Effect Of Initial Water Content Research Articles

Molecular Dynamics Simulation of the Effects of Different Initial Water Content on Methane Hydrate Decomposition

Gas hydrate is mainly distributed in deep sea-floor sediments and permafrost regions. The water content of these sediments varies with the type of reservoir and affects the rate of hydrate decomposition. In this work, the decomposition process of methane hydrate under four different initial water contents was investigated by molecular dynamics simulation. The results were analyzed by the system conformation, radial distribution function (RDF), and mean square displacement (MSD), which revealed the microscopic mechanism of the effect of the initial water content on the decomposition rate of hydrate. The results demonstrate that the hydrate decomposition starts from the boundary to the middle, and the cage structure is destroyed layer by layer. Methane molecules continue to escape from the hydrate cages as the hydrate decomposes, and subsequent decomposition of the hydrate is inhibited when its solubility in water reaches saturation. The higher the initial water content is, the faster the decomposition rate of hydrate is. The movement distance of methane gas is affected by the initial water content. The higher the initial water content, the smaller the MSD of methane molecules.

Effect of Initial Water Content on the Collapsibility of Natural and Cement-Treated Gypseous Soils

Abstract Soils that exhibit high volume change when its water content is changed are considered collapsible soils. Gypseous soils are one of the main types of collapsible soils which can be found in arid and semiarid areas. In this study, the effect of initial water content on the collapsibility properties of natural and treated gypseous soils with 5% of cement is experimentally investigated. The soils tested at different initial moisture content i.e. 5 %, 10 %, 15 %, 20 %. Two types of soil were used with different gypsum content 28.43 % and 43.62 % named soil 1 and soil 2 respectively. The soils were taken from Tikrit city in Saladin governorate – Iraq. The results show that the initial water content has significant effect on the collapse potential. The reduction in collapse for natural soils reaches up to 70 % when the initial water content was 20 %. Furthermore, the reduction in collapse for natural soils was greater than that for treated soils with different initial water content. It can be concluded that increasing initial water content can reduce the sudden collapse which is a major problem.

Effect of initial water content on the dewatering performance of freeze-thaw preconditioned landfill sludge

Freeze-thawing (F/T) is an effective method of sludge dewatering preconditioning and has been studied in many studies. However, previous studies have taken landfill sludge from different regions, filled for different length of time or at different depth, resulting in large differences in initial water content and different treatment effects. Therefore, the effect of initial water content on the dewatering characteristics of F/T preconditioned landfill sludge has been investigated. The sludge with different initial water contents was firstly preconditioned by one F/T cycle. Then the F/T sludge was vacuum filtered and compared with the dewatering performance of FeCl3 preconditioned sludge with the same water content. Finally, the mechanism of the initial water content on the effect of F/T preconditioning was analyzed by the change of sludge internal composition. The results show that the higher the initial water content of the sludge, the greater the improvement of its dewatering performance after F/T preconditioning. The specific resistance and water content after filtration of sludge after F/T conditioning decreased greatly with the increase of the initial water content, reaching their respective minimum values of 13.3 × 1012 m/kg and 58.3% at 85% and 87.5%. These values are lower than the optimal values observed for the sludge conditioned by FeCl3. With the rise in initial water content, the driving force at the ice-water interface gains strength. Small particles aggregate into larger flocs, forming stable drainage channels that enhance the dewatering performance of sludge. Once the initial water content surpasses 85%, the squeezing force exerted by ice crystals amplifies the degree of cracking in sludge particles, releasing bound water and further decreasing the water content of sludge.

Numerical investigation on the effect of initial water content on dynamic responses of unsaturated sandy and clayey embankments

High water contents and poor compaction during construction have been reported to cause severe embankment damage during earthquakes. In this paper, a fully coupled soil-water-air finite element method is adopted to reveal the failure mechanism of unsaturated embankments subjected to earthquakes. And the dynamic responses of sandy and clayey unsaturated embankments with different water contents and dry densities are carefully investigated. It is found that the sandy embankments compacted above the optimum water content (OWC) during construction have a sliding potential triggered by liquefaction during earthquakes, while the sandy embankments compacted at or below the OWC only show slight subsidence due to the contribution of suction to soil strength. The stability of the clayey embankments worsens with increasing water content. The clayey embankments with a high water content exhibit substantial subsidence at the crest and bulging at the laterals, which are different from the failure mode of sandy embankments during earthquakes.

