Ariake Clay Research Articles

Simultaneous removal of fluoride and nitrate from an aqueous mixture and semiconductor wastewater by sodium chloride mediated electro-generated aluminas (EGAs): Conversion of recovered fluoride into fluorapatite using plasterboard waste

Electro-generated aluminas (EGAs) were synthesized using sodium chloride electrolyte of 100 mM with Al/Al and Al/Fe electrodes operated at 800 mA for 1.5 h. The synthesized mesoporous EGAs, EGA (Al) and EGA (Fe) belonging to H2 type hysteresis contain the boehmite and bayerite phases as confirmed by XRD analysis and whose proportions are estimated to be 49.6 ± 0.3% and 50.4 ± 0.3% respectively by thermo-gravimetric study. The batch adsorption studies were conducted using the binary (F−/NO3−) mixture from which the adsorption efficiency was studied as a function of time (0–60 min), pH (3–10), initial concentration of fluoride or nitrate (100, 300, 500 and 1000 mgL−1) and temperature (15 °C, 25 °C, 35 °C and 45 °C) using EGA (Al) and EGA (Fe) adsorbents. The adsorptive removal of fluoride and nitrate from real effluent samples using EGAs was significant particularly in effluents E1 and E3 with residual concentrations within the safe limit of World Health Organization (WHO). Regeneration using 100 mM NaOH was quite consistent up to five consecutive cycles and the recovered fluoride was converted into fluorapatite. Taking into account the regeneration aspect, the cost analysis showed that 1 g EGA (Al) and EGA (Fe) was 0.464 USD and 0.508 USD respectively. The endothermic nature of adsorption through chemical forces was confirmed by the compliance of pseudo – second – order (kinetic), Langmuir and DKR (isotherm) models (R2 ≈ 0.99) along with thermodynamic parameters. Characterization of EGAs using FTIR, FESEM, XRD, XPS and BET was done to understand the adsorptive behavior between EGAs and the adsorbate (F−/NO3−) ions. The exhausted EGAs after fifth cycle of regeneration was mixed with ariake clay, plasterboard waste and cement in proper proportions and, made as specimens for the construction of bank bodies.

A conceptual model for the shakedown response of soft clay to high-cycle, low-amplitude undrained loading

Soft soils beneath transportation infrastructures suffer dynamic traffic loads with high-frequency and high-cycle characteristics, which mainly present shakedown development of deformation yet probably induce notable deformation at the stable state. However, conventional constitutive models are still not available for the long-term behavior description of soft soils under high-cycle traffic loading. Herein, a conceptual model for high-cycle, low-amplitude undrained loading was proposed incorporating a shrinking yield surface and an expanding boundary surface, which individually indicated the weakening behavior caused by an increase in excess pore water pressure and the hardening effect due to contractive plastic deformation. Given the shakedown responses of soft soils, a mapping ratio and a one-time calculation approach were employed. Thus, the effect of loading frequency on the response of soft soil can be considered, and the calculation efficiency was greatly improved. Then, the evaluation of model parameters and parametric analyses on the loading frequency, shrinking yield surface, expanding boundary surface and mapping ratio were carried out to examine the performance of the proposed model. To further validate the proposed model, undrained cyclic triaxial tests on reconstituted Ningbo clay were conducted, and high-cycle undrained triaxial tests on Kaolin clay and Ariake clay were referenced. The predicted developments of accumulated plastic deviatoric strain and excess pore water pressure with the number of load cycles reached acceptable consistencies with the experimental results. Moreover, the effects of confining and deviatoric stresses were investigated. Not only rational developments of excess pore water pressure and plastic deviatoric strain but also nearly identical results under the same cyclic stress ratio (CSR) were obtained, which adequately confirmed the feasibility and reliability of the proposed model. Although this model was developed based on isotropically consolidated soils and contained varied parameters for different CSRs, it provides a framework contributing to rigorous model development for high-cycle conditions.

