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Influence of repeated freeze-thaw on dynamic modulus and damping ratio properties of silty sand

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Research in Cold and Arid Regions 2013年第5期5卷 572-576页

作者： TianLiang Wang Chao Ma Han Yan JianKun Liu School of Civil Engineering Shijiazhuang Tiedao University Key Laboratory of Roads and Railway Engineering Safety Control of Ministry of Education Shijiazhuang Tiedao University School of Civil Engineering Beijing Jiaotong University Northwest Corporation China Railway Construction Engineering Group

Under repeated freezing and thawing in deep seasonal frozen regions, the stability and strength of the soil are imposed in the form of large uneven settlement, instability and strength reduction, which affect the normal operation of railway lines. This study is to obtain the influencing rules of freeze-thaw on the dynamic properties （dynamic strain, confining pressure and compactness） of silty sand. Based on an amount of inner tests, the dynamic modulus and damping ratio properties of silty soil subjected to repeated freeze-thaw cycles were deeply researched and analyzed. The results are as follows： At the same dynamic strain, the relationship of dynamic stress and freeze-thaw cycles presents negative cor- relation, and the relationship of dynamic stress, confining pressure and compactness present positive correlation. The dynamic modulus double decreases while the damping ratio double increases with incremental increase in dynamic strain. The dynamic modulus sharply decreases while the damping ratio increases with incremental increase in freeze-thaw cycles, and then the changes level off after six freeze-thaw cycles. The dynamic modulus increases while the damping ratio decreases as the confining pressure and compactness increase at the same strain level.

关键词： freeze-thaw cycles silty sand dynamic modulus damping ratio

Interaction of the Mining Environment on the Properties of Hydraulic Mortars in silty sands in Togo

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Open Journal of Civil Engineering 2022年第1期12卷 1-13页

作者： Kossi Bollanigni Amey É quipe de Recherche en Mécanique (ERM) Ecole Nationale Supérieure d’Ingénieurs de l’Université de Lomé Lomé Togo Equipe de Recherche et Développement de l’Institut FORMATEC Lomé Togo

The objective of this study is to determine the influence of the surrounding soils on the granular properties of the silty sands of Togo and on the resistance of the mortars. sand compositions are made by substituting silty sands with clay soil, vegetal soil, lateritic soil or fine elements (sands in Togo. After identification tests, the mixtures were used to prepare test specimens of mortar which are subjected to bending and compression. It appears that additions of clay and plastic soils (ES = 0, VBM > 0.53 and IP > 19) from 10% to 35% cause drops in resistance of mortars from 7% to 96%;this loss is 8% to 70% for the rates of addition of less clayey soil (ES = 33, VBM = 0.40 and IP = 0) at rates of 10% to 100%. As for fine powdery soils (ES = 56.53 and VBM = 0.25), they have virtually no influence on resistance (loss of less than 3% for rates of 100%). Construction stakeholders thus have a decision-making tool for the choice of silty sand extraction zones according to the surrounding land and the quality of the desired concrete.

关键词： Mortar silty sand Pollutants Physical and Mechanical Properties

Experimental Study on Suspended Sediment Concentration and Its Vertical Distribution under Spilling Breaking Wave Actions in silty Coast

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China Ocean Engineering 2011年第4期25卷 565-575页

作者：夏云峰徐华陈中吴道文张世钊 Nanjing Hydraulic Research Institute The State Key Laboratory of Hydrology-Water Resources & Hydraulic Engineering Waterway and Sediment Engineering of MC Shanghai Waterway Engineering Design and Consulting Co. LtdShanghai 200120China

In this paper, flume experiments are focused on sediment transport inside and outside the surf zone. According to the energy dissipation balance principle of sediment-laden flow and the similarity between energy dissipation of spilling breaking wave and hydraulic jump, formulas are proposed to predict time averaged suspended sediment concentration under both non-breaking and breaking waves. Assuming that the sediment diffusion coefficient, which is related with energy dissipation, is proportional to water depth, formulas are proposed to predict close-to-bed suspended sediment concentration and vertical distribution of suspended sediment under spilling breaking waves, and the prediction shows a good agreement with the measurement.

