian context. From methodological stand field measurements require to study the soil respiration variation over 24 hours after a wet period. This methodological test has shown that soil respiration has a quadratic curve during the day, becoming almost linear during the night. The temperature and soil moisture have explained together the variation over 24 hours (at least 73% ; p< 0.001). These observations have been used to propose a method for estimating the mean daytime and nighttime soil respiration after wetting the soil. Indeed the method proposed in this study has the advantage of being based on a small number of measurements and is, therefore, easier to implement to monitor 24-h soil respiration after the first rains following a long dry period. A first experiment has shown that the wetting of the soil and mulching increased soil carbon mineralization. However, wetting-drying cycles on soil did not increase the cumulative mineralization of soil carbon more than keeping the soil continuously moist. Indeed, in northern Cameroon, the rapid mineralization of crop residues makes it difficult to increase soil carbon stocks by mulching. In a second laboratory experiment, the wetting-drying cycles did not increase organic carbon and nitrogen mineralization from soils added with straw. However, carbon dioxide emissions increased on straw amended soils compared to soils without straw. This addition of the labeled straw increased mineralization of soil organic matter (priming effect). The mineralization of the straw also decreased with the wetting-drying cycles, thus the amount of straw remaining on soils was 102 µg C g-1 soil on re-wetted soils compared to 48 µg C g-1 soil for those with constant moisture. The lack of response for C and N mineralization during wetting-drying cycles may be linked to a decrease of microbial activity during dry periods and the lack of a steady increase in the carbon mineralization rate with subsequent wetting-drying cycles
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Zhang, Zhidong. "Modelling of sorption hysteresis and its effect on moisture transport within cementitious materials." Thesis, Paris Est, 2014. http://www.theses.fr/2014PEST1055/document.
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La durabilité des structures en béton armé ainsi que leur durée de vie sont étroitement liées à la mise en œuvre simultanée de nombreux phénomènes physiques et chimiques. Ceux-ci sont de diverses natures mais restent, en général, fonction des propriétés hydriques des matériaux étudiés. Ainsi, la prédiction des dégradations potentielles d'un matériau cimentaire requiert l'étude du transport de l'eau liquide et des phases gazeuses à travers ce dernier, considéré comme un milieu poreux. En milieu naturel, les structures subissent des variations périodiques de l'humidité relative extérieure (HR). Cependant, la plupart des modèles de transfert hydrique préexistants dans la littérature, s'intéresse uniquement au processus de séchage. Il existe peu de modèles décrivant à la fois l'humidification et le séchage du matériau (ces deux phénomènes se produisent dans le matériau en condition naturelle d'humidité relative (HR)). Tenir compte des phénomènes d'hystérésis dans les transferts hydriques réduit à nouveau le nombre de modèles à disposition. Ainsi, cette thèse s'attache à proposer une meilleure compréhension de l'état hydrique du béton en fonction des variations d'humidité relative extérieure, sur la base d'une nouvelle campagne expérimentale et de modélisations numériques. Un soin sera apporté afin de tenir compte dans les modèles numériques des effets d'hystérésis. Dans ce travail, nous détaillerons, tout d'abord, un modèle multi-phasiques complet. Un modèle simplifié est obtenu, sur la base de considérations théoriques et de vérifications expérimentales dans le cas où la perméabilité intrinsèque à l'eau liquide reste très inférieure à la perméabilité intrinsèque au gaz. Une étude comparative des modèles d'hystérésis couramment utilisés permet d'obtenir un jeu de modèles proposant les meilleures prédictions d'isothermes de sorption d'eau et de leurs hystérésis. Par la suite, le modèle de transport simplifié est couplé avec les modèles d'hystérésis sélectionnés afin de simuler les transferts hydriques dans des bétons soumis à des cycles d'humidification-séchage. La comparaison avec des données expérimentales révèle que la prise en compte de l'hystérésis de l'isotherme de sorption d'eau ne peut pas être négligé. De plus, il est montré que les prédictions obtenues avec des modèles d'hystérésis théoriques, sont les plus cohérentes avec les résultats expérimentaux, en particulier, pour des chemins secondaires d'hystérésis. Plusieurs scénarios (conditions environnementales, bétons différents) sont également simulés. Les résultats obtenus pointent à nouveau la nécessité de tenir compte de l'hystérésis lors de la modélisation des transferts hydriques à travers des matériaux cimentaires soumis à des variations d'humidité relative. La définition d'une profondeur pour laquelle le profil hydrique