Exploring effects of initial water content of recycled aggregate and additional water consumption on the permeability resistance of concrete to chlorine salt

Recycled aggregate concrete (RAC) technology is conducive to resource conservation and environmental protection, but the high-water absorption of recycled aggregate makes it difficult to control the durability of RAC. In this study, the combined effects of initial moisture and additional moisture of recycled coarse aggregate (RCA) on the resistance to chloride ion penetration of concrete were investigated. The results show that, when the initial humidity of RCA is lower than 0.25 and the additional water consumption is low, RAC shows a rapid decay of dynamic elastic modulus. In contrast, when the sum of initial water content and additional water content is greater than 80%, the higher the initial water content, the better the compactness and impermeability of concrete. At the same time, the initial water and additional water of RCA have a great impact on the quality of RAC and the depth of damage layer. When the initial water content of RCA is high, the corrosion resistance of RAC decreases with the increase of the additional water. After comprehensive consideration, it is recommended to use RCA with 50% initial water and less than 40% additional water to obtain good durability.

Effect of initial water content on soil failure mechanism of loess mudflow disasters

The frequency of mudflow disasters induced by rainfall in the Loess Plateau is increasing with the occurrence of global warming. The initial water content is one of the basic properties of soil, which affects the initiation of loess mudflow. In this work, the field study of the debris flow gullies in Yan’an City, Shaanxi Province, China, was conducted, and the main factors that induce gully loess mudflow were summarized. Based on the investigation results, a flume model was designed to carry out flume tests with different initial soil water contents. The experimental results demonstrate the following. (1) Different initial soil water contents lead to different soil failure models. The damage of soil by water flow when the soil water content is in the range of 0−5% is mainly gully erosion; that within the range of 10−15% is mainly rill surface erosion; that within the range of 20−25% is mainly dam breach failure. (2) When the water content of loess is equal to or less than 5% or equal to or greater than 20%, soil can promote the formation of loess mudflow, and the destruction of soil is more likely to cause mudflow disasters. In contrast, when the water content is within 10−15%, loess mudflow is not easily produced. The research results of the initial water content provide not only theoretical support for the study of loess mudflow disasters, but also a reference for the prevention and control of loess mudflow disasters in the Loess Plateau.

Study on soil freezing characteristic curve during a freezing-thawing process

Soil freezing characteristic curve (SFCC) defines the relationship between unfrozen water content and subzero temperature. The SFCC is widely applied to estimate the soil properties. The current study explored the effects of initial water content, dry density, soil type and desalination on the SFCC during a freezing-thawing process. It showed that the initial water content, soil type and desalination had great impacts on SFCC, while the dry density had an insignificant effect on SFCC. Hysteresis behavior was observed for all the soil samples. The hysteresis behavior was obvious in the temperature range of -5°C < T < 0, but not obvious in the temperature range of T ≤ -10 °C. A new equation containing freezing/thawing point was proposed to model the SFCC. The new model and four SFCC models were evaluated with measured data in this study. It showed that the new model performed best among these models. The new model accurately mimics the SFCC and is continuous near the freezing/thawing point and 0 °C. It can be easily incorporated into numerical algorithms for coupled heat and mass transfer in cold regions.

