Effect Of Pore Water Chemistry Research Articles

Effect of pore water chemistry on the ring shear behavior and the rate dependency of residual strength

The rate dependency of residual strength plays an important role in the selection of residual strength parameters to design the remediation works for reactivated landslides. In the literature, it is shown that the rate dependency of residual strength depends on some factors such as types of soil, range of shear rates, range of effective normal stresses, and pore water chemistry. Recently, the effect of pore water chemistry on the rate dependency of residual strength soil has been examined. However, the ring shear behavior and the rate dependency of residual strength of soil having different pore fluids should be more evaluated. In this study, the effect of the pore fluids of distilled water and 1 M NaCl on the rate dependency of residual strength of kaolin clay was investigated in the Bishop ring shear apparatus. The ring shear tests were conducted at different shearing rates from 0.02 mm/min to 20 mm/min under the effective normal stress of 98 kPa. The research results showed that the pore fluid chemistry affected the shear displacement required to reach the peak strength, the vertical displacement, and the peak strength of kaolin clay. These parameters also exhibited rate dependency, especially at the fast shear rates. The research also indicated that the pore fluid chemistry had a significant effect on the rate dependency of residual strength. Accordingly, the rate dependency of residual strength of kaolin mixed with distilled water showed a positive tendency while that of kaolin with 1 M NaCl as the pore fluid was the neutral tendency.

Effect of pore water chemistry on the behaviour of a kaolin–bentonite mixture during drying and wetting cycles

The behaviour of a kaolin–bentonite mixture with different pore water chemistry, i.e. distilled water, NaCl and CaCl2 solutions, was investigated through a number of cyclic drying and wetting tests. Experimental tests were carried out on compacted samples of the expansive soil (i.e. mixture of 80% kaolin and 20% bentonite) in a modified oedometer with different pore water chemistry under a surcharge pressure of 10 kPa. The vertical and radial deformations of the samples were determined during different stages of drying and wetting. In addition, the soil–water characteristic curve was established by the filter paper technique for samples with different pore water chemistry. The results indicate that the shrinking–swelling deformation was nearly the same when the equilibrium condition was attained. Furthermore, the paths of drying and wetting converged to an S-shaped curve at equilibrium condition. This curve consists of one linear and two curvilinear portions, and the majority of the deformation occurred in the linear section. The hysteresis phenomenon was also studied through the void ratio and suction, and the results indicated that the hysteresis is gradually diminished with increasing the number of drying and wetting cycles.

Studying of the combined salts effect on the engineering properties of clayey soil

In recent years, a number of studies had been performed to investigate the effect of pore water chemistry on the strength and compressibility characteristics of soil. Although the effect of chloride and sulfates salts separately in pore fluids on the geotechnical properties of soil seems to be well understood, but the influence of combined effect of sulfates and chlorides in pore water on the behavior of soil is still unclear mostly due to the limited numbers of studies as well as the complexity of processes that may occur in soil (with the presence of salts) in pore water-soil interaction. Southern regions of Iraq, especially Basra suffers from low water levels in the summer season in addition to the lack of rain water, which causes a significant increase of salt in the Shatt al Arab. Water salinity continues to increase with time. To investigate the combined impacts of water salinity on the behavior of clayey soils, the basic characteristics of the soil brought from Al-Nahrawan site was studied. Chemical methods were done with three types of water (distilled, water of highly saline as Shatt Al-Arab water and water of Tarmiya as moderate saline water). The effect of water salinity on the geotechnical properties of fine grain soil was investigated. Different laboratory tests such as Atterberg limits, standard compaction, consolidation and shear strength of soil .Results showed that the presence of perceptible amounts of dissolved salts in water can lead to changes in the engineering properties of the soil.