State parameter governing the mechanical properties of cement-treated clays

A new state parameter that is capable of characterizing the mechanical properties of cement-treated clays with different mixing proportions, curing time, and stress conditions is developed in this study. The development is conducted by combining the effect of stress level based on the critical state theory with the effective void ratio. Based on the experimental data of cement-treated Bangkok clay performed in this study together with those of cement-treated Singapore marine and Ariake clays reported in previous studies, the analyses reveal that the state parameter is proven to be an efficient parameter for characterizing the mechanical properties of cement-treated clays with different base clays under various mixing proportions and curing times tested under various stress conditions. Furthermore, empirical equations to assist the establishment of the effective void ratio on the critical state locus from the plastic limit value of the base clay are suggested based on regression analyses. The state parameter can thus be computed and the engineers can preliminarily estimate the mechanical properties of cement-treated clay in the planning stage.

The effects of the depositional environment and post-depositional processes on the engineering properties of Quaternary clays in the Saga Plain

Core samples to a depth of approximately 50 m and undisturbed soil samples were retrieved from eight locations in the Saga Plain, Japan, to investigate the effects of the depositional environment and post-depositional processes on the engineering properties of Quaternary clays in the Saga Plain. The engineering properties of these soil samples were measured, and the test results showed that the clays in the Saga Plain have a high void ratio, high water content, high compressibility, high sensitivity, and low stiffness. The one-dimensional compression curves plotted above the sedimentation compression line proposed by Burland, and the compression index was high, which indicated that the clays had been cemented to some degree. The clays have high strength sensitivity and high stress sensitivity, indicating that they have strong structures. It was considered that a considerable amount of volcanic ash from the four large volcanic eruptions that occurred during the deposition of these clays settled into the clays, resulting in a certain degree of cementation, which was attributed as the main driver of the strong structure in these clays. Comparisons of the NaCl concentration, pH, and oxidation-reduction potential (ORP) of the clay samples representing the initial depositional environment and the current ground environment showed that salt leaching occurred in the Ariake clay formation, and that the ground environment changed. When the NaCl concentration was less than approximately 2 g/L, the strength sensitivity of the Ariake clay samples with low-activity clay minerals significantly increased due to the decrease in the liquid limit and subsequent significant decrease in the remolded undrained shear strength. Therefore, salt leaching was probably a main cause of the high strength sensitivity of the clays in the Saga Plain. The depositional environment at some locations changed from an alkaline, reducing environment, to an acidic, oxidative environment, with the potential to change into a strongly acidic environment, which could have deteriorated the strength of the cement/lime-treated clays in the Saga Plain.

Holocene Deposits in Saga Plain: Leaching Mechanism and Soil Sensitivity

The Saga Plain in Japan contains a 10–30 m thick Holocene clayey soil deposit with a natural water content generally more than 100% and a liquidity index (I L ) larger than 1.0. Most of this is a marine deposit known as the Ariake clay formation. Using salinity in the pore water of this deposit as an index, the mechanism of post-depositional salinity leaching from the Ariake clay formation has been investigated. This has been achieved using current measurements of the salinity distribution in the deposit and the groundwater flow velocity in an underlying Pleistocene gravelly sand layer, together with advection–diffusion analyses. It is suggested that diffusion together with possible rainfall percolation and/or upward seepage flow from the Pleistocene gravelly sand layer was the main mechanism causing salinity leaching. Detailed analysis of the test results from four boreholes indicates that for the locations where the activity of the clay minerals was less than 1.25, salinity leaching probably accounts for the observed low undrained shear strength (<0.5 kPa) of remoulded soil samples, high values of the sensitivity (S t ), and the formation of a quick clay.

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.

Evaluation of the uplift behavior of plate anchor in structured marine clay

ABSTRACTThe uplift behavior of a plate anchor in a structured clay (soft Ariake clay) is investigated through a series of laboratory tests and method of finite element analysis. The tests are adopted to identify the factors influencing the behavior of the anchor, including the thixotropic nature of Ariake clay, consolidation time, and embedment ratio of the anchor. A finite element method (FEM) is used to analyze and predict the uplift behavior of the anchor plate well in the elastic region and the yield load. The results from both the laboratory tests and the FEM analysis suggest that the embedment ratio for a deep anchor in Ariake clay is close to 4. Further increase in embedment ratio improves the capacity to a lesser extent. FEM overestimates the failure load of the uplift anchor in soft Ariake clay by about 20%. This may be ascribed to the hypothesis in the FEM analysis that there is continuous contact between the clay and the anchor until failure. Vesic’s theory for deep anchors, which may be used to predict the ultimate pullout resistance of the plate anchor in reconstituted Ariake clay, is verified to be applicable. In this paper, the plastic flow zone around the anchor is discussed using FEM which makes the behavior of anchor more understandable during the design stage.

