Increase In Silt Content Research Articles

A Case Study of Petroleum Degradation in Different Soil Textural Classes.

Patents have been granted for a number of techniques for petroleum biodegradation including use of micro-organisms for degradation of hydrocarbon-based substances and for hydrocarbon degradation in oil reservoirs, but there is a dearth of information on hydrocarbon degradation in different soil textures. Hence, this work investigated the effects of different soil textures on degradation of petroleum hydrocarbons during a six-week period. Five soil textural classes commonly found in Port Harcourt metropolis, Nigeria, namely sand, loamy sand, sandy loam, silty clay and clay, were employed. The soils were contaminated with the same amount of crude oil and then remediated by biostimulation. Selected soil properties were monitored over time. Bacterial numbers declined significantly in the fine soil textures after petroleum contamination, but were either unaffected or increased significantly in the coarser soil textures. Hydrocarbon losses ranged from 42% - 99%; the sandy loam had the highest, while the clay soil had the least total hydrocarbon content (THC) reduction. The total heterotrophic bacterial (THB) counts generally corroborated the THC results. Fold increase in bacterial numbers due to remediation treatment decreased with increasing clay content. The results suggest that higher sand than clay content of soil favours faster hydrocarbon degradation. Hydrocarbon degradation efficiency increased with silt content among soil groupings such as fine and coarse soils but not necessarily with increasing silt content of soil. Thus, there seems to be cut-off sand and clay contents in soil at which the effect of the silt content becomes significant.

Engineering behavior and correlated parameters from obtained results of sand–silt mixtures

The results of an experimental study on sands with low-plastic silt content are presented. Flexible wall permeameter tests, drained and undrained triaxial compression tests, one-dimensional consolidation tests, and undrained cyclic triaxial tests were performed on specimens with a low plastic silt content of 0%, 15%, 30%, 40%, 50% and 60% by weight. The soil specimens were tested under three different categories: (1) at a constant void ratio index; (2) at the same peak deviator stress in a triaxial test; and (3) at a constant relative density. The results were observed to be somewhat different from previous studies with non-plastic silt content and plastic fine content. Cyclic triaxial tests showed that an increase in silt content causes a decrease in the cyclic resistance ratio with a silt content up to 40–50% and thereafter causes an increase in the cyclic resistance ratio with further increases in silt content. The results of triaxial tests indicated that the value of the peak deviator stress changed with different types of specimens, and the greater internal friction an angle has, the stronger is the liquefaction resistance. Flexible wall permeameter tests concluded that the saturated hydraulic conductivity slowly decreases with an increase in silt content in the range from 0% to 30% and considerably decreases with a silt content greater than 30%. A one-dimensional consolidation test postulated that increasing silt content decreases the coefficient of consolidation. In addition, the global void ratio did not appear to be a pertinent parameter in explaining the behavior of sand–silt mixtures, while fine content and intergranular void ratio were suitable parameters for explaining the behavior of sand–silt mixtures. Finally, correlated parameters from obtained results were also presented in this study.

Compaction Properties of Silty Soils in Relation to Soil Texture, Moisture Content and Organic Matter

Soil compaction is recognized as an increasingly challenging problem with regard to root growth and yield reduction in agricultural production in Thailand. The aim of this research was to study the effect of soil texture, moisture content and organic matter on the compaction properties of silty soils. Three soils with different silt contents were studied-loam, silty clay loam and silt loam. The study showed that compacting silt loam soil using the modified Proctor test resulted in a higher bulk density than from the oedometer test at 200 kPa. Statistical analysis showed that soil type and the moisture content significantly affected both the bulk density and penetration resistance. However, organic matter showed a significant effect only on the bulk density. The bulk density increased with increased moisture content. The bulk densities of compacted soils were higher in the order of loam, silt loam and silty clay loam. The penetration resistance seemed to increase with increased silt content. The differences in the bulk density and penetration resistance among these three soils decreased as the moisture content increased. Adding organic matter at 5% by weight to soils resulted in lower bulk densities of the soil using the oedometer test, with reductions of 3.9, 3.8 and 7.7% for loam, silty clay loam and silt loam, respectively. In order to avoid effects on root growth, it is recommended that machines with 200 kPa of tire contact pressure should only work in fields with a moisture content not exceeding 20.27, 18.74 and 17.88% for loam, silt loam and silty clay loam, respectively.