Effect of pore water chemistry on anisotropic behavior of clayey soil and possible application in underground construction

The effect of pore water chemistry on anisotropic behavior of consolidation and shear strength of reconstituted Ariake clay has been investigated experimentally. Two types of chemicals added into the pore water of the soil for enhancing flocculation microstructure of soil particles are sodium chloride (salt) (NaCl), and calcium chloride (CaCl2); and two dispersants added are sodium triphosphate (Na5P3O10) and sodium hexametaphosphate (Na6P6O18), respectively. The concentrations of these chemicals in pore water were 2–3%. Degrees of anisotropy of the coefficient of consolidation and undrained shear strength decreased with adding NaCl and CaCl2, but increased with adding the dispersants. Degree of anisotropy also increased with one-dimensional (1D) deformation and the samples with dispersive additives had higher increase rate. It has been confirmed qualitatively by scanning electron microscopy (SEM) images that adding dispersive chemicals promoted the formation of dispersive microstructure and increased the degree of anisotropy, and the chemicals enhancing flocculent microstructure had an inverse effect. The possible application of the findings to underground construction has been discussed also.

Modelling the effects of pore-water chemistry on the behaviour of unsaturated clays

Due to their various applications in geo-environmental engineering, such as in landfill and nuclear waste disposals, the coupled chemo-hydro-mechanical analysis of expansive soils has gained more and more attention recently. These expansive soils are usually unsaturated under field conditions; therefore the capillary effects need to be taken into account appropriately. For this purpose, based on a rigorous thermodynamic framework (Lei et al., 2014), the authors have extended the chemo-mechanical model of Loret el al. (2002) for saturated homoionic expansive soils to the unsaturated case (Lei, 2015). In this paper, this chemo-mechanical unsaturated model is adopted to simulate the chemo-elastic-plastic consolidation process of an unsaturated expansive soil layer. Logical tendencies of changes in the chemical, mechanical and hydraulic field quantities are obtained.

On the pore water chemistry effect on spectral induced polarization measurements in the presence of pyrite

In order to expand the application of the induced polarization (IP) method as a technique for monitoring metallic mineral dissolution and precipitation mechanisms, we studied the effects of variations in pore water chemistry on the spectral induced polarization (SIP) response of a mixture of silica-sand and pyrite particles in the laboratory. We investigated the dependence of the SIP response on both pore water conductivity and pH for various chemical compositions: redox-passive (P) versus redox-active (A) ions, using CaCl2 as P-ions, and FeSO4 and FeCl3 as A-ion brines. The effect of pore water chemistry was evaluated by means of a recently proposed volumetric specific capacitance model. The SIP response (IP-effect) was primarily determined by the pore water conductivity and the specific capacitance was only weakly dependent on the chemical composition and pHw. We found that the specific capacitance varies to first order over a limited range and approximates a single value (≈302Fm−3 in average). However, variations in the specific capacitance as a function of active versus inactive ion chemistry might be important to consider when using IP to monitor specific mineral dissolution and precipitation processes.

A Comparison of the Elemental Composition of Leaf Tissue of Spartina Patens and Spartina Alternifora in Louisiana’s Coastal Marshes

Elemental concentrations in leaf tissue can identify limiting conditions in crops and can be useful in managing and restoring marshes. Coastal management and restoration plans frequently include Spartina spp. because they are common plants in coastal wetlands across North America. Researchers frequently compare results of stoichiometric studies among Spartina spp. to corroborate results, although their stoichiometry may not be comparable. We compare the stoichiometry of paired samples of Spartina patens and Spartina alterniflora collected across Louisiana. Overall differences in stoichiometry between species, seasonal changes, and effects of porewater chemistry were quantified. Manganese (Mn) concentrations and calcium (Ca) concentrations were higher in S. alterniflora and the difference in [Ca] increased seasonally. Sodium concentrations were similar, except during prolonged inundation. Short flooding durations decreased carbon (C):nitrogen (N) without increasing [Mn] or flooding stress in both species.