1D deformation induced permeability and microstructural anisotropy of Ariake clays

The permeability behavior of Ariake clays has been investigated by constant rate of strain (CRS) consolidation tests with vertical or radial drainage. Three types of Ariake clays, namely undisturbed Ariake clay samples from the Saga plain, Japan (aged Ariake clay), clay deposit in shallow seabed of the Ariake Sea (young Ariake clay) and reconstituted Ariake clay samples using the soil sampled from the Saga plain, were tested. The test results indicate that the deduced permeability in the horizontal direction (<TEX>$k_h$</TEX>) is generally larger than that in the vertical direction (<TEX>$k_v$</TEX>). Under odometer condition, the permeability ratio (<TEX>$k_h/k_v$</TEX>) increases with the vertical strain. It is also found that the development of the permeability anisotropy is influenced by the inter-particle bonds and clay content of the sample. The aged Ariake clay has stronger initial inter-particle bonds than the young and reconstituted Ariake clays, resulting in slower increase of <TEX>$k_h/k_v$</TEX> with the vertical strain. The young Ariake clay has higher clay content than the reconstituted Ariake clay, resulting in higher values of <TEX>$k_h/k_v$</TEX>. The microstructure of the samples before and after the consolidation test has been examined qualitatively by scanning electron microscopy (SEM) image and semi-quantitatively by mercury intrusion porosimetry (MIP) tests. The SEM images indicate that there are more cut edges of platy clay particles on a vertical plane (with respect to the deposition direction) and there are more faces of platy clay particles on a horizontal plane. This tendency increases with the increase of one-dimensional (1D) deformation. MIP test results show that using a sample with a larger vertical surface area has a larger cumulative intruded pore volume, i.e., mercury can be intruded into the sample more easily from the horizontal direction (vertical plane) under the same pressure. Therefore, the permeability anisotropy of Ariake clays is the result of the anisotropic microstructure of the clay samples.

Effect of MGO additive on preventing leakage of Cr(VI)

The effect of a new additive, oxide magnesium (MgO), on preventing or reducing the leakage of Cr(VI) from a fly ash (coal ash) has been investigated by batch contact and column percolation tests. The test results indirectly indicate that the MgO additive has an obvious effect on reducing Cr(VI) to Cr(III), which is less environmentally hazardous. However, the process of reducing Cr(VI) to Cr(III) may be reversible because adding H2SO4 or CaH2O2 into the balanced solid-liquid mixture for partially simulating possible environmental change increased Cr(VI) concentration in the liquid phase. Adding 10% to 30% of Ariake clay into the fly ash not only further reduced Cr(VI) concentration, but also reduced total Cr concentration. Hence, Cr(III) ions may be absorbed by the clay minerals. For the conditions investigated, the column percolation test resulted in higher initial Cr(VI) concentration in the liquid phase than that of the batch contact test. Further, the results of the column percolation test using the samples with different curing time (up to three weeks) indicate that with MgO additive, curing the sample does not have an obvious effect on Cr(VI) concentration.

