scholarly journals Thixotropic Hardening of Fao Clay

2019 ◽  
Vol 25 (5) ◽  
pp. 68-78
Author(s):  
Ahmed Shakir Kamil ◽  
Ala Nasir Aljorany
Keyword(s):  
Shear Strength ◽  
Soil Structure ◽  
Thick Layer ◽  
Soil Samples ◽  
Silty Clay ◽  
Driven Piles ◽  
Undisturbed Soil ◽  
Clayey Silt ◽  
Natural Water Content ◽  
Intact Soil

Fao region is characterized by weak soft silty clay to clayey silt thick layer which extends to a depth of about 20 m. The construction of some structures on such soils may needs piles. During the installation of driven piles, the soil geotechnical properties are exposed to significant changes result due to shearing under large shear strains. These changes significantly decrease the shear strength of the virgin soil due to the destruction of soil structure caused by remolding. The degradation of shear strength is usually followed by strength regaining which is called “Thixotropy”. In this study, the thixotropic effect on Fao clay was investigated. Many disturbed and undisturbed soil samples were brought from Fao region. Some of the soil samples were thoroughly remolded in the laboratory in its natural water content and molded as direct shear specimens. More than 180 specimens were prepared and tested over 36 weeks in order to accurately assess the percentage of strength regaining with time passing. The results show that soil remolding causes about a 45 % reduction in shear strength in comparing with the shear strength of the intact soil. This reduced percent in shear strength was almost fully regained after 25 weeks due to thixotropic effect.  

Performance of a raft foundation supporting a multistorey structure

1988 ◽  
Vol 25 (1) ◽  
pp. 138-149 ◽  
Author(s):  
A. O. Landva ◽  
A. J. Valsangkar ◽  
J. C. Alkins ◽  
P. D. Charalambous
Keyword(s):  
Soil Structure ◽  
Thick Layer ◽  
Field Testing ◽  
Soil Structure Interaction ◽  
Foundation Soil ◽  
Structure Interaction ◽  
Raft Foundation ◽  
Undisturbed Samples ◽  
Clayey Silt ◽  
Load Cells

A nine-storey structure was recently constructed on a raft founded on a 30 m thick layer of clayey silt at Fredericton, New Brunswick. Detailed soil investigations included conventional borings and self-boring pressuremeter, field vane, and flat dilatometer tests performed at the site. In addition to the field testing, undisturbed samples were obtained and tested in the laboratory to determine the compressibility and shear strength characteristics. To compare the performance of the foundation with the design assumptions, instrumentation consisting of piezometers, contact pressure load cells, and settlement points was installed. The instrumentation was monitored at regular intervals during the construction stage and at 6 month intervals following the completion of the building. This report presents (i) the results of the field and laboratory testing, (ii) the results of the field monitoring, and (iii) the results of a finite element computer analysis of the foundation-soil interaction. Key words: raft foundation, instrumentation, clayey silt, compressibility, soil tests, soil–structure interaction.

scholarly journals The Utilization of Remote Sensing Imagery and Inverse Distance Weighted Scheme to Simulate the White Oil Effects on Soil Geotechnical Properties

2021 ◽  
pp. 2824-2833
Author(s):  
L. A. Jawad ◽  
H. W. Abdulwadud ◽  
Z. A. Hameed
Keyword(s):  
Spatial Interpolation ◽  
Liquid Limit ◽  
Soil Samples ◽  
Strength Parameter ◽  
Undisturbed Soil ◽  
Inverse Distance Weighted ◽  
Area Of Interest ◽  
Clayey Silt ◽  
Distance Weighted ◽  
Inverse Distance

     This research aims to utilize a complementarity of field excavations and laboratory works with spatial analyses techniques for a highly accurate modeling of soil geotechniques properties (i.e. having lower root mean square error value for the spatial interpolation). This was conducted, for a specified area of interest, firstly by adopting spatially sufficient and  well distributed samples (cores). Then, in the second step, a simulation is performed for the variations in properties when soil is contaminated with commonly used industrial material, which is white oil in our case. Cohesive (disturbed and undisturbed) soil samples were obtained from three various locations inside Baghdad University campus in AL-Jadiriya section of Baghdad, Iraq. The unified soil categorization system (USCS) was adopted and soil was categorized  as clayey silt of low plasticity (CL). The cores were contaminated in a synthetically manner using two specified values of white oil (5 and 10 % of its dry weight). Then, the samples were left for three days to certify homogeneity. The results of laboratory tests were enhanced by spatial interpolation mapping, using Inverse Distance Weighted scheme for normal soil samples and those with synthetic pollution. The liquid limit rates were raised slightly as contamination rates raised, while particle size was reduced; in contrary, shear strength parameter values were decreased.