Experimental study on the determination of small strain-shear modulus of loess soil

The primary aim of this study was to investigate the collapse potential of loess soil in Egypt, the factors affecting the dynamic properties of this soil and establish relationships between them. Whether engineered or natural, may exist in seismic zones; or may be subjected to small strain vibrations, therefore, there is a need to assess the wetting dynamic properties of collapsible soils.A series of oedoemeter and resonant column tests were conducted to study the effect of applied pressure, void ratio, water content and silt content on the collapse potential (Cp), maximum shear modulus (Gmax) and damping ratio (DT) of the tested samples. The results indicate significant increase in the collapse potential and reduction in (Gmax) with the increase of silt content. The results, also, indicate that the (Cp) is less for sample with higher initial relative densities and initial water content.Test results also show that (Gmax) increases with the increase of confining pressure and relative density. The change in damping properties is not significant under the effect of silt content and water content, and it reduces slightly with the increase of confining pressure and relative density. Empirical equations based on the results of the experimental work were proposed to predict (Gmax) with respect to (Cp), voids ratio and applied pressure.

Establishing Correlations and Scale-Up Factor for Estimating the Petroleum Biodegradation Rate in Soil

ABSTRACTThe proper design of a bioremediation strategy for petroleum-contaminated sites requires a reasonable estimate of the biodegradation rate constant, which is not easy due to spatial heterogeneity. Accordingly, predictive models were developed by completing a bioventing study at the meso-scale. Reactors holding 4 kg of disturbed soil were tested using five different types of soils. Using statistical analysis, a two-stage process was observed, with a fast rate of hydrocarbon degradation in the first 8 days and a slower rate in the remaining 22 days. Review of the correlations showed that the initial population of petroleum-degrading bacteria and increasing silt content had a positive effect on the degradation. A negative impact on the degradation rate was seen by increasing the fraction of organic matter and clay content. Comparison of previously completed micro-scale and meso-scale degradation rates gave a scale-up factor (SF) of 1.8 ± 0.5. Soils with an increased sand fraction had slightly higher SF values, whereas soils high in organic matter content had lower SF values. The measured SF values and developed correlations will help practitioners with site closure decisions, indicating the need for additional SF work to allow better transfer of meso-scale data to the field.

Cyclic behaviour of dry silty sand reinforced with a geotextile

Recent studies on construction material technology have indicated that soil reinforcement improves resistance of soil against compression and tension. Due to the wide use of geotextile reinforcement in road construction, the potential benefit of geotextile reinforcement in cyclic loading should be investigated. In this study we performed a series of cyclic triaxial tests to examine dry silty sand reinforced with geotextile when subjected to dynamic loading. These tests were conducted on reinforced and unreinforced dry sand and sand mixed with varying amounts of silt (0–50%). The main factors affecting the cyclic behaviour, such as the arrangement and number of geotextile layers, confined pressure and silt content are examined and discussed in this paper. The results indicate that geotextile inclusion and increased confining pressure increase the axial modulus and decreased cyclic ductility of dry sand for all silt contents examined. Also, it was found that by increasing the silt content by up to about 35 percent the axial modulus in reinforced and unreinforced sand is decreased and cyclic ductility increased. With further increases in silt content, these values are increased for cyclic axial modulus and decreased for cyclic ductility.