Depositional environment and geotechnical properties of Shanghai clay: a comparison with Ariake and Bangkok clays

Shanghai soft clay was deposited in the Yangtze River Delta in the Late Pleistocene and Holocene eras. The general engineering properties of this clay have been studied in the last few decades. However, limited research on its depositional history and impact on geotechnical properties is available. In this paper, the depositional history of Shanghai clay was reproduced based on sea level changes and other geological information. The unique depositional environment was compared with two other Asian clays, Ariake clay in Japan and Bangkok clay in Thailand. The physical, mineralogical and mechanical properties of different strata were investigated by a series of laboratory tests. It was found that silt-sized grain particles dominated the clay materials and illite is the major clay mineral, while clay-sized grains and smectite are predominant in Ariake and Bangkok clays. The liquid limit, plastic limit and activity are lower than the Ariake and Bangkok clays. Oedometer tests and undrained triaxial tests indicated a less sensitive structure. Stronger hydraulic conditions (faster stream velocity) and the origin of material in the middle and lower reaches of the Yangtze River account for the large amount of silt-sized particles and illite. A less saline depositional environment is the main reason for the weaker structure in Shanghai clay than the two other Asian clays.

海水環境下におけるセメント処理した有明粘土の劣化の進行に関する検討

In construction, chemical soil stabilization method, such as adding cement and quick lime has been often applied to increase the strength of soft ground and surplus soil. However, in some specific natural environments, such a stabilization method may cause significant reduction of the strength of treated-soil. In this paper, Ordinary Portland cement was used as a stabilizer for examining the durability of chemical stabilized Ariake clay under seawater condition. In order to prepare deteriorated specimens, original Ariake clay was mixed with different contents of cement (50, 70, 100kg/m3) and immersing artificial seawater with different NaCl concentration (10, 20, 30g/L). The deterioration progress of cement-treated Ariake clay was investigated by using the micro cone penetration test. It is shown from the test results that the deterioration of cement-treated soil progresses in proportion to square root of seawater contacting duration. In addition, an empirical prediction formula of deterioration rate of cement-treated Ariake clay considering effect of Mg ion concentration in seawater and water-cement ratio in the treated soil is proposed according to experimental results.

生石灰および高炉セメントを用いた有明粘土固化処理土の強度予測方法

粉体の生石灰および高炉セメントを用いた有明沖積粘土の固化処理土の強度予測式を提案した。生石灰改良土に関する強度予測式は，生石灰配合量および被改良土の理化学分析値から得られた油分，溶解性生石灰シリカを説明因子とした重回帰分析により求めた。また，高炉セメント改良土に関する強度予測式は，高炉セメント配合量および溶解性高炉セメントシリカを説明因子として同様に求めた。強度予測式の重回帰係数Rは，生石灰改良土の場合は0.8693，高炉セメント改良土の場合は0.8787であった。さらに実測強度と予測強度の回帰直線より，地盤改良工事における配合設計方法を提案した。提案した強度予測方法は，有明沖積粘土地盤改良工事の品質管理における一軸圧縮試験の補助的役割を果たせる可能性を示した。

Numerical Modeling of Geotextile-Reinforced Embankments over Deep Cement Mixed Columns Incorporating Strain-Softening Behavior of Columns

Geotextile-reinforced embankments over deep cement mixed (DCM) columns are widely used for the construction of highway embankments over soft clay with low shear strength and high compressibility. Numerical modeling based on the finite element method (FEM) is widely used to investigate the behavior of these embankments during construction and serviceability, incorporating consolidation of the foundation soil over time. However, not much attention has been paid to the strain-softening behavior of DCM columns beyond yield, which is essential in ultimate limit-state computations to determine the stability of embankments during the failure of columns. This paper presents a constitutive model, which is an extension of the Mohr-Coulomb model, for the simulations of strain-softening behavior of cement admixed clays. The model is validated using triaxial test data found in the literature for cement admixed Singapore and Hong Kong marine clays and Ariake clay. A two-dimensional (2D) coupled mechanical and hydraulic numerical implementation of a geotextile-reinforced DCM column-supported (GRCS) embankment constructed over a very soft soil in Finland is carried out incorporating strain-softening behavior of DCM columns. Even though the isolated columns and overlapped column walls used in this embankment do not yield significantly under the service loads, the model simulations show good agreement with field data, confirming the capability of the 2D plane strain finite-element model in predicting the GRCS embankment behavior. Finally, the finite-element model with strain-softening DCM columns is used to investigate the progressive failure of a typical hypothetical GRCS embankment with isolated columns in a square pattern. Results clearly illustrate the bending failure mode caused by progressive softening of the DCM columns, including the plastic hinge development within the columns.