An efficient microbial sealing of rock weathering cracks using bio-carbonation of reactive magnesia cement

Bio-carbonation of reactive magnesia cement (RMC) was proposed as a promising strategy to stabilize the weathered stone grains for the efficient sealing of rock weathering cracks near surface. The physical and mechanical properties of the sandstone grains stabilized by bio-carbonation of RMC was first investigated to verify the feasibility of applying the method to the rock weathering cracks when subjected to the condition of compression failure. Except for initial water content, RMC content and urea concentration, two new effects including bacteria concentration and bacteria solution composition on the underlying stabilization mechanism were systematically studied. The experimental results showed that bio-carbonation of RMC can effectively stabilize the sandstone grains. The highest unconfined compressive strength (UCS) of bio-carbonated sample was up to 5.5 MPa, which was 7.8 times higher than that of the sample stabilized by RMC hydration only. UCS increased as the RMC content and bacteria concentration increase, while the effects of initial water content and urea concentration were opposite. The dry density, resistance of water absorption, electrical resistivity and P-wave velocity were in proportion to the UCS. The effect of bacteria solution composition indicated that the well stabilization performance can be attributed to the coupling effect of the biomolecules and bacteria. Biomolecules-induced amorphous brucite can form a dense structure to fill the pore spaces. Bacteria-induced hydrated magnesium carbonates (HMCs) can form a stable spatial network structure with high cementation strength. The bacteria and biomolecules inhibited the air-based carbonation but facilitated the bacteria-based bio-carbonation and made the microstructure denser. A better bio-carbonation effect and stabilization performance can be obtained by increasing bacteria activity, such as increasing bacteria concentration or using low concentration of urea.

The Effect of Initial Water Content and Density on the Swelling-Shrinkage and Cracking Characteristics of Compacted Clay

The swelling-shrinkage and cracking characteristics of compacted clay under the coupling effect of initial conditions are rarely studied. The dry-wet cycle test of compacted clay with varying initial water contents and densities was performed in this study; the size and cracking conditions were investigated. The results showed that when the initial moisture content was 21% and the dry density was 1.65 g/cm3, the longitudinal expansion amount of the compacted clay was relatively small. However, it was rather large when the initial water content was 17% and 19%. Under the same dry density, the final vertical shrinkage ratio of the sample with a water content of 21% was the smallest, while that of the samples with a water content of 23% and 25% was rather big. Under the same water content, the final vertical shrinkage ratio decreased with the increase in dry density. After three wetting-drying cycles, compacted clay with a dry density of 1.65 g/cm3 and an optimal initial water content of 21% produced the fewest cracks and had the lowest cracking factor (CF) (only 7.58%). The compacted clay specimens with the dry densities of 1.55 g/cm3 and 1.60 g/cm3 had rather significant cracking at the same initial moisture content of 21%. The mercury intrusion porosimetry (MIP) test demonstrated that in the first two dry and wet cycles, the distribution of large pores decreased and that of tiny pores increased. After the third cycle, the distribution of small and medium pores decreased slightly. The results of this study will provide theoretical guidance for selecting cover soils in landfills.

Effect analysis of initial water content and temperature on the adsorption of VOCs by activated carbon based on molecular simulation

To analyse the effects of initial water content (IWC) and temperature on the adsorption behaviour of VOCs on activated carbon (AC), the grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) methods were used. Benzene and acetone are regarded as two representative components of VOCs, and their adsorption properties in AC models with four different IWC at 298.15 K were investigated. Their adsorption properties at four different temperatures (278.15, 288.15, 298.15, and 308.15 K) were also investigated. The simulated pressures were set in the range of 3 × 10−4 to 3 kPa (benzene) and 10 × 10−4 to 10 kPa (acetone). The results show that water molecules can impede the adsorption of benzene and acetone, decreasing the saturated adsorption capacity, the isosteric heat, and monomolecular interaction energy. However, the pre-loaded water molecules can enhance the electrostatic interaction at low pressure, which affects the isosteric heat and monomolecular interaction energy, but the pore volume is still the main influencing factor. Before reaching the saturated adsorption capacity, the higher the temperature, the lower the adsorption capacity, and the monomolecular interaction energy follows the same trend. The results provide mechanistic insights into how the IWC and temperature affect the adsorption properties of AC for VOCs.