du béton est modifié par les variations périodiques d'humidité relative permet de mieux comprendre comment la modélisation de la pénétration des espèces ioniques est influencée par les cycles d'humidification-séchage. Par ailleurs, notre analyse révèle qu'il est pertinent de considérer l'effet de Knudsen pour la diffusion de la vapeur afin d'améliorer la prédiction de la diffusivité apparenteThe durability of reinforced concrete structures and their service life are closely related to the simultaneous occurrence of many physical and chemical phenomena. These phenomena are diverse in nature, but in common they are dependent on the moisture properties of the material. Therefore, the prediction of the potential degradation of cementitious materials requires the study of the movement of liquid-water and gas-phase transport in the material which is considered as a porous medium. In natural environment, structures are always affected by periodic variations of external relative humidity (RH). However, most moisture transport models in the literature only focus on the drying process. There are few researches considering both drying and wetting, although these conditions represent natural RH variations. Even few studies take into account hysteresis in moisture transport. Thus, this work is devoted to better understand how the moisture behaviour within cementitious materials responds to the ambient RH changes through both experimental investigations and numerical modelling. In particular, hysteretic effects will be included in numerical modelling. In this thesis, we first recalled a complicate multi-phase continuum model. By theoretical analysis and experimental verification, a simplified model can be obtained for the case of that the intrinsic permeability to liquid-water is smaller than the intrinsic permeability to gas-phase. The review of commonly-used hysteresis models enabled to conclude a set of best models for the prediction of water vapour sorption isotherms and their hysteresis. After that, the simplified model was coupled with selected hysteresis models to simulate moisture transport under drying and wetting cycles. Compared with experimental data, numerical simulations revealed that modelling with hysteretic effects can provide much better results than non-hysteresis modelling. Among different hysteresis models, results showed that the use of the conceptual hysteresis model, which presents closed form scanning loops, can provide more accuracy predictions. Further simulations for different scenarios were also performed. All comparisons and investigations enhanced the necessity of considering hysteresis to model moisture transport for varying relative humidity at the boundary. The investigation of moisture penetration depth could provide a better understanding of how deep moisture as well as ions can move into the material. Furthermore, the analysis revealed that the consideration of Knudsen effects for diffusion of vapour can improve the prediction of the apparent diffusivity
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Bavoso, Marina Araujo. "Resiliência física de solos sob plantio direto." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/11/11140/tde-13082012-102952/.
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A resiliência física de solos é proveniente de processos regenerativos que incluem ciclos de umedecimento e secamento, congelamento e descongelamento assim como as atividades biológicas. Este estudo testou a hipótese de que as propriedades físicas do solo,tais como a permeabilidade do solo ao ar, densidade do solo, porosidade de aeração e porosidade total são indicadores físicos eficientes para quantificar a resiliência de solos de diferentes texturas submetidos ao estresse mecânico (compactação) e após subseqüentes ciclos de umedecimento e secamento. O objetivo foi avaliar o comportamento e a resiliência do solo por meio de propriedades físicas de um Latossolo Vermelho. Foram retiradas 25 amostras indeformadas (0-0,05m) de dois solos: solo I com textura argilosa e solo II com textura franco argilo arenosa, realizando as determinações das propriedades físicas nos tratamentos: antes da compactação(A), depois da compactação (C0) e após ciclos de umedecimento e secamento (C1,C2,C3,C4). As propriedades densidade do solo e porosidade total não apresentaram recuperação da condição inicial após a compactação nos solos I e II, as propriedades conteúdo volumétrico de água e porosidade de aeração apresentaram recuperação parcial apenas no solo I, para o solo II também não apresentaram recuperação, e a permeabilidade do solo ao ar foi a propriedade que apresentou a melhor recuperação assim como foi a que apresentou maior resiliência. Em relação ao distinto comportamento dos dois solos, observou-se que o solo I foi mais resiliente que o solo II nas propriedades que apresentaram recuperação.The soil physical resilience comes from regenerative processes which include cycles of wetting and drying, freezing and thawing as well as biological activities. This study tested the hypothesis that the physical