Effect of pore water chemistry on the hydro-mechanical behaviour of Lianyungang soft marine clay

The effect of pore water chemistry on the hydro-mechanical behaviour of soft marine clay of Lianyungang was investigated. Field investigation and piezo-cone penetration tests at two sites with 0.56% and 4.91% salinity respectively were first performed, and a significant difference was observed in terms of Atterberg's limits (LL and PL), density, net tip resistance, sleeve friction and pore water pressure parameter, suggesting a significant effect of pore water chemistry. To confirm this observation, identification tests were extended to an artificial soil corresponding to a mixture of kaolinite/bentonite with different salinities. The results obtained confirm the significant effect of pore water chemistry. To further clarify this effect, oedometer tests were performed with both site water and deionised water. The results indicated that the compression index, swelling index, and secondary consolidation coefficient are higher in the case of deionised water, whereas the oedometer modulus, consolidation coefficient and hydraulic conductivity are larger in the case of site water. However, the ratio between secondary consolidation coefficient and compression (or swelling) index indicates no significant effect of pore water salinity. After completion of the oedometer tests, the microstructure features were studied by the mercury intrusion porosimetry. The results showed that deionised water led to an increase of porosity, whereas the site water led to a decrease of porosity.

Effect of pore-water chemistry on undrained shear behaviour of saturated loess

Pore-water chemistry can have a fundamental influence on the shear behaviour of soil. To study the effects of salt concentration and desalinization on undrained shear behaviour, a series of ring shear tests was conducted on Chinese loess saturated with various NaCl solutions of differing concentration, under the same initial void ratio and consolidating stress conditions. Results showed that the peak and steady-state shear strengths increase as the NaCl concentration increases only up to a certain level. When this level is exceeded, any further increase of NaCl concentration results in lower shear strengths. After desalinization the peak and steady-state shear strengths recover to those of the original sample, showing that the salinization of loess is reversible. A pore pressure ratio of 0.6 can be used as a criterion to assess whether liquefaction can be induced in saturated loess. These findings may provide a useful explanation for progressive or seasonal activity of some irrigation-induced loess landslides in the Chinese Loess Plateau.

Long-term effect of water chemistry on the swelling pressure of a bentonite-based material

Compacted bentonite-based materials have been proposed as possible sealing and backfill materials in geological repositories for the high-level radioactive waste disposal in several countries. During the long time lifespan of a repository, as the chemical composition of pore water can change, the swelling and sealing capacity of the material may also change. From a point of view of storage safety assessment, it is important to evaluate this possible change of swelling capacity. In this study, a mixture of bentonite and crushed Callovo-Oxfordian claystone was investigated. The long-term effect of pore water chemistry on the swelling pressure was studied at constant-volume conditions for 700days. Distilled water and synthetic water having the chemical composition similar to that of in-situ pore water were used for hydration. The results obtained in an initial period of 100h revealed no significant influence of the water composition on the swelling pressure evolution, and the maximum swelling pressures observed were close to 4.30MPa for a dry density of 1.70Mg/m3. Over a longer time period, on the contrary, the swelling pressure eventually decreased for all samples, especially for the sample saturated with synthetic water. In addition, comparison of a one-step soaking test with a multi-step soaking test showed no wetting procedure effect on the long term swelling behaviour. All the results are analysed by considering the physico-chemical interaction between the minerals of claystone, minerals of bentonite and different fluids involved.

Cyclic Shear Strength of Soil with Different Pore Fluids

The effects of pore water chemistry on the cyclic behavior of fine-grained soil were examined by performing undrained cyclic ring-shear tests on a natural soil treated with solutions of sulfuric acid (H2SO4), sodium hydroxide (NaOH), and sodium chloride (NaCl). In addition, different amounts of the chemicals were used to clarify the influence that ion concentrations in the pore fluid can have on the cyclic shear strength of soil. The results of laboratory tests indicated that cyclic shear strength was sensitive to changes in the pore fluid composition, and changes in cyclic behavior of soil became more pronounced as the concentration of each chemical increased.