Effects of silt contents on the static and dynamic properties of sand-silt mixtures

This paper presents a detailed study focused on investigating the effects of silt content on the static and dynamic properties of sand-silt mixtures. Specimens with a low-plastic silt content of 0, 15, 30 and 50% by weight were tested in static triaxial, cyclic triaxial, and resonant columns in addition to consolidation tests to determine such parameters as compression index, internal friction angle, cohesion, cyclic stress ratio, maximum shear modulus, normalized shear modulus and damping ratio. The test procedures were performed on specimens of three cases: constant void ratio index, e = 0.582; same peak deviator stress of 290 kPa; and constant relative density, <TEX>$D_r$</TEX> = 30%. The test results obtained for both the constant-void-ratio-index and constant-relative-density specimens showed that as silt content increased, the internal friction angle, cyclic stress ratio and maximum shear modulus decreased, but cohesion increased. In testing of the same deviator stress specimens, both cohesion and internal friction angle were insignificantly altered with the increase in silt content. In addition, as silt content increased, the maximum shear modulus increased. The cyclic stress ratio first decreased as silt content increased to reach the threshold silt content and increased thereafter with further increases in silt content. Furthermore, the damping ratio was investigated based on different silt contents in three types of specimens.

Effect of non-plastic silt content on the liquefaction behavior of sand–silt mixture

To identify the effect of non-plastic silt on the cyclic behavior of sand–silt mixtures, total sixty undrained cyclic triaxial stress-control tests were carried out on sand–silt mixtures. These tests were conducted on specimens of size 71mm diameter and 142mm height with a frequency of 1Hz. Specimens were prepared at a constant relative density and constant density approach. The effect of relative density, confining pressure as well as magnitude of cyclic loading was also studied. For a constant relative density (Dr=60%) the effect of limiting silt content, pore pressure response and cyclic strength was observed. The rate of generation of excess pore water pressure with respect to cycles of loading was found to initially increase with increase in silt content till the limiting silt content and thereafter it reverses its trend when the specimens were tested at a constant relative density. The cyclic resistance behavior was observed to be just opposite to the pore pressure response. Permeability, CRR and secant shear modulus decreased till limiting silt content; after that they became constant with increasing silt content.

Grain shape effect on the anisotropic behaviour of silt–sand mixtures

The anisotropy of sand–silt mixtures has not been fully studied in terms of the effects of different grain shapes and silt content. This study investigated the effects on anisotropy in three different sands with various silt contents and grain shapes. The tests performed in this research include 90 hollow cylinder torsion shear tests conducted on three types of sand: Hamadan sand with high angularity, Firoozkuh sand with medium angularity and Tehran sand with low angularity. The samples had silt contents of 0, 15, 30 and 50 per cent. To define the shape criteria in this study, two ratios were defined. The first was roundness, which can be obtained from the ratio of the radius of the corners of the grains to the largest circle that encompasses the entire grain; this ratio is denoted by rr. The second criterion was sphericity, which can be obtained by dividing the smallest pictorial width by the minimum graphical length; this ratio is denoted by rs. Under similar initial effective confining pressures, sand with high roundness and sphericity showed contractive behaviours. An increase in silt content, as well as in the ratios rr and rs, decreased the sample strength. Moreover, increasing these two ratios caused the stress–strain curves to be close to one another.

Assessment of aggregate resources: an integrated geophysical approach

ABSTRACTFluvio‐glacial sand and gravel provide an important resource for the construction industry. The efficient and economic extraction of such geologically complex deposits requires a detailed understanding of their grade distribution. This is typically undertaken as point observations over the resource using a borehole drilling programme. We investigate the viability of using measurements of the elastic and electrical properties of the subsurface, derived from geophysical profiles, to determine the spatial variability of aggregate quality.A refraction seismic, surface wave seismic and resistivity survey was carried out over a fluvioglacial sand and gravel deposit at Scorton, Yorkshire, UK, on agricultural land adjacent to an active quarry. Two 190 m profiles, with borehole control at their extremes, were acquired with a 2 m source and receiver spacing. The P‐ and S‐wave velocities ( and ), together with resistivity and depth distributions were determined down to c. 20 m. The subsurface was divided into four layers: uncon‐solidated sand and gravel; dry consolidated sand and gravel; saturated sand and gravel; and basal clay.The work flow initially involved processing and interpreting the three geophysical techniques independently. Crossplots of the elastic and electrical parameters were used to distinguish unconsolidated from consolidated material; the water table; increased silt content; and recognize the basal clay. The Vp/Vs ratio proved very powerful at discriminating fine material () from coarse material (Vp/Vs ~ 1.5). Regression analysis of crossplots produced P‐ and S‐wave relationships for the material, while electro‐acoustic relationships were less successful, especially below the water table. The results of the petrophysical analysis were used to set up guided inversions for the resistivity survey. Careful use of the refraction results as an a priori model for the resistivity survey was found to improve the resistivity inversion, though use of a sharp boundary introduced edge effects at the water table.The results from the integrated analysis were combined with the guided inversions into a final interpretation that enabled silt content, particle size and clay lenses to be mapped, which were not identified in the separately processed data.