properties of soil such as soil permeability, bulk density, aeration porosity and total porosity are efficient physical indicators to quantify the resilience of soils of different textures subjected to mechanical stress (compression) and after subsequent cycles of wetting and drying. The objective was to evaluate the behavior and soil resilience by means of physical properties of an Oxisol. Undisturbed samples were taken 25 (0-0.05 m) of two soils: clayey soil and soil with sandy clay loam texture, making determinations of physical properties in the treatments before compression (A), after compaction (C0) and after wetting and drying cycles (C1, C2, C3, C4). The bulk density properties and porosity did not recover the initial condition after compression in the soil I and II, the properties volumetric content of water and air-filled porosity showed only partial recovery in the soil I, II to the soil also showed no recovery and soil permeability to air was the property that showed the best recovery as well as showed the greatest resilience. Regarding the different behavior of the two soil, it was observed that the soil I was more resilient soil II in which showed recovery properties
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Hong, Katherine. "Cyclic wetting and drying and its effects on chloride ingress in concrete." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0022/MQ34117.pdf.
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Loubser, M. J. (Michael John). "Weathering potential of wetting and drying of sandstone and basalt : a laboratory isolation study." Diss., University of Pretoria, 2010. http://hdl.handle.net/2263/29251.
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The cyclic wetting and drying of a rock is considered to be one of a number of physical weathering processes that have an effect on the weathering of rock. While the presence of moisture is known to be of critical importance for the activation and enhancement of a number of other known weathering processes, such as cryogenic weathering, salt weathering and slaking it is possible that the mere cyclic application and removal of moisture over time may also have an effect on the physical structure of a rock. The precise nature of the process is not well understood, however. This document begins by investigating the studies that have previously been undertaken to determine how the wetting and drying weathering process is defined and to ascertain the current state of knowledge regarding this process. After an establishment of background context, a physical experiment is carried out on Clarens Formation sandstone and Marion Island basalt to note the relationship between cyclic wetting and drying and the changing physical properties of the rocks. The rocks were subjected to 105 wetting and drying cycles over a period of 21 weeks. At the beginning of the experiment, physical rock properties were measured by way of the method laid out by Cooke (1979) and again at the end of the experiment. Since the experiment was carried out under static environmental conditions, the comparison of physical rock properties gives a good indication of how the rocks have altered their structure over the experimental time period. The results obtained in this experiment show that different rock types will change in different ways when exposed to a common weathering process. The basalt samples experienced no mass loss at, while the sandstones did. The sandstones, which are rocks that are of common lithology and of very similar physical and chemical structure reacted to the wetting and drying weathering process in ways that could not be predicted without experimentation. The data does show a clear causal link between the application of external stimuli and rock property change, however. Changes in physical rock properties are not always straightforward and linear, but evolve dynamically over time, often yielding results that appear to oppose those intuitively predicted. A number of questions are asked regarding the philosophical approach that is taken to process isolation studies, with emphasis given to the careful consideration of the place that such studies have in the realm of process geomorphology. While process isolation studies may give an excellent indication of what a particular weathering process may be capable of under certain conditions and on certain rock types, they should not be regarded as indicative of what is occurring in the field. Additionally, it has become clear that it is not possible to predict how a specific rock type may respond to a specific weathering process without physical experimentation since the number of variables present in a typical weathering system are simply too vast to easily categorise.Dissertation (MSc)--University of Pretoria, 2010.
Geography, Geoinformatics and Meteorology
MSc
Unrestricted
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Golden, Gavin. "The effect of cyclic wetting and drying on the corrosion rate of steel in reinforced concrete." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/13654.