The Effect of Pore Water Chemistry on the Biodegradation of the Exxon Valdez Oil Spill

Knowledge of the oxygen and nutrient concentra- tions in an oil-contaminated Prince William Sound (PWS) beach is important for understanding of the oil persistence over two decades after the Exxon Valdez spill. It was tradi- tionally believed that there was enough oxygen in the conta- minated shorelines to sustain aerobic microbial metabolism of oil and that nutrients were the major factors limiting oil biodegradation. In the present study, we analyzed the oxy- gen and nutrients levels in both clean and oily areas on a PWS beach that was heavily contaminated by the Exxon Valdez oil spill. We found that the level of nitrogen and phosphorous were 0.454 mg-N L −1 and 0.033 mg-P L −1 , respectively, which is not sufficient to fully support micro- bial growth, confirming that nutrient concentration was a major factor limiting oil transformation by biological ways. We also observed that the oxygen level varied from higher than 3 mg L −1 in the clean wells to about 1 mg L −1 (near anoxic level) in the oily wells. In addition, the lowest nitrate levels were observed at the oily wells. Altogether, these re- sults suggest that the low level of efficient electron acceptors (oxygen and nitrate) detected at the oily spot is responsible for slow and potentially inefficient biodegradation of the oil.

Succession of methanotrophs in oxygen–methane counter-gradients of flooded rice paddies

Little is known about population dynamics and contribution of specific taxa to methane oxidation in flooded rice paddies. In this article we investigate the succession of methanotrophs in oxygen-methane counter-gradients. We used a gradient microcosm system that simulates oxic-anoxic interfaces of a water-saturated paddy soils, and measured pmoA-based (gene encoding particulate methane monooxygenase) terminal restriction fragment length polymorphism (T-RFLP) profiles at both the transcription (mRNA) and the population (DNA) levels. The DNA T-RFLP profiles indicated that the methanotrophic community present clearly differed from the active methanotrophic community. We observed a succession of the methanotrophic community over time without any direct effect of pore water chemistry on the community structure. Both the total population and the active subpopulation changed with time, whereas methane oxidation rates remained nearly constant. Hence, we suggest that a diverse microbial seed bank of methanotrophs is important in maintaining the function in a dynamic ecosystem.

Undrained cyclic behavior of bentonite–sand mixtures and factors affecting it

In this work, the cyclic behavior of bentonite–sand mixtures and factors affecting it were studied by means of a ring-shear apparatus and a scanning electron microscope. It was found that bentonite content had a significant influence on the liquefaction potential of the studied soils. A small amount of bentonite in the mixtures would cause the formation of “loose” microstructures, resulting in the occurrence of rapid liquefaction under cyclic loading, while a high bentonite content would cause the formation of clay matrixes, thus raising the soil resistance to liquefaction. In addition, the effect of pore water chemistry on the cyclic behavior of a high plasticity bentonite–sand mixture was carefully examined. It was also found that the presence of ions in pore water would change the clay microfabric, making it more open and thus more vulnerable to liquefaction. Finally, the effects of loading frequency on the cyclic behavior of mixtures with different amounts of bentonite were investigated. It was found that as the bentonite content increased, the influence became more pronounced.

Major ion and electrical potential distribution in soil under electrokinetic remediation.

To assess the effect of pore water chemistry on the contaminant removal rate, we monitored major ion concentrations in the pore water and the electrical potential distribution of a soil during electrokinetic remediation treatment. On application of the voltage, the soil near the anode became acidic due to the electrolytic generation of H+, and the acid region gradually spread toward the cathode. The major cation in the acid region was, however, not H+ but Al3+ that arose from the acid-induced dissolution of soil minerals, and it migrated very slowly toward the cathode. The measured pH and accompanying ion concentrations indicated that the anomalously slow migration of Al3+ was due to its precipitation-dissolution reaction at the acid front. The stagnancy of Al3+ increased the ionic concentration, flattened the electrical potential profile, and in turn, diminished electromigration in the acid region. This seems to be one of the causes of the relatively low removal rate of cationic and anionic contaminants in electrokinetic treatments.