Analysis of cement-treated clay behavior by micromechanical approach

Experimental results show the significant influence of cement content on the mechanical properties of cement-treated clays. Cementation is produced by mixing a certain amount of cement with the saturated clay. The purpose of this paper is to model the cementation effect on the mechanical behavior of cement-treated clay. A micromechanical stress-strain model is developed considering explicitly the cementation at inter-cluster contacts. The inter-cluster bonding and debonding during mechanical loading are introduced in two ways: an additional cohesion in the shear sliding and a higher yield stress in normal compression. The model is used to simulate isotropic compression and undrained triaxial tests under various confining stresses on cement-treated Ariake clay and Singapore clay with various cement contents. The applicability of the present model is evaluated through comparisons between numerical and experimental results. The evolution of local stresses and local strains in inter-cluster planes are discussed in order to explain the induced anisotropy due to debonding at contact level under the applied loads. The numerical simulations demonstrate that the proposed micromechanical approach is well adapted for taking into account the main physical properties of cement-treated clay, including damage and induced anisotropy under mechanical loading.

Interpretation of coefficient of consolidation from CRS test results

Constant rate of strain (CRS) consolidation tests were conducted for undisturbed Ariake clay samples from three boreholes in Saga Plain of Kyushu Island, Japan. The coefficients of consolidation () were interpreted from the CRS test results by small- and large-strain theory. Large-strain theory was found to interpret smaller values and less strain rate effect on than that by small-strain theory. Comparing the theoretical strain distributions within a soil specimen to those obtained by numerical simulation shows that the small-strain theory can be used only for the dimensionless parameter (where is strain rate and is the specimen height), and the large-strain theory can be used for a larger range of strain rates. Applying the criterion to undisturbed Ariake clay with a value of about , it is suggested that the large-strain theory should be adopted for calculating the value when > 0.03%/min.

Finite element simulation of an embankment on soft clay – Case study

Numerical simulations and field measurements of an embankment constructed on a deposit of soft Ariake clay in Saga, Japan are compared and discussed. The simulations were made both before (Class-A) and after (Class-C) the field data became known. It is shown that the Class-A prediction resulted in poor simulations of the measured settlement–time curves, mainly due to over-estimation of the magnitude of the yield stresses of the subsoils (i.e., the sizes of the yielding loci) and under-estimation of the compressibility, hydraulic conductivity and the slope (M) of the critical state line. It is demonstrated that: (a) appropriate site investigation, soil testing and interpretation of the test results are essential for accurate prediction of the behaviour of an earth structure constructed on soft clayey deposits; (b) when using a soil model developed within the framework of Critical State Soil Mechanics to make such predictions, M value should be directly determined from tests with an appropriate effective stress path; and (c) yield stresses of soft soil layers can be calibrated by comparing the predicted undrained shear strengths (Su) with measured values, provided the effect of strain rate and/or strain softening on the value of Su is properly considered. The results of this analysis indicate that Bjerrum’s strain rate correction factor can be adopted as a first approximation of the correction factor applied to field or laboratory measured values of Su.

Anisotropic Consolidation Behavior of Ariake Clay from Three Different CRS Tests

Abstract Three types of constant rate of strain (CRS) consolidation tests were conducted on samples of undisturbed Ariake clay, using a newly developed consolidometer, to investigate the anisotropic consolidation behavior of the clay. CRS tests conducted using vertically cut specimens (with respect to the in situ condition) tested with vertical (or end) drainage (with respect to test condition) were designated as CRS-V-V tests. Specimens cut vertically but with radial drainage were designated CRS-V-R, whereas those cut horizontally and tested with vertical drainage were designated CRS-H-V. The test results show that the ratio of the consolidation yield stress of a horizontally cut specimen (pch) to that of a vertically cut specimen (pcv) is in a range from 0.5 to 1.0. Both pcv and pch increased about 15 % with a tenfold increase in strain rate, but there was no clear difference in the degree of strain-rate dependency for pcv and pch. Values of the coefficient of consolidation obtained from CRS-H-V (chh) and CRS-V-R (chv) test are larger than those measured in CRS-V-V (cv) tests, and it has been identified that these differences arise mainly from the anisotropy of hydraulic conductivity (k). The ratio of k in the horizontal direction (kh) measured in a CRS-V-R test to that in the vertical direction (kv) from a CRS-V-V test is about 1.65, and the ratio of chv/cv is about 1.54. The value of kh from a CRS-H-V test is generally smaller than that from a CRS-V-R test.