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Preventing chloride-induced reinforcement corrosion in marine concrete structures remains a concern for structural engineers. Marine structures are typically exposed to high chloride concentrations through direct exposure to sea water, which provides the primary conditions required for reinforcement corrosion. The progress of corrosion can be controlled through anodic, cathodic or resistivity processes. However, high chloride concentrations tend to prevent anodic control from governing the corrosion rate, while direct exposure to moisture generally prevents resistivity control. Consequently, cathodic control remains an important process in the marine environment to restrict the progress of corrosion. The primary cathodic reaction in reinforcement corrosion is the reduction of oxygen, and as a result the availability of oxygen is a key factor when considering reinforcement corrosion in the marine tidal zone. The corrosion rate may be effectively reduced if the drying time of the concrete during tidal cycles is sufficiently short, thereby reducing the oxygen supply at the level of the embedded steel.
Books on the topic "Wetting-Drying cycles"
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Hong, Katherine. Cyclic wetting and drying and its effects on chloride ingress in concrete. Ottawa: National Library of Canada, 1998.
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Yang, Kun. Observed Regional Climate Change in Tibet over the Last Decades. Oxford University Press, 2017. http://dx.doi.org/10.1093/acrefore/9780190228620.013.587.
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The Tibetan Plateau (TP) is subjected to strong interactions among the atmosphere, hydrosphere, cryosphere, and biosphere. The Plateau exerts huge thermal forcing on the mid-troposphere over the mid-latitude of the Northern Hemisphere during spring and summer. This region also contains the headwaters of major rivers in Asia and provides a large portion of the water resources used for economic activities in adjacent regions. Since the beginning of the 1980s, the TP has undergone evident climate changes, with overall surface air warming and moistening, solar dimming, and decrease in wind speed. Surface warming, which depends on elevation and its horizontal pattern (warming in most of the TP but cooling in the westernmost TP), was consistent with glacial changes. Accompanying the warming was air moistening, with a sudden increase in precipitable water in 1998. Both triggered more deep clouds, which resulted in solar dimming. Surface wind speed declined from the 1970s and started to recover in 2002, as a result of atmospheric circulation adjustment caused by the differential surface warming between Asian high latitudes and low latitudes.The climate changes over the TP have changed energy and water cycles and has thus reshaped the local environment. Thermal forcing over the TP has weakened. The warming and decrease in wind speed lowered the Bowen ratio and has led to less surface sensible heating. Atmospheric radiative cooling has been enhanced, mainly through outgoing longwave emission from the warming planetary system and slightly enhanced solar radiation reflection. The trend in both energy terms has contributed to the weakening of thermal forcing over the Plateau. The water cycle has been significantly altered by the climate changes. The monsoon-impacted region (i.e., the southern and eastern regions of the TP) has received less precipitation, more evaporation, less soil moisture and less runoff, which has resulted in the general shrinkage of lakes and pools in this region, although glacier melt has increased. The region dominated by westerlies (i.e., central, northern and western regions of the TP) received more precipitation, more evaporation, more soil moisture and more runoff, which together with more glacier melt resulted in the general expansion of lakes in this region. The overall wetting in the TP is due to both the warmer and moister conditions at the surface, which increased convective available potential energy and may eventually depend on decadal variability of atmospheric circulations such as Atlantic Multi-decadal Oscillation and an intensified Siberian High. The drying process in the southern region is perhaps related to the expansion of Hadley circulation. All these processes have not been well understood.
Book chapters on the topic "Wetting-Drying cycles"
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D’Agostino, Delia. "Modelling of Wetting and Drying Cycles in Building Structures." In Drying and Wetting of Building Materials and Components, 113–43. Cham: Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-04531-3_6.
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Dong, Jungui, Guoyuan Xu, Hai-bo Lv, and Junyan Yang. "Instrument for Wetting-Drying Cycles of Expansive Soil Under Loads." In Springer Series in Geomechanics and Geoengineering, 492–95. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-97112-4_110.
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Matos, Ana Mafalda, Sandra Nunes, Stefan Chaves Figueiredo, Erik Schlangen, and José L. Barroso Aguiar. "Chloride Ion Penetration into Cracked UHPFRC During Wetting-drying Cycles." In RILEM Bookseries, 227–38. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-76551-4_21.