scholarly journals Levels of induced pressure and compaction as caused by forest harvesting operations

CERNE ◽  
2013 ◽  
Vol 19 (1) ◽  
pp. 83-91 ◽  
Author(s):  
Paula Cristina Caruana Martins ◽  
Moacir de Souza Dias Junior ◽  
Josemar da Silva Carvalho ◽  
Arystides Resende Silva ◽  
Sebastião Machado Fonseca
Keyword(s):  
Uniaxial Compression ◽  
Soil Compaction ◽  
Soil Structure ◽  
Forest Harvesting ◽  
Soil Samples ◽  
Uniaxial Compression Test ◽  
Traffic Intensity ◽  
Undisturbed Soil ◽  
Before And After ◽  
Red Latosol

This study aimed to determine levels of pressure and compaction induced by forest harvesting operations in a Red Latosol (LV) under planted eucalyptus. Undisturbed soil samples were collected from layers 0-3 and 15-18 cm and then used in a uniaxial compression test. Sampling was done before and after harvesting operations. Equipment being evaluated included: harvester, feller buncher, forwarder, self-loading adapted tractor, standard truck, wide-tire truck and grapple saw. Average pressures induced by the grapple saw were 320 kPa and 272 kPa, causing compaction in 80% and 20% of samples respectively from layers 0-3 cm and 15-18 cm, which indicates substantial degradation of soil structure in areas where timber is processed. In layer 0-3 cm, average pressures induced by the harvester and by the feller buncher were 240 kPa and 263 kPa respectively, while in layer 15-18 cm pressures were 234 kPa and 239 kPa respectively. The feller buncher caused higher soil compaction than the harvester in layer 0-3 cm, yet in layer 15-18 cm they had similar behavior. All timber forwarding equipment led to soil compaction. The wide-tire truck was the forwarding implement promoting the highest rate of compaction, in both residue conditions. Traffic intensity 7 promoted the highest rate of soil compaction.

scholarly journals Effect of reclamation on the structure of silty-clay soils irrigated with saline-sodic waters

2015 ◽  
Vol 29 (1) ◽  
pp. 23-30 ◽  
Author(s):  
Giovanna Cucci ◽  
Giovanni Lacolla ◽  
Marcello Pagliai ◽  
Nadia Vignozzi
Keyword(s):  
Aggregate Stability ◽  
Total Porosity ◽  
Calcium Sulphate ◽  
Drainage Water ◽  
Soil Samples ◽  
Sodium Absorption ◽  
Silty Clay ◽  
Undisturbed Soil ◽  
Thin Sections ◽  
Sodium Absorption Ratio

Abstract The objective of the work was to evaluate, by using the micromorphometric method, the effects of reclamation on porosity of two different clay loam soils irrigated with saline-sodic waters. Soil samples of the Ap horizon were put in cylindrical containers and irrigated with 9 types of saline-sodic waters (3 levels of salinity combined with 3 levels of sodicity). After a 4-year period, correction treatments were initiated by addition of calcium sulphate and leaching until electrical conductivity and sodium absorption ratio values of the drainage water matched 3 dS m-1 and 9, respectively. After 2 years of correction treatments, undisturbed soil samples were taken from the surface layer and soil thin sections for porosity measurements. Both soils did not show critical macroporosity values (> 10%, below this threshold a soil is classified as compact). Nevertheless, the soils exhibited a different behaviour: total porosity of the Pachic Haploxeroll soil was not affected by difference in water salinity and alkalinity; on the contrary, the Udertic Ustochrept soil showed a lower porosity associated with higher salt concentration in the irrigation waters. This may be due to the different iron and aluminium sesquioxides content and, as a consequence, a different effect on soil aggregate stability.

scholarly journals Structural sustainability of cambisol under different land use system

2012 ◽  
Vol 36 (6) ◽  
pp. 1724-1732 ◽  
Author(s):  
Paula Cristina Caruana Martins ◽  
Moacir de Souza Dias Junior ◽  
Ayodele Ebenezer Ajayi ◽  
Fátima Maria de Souza Moreira
Keyword(s):  
Land Use ◽  
Bearing Capacity ◽  
Soil Structure ◽  
Secondary Forest ◽  
Soil Samples ◽  
Load Bearing Capacity ◽  
Undisturbed Soil ◽  
Load Bearing ◽  
Land Use Systems ◽  
Land Use System