Postliquefaction Undrained Shear Behavior of Sand-Silt Mixtures at Constant Void Ratio

A detailed study on the postliquefaction undrained shear behavior of sand-silt mixtures at constant void ratios is presented in this article. The influence of different parameters such as density, amplitude of cyclic shear stress, and drainage conditions on the postliquefaction undrained response of sand-silt mixtures has been investigated, in addition to the effect of fines content. The results showed that the limiting silt content plays a vital role in the strength of the soil under both cyclic and monotonic shear loading. Both the liquefaction resistance and postliquefaction shear strength of the soils are found to decrease with an increase in the fines content until the limiting silt content is reached. However, further increase in the silt content beyond the limiting silt content increases the liquefaction resistance as well as the postliquefaction shear strength of the soils. It is also observed that these variations on the liquefaction and postliquefaction resistance of soils are closely related to the variations in relative density.

Methane production and ebullition in a shallow, artificially aerated, eutrophic temperate lake (Lake Elsinore, CA)

Methane is an important component of the gases released from lakes. Understanding the factors influencing the release is important for mitigating this greenhouse gas. The volume of methane (CH4) and other gases in sediments, and the rate of CH4 ebullition, were determined for an artificially aerated, shallow, eutrophic freshwater lake in Southern California. Gas volume was measured at 28 sites in July 2010, followed by monthly sampling at 7 sites through December 2011. Gas volumes measured in July 2010 at the 28 sites exhibited a complex dependence on sediment properties; the volume of CH4 and other gases was negligible in very coarse-textured sediment with low water and organic carbon contents. Gas volumes increased strongly with increased silt content, and were highest in sediments with intermediate water contents (60 to 70%), organic carbon contents (2 to 3%) and depths (approximately 4m). Methane was the dominant gas collected from sediment (80 to 90%), while carbon dioxide comprised roughly 2 to 3% of sediment gas in the lake. Gas sampling during cool winter months revealed very low or undetectable volumes of gas present, while sediment gas volumes increased markedly during the spring and early summer months, and then declined in late summer and fall. The rate of CH4 ebullition, quantified with an echosounder, also varied markedly across the lake and seasonally. High rates of ebullition were measured at all 7 sites in July 2011 (up to 96mmolCH4m−2d−1), while the rates were >50% lower in September and negligible in December 2010. Ebullition rates were inversely correlated with depth and most other sediment properties, but strongly positively correlated with sand content. No simple relationship between ebullition rate and sediment gas volume across the set of sites was found, although ebullition rates at individual sites were strongly related to gas volume.

Interfacial shear strength of silty sand–geogrid composite

This study has been carried out to investigate the interface shear strength of sand reinforced by high-density polyethylene cogged geogrid, with variation in fines content from 0 to 45%. To this end, a set of large direct shear tests (30 × 30 × 15 cm) was systematically conducted. The behaviour of sand and silty sand reinforced with a special type of cogged geogrid is studied in terms of interfacial shear strength of the soil. An analysis of test results indicates that the reinforcement improved the shearing behaviour of the sand and silty sand samples. Attaining the peak strength at greater shear strain due to reinforcement and lowering the post-peak loss of strength of specimens with higher silt content, compared to the specimens with lower silt content, are the indications implying that the reinforcement and increasing the silt content tend to transform the shearing behaviour of sand and silty sand specimens from a brittle to a ductile manner. The results also indicated that as the silt content increases up to 35%, the combined shear strength decreases. Further increase in the silt content made no significant change to the combined shear strength of the soil samples.