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Zhang, Zongtang, Wenhua Gao, Junqi Zhang, Zhimin Zhang, Meihui Yi, and Xiaoyu Tang. "Disintegration Characteristics and Fractal Features of Red Sandstone During Drying–Wetting Cycles." In Lecture Notes in Civil Engineering, 331–45. Singapore: Springer Singapore, 2020. http://dx.doi.org/10.1007/978-981-15-2349-6_21.
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Bin Wan Ibrahim, Mohd Haziman, Shahiron Shahidan, Hassan Amer Algaifi, Ahmad Farhan Bin Hamzah, and Ramadhansyah Putra Jaya. "CBA Self-compacting Concrete Exposed to Seawater by Wetting and Drying Cycles." In Properties of Self-Compacting Concrete with Coal Bottom Ash Under Aggressive Environments, 59–75. Singapore: Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-16-2395-0_4.
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Nabil, Maafi, Akchiche Mustapha, and Sara Rios. "Long Term Evaluation of Wetting-Drying Cycles for Compacted Soils Treated with Lime." In Recent Advances in Geo-Environmental Engineering, Geomechanics and Geotechnics, and Geohazards, 277–81. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-030-01665-4_64.
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Jha, Arvind Kumar, and Manuj Sharma. "Effect of Wetting–Drying Cycles on Strength Behavior of Lime Stabilized Expansive Soil." In Lecture Notes in Civil Engineering, 23–33. Singapore: Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-33-6466-0_3.
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Abdalla, Tavga Aram, and Nihad Bahaaldeen Salih. "Wetting and Drying Cycles Influences on Geotechnical Properties of Lime-Stabilized Clayey Soil." In Current Trends in Geotechnical Engineering and Construction, 278–89. Singapore: Springer Nature Singapore, 2022. http://dx.doi.org/10.1007/978-981-19-7358-1_24.
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Cardoso, Rafaela, Vasco Fernandes, Tiago Moço Ferreira, and Paulo Fonseca Teixeira. "Settlement Prediction of High Speed Railway Embankments Considering the Accumulation of Wetting and Drying Cycles." In Unsaturated Soils: Research and Applications, 291–98. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-31343-1_37.
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Rosone, Marco, Camillo Airò Farulla, Clara Celauro, and Alessio Ferrari. "Volumetric Behaviour of Lime Treated High Plasticity Clay Subjected to Suction Controlled Drying and Wetting Cycles." In Advances in Laboratory Testing and Modelling of Soils and Shales (ATMSS), 165–72. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-52773-4_18.
Full textConference papers on the topic "Wetting-Drying cycles"
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Ali, Alexis, Mostafa Mohamed, Mohamed Abdel Aal, Alma Schellart, and Simon Tait. "Thermal and Hydraulic Properties of Sandy Soils during Drying and Wetting Cycles." In Geo-Shanghai 2014. Reston, VA: American Society of Civil Engineers, 2014. http://dx.doi.org/10.1061/9780784413456.014.
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Chen, Kaisheng, and Ronghua Zhu. "Study of the deformation characteristics for red clay under drying-wetting cycles." In 5th International Conference on Civil Engineering and Transportation. Paris, France: Atlantis Press, 2015. http://dx.doi.org/10.2991/iccet-15.2015.95.
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"Delayed Ettringite Formation in Concrete: Tests Based on Drying and Wetting Cycles." In SP-212: Sixth CANMET/ACI: Durability of Concrete. American Concrete Institute, 2003. http://dx.doi.org/10.14359/12734.
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Starcher, Ryan D., Sarah L. Gassman, and Charles E. Pierce. "The Durability of Chemically Treated Soils Subjected to Cycles of Wetting and Drying." In Geo-Chicago 2016. Reston, VA: American Society of Civil Engineers, 2016. http://dx.doi.org/10.1061/9780784480144.072.
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"Surface Strain Experienced by Mortar in Wetting-Drying Cycles and Deicer Salt Application." In SP-170: Fourth CANMET/ACI International Conference on Durability of Concrete. American Concrete Institute, 1997. http://dx.doi.org/10.14359/6857.
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Mijares, Ramil G., and Milind V. Khire. "Soil Water Characteristic Curves of Compacted Clay Subjected to Multiple Wetting and Drying Cycles." In GeoFlorida 2010. Reston, VA: American Society of Civil Engineers, 2010. http://dx.doi.org/10.1061/41095(365)37.