Incongruous management techniques have been associated with some significant loss of agricultural land to degradation in many parts of the world. Land degradation results in the alteration of physical, chemical and biological properties of the soil, thereby posing a serious threat to sustainable agricultural development. In this study, our objective is to evaluate the changes in a Cambisol structure under six land use systems using the load bearing capacity model. Sampling was conducted in Amazonas Region, Brazil, in the following land use: a) young secondary forest; b) old secondary forest; c) forest; d) pasture; e) cropping, and f) agroforestry. To obtain the load bearing capacity models the undisturbed soil samples were collected in those land use systems and subjected to the uniaxial compression test. These models were used to evaluate which land use system preserved or degraded the Cambisol structure. The results of the bulk density and total porosity of the soil samples were not adequate to quantify structural degradation in Cambisol. Using the forest topsoil level (0-0.03 m) as a reference, it was observed that pasture land use system was most severe in the degradation of the soil structure while the structure were most preserved under old secondary forest, cropping system and forest. At the subsoil level (0.10-0.13 m depth), the soil structure was most degraded in the cropping land use system while it was most preserved in young secondary forest and pasture. At the 0.20-0.23 m depth, soil structure degradation was most severe in the old secondary forest system and well preserved in young secondary forest, cropping and agroforestry.

scholarly journals Experimental Study on Variation Law and Mechanism of Soil Shear Strength Parameters along the Slope

2019 ◽  
Vol 2019 ◽  
pp. 1-11
Author(s):  
Yanhai Wang ◽  
Jianlin Li ◽  
Qiao Jiang ◽  
Yisheng Huang ◽  
Xinzhe Li
Keyword(s):  
Shear Strength ◽  
Direct Shear Test ◽  
Shear Test ◽  
Three Gorges Reservoir Area ◽  
Silty Clay ◽  
Direct Shear ◽  
Shear Strength Parameters ◽  
Strength Parameters ◽  
Undisturbed Soil ◽  
Soil Shear Strength

Under the action of rainwater seepage, geological origin, and human activities, the soil shear strength parameters will have spatial variability along the slope direction. After collecting samples of silty clay at a slope in the Three Gorges Reservoir area as the research object, not only the large-scale direct shear test was carried out on the site but also the direct shear test, water content test, density test, and particle grading analysis test were carried out in the laboratory with the undisturbed soil. The variation law and mechanism of soil shear strength parameters along slope were studied. The results indicate the following: (1) The coefficient of variation of shear strength parameters along the slope is relatively large. With the decrease of the elevation of the test location, the cohesion value tends to be strengthened, while the friction angle tends to degrade. (2) The mechanism of the variation law of soil shear strength parameters along the slope, which is mainly due to the decrease of the elevation, the decrease of the edges and angles between the particles, and the increase of the clay content is determined. (3) The variation model of shear strength parameters along the slope is proposed, which can provide a reference for relevant projects.

The relation between soil structure and solute transport under raised bed cropping and conventional cultivation in south-western Victoria

Soil Research ◽  
2007 ◽  
Vol 45 (8) ◽  
pp. 577 ◽  
Author(s):  
J. E. Holland ◽  
R. E. White ◽  
R. Edis
Keyword(s):  
Solute Transport ◽  
Soil Structure ◽  
Preferential Flow ◽  
Soil Samples ◽  
Water Volume ◽  
Undisturbed Soil ◽  
Resin Impregnation ◽  
Cultivated Soil ◽  
Raised Bed ◽  
Western Victoria

This study examined the relationship between soil structure and solute transport in a texture contrast soil under 2 different tillage treatments—raised beds and conventional cultivation—in south-western Victoria. Undisturbed soil samples were collected for resin-impregnation and image analysis. This enabled several descriptive parameters of macropore structure to be calculated. Large, undisturbed soil samples were also collected for a solute transport experiment using a KCl solution. A convective log-normal transfer function was used to model Cl– movement. The assessment of soil structure showed that the raised beds contained a better connected pore network than the conventionally cultivated soil. Solute transport was faster through the raised bed soil when close to saturation (at –5 mm tension). Under these conditions, the solute transport parameters showed a smaller ratio of transport volume to soil water volume in the raised bed than the conventionally cultivated soil. Together, these data strongly indicate that the raised beds had greater pore connectivity and were able to transmit solute faster and more efficiently than the conventionally cultivated soil. It is concluded that raised bed soils are better structured and provide less risk from waterlogging than conventionally cultivated soils. However, there is greater potential for preferential flow of pesticides and solutes in raised bed soils.