Experimental Study on the Effect of Initial Water Content and Temperature Gradient on Soil Column Segregation Frost Heave

A series of freezing experiments were carried out on the Qinghai silty clay using a one-dimensional soil column particle image velocimetry (PIV) system. The effects of the initial water content and temperature gradient on the frost heave of the soil column were analysed. The experimental results show that the total volumetric water content after the Qinghai silty clay freezing is much greater than the initial water content before freezing, and the total volumetric water content at the segregated layer reaches the maximum value. The average unfrozen water content firstly increases sharply with time and then decreases slowly. The obvious horizontal layered segregation cracks filled with unsaturated needle-columnar ice lenses have occurred above the soil column frozen fringe. The thickness of segregated ice is about 43% of the total frost heave. There is a small frost heave in the frozen fringe and a small compression deformation amount in the unfrozen zone. Under the same temperature gradient conditions, the soil column with the low initial water content has a smaller frozen depth, larger total volumetric water content, more water intake, smaller segregated ice thickness, and less total frost heave amount than that of the soil column with the high initial water content. Under the same initial water content conditions, the soil column with a large temperature gradient has a greater frozen depth, consistent total volumetric water content, larger segregated ice thickness, and greater total frost heave amount than that of the soil column with a small temperature gradient.

Study on screening of fermentation agents and optimization of the fermentation process for pharyngitis tablet residue.

This study aimed to screen an appropriate starter and determine the optimal fermentation process parameters to optimize the fermentation process of nutrient components and bioactive contents in pharyngitis tablet residue. This study included two experiments. In experiment I, single-factor experimental design was used to study the effects of different biological starters (cellulase preparation; Lactobacillus Plantarum and Bacillus subtilis preparation; mixture of cellulase + Lactobacillus Plantarum and Bacillus subtilis) on the nutritional values and bioactive ingredient contents in pharyngitis tablet residue. In experiment II, orthogonal design experiment was adopted to study the effects of initial water content (45, 50, and 55%), fermentation temperature (35, 37, and 40°C), and fermentation time (24, 48, and 72 h) on the changes in nutrient components, biologically activity contents, and toxin contents of the residue after optimal fermentation agent treatment. Cellulase preparation was found to be the optimal starter. The optimal fermentation conditions were: initial water content, 55%; fermentation temperature, 37°C; and fermentation time, 72 h. The contents of aflatoxin B1 and vomit toxin were in line with Chinese feed hygiene production standards. The fermentation quality of pharyngitis tablet residue can be improved by using the optimal starter and fermentation conditions.

Effect of initial water content and dry density on the self-healing of desiccation cracks in compacted hipparion red clay

The self-healing of desiccation cracks in compacted clayey soils is important for mechanism revelation of cracking behavior in compacted soils. Although the crack self-healing behavior has been found, the influence of soil physical indices on it is still unclear, especially initial water content and dry density of specimen. This study aims to identify and evaluate the effect of initial water content and dry density on self-healing of desiccation cracks. Firstly, a series of desiccation tests were conducted on compacted Hipparion red clay specimens under different initial conditions. Secondly, the two-dimensional morphology of desiccation cracks and strain field changes on specimen surface were examined using the pore and crack analysis system and digital image correlation techniques. The result shows that the desiccation cracks on specimen surface exhibits self-healing behavior during drying. Based on the observed crack self-healing behavior, the desiccation cracking of compacted Hipparion red clay undergoes four stages including initiation, development, self-healing, and stabilization. During the self-healing stage, the critical water content for occurrence of crack self-healing and the crack self-healing amount referring to the crack ratio reduction from peak value to the stable value, are dry density dependent and water content dependent variables. In particular, the higher the initial water content and the lower the dry density of compacted specimen are, the larger the crack self-healing amount is. This crack self-healing difference in specimen with different initial conditions is caused by the vertical anisotropic shrinkage of substrate soil below non-propagating cracks due to its pore structure difference. This study provides a new perspective on the mechanism of desiccation crack in clayey soils affected by initial conditions.