Stress-Strain and Strength Characteristics of Silt-Clay Transition Soils

AbstractThe influence of nonplastic silt content on the stress-strain, volume change, and strength characteristics of anisotropic silt-clay transition soils is investigated. A series of one-dimensional compression tests, isotropic compression tests, and undrained and drained triaxial tests on three soils of similar base clay but different nonplastic silt contents are performed on cross-anisotropic specimens prepared from consolidation of slurries. Tests with major loading directions both parallel and perpendicular to the specimens’ axis of deposition are performed. It is observed that the tested silt-clay soils are less compressible with increasing silt content during one-dimensional and isotropic compression tests. During drained and undrained triaxial tests, the normally consolidated soils at the same consolidation stress show larger values of stiffness and drained and undrained shear strengths with increasing silt content. The silt-clay soils also show larger pore pressure changes during undrained tria...

토양 정화 방법에 따른 토양의 물리화학적 특성 변화

Various methods are used to remediate soil contaminated with heavy metals or petroleum. In recent years, harsh physical and chemical remediation methods are being used to increase remediation efficiency, however, such processes could affect soil properties and degrade the ecological functions of the soil. Effects of soil washing, thermal desorption, and land farming, which are the most frequently used remediation methods, on the physicochemical properties of remediated soil were investigated in this study. For soils smaller than 2 mm, the soil texture were changed from sandy clay loam to sandy loam because of the decrease in the clay content after soil washing, and from loamy sand to sandy loam because of the decrease in the sand content and increase in silt content during thermal desorption, however, the soil texture remained unchanged after land farming process. The water-holding capacity, organic matter content, and total nitrogen concentration of the tested soil decreased after soil washing. A change in soil color and an increase in the available phosphate concentration were observed after thermal desorption. Exchangeable cations, total nitrogen, and available phosphate concentration were found to decrease after land farming; these components were probably used by microorganisms during as well as after the land farming process because microbial processes remain active even after land farming. A study of these changes can provide information useful for the reuse of remediated soil. However, it is insufficient to assess only soil physicochemical properties from the viewpoint of the reuse of remediated soil. Potential risks and ecological functions of remediated soil should also be considered to realize sustainable soil use.

전북지역 과수원의 토양특성이 미생물 분포에 미치는 영향

This study was conducted to investigate impacts of soil properties on microbial distribution in Jeonbuk orchard fields. Soil samples were collected from 110 sites cultivated with different fruit plants. The population of aerobic bacteria and fungi and the content of soil microbial biomass carbon (C) were found to increase with increasing silt content in the soils. Different activity of dehydrogenase was not observed among the different textures of soil. Microbial distribution, amount of microbial biomass C, and dehydrogenase activity in the soils were not significantly different among the topographic sites. However, in pear and grape fruit plant fields, coliform group of bacteria was found in relatively higher population, 133.0x10 3 CFU g -1 and 107.4x10 3 CFU g -1 , respectively. Microbial groups were simplified and their density was reduced with increasing the cultivation periods of fruit plants. The soil microbial distribution was proportionally correlated with some of soil properties such as soil pH, soil organic matter (SOM) content, and exchangeable Mg content; in particular, the population of Bacillus sp. was proportionally correlated with soil pH and exchangeable Mg content. The amounts of microbial biomass C and the dehydrogenase activity in the soils were significantly correlated with the contents of SOM and exchangeable Ca ion (p<0.01).

Experimental Study on Expansive Soil Improved with Cation Modifier

The improvement of expansive soil with chemical medicine has been concerned by geotechnical engineers. The cation modifier is used to improve the expansive soil in embankment engineering of an express highway in Yunnan province. The modified test results indicate that the hydrophilic nature and swelling-shrinkage properties of samples are changed drastically. The free swelling ratio decrease and the particle size gradation, strength characteristics and hydrological properties of the treated expansive soil are improved by a wide range. The clay content decreases, but the silt content increases. The void ratio decreases sharply, but the fabric becomes more compact. The change of dry density with water content changing is less, but the water stability of modified soil is improved. The indexes are satisfied with the project requests and the engineering cost reduces.