关键词： silty sand breaking wave energy dissipation suspended sediment concentration vertical distribution

A multi-attribute decision making approach of mix design based on experimental soil characterization

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Frontiers of Structural and Civil Engineering 2018年第3期12卷 361-371页

作者： Amit K. BERA Tanmoy MUKHOPADHYAY Ponnada J.MOHAN Tushar K. DEY Faculty of Science & Technology The ICFAI University Dehradun India College of Engineering Swansea University Swansea UK Department of Civil Engineering National Institute of Technical Teachers' Training and Research (NIT'ITR) Kolkata India

The clay mineral composition is one of the major factors that governs the physical properties of silty sand subgrade. Therefore, a thorough knowledge of mineral composition is essential to predict the optimum engineering properties of the soil, which is generally characterized by different indices like maximum dry density （MDD）, California bearing ratio （CBR）, unconfined compressive strength （UCS） and free swelling index （FSI）. In this article, a novel multi- attribute decision making （MADM） based approach of mix design has been proposed for silty sand- artificial clay mix to improve the characteristic strength of a soil subgrade. Experimental investigation has been carried out in this study to illustrate the proposed approach of selecting appropriate proportion for the soil mix to optimize all the above mentioned engineering properties simultaneously. The results show that a mix proportion containing approximately 90% silty sand plus 10% bentonite soil is the optimal combination in context to the present study. The proposed methodology for optimal decision making to choose appropriate combination of bentonite and silty sand is general in nature and therefore, it can be extended to other problems of selecting mineral compositions.

关键词： silty sand bentonite soil soil mix design multi-attribute decision making

Intergrain contact density indices for granular mixes——Ⅱ: Liquefaction resistance

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Earthquake Engineering and Engineering Vibration 2007年第2期6卷 135-146页

作者： S. Thevanayagam Dept. of Civil Struct. & Env. Eng. State Univ. of New York Buffalo NY 14260 USA

Whether the presence of non-plastic silt in a granular mix soil impact its liquefaction potential and how to evaluate liquefaction resistance of sand containing different amounts of silt contents are both controversial issues. This paper presents the results of an experimental evaluation to address these issues. Two parameters, namely, equivalent intergranular void ratio （ec）eq and equivalent interfine void ratio （ef）eq, proposed in a companion paper （Thevanayagam, 2007） as indices of active grain contacts in a granular mix, are used to characterize liquefaction resistance of sands and silty sands. Results indicate that, at the same global void ratio （e）, liquefaction resistance of silty sand decreases with an increase in fines content （Cv） up to a threshold value （Crth）. This is due to a reduction in intergrain contact density between the coarse grains. Beyond Crth, with further addition of fines, the interfine contacts become significant while the inter-coarse grain contacts diminish and coarse grains become dispersed. At the same e, the liquefaction resistance increases and the soil becomes stronger with a fttrther increase in silt content. Beyond a limiting fines content （CrL）, the liquefaction resistance is controlled by interfine contacts only. When Cr〈Crth, at the same （e）eq, the liquefaction resistance of silty sand is comparable to that of the host clean sand at a void ratio equal to （ec）eq. When CF〉CFth, at the same （ef）eq, the cyclic strength of a sandy silt is comparable to the host silt at a void ratio equal to （ef）eq.

关键词： sand silt fines silty sand liquefaction cyclic strength

Intergrain contact density indices for granular mixes——Ⅰ: Framework

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Earthquake Engineering and Engineering Vibration 2007年第2期6卷 123-134页

作者： S. Thevanayagam Dept. of Civil Struct. and Envir. Eng. State University of New York Buffalo NY 14260 USA

Mechanical behavior such as stress-strain response, shear strength, resistance to liquefaction, modulus, and shear wave velocity of granular mixes containing coarse and fine grains is dependent on intergrain contact density of the soil. The global void ratio e is a poor index of contact density for such soils. The contact density depends on void ratio, fine grain content （Cv）, size disparity between particles, and gradation among other factors. A simple analysis of a two-sized particle system with large size disparity is used to develop an understanding of the effects of Cv, e, and gradation of coarse and fine grained soils in the soil mix on intergrain contact density. An equivalent intergranular void ratio （ec）oq is introduced as a useful intergrain contact density for soils at fines content of less than a threshold value Crth. Beyond this value, an equivalent interfine void ratio （ef）eq is introduced as a primary intergrain contact density index. At higher values of Cv beyond a limiting value of fine grains content CVL, an interfine void ratio ef is introduced as the primary contact density index. Relevant equivalent relative density indices （Drc）eq and （Drf）eq are also presented. Experimental data show that these new indices correlate well with steady state strength, liquefaction resistance, and shear wave velocities of sands, silty sands, sandy silts, and gravelly sand mixes.