Utilization of flue gas desulfurization gypsum to produce green binder for dredged soil solidification: Strength, durability, and planting performance

The massive deposition of sediment in the Yellow River leads to the waste of land resources and is also prone to environmental disasters. In this study, the industrial by-product, flue gas desulfurization gypsum (FGDG), was incorporated with Portland cement (PC) and fly ash (FA) to treat the dredged soil (DS) from the Yellow River. The effects of initial water content of DS (w0), binder content (Aw), and the FGDG content in binder on the strength development and durability of solidified dredged soil (SDS) were analyzed via a series of UCS, pH value, and dry-wet cycles tests. Additionally, the planting performance of SDS was evaluated by planting wheat grass, and the microstructure characteristics were conducted by X-ray diffraction (XRD) analysis, thermogravimetric (TG) analysis, and scanning electron microscope (SEM) method. The results indicate that, when the binder containing 50% FGDG, the SDS sample has good strength and resistance to dry-wet cycles, and decreasing w0, increasing Aw, or reducing the FGDG content in binder can obviously improve the strength and durability of SDS. Furthermore, increasing the FGDG content in binder is more beneficial to germination and growth of plants. The micro-analysis shows that, during the dry-wet cycles test, the amount of hydration products (i.e., C–S–H and AFt) in SDS increased significantly, and the structure became denser, resulting in the increase of strength. During planting, the pH of SDS decreased rapidly to about 8.5, mainly because the root respiration accelerated the carbonization of Ca(OH)2 crystals in sample.

Experiment study on normalized compression behaviour of marine diatomaceous soil considering microstructure of biogenic silica

There are many sites in the world where diatom microfossils have been detected, but very little is known about their effect on sediment geotechnical properties. Diatomaceous soils (herein called “biogenic silica soils”) are usually composed by a mix of sand, fine-grained clay and diatom (and, or radiolarian). This paper presents an experimental investigation on the compression behaviour of biogenic silica-kaolin (BSi-K) clay mixtures and natural marine diatomaceous soils. The results show that the BSi composition dominates the compression when the BSi content is higher than 50%. The microstructure of biogenic silica frustules is first characterized and a skeletal void volume model (BSi-SVV model) is proposed. By using this model, the addition water in biogenic silica frustules can be quantitatively evaluated, which is up to 92.6% as the BSi content is 78%. It can be explained as the cause of high natural water content and low plasticity of diatomaceous soils. By introducing the effective void ratio, the compression curves can be normalized; furthermore, a new intrinsic compression line (BSi-ICL) suitable for BSi-K clay mixtures is developed based on the intrinsic compressibility concept of Burland (1990). It is considered as an extension of Burland's ICL. Finally, the effect of initial water content on the normalized compression behaviour is investigated. The findings in this study can provide a deeper insight into the geotechnical properties of marine diatomaceous soils.

Effects of initial water content on compression behaviour of municipal sewage sludge

To investigate effects of initial water content on compression behaviour of municipal sewage sludge and clarify its intrinsic compression characteristics. Oedometer tests were conducted on sludge with various initial water content of 0·13–1·48 times the liquid limit. It is observed that the sludge is organic high liquid limit silt, whose e–log σ′v compression curves are inverse ‘S’ shape due to organic floc structure of sludge potentially. When the effective vertical stress σ′v > 100 kPa, a clear gap of compression curves of various initial water content still exists, different from Burland's viewpoint that compression curves tend to be consistent. Burland's concept of intrinsic compression line (ICL) is adopted for correlating compression curves of sludge well, and an ICL of the sludge is derived. The ICL of sludge is below ones reported by Hong and Burland when σ′v < 100 kPa, due to the difference in initial water content. A generalised void index is tentatively proposed by introducing generalised intrinsic parameters e*y1 and e*y2, which may be related to the loading history of the soil and the maximum load that the soil may bear in future engineering, respectively.