Effects of Non-Plastic Silts on Liquefaction Potential of Solani Sand

Loose saturated cohesionless soils are most susceptible to liquefaction, however there are strong historical evidence suggesting that soils containing fines such as silty sands are also prone to liquefaction during earthquakes. The liquefaction of silty sands has been observed in a number of recent case studies. This paper presents the effects of fine silts on liquefaction potential of sandy soil. Tests have been conducted on the vibration table at different accelerations and pore water pressure is measured. During the lab investigation, locally (Roorkee, India) available Solani Sand and Dhanauri Silt have been used. The soil samples have been prepared by varying silt content and the initial relative density. The results of the study performed are used to clarify the effects of non-plastic fines content on the Solani sand. As the silt content increases, the number of cycles required to produce maximum pore water pressure increases. For a particular level of excitation, rate of pore water pressure generation is maximum at critical silt content. It is observed that critical silt content to generate maximum pore water pressure is different for different accelerations. Further, effect of silt content is very much dependent on relative density.

Relationships between shallow-water cumacean assemblages and sediment characteristics facing the Iranian coast of the Persian Gulf

During two sampling campaigns carried out in August 1998 and November 2002, 232 cumaeans from eight species belonging to the families Bodotriidae and Nannastacidae were collected. This paper presents the first ecological data on a shallow water tropical cumacean assemblage from the Persian Gulf, where 50% of the existing species were recently described as new for the science. Neither the environmental conditions (except for the sediment organic content) nor the cumacean assemblage descriptors differed between the two sampling periods. However, two different species dominated in each period (i.e. Eocuma travancoricum and Heterocuma inerme in 1998 and 2002, respectively) and the MDS analysis revealed differences in the assemblage composition between periods, particularly for the deepest sampling stations. An increasing density together with the increase in gravel content, and a decreasing density together with the increasing silt content characterized the distribution pattern of both the whole cumacean assemblages and the two dominant species, the latter being also positively correlated with the mean grain size and negatively correlated with depth and organic matter (E. travancoricum) and with depth (H. inerme).

Environmental change implied by the relationship between pollen assemblages and grain-size in N.W. Chinese lake sediments since the Late Glacial

This paper contributes to an understanding of the relationship between pollen assemblages and grain-size in north-west China. Based on the relationship, we have reconstructed the environmental and vegetation history from sediments from Zhuye Lake, located in the marginal area of the Asian monsoon. During the Late Glacial (before ~ 13 cal ka BP), the high content of sand is correlated with low pollen concentrations, which implies an arid environment and low vegetation cover in the drainage. The relatively high percentages of Pinus and Quercus pollen, derived from nearby high elevations, may indicate particularly low vegetation cover in the lower part of the watershed. Between 13 and 7.7 cal ka BP, increasing silt content is correlated with high percentages of Picea pollen. Fluvial flow and effective humidity at high elevations, as well as lake-level, all increase. Following this, an abrupt environmental change which is likely caused by some change in lake geomorphology persists for about 300 years. The Holocene Optimum is between 7.4 and 4.7 cal ka BP in this region. Pollen concentrations reach their highest values in the section. The abundant herb pollen reflects the high vegetation cover in the lower part of the watershed. The silt and the fine components in the sediments are high and stable indicating optimal moisture conditions. Between 4.7–1.5 cal ka BP the lake-level fell and silty peat was formed at the site. The pollen concentration decreased in contrast to the high pollen concentration in the Holocene Optimum. In the last 1500 years the lake-level fell while terrestrial sediments were deposited at the site. In this phase Chenopodiaceae, Nitraria and Ephedra reach their highest values in the section reflecting an arid environment. In Zhuye Lake and the surrounding area environmental changes are mainly controlled the combined effects of the East Asian monsoon and the Westerlies since the Late Glacial. In the last ~ 1.5 cal ka BP the intensive arid trend may be correlated with changes in the Westerlies.