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wetting-drying effect on the strength and microstructure of cementphosphogypsum stabilized soils

Journal of Rock Mechanics and Geotechnical Engineering 2024年第3期16卷 1049-1058页

作者： Lingling Zeng Xia Bian Jiaxing Weng Tao Zhang College of Civil Engineering Zhejiang University of TechnologyHanzhou310014China Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering Hohai UniversityNanjing210098China State Key Laboratory for Geomechanics and Deep Underground Engineering China University of Mining and TechnologyXuzhou221116China Jiangsu Water Source Company Ltd.of the Eastern Route of the South-to-North Water Diversion Project Nanjing210000China Power China Zhongnan Engineering Corporation Limited Changsha410027China

Phosphogypsum has often been used as an effective and environmentally friendly binder for partial replacement of cement,improving the engineering properties of slurries with high water ***,the influence of phosphogypsum on the physicomechnical properties of stabilized soil subjected to wettingedrying cycles is not well understood to *** this study,the effect of phosphogypsum on the durability of stabilized soil was studied by conducting a series of laboratory experiments,illustrating the changes in mass loss,pH value and unconfined compressive strength(qu)with wettingdrying *** test results showed that the presence of phosphogypsum significantly restrained the mass loss in the early stage(lower than the 4th cycle),which in turn led to a higher qu of stabilized soil than that without *** the 4th cycle,a sudden increase in mass loss was observed for stabilized soil with phosphogypsum,resulting in a significant drop in qu to a value lower than those without phosphogypsum at the 6th *** addition,the qu of stabilized soils correlated well with the measured soil pH irrespective of phosphogypsum content for all wettingedrying *** to the microstructure observation via scanning electron microscope(SEM)and X-ray diffraction(XRD)tests,the mechanisms relating the sudden loss of qu for the stabilized soils with phosphogypsum after the 4th wetting-drying cycle are summarized as follows:(i)the disappearance of ettringite weakening the cementation bonding effect,(ii)the generation of a larger extent of microcrack,and(iii)a lower pH value,in comparison with the stabilized soil without phosphogypsum.

关键词： wetting-drying Phosphogypsum Microstructure Durability

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Centrifugal and field studies on water infiltration characteristics below canals under wetting-drying-freezing-thawing cycles

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Journal of Central South University 2021年第5期28卷 1519-1533页

作者： ZHU Rui CAI Zheng-yin HUANG Ying-hao ZHANG Chen GUO Wan-li ZHU Xun Geotechnical Engineering Department Nanjing Hydraulic Research InstituteNanjing 210024China College of Civil and Transportation Engineering Hohai UniversityNanjing 210098China

Seepage is one of the main causes for the deformation and instability of canal slopes in Xinjiang,*** this study,centrifugal model tests under wetting-drying(WD)and wetting-drying-freezing-thawing(WDFT)cycles were performed to investigate the water infiltration characteristics below a *** results show that the shallow soil of the canal models was fully saturated in the wetting *** with the canal model under the WD cycles,the canal model under the WDFT cycles had larger saturated areas and a higher degree of saturation below the canal top after each cycle,indicating that the freezing-thawing(FT)process in the WDFT cycles promoted the water infiltration behavior below the canal *** cracks on the surface of the canal model under the cyclic action of WDFT developed further and had a higher connectivity,which provided the conditions for slope instability from a transverse tensile crack running through the canal *** this basis,a field test was conducted to understand the water infiltration distribution below a typical canal in Xinjiang,China,which also verified the accuracy of the centrifugal *** study provides a preliminary basis for the maintenance and seepage treatment of canals in Xinjiang,China.