Strength criterion for frozen silty clay considering the effect of initial water content

The initial water content and confining pressure significantly affect the deformation and strength behaviors of frozen soils. To investigate the influence of the initial state of water on the mechanical properties of frozen silty clay (FSC), triaxial compression tests are conducted on artificial FSC with five initial water contents (12.5%, 14.0%, 16.0%, 18.0%, and 20.0%) at the temperature of −6 °C. The results show that when the initial water content is 12.5%, the frozen soil samples present strain softening and strain hardening successively with increasing confining pressure. As the initial water content increases, the degree of strain hardening under the same confining pressure gradually weakens. The frozen soil samples mainly present strain softening when the initial water content is more than or equal to 18%. According to the test results, when the initial water contents ranging from 12.5% to 20%, the relationship between the strength and mean stress has three forms: increases nonlinearly, increases first and then decreases, and maintains an approximately constant value. Linear and nonlinear strength envelope equations based on different types of strength envelopes are proposed. Additionally, the relationship between the initial water content and internal friction angle is analyzed. In the p-q plane, based on the nonlinear strength characteristics of FSC with initial water contents of 12.5%, 14.0%, and 16.0%, a modified mean stress expression p* is derived to represent the nonlinear strength criterion equation according to the modified Cam-Clay model. Furthermore, a shape function in the deviatoric plane is proposed by modifying the Lade–Duncan model, and a strength criterion is established by integrating the strength functions in the p-q and deviatoric planes. The proposed strength criterion can effectively represent the nonlinear strength behaviors of FSC, including the effects of the initial water content, ice melting, and crushing.

Factors affecting the swelling pressure for Jerash expansive soil

  In this study for factors effecting the swelling pressure of jerash expansive soils were investigated in this study, effect of initial dry density and effect of initial water content on the jerash expansive soil were investigated.It show that as the initial dry density decrease from 1.85 gm/cm3  to1.25 gm/cm3 , the swelling pressure also decrease are from 3.1  to 0.25gm/cm2   also it show that as the initial water content increase from 0%to 15% , the swelling pressure of jerash expansive soil decrease from 2.65 gm/cm2  to 1.35 gm/cm2  .
  

The effect of initial water content on the swelling pressure of soils

Swelling soils cause serious damage to engineering structures, and they pose a problem worldwide. The fluctuation of water content is one of the most important factors that cause the swelling pressure of soils, especially for soils in arid and semi-arid regions. The swelling soils in these regions are exposed to cycles of volume increase and decrease in the rainy and dry periods. Thus, low-rise buildings and infrastructure constructed on or in these soils are exposed to potential damage. Although the relationship between swelling parameters and the physical-index properties of soils have been investigated in detail in previous research, the effect of variations in the initial water content on the swelling pressure of soils has not yet been sufficiently studied. For this reason, samples were prepared at the same dry unit weight and with different initial water contents to examine the effect of water content on the swelling behaviour of soils. According to swelling test results reported here, there is a statistically significant linear relationship between initial water content and swelling pressure. Some predictive empirical models with high correlation coefficients are obtained. In addition, a new approach called swelling pressure designation (SPD) is recommended for prediction of the swelling pressure of soils of any water content.

Primary and secondary compression behavior of dredged clay at low effective stresses

This study presents an experimental investigation on the time-dependent compression behavior of dredged clay samples at high initial water contents under lower effective stress. A series of laboratory one-dimensional consolidation tests with or without aging were conducted on dredged clay samples with various initial water contents. Test results showed that initial water content has a significant effect on the primary compression of dredged clay specimen. All dredged clay specimens follow the same decreasing trend in void ratio with time. Compared with the significant decrease in void ratio in the primary consolidation stage, void ratio decreases less significantly with time in the secondary consolidation stage and tends to level off. The aging strain will not continue increasing as the increase in initial water content more than two times the liquid limit. Aging strain of specimens at different initial water contents consistently increase linearly with the increasing time. The value of secondary compression index is influenced by both aging time and initial water content. It consistently reduces with increasing aging time yet increases with increasing initial water content. We should fully consider the effect of initial water content and aging time on the secondary compression index to predict the secondary compression settlement.