The effect of calcium ions in pore water on the residual shear strength of kaolinite and sodium montmorillonite

This paper reviews the literature concerning the effects of pore water chemistry on residual shear strength (τ;.). It presents the results of index limit and residual shear strength testing undertaken on kaolinite and sodium montmorillonite, using concentrations of calcium chloride similar to the calcium levels measured in groundwaters obtained from landslipped calcareous mudrock of the Fuller's Earth Formation. The residual shear strength of the sodium montmorillonite increased markedly for the sample treated and tested with 80 mg/1 Cat+ compared with that tested with deionized water. Greater concentra-tions of Ca2+ resulted in only a marginal further increase in the residual shear strength. These changes were also reflected in the interpreted parameters, Ør' and c;. The liquid limit of the montmorillonite decreased dramatically when the samples were treated with 80 mg/1 Ca2+, and this effect persisted and/or was slightly enhanced when the concentration of Ca2+ was increased. The residual shear strength and Atterberg limits of kaolinite were much less sensitive to Ca2+. The paper briefly discusses the implications of the findings for slope stabi-lity and the importance of using an appropriate chemical solution in the water bath when under-taking residual shear strength testing. As the laboratory-measured τ; is shown to vary with the chemistry of the pore water, this provides a possible explanation for the difference between results calculated by back-analysis and those obtained in the laboratory using deionized water. Attention is drawn to the necessity of defining the complete residual failure envelope as, if this is curved, the residual shear strength parameters &tu;;, &slah; and c;) will vary with σn. Ce papier passe en revue les ouvrages traitant des effets de la chimie de Peau de porosit6 sur la résistance résiduelle au cisaillement (τ ). Il présente les r&acutesultats d'essais de mesure de limite de liquidit&acute et de résistance résiduelle au cisaillement, conduits, sur de la kaolinite et de la montmorillonite de sodium en utilisant des concentrations de chlorure de calcium identiques aux concentrations de calcium mesurées dans les eaux souterraines de la pélite calcaire éboulée de la formation de terre à foulon. La résistance résiduelle au cisaillement de la mont-morillonite de sodium a augment&acuté de manière significative pour l&gravechantillon traité et testé avec 80 mg/1 de Ca2+ par rapport à celui qui était testé avec de Peau d&acuteionisée. Les concen-trations supérieures de Cat+ Wont conduit qu'à une augmentation supplémentaire marginale de la résistance résiduelle au cisaillement. Ces changements se sont aussi traduits dans les paramètees interprétés, Ør' et c;. La limite li-quide de la montmorillonite a considérablement baissé quand les échantillons étaient traités avec 80 mg/1 de Ca2+ et cet effet a persisté, voire a &acuteté 1égèrement renforcé quand la concentration de Ca2+ augmentait. La résistance résiduelle au cisaillement et les limites d'Atterberg de la kaolinite étaient beaucoup moins sensibles à la pr´sence de Ca2+. Le papier discute sommairement des conséquences des résultats trouvés en cc concerne la stabilité de pente et de l'impor-tance de ľutilisation d'une solution chimique appropriée dans le bain ďean lors de la con-duite des essais de résistance résiduelle au cisaillement. Comme on a montré que le τr; mesuré en laboratoire variait avec la chimie de Ľeau de porosité, on a une explication possible de la différence entire les r&acutesultats calculés par titrage en retour et ceux provenant du labora-toire et faisant appel à de Peau déionisée. On attire Ľattention sur la nécessit&acte; de définir une enveloppe de rupture résiduelle complète car, si elle est courbe, les paramètres de résistance résiduelle au cisaillement (τ, &slash et c;) varieront avec σn.