The impact of freeze-thaw-cycles on soil structure and soil hydraulic properties

2021 ◽  
Author(s):  
Frederic Leuther ◽  
Steffen Schlüter
Keyword(s):  
Soil Structure ◽  
Hydraulic Properties ◽  
Initial Structure ◽  
Silty Clay ◽  
Soil Hydraulic Properties ◽  
Pore System ◽  
Undisturbed Soil ◽  
Freeze Thaw ◽  
Soil Hydraulic ◽  
The Impact

<p>The ploughing of soils drastically alters soil structure and at the same time reduces its stability against external stresses. A fragmentation of these artificially produced soil clods during winter time is often observed in areas with air temperatures fluctuating around the freezing point. In this study, the cumulative effects of multiple freeze-thaw cycles (FTCs) on soil structure and soil hydraulic properties were analyzed for two different soil textures, a silty clay loam with a substantial amount of swelling clay minerals and a silty loam with less swell/shrink dynamics. The soil material was brought into two different initial states: (i) undisturbed soil cores taken from the topsoil from a grassland, and (ii) cylinders repacked with soil clods taken from a ploughed field nearby. FTCs were simulated under controlled conditions in the lab, changes in soil structure ≥48 µm were regularly recorded using X-ray µCT. After 19 FTCs, the impact on hydraulic properties were measured and the resolution of structural characteristics were increased to 10 µm by subsampling.</p><p>The effect of FTC on soil structure was found to be dependent on the initial structure, soil texture and number of FTCs. Freezing and thawing induced a consolidation of the repacked soil clods taken from both field sites, resulting in a systematic reduction in pore sizes and macro-pore connectivity. The macro-pore system of the undisturbed samples was only slightly affected. Fragmentation of soil elements larger than 0.8 to 1.2 mm increased the connectivity of pores smaller than 0.5 to 0.8 mm. Frost action increased the unsaturated hydraulic conductivity of all treatments, while the water retention was only slightly affected. This leads to the conclusion that multiple FTCs enforces a well-connected meso-pore system at the expense of a fragile macro-pore system. A change in soil structure that benefits farmers but could be reduced in the face of milder winters due to global warming.</p>

scholarly journals Traffic effects on the soil preconsolidation pressure due to eucalyptus harvest operations

2005 ◽  
Vol 62 (3) ◽  
pp. 248-255 ◽  
Author(s):  
Moacir de Souza Dias Junior ◽  
Fernando Palha Leite ◽  
Edson Lasmar Júnior ◽  
Cezar Francisco Araújo Junior
Keyword(s):  
Soil Compaction ◽  
Soil Structure ◽  
Soil Samples ◽  
Compression Tests ◽  
Undisturbed Soil ◽  
Structure Degradation ◽  
Preconsolidation Pressure ◽  
Before And After ◽  
Two Stages ◽  
Wood Transport

One of the limitations for reaching sustainable forest development is related to the traffic of machines and vehicles during harvest operations and wood transport, which may cause soil structure degradation. Seeking a way to analyze this problem, the objective of this study was to determine the traffic effects due to harvest operations and wood transport, on the preconsolidation pressure (sigmap) in a Typic Acrustox cultivated with eucalyptus. This study was conducted using undisturbed soil samples collected at the 0.1-0.125 m depth. Undisturbed soil samples were used in the uniaxial compression tests. Soil sampling consisted of two stages, before and after the mechanized harvest operations. The traffic effects on the sigmap in the dry season indicated that the soil compaction process was neither evident nor important. However, in the rainy season the traffic effects on the sigmap indicated that the operations performed with Harvester and Forwarder caused greater soil compaction than those with Motorized Saw and Manual, which caused less soil compaction.

Analyses on the Differences of the Consolidated Quick Direct Shear Strength Index of the Silty Clay

2011 ◽  
Vol 71-78 ◽  
pp. 1907-1910
Author(s):  
Tian Yun Liu ◽  
Ai Min Liu ◽  
Zhi Fa Yu
Keyword(s):  
Shear Strength ◽  
Friction Angle ◽  
Soil Samples ◽  
Silty Clay ◽  
Direct Shear ◽  
Strength Index ◽  
Shear Tests ◽  
Direct Shear Tests ◽  
Before And After ◽  
Different Levels

It is found that great differences exist in the consolidated quick direct shear strength index of the silty clay based on several consolidated quick direct shear tests with different rate of shear. In this letter, the changes of the water-content coefficients of the soil samples before and after the tests are analyzed. The results indicate that the drain consolidation phenomenon exists during the consolidated quick direct shear tests. Different rates of shear are corresponding to different levels of drain consolidation, and then the strength index is different. Furthermore, the reason of the fact that the friction angle of the silty clay relatively increases with different rates of shear, while the cohesive strength decreases relatively is explained.

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