关键词： sand silt silty sand sandy silt cyclic strength shear wave velocity intergrain contact density

Influence of grass plantation on the rainfall-induced instability of gentle loose fill slope

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Biogeotechnics

Biogeotechnics 2024年第4期2卷 52-57页

作者： Pei Tai Fan Wu Bohan Bai Zhaofeng Li Rui Chen Lulu Zhang School of Civil and Environmental Engineering Harbin Institute of TechnologyShenzhenShenzhen 518055China Guangdong Provincial Key Laboratory of Intelligent and Resilient Structures for Civil Engineering Shenzhen 518055China State Key Laboratory of Ocean Engineering Collaborative Innovation Centre for Advanced Ship and Deep‑Sea ExplorationShanghai Jiaotong UniversityShanghai 200240China

The understanding of rainfall-induced landslides on gentle, loose-fill slopes is limited in comparison to steep slopes. Hence, two physical model tests were conducted on silty sand slopes under continuous rainfall: one on a bare slope and the other on a slope planted with ryegrass. The slope angle of 25° is much lower than the internal friction angle of slope material (34.3°), which makes the model test fall well into the category of gentle slope. For the initially unsaturated bare slope, a rainfall event with return period of 18 years could trigger a rapid and retrogressive global sliding, which differs from previous findings that gentle slopes would only experience shallow failure. A sudden increase in pore-water pressure was simultaneously observed, which might be generated by the wetting-induced collapse of unsaturated loose soil. On the other hand, the stability of the slope with grass plantation was significantly enhanced, and it was able to withstand rainfall event more severe than those with a return period of 100 years, with only minimal deformation. The results suggest that the gain in shear strength due to ryegrass roots surpasses the additional sliding force caused by the increased water retention capability. Additionally, it is found that the abrupt change in pore pressure was no longer indicative of slope failure in the case of the grass-reinforced slope.

关键词： Gentle slope silty sand Ryegrass Rainfall Failure pattern

Shear Resistance of Siltous sands Improved with Bridelia Tannins

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Geomaterials 2024年第1期14卷 1-11页

作者： Sinko Banakinao Soviwadan Drovou Komlan Lolo Kodjo Attipou Department of Civil Engineering Polytechnic School of Lomé University of Lomé Lomé Togo Laboratory of Structure and Mechanic of Materials (LaS2M) University of Lomé Lomé Togo

The ruin of several civil engineering works occurs due to shear rupture of the ground. When the stress is greater than the shear resistance, the internal friction angle and the cohesion of the soil loosen and rupture occurs. Cement and lime are often used to stabilize soils and improve soil strength. The costs and environmental problems of these technologies raise concerns and challenge researchers to innovate with clean, inexpensive materials, accessible to the most disadvantaged social classes. The question that this study seeks to answer is whether the binders derived from plant tannins, which also stabilize soils, improve the shear resistance of these soils. To do this, we determined for silty sand the shear parameters, notably the cohesion and the angle of internal friction in the non-stabilized state and when they are stabilized with the powder of the bark of the Bridelia under different water states. The results show that the addition of Bridelia powder to silty sand increases the cohesion of the soil by nearly 70.71% and the friction angle by 4.31%. But in unfavourable water conditions, the cohesion and internal friction angle of the silty sand material improved with Bridelia bark powder drops drastically by nearly 81.56%. but does not dissolve completely as for the same material. When it is not stabilized. This information is an invaluable contribution in the search for solutions to increase the durability of earthen constructions by improving the water-repellent properties of soils.

关键词： silty sand Bridelia Tannins Shear Resistance Cohesion Angle of Friction