关键词： wetting-drying freezing-thawing water infiltration crack canals centrifugal model test

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Effect of cement on the stabilization of loess

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Journal of Mountain Science 2017年第11期14卷 2325-2336页

作者： ZHANG Chong-lei JIANG Guan-lu SU Li-jun ZHOU Gong-dan Key Laboratory of Mountain Hazards and Earth Surface Processes Institute of Mountain Hazards and Environment Chinese Academy of Sciences Key Laboratory of High-speed Railway Engineering of Ministry of Education School of Civil Engineering Southwest Jiaotong University CAS Center for Excellence in Tibetan Plateau Earth Sciences University of Chinese Academy of Sciences

Considering the potential use of cementstabilized loess(CSL) as a construction material for structures that are subjected to frequent loess landslides, this paper explores the stabilization and improvement of geotechnical characteristics of loess achieved by the addition of 0%-9% cement by dry weight. Laboratory evaluations investigated the consistency limits, compaction, compressibility, California bearing ratio(CBR), direct shear strength, and unconfined compression strength(UCS) of CSL for different curing stages. A durability index was quantified to estimate the influence of wetting-drying(w-d) cycles on CSL strength, and an optimum cement dosage was also identified. The results reveal that the cohesion of CSL is substantially more sensitive to structure than its friction angle and that cohesion is responsible for shear strength increase after remoulding. The cement proportions have an effective role in the enhancement of compressibility. The development of UCS can be categorized into the early stage(14 days). The increase in strength primarily occurred in the first 14 days. The w-d cycles have a significantinfluence on the decrease in compression strength. The CBR value increases with increments of additional proportions and compaction times. The relationships of UCS versus the compressibility modulus and UCS versus CBR are established to facilitate the mix design for strength. A rational predictive exponential equation is proposed to predict the durability index for different w-d cycles.

关键词： Landslide Cement Loess stabilization Durability index wetting-drying cycle

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Processes and mechanisms of multi-collapse of loess roads in seasonally frozen ground regions: A review

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Research in Cold and Arid Regions 2015年第4期7卷 456-468页

作者： GuoYu Li Wei Ma Fei Wang YanHu Mu YunCheng Mao Xin Hou Hui Bing State Key Laboratory of Frozen Soil Engineering Cold and Arid Regions Environmental and Engineering Research InstituteChinese Academy of Sciences University of Chinese Academy of Sciences Communication Research Institute of Gansu Province

Usually, the collapsible loess widely distributed across the world can serve as a type of foundation soil that meets its strength requirement after dense compaction and elimination of collapsibility. However, many problems such as cracks and differential settlement still occur in loess roads in the seasonally frozen ground regions after several years of op- eration. Many studies have demonstrated that these secondary or multiple collapses primarily result from the repeated freezing-thawing, wetting-drying, and salinization-desalinization cycles. Therefore, we conducted a research program to （1） monitor the in-situ ground temperatures and water content in certain loess roads to understand their changes, （2） study the effects of freezing-thawing, wetting-drying, and salinization-desalinization cycles on geotechnical properties and micro-fabrics of compacted loess in the laboratory, and （3） develop mitigative measures and examine their engineered effectiveness, i.e., their thermal insulating and water-proofing effects in field and laboratory tests. Our results and advances are reviewed and some further research needs are proposed. These findings more clearly explain the processes and mechanisms of secondary and multiple collapse of loess roads. We also offer references for further study of the weakening mechanisms of similar structural soils.

关键词： mechanics of loess loess roads secondary or multiple collapse freezing-thawing wetting-drying saliniza-tion-desalinization

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Study of Shrinkage and Swelling Phenomena in Clay Soils of Fanaye (Middle Senegal River Valley): Simulation of Water Transfers in a Soil Column

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Open Journal of Soil Science 2022年第4期12卷 151-169页

作者： Fary Diome Landing Biaye Institut of Earth Sciences Faculty of Sciences and Techniques Cheikh Anta Diop University of Dakar Dakar Senegal

Soil degradation due to shrinkage and swelling of these clay soils is a problem for agriculture. To understand the physical properties of the soils in this agricultural area, we will use an undisturbed soil monolith 60 cm high and 23 cm in diameter in the laboratory. This study quantified the swelling and shrinkage of these soils during a 10-month experiment. The determination of the hydrodynamic parameters of this monolith made it possible to simulate water transfers in a soil of constant volume and a water transfer in a soil of variable volume. The results of this simulation show significant differences between these two cases, hence the need to integrate the variations in soil volume into the simulation processes of water transfers.

关键词： Clay Swelling Shrinkage-Sampling wetting-drying Hydrodynamic Parameters

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