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Pathak, Y. P., and M. C. Alfaro. "Laboratory Simulation of Seasonal Wetting-Drying Cycles on Geosynthetic-Reinforced Clay Slopes and Embankments." In Geo-Frontiers Congress 2005. Reston, VA: American Society of Civil Engineers, 2008. http://dx.doi.org/10.1061/40782(161)23.
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Lu, Chunhua, Y. Gao, and R. Liu. "Effect of Transverse Crack on Chloride Penetration into Concrete Subjected to Drying–Wetting Cycles." In International Conference on the Durability of Concrete Structures. Purdue University Libraries Scholarly Publishing Services, 2014. http://dx.doi.org/10.5703/1288284315398.
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NSHIMIYIMANA, PHILBERT, CESAIRE HEMA, SEICK OMAR SORE, OUSMANE ZOUNGRANA, ADAMAH MESSAN, and LUC COURARD. "DURABILITY PERFORMANCES OF COMPRESSED EARTH BLOCKS EXPOSED TO WETTING–DRYING CYCLES AND HIGH TEMPERATURE." In ECO-ARCHITECTURE 2022. Southampton UK: WIT Press, 2022. http://dx.doi.org/10.2495/arc220121.
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Borges, Paulo H. R. "Volume changes, cracking and durability of cement grouts subjected to accelerated wetting and drying cycles." In International RILEM Conference on Volume Changes of Hardening Concrete: Testing and Mitigation. RILEM Publications, 2006. http://dx.doi.org/10.1617/2351580052.026.
Full textReports on the topic "Wetting-Drying cycles"
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Snyder, Victor A., Dani Or, Amos Hadas, and S. Assouline. Characterization of Post-Tillage Soil Fragmentation and Rejoining Affecting Soil Pore Space Evolution and Transport Properties. United States Department of Agriculture, April 2002. http://dx.doi.org/10.32747/2002.7580670.bard.
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Tillage modifies soil structure, altering conditions for plant growth and transport processes through the soil. However, the resulting loose structure is unstable and susceptible to collapse due to aggregate fragmentation during wetting and drying cycles, and coalescense of moist aggregates by internal capillary forces and external compactive stresses. Presently, limited understanding of these complex processes often leads to consideration of the soil plow layer as a static porous medium. With the purpose of filling some of this knowledge gap, the objectives of this Project were to: 1) Identify and quantify the major factors causing breakdown of primary soil fragments produced by tillage into smaller secondary fragments; 2) Identify and quantify the. physical processes involved in the coalescence of primary and secondary fragments and surfaces of weakness; 3) Measure temporal changes in pore-size distributions and hydraulic properties of reconstructed aggregate beds as a function of specified initial conditions and wetting/drying events; and 4) Construct a process-based model of post-tillage changes in soil structural and hydraulic properties of the plow layer and validate it against field experiments. A dynamic theory of capillary-driven plastic deformation of adjoining aggregates was developed, where instantaneous rate of change in geometry of aggregates and inter-aggregate pores was related to current geometry of the solid-gas-liquid system and measured soil rheological functions. The theory and supporting data showed that consolidation of aggregate beds is largely an event-driven process, restricted to a fairly narrow range of soil water contents where capillary suction is great enough to generate coalescence but where soil mechanical strength is still low enough to allow plastic deforn1ation of aggregates. The theory was also used to explain effects of transient external loading on compaction of aggregate beds. A stochastic forInalism was developed for modeling soil pore space evolution, based on the Fokker Planck equation (FPE). Analytical solutions for the FPE were developed, with parameters which can be measured empirically or related to the mechanistic aggregate deformation model. Pre-existing results from field experiments were used to illustrate how the FPE formalism can be applied to field data. Fragmentation of soil clods after tillage was observed to be an event-driven (as opposed to continuous) process that occurred only during wetting, and only as clods approached the saturation point. The major mechanism of fragmentation of large aggregates seemed to be differential soil swelling behind the wetting front. Aggregate "explosion" due to air entrapment seemed limited to small aggregates wetted simultaneously over their entire surface. Breakdown of large aggregates from 11 clay soils during successive wetting and drying cycles produced fragment size distributions which differed primarily by a scale factor l (essentially equivalent to the Van Bavel mean weight diameter), so that evolution of fragment size distributions could be modeled in terms of changes in l. For a given number of wetting and drying cycles, l decreased systematically with increasing plasticity index. When air-dry soil clods were slightly weakened by a single wetting event, and then allowed to "age" for six weeks at constant high water content, drop-shatter resistance in aged relative to non-aged clods was found to increase in proportion to plasticity index. This seemed consistent with the rheological model, which predicts faster plastic coalescence around small voids and sharp cracks (with resulting soil strengthening) in soils with low resistance to plastic yield and flow. A new theory of crack growth in "idealized" elastoplastic materials was formulated, with potential application to soil fracture phenomena. The theory was preliminarily (and successfully) tested using carbon steel, a ductile material which closely approximates ideal elastoplastic behavior, and for which the necessary fracture data existed in the literature.