A Comparison of Nitrate Distribution in Shallow Groundwater of Two Agricultural Areas in Sri Lanka and in Japan

This paper compares the effects of adding fertilizer in nitrate pollution of groundwater in the Udunuwara area in Sri Lanka and the Shiroishi Plain in Japan. Excessive application of nitrogen fertilizers to soils contributes to contamination of groundwater by nitrates. As nitrate is one of the most identified contaminant in groundwater several environmental protection agencies maximum contamination level for nitrate is 10 mg/l as NO3-N. The problem becomes severe in rural areas where people depend entirely on dug wells in the shallow groundwater table for their drinking water supply. Several locations were selected from the Udunuwara area of Sri Lanka for the detailed study. Nineteen shallow dug wells and 4 deep tube wells were selected for water sampling beginning of January to March 1998.Shiroishi Plain in Japan reclaimed from the Ariake Sea has a soil layer consisting of Ariake clay. The total 82 drug wells of average depth 1.5 m had been drilled around the area. Sample were collected in December 2000 and continued for one year around. Nitrate concentration in groundwater was measured by Cadmium reduction method.The results showed a varying nitrate distribution pattern compared to that the Udunuwara area. The effect of fertilizer application on groundwater depends on soil type, fertilizer type and amount used, crop type and climatic condition. The highly permeable soil around Udunuwara area showed that shallow groundwater is highly vulnerable for nitrate than the poorly drained soil of the Shiroishi Plain in Japan. As the people living in Shiroishi Plain use deep groundwater for domestic purposes, drinking water is safe (less than Maximum Contaminated Level for nitrate in drinking water for Japan-10 mg/l as NO3-N) as far as the nitrate contamination is concerned. The results of these studies suggest that applying the correct rate of N fertilizer at the optimum time would have a substantial effect on reducing nitrate-N losses. Key Words: Nitate Contamination; Groundwater; Land Reclamation; Fertilizer DOI: http://dx.doi.org/10.4038/suslj.v9i1.3736 Sabaramuwa University Journal, Volume 9 Number 1; December 2010, pp 81-95

Field Evaluation on the Strength Increase of Marine Clay under Staged Construction of Embankment

This article presents a case history of an embankment constructed on the soft Ariake clay on the bank of Rokkaku River, Saga, Japan. The staged method was used in the construction of embankment. To shorten the time of construction, the soft subsoil was treated by a prefabricated vertical drain (PVD). The physical and mechanical properties of soft subsoil, such as water content, unit weight, and unconfined compressive strength, were investigated before and during embankment construction. Based on the field data, the strength increase of Ariake clay during construction was revealed. A nonlinear relationship between strength increment and the degree of consolidation was found. Finite element method (FEM) was employed to investigate the strength increase behavior. The results showed that it is difficult to predict the filed behavior of strength increase using Cam-clay model. Based on the concept of structure loss of structured clay, the strength variation of Ariake clay during consolidation is discussed.

Comparison of the Clay Fraction of Ariake Clay Determined by Japanese and ASTM Standards

This study compares the clay fraction percentage determined by Japanese standard JIS A1204/JGS 0131 and ASTM standard D422-63 for the clay samples obtained from the surface of sea bottom sediments in Ariake Bay, Japan. These two standards differ in the amount of dispersant to be added for the dispersion of soil suspensions. The Japanese and ASTM standards suggest adding sodium hexametaphosphate solution as the dispersant so that the final concentration of the dispersant in soil suspension for hydrometer test becomes 2 and 5 g/L, respectively. The test results indicated that the treatment by the Japanese standard gave less dispersion in the soil suspension compared to the ASTM standard, and hence resulted in the underestimation of clay fraction percentage of all the samples.