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Or, Dani, Shmulik Friedman, and Jeanette Norton. Physical processes affecting microbial habitats and activity in unsaturated agricultural soils. United States Department of Agriculture, October 2002. http://dx.doi.org/10.32747/2002.7587239.bard.
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experimental methods for quantifying effects of water content and other dynamic environmental factors on bacterial growth in partially-saturated soils. Towards this end we reviewed critically the relevant scientific literature and performed theoretical and experimental studies of bacterial growth and activity in modeled, idealized and real unsaturated soils. The natural wetting-drying cycles common to agricultural soils affect water content and liquid organization resulting in fragmentation of aquatic habitats and limit hydraulic connections. Consequently, substrate diffusion pathways to soil microbial communities become limiting and reduce nutrient fluxes, microbial growth, and mobility. Key elements that govern the extent and manifestation of such ubiquitous interactions include characteristics of diffusion pathways and pore space, the timing, duration, and extent of environmental perturbations, the nature of microbiological adjustments (short-term and longterm), and spatial distribution and properties of EPS clusters (microcolonies). Of these key elements we have chosen to focus on a manageable subset namely on modeling microbial growth and coexistence on simple rough surfaces, and experiments on bacterial growth in variably saturated sand samples and columns. Our extensive review paper providing a definitive “snap-shot” of present scientific understanding of microbial behavior in unsaturated soils revealed a lack of modeling tools that are essential for enhanced predictability of microbial processes in soils. We therefore embarked on two pronged approach of development of simple microbial growth models based on diffusion-reaction principles to incorporate key controls for microbial activity in soils such as diffusion coefficients and temporal variations in soil water content (and related substrate diffusion rates), and development of new methodologies in support of experiments on microbial growth in simple and observable porous media under controlled water status conditions. Experimental efforts led to a series of microbial growth experiments in granular media under variable saturation and ambient conditions, and introduction of atomic force microscopy (AFM) and confocal scanning laser microscopy (CSLM) to study cell size, morphology and multi-cell arrangement at a high resolution from growth experiments in various porous media. The modeling efforts elucidated important links between unsaturated conditions and microbial coexistence which is believed to support the unparallel diversity found in soils. We examined the role of spatial and temporal variation in hydration conditions (such as exist in agricultural soils) on local growth rates and on interactions between two competing microbial species. Interestingly, the complexity of soil spaces and aquatic niches are necessary for supporting a rich microbial diversity and the wide array of microbial functions in unsaturated soils. This project supported collaboration between soil physicists and soil microbiologist that is absolutely essential for making progress in both disciplines. It provided a few basic tools (models, parameterization) for guiding future experiments and for gathering key information necessary for prediction of biological processes in agricultural soils. The project sparked a series of ongoing studies (at DTU and EPFL and in the ARO) into effects of soil hydration dynamics on microbial survival strategy under short term and prolonged desiccation (important for general scientific and agricultural applications).
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FLEXURAL STRENGTH OF WEATHERED GRANITES UNDER WETTING – DRYING CYCLES: IMPLICATIONS TO STEEL STRUCTURES. The Hong Kong Institute of Steel Construction, September 2019. http://dx.doi.org/10.18057/ijasc.2019.15.3.2.
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