When using cutoff walls to prevent the migration of mobile contaminants in aquifers, we should ensure that these cutoff walls maintain both low hydraulic conductivity and high homogeneity before the ...start of their operation. However, the on-site assessment of the properties of their main component, soil-bentonite (SB), is challenging because of the difficulty in the obtention of high-quality solid core samples after installation. This paper discusses an experimental approach for on-site quality control/quality assurance (QC/QA) immediately after installation to enhance the reliability of SB cutoff walls as containment barriers. In particular, the piezocone penetration test (CPTU) was conducted using a large-scale soil tank in which SB – prepared with different contents of bentonite powder – was filled to simulate vertically homogeneous or heterogeneous SB cutoff walls. The response to the penetration test varied according to the bentonite content, suggesting that the piezocone penetration test can be used for QC/QA of constructed soil-bentonite cutoff walls. Corrected cone resistance values were larger in layers prepared with lean SB mixture than in those prepared with rich SB mixture, with a difference similar to that of undrained shear strength as evaluated by triaxial compression tests. It was also found that the hydraulic barrier performance of SB cutoff walls could be assessed via a pore pressure dissipation test during CPTU, within one order of magnitude accuracy in a short period. A basic process for QC/QA using the piezocone penetration test in the field is proposed for the practical interpretation of experimental results.
•pH has significant effect on membrane behaviors, especially on alkaline condition.•Acidic solution shows the existence of erosion effect on membrane behaviors.•Bentonite amended Fukakusa clay ...possess excellent buffer capacity to resist pH change.•Enhancing pH will cause the larger soil cluster and narrower permeable paths.•The mechanisms of the membrane performance change were discussed.
Bentonite has been proven to be effective in enhancing the membrane behavior of clay, by which landfill liners can have better barrier performance toward the migration of contaminants. In this study, sodium bentonite amended locally available natural clay (Fukakusa clay) was investigated for its membrane behavior. The chemico-osmotic efficiency coefficient, ω, was obtained under different concentrations of KCl solution (1, 5, 10, and 50mM) at pH ranging from 4.0 to 11.0. It was found that ω continually decreased as the KCl concentration increased, which is consistent with Gouy–Chapman theory. pH values were found to have a significant effect on membrane behaviors, especially on the alkaline condition. According to the results, the membrane behavior under alkaline condition was 1.2–2.5 times higher than that under acidic conditions. The similarity of membrane behavior between 4.0 and 7.0 reflect the existence, but very slight erosion effect, of acidic solution. It was further found that bentonite amended Fukakusa clay possess excellent buffer capacity to resist pH change. The mechanisms of the membrane performance change were discussed with the assistance of X-ray Diffraction patterns (XRD), free swelling results, X-ray Fluorescence results (XRF), scanning electron microscope (SEM) and camera images.
Heavy metal-contaminated soil and wastewater have been attracting an increasing amount of attention due to the potential threat to the surrounding environment and human health. Thus, in this study, ...citric acid (CA) and citric acid-containing wastewater (CACW) were selected for an evaluation of the influence of the contamination level of the soil, the concentration of citric acid, the contact time, the soil pH, and the ionic interaction on the desorption characteristics of three heavy metals (i.e., Cr(III), Mn(II), and Ni(II)). According to the experimental results, a high concentration of citric acid, an acidic condition, a low level of contamination, and a lengthy contact time were found to be beneficial for desorbing the heavy metals from the contaminated soil. Based on the experimental and calculated results, the H+ ions and organic ligands made substantial contributions to the release and adsorption of the heavy metals. The metal ions on the low selectivity sorption sites were leached out earlier than those on the high selectivity sorption sites. The removal percentages of Cr(III), Mn(II), and Ni(II) using CA with a contact time of 6 h were 39.9%, 77.0%, and 62.8%, respectively. By using the CACW as a desorbent, the removal percentages of Cr(III), Mn(II), and Ni(II) with a contact time of 6 h reached 21.4%, 26.9%, and 63.4%, respectively. This suggests a promising practical application of CACW for removing heavy metals from contaminated soil.
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Ways to reduce the duration of column percolation tests specified in ISO/TS 21268-3 were proposed.Four equilibrium periods and two flow rates on four different soils were ...tested.The time to perform column percolation tests can be shortened from 20 to 30days to 7⿿9 days.The recommended initial equilibrium period is 12⿿16h, shorten from 48h.The recommended flow rate is 36mL/h which is three times that specified in ISO/TS 21268-3.
Column percolation tests may be suitable for prediction of chemical leaching from soil and soil materials. However, compared with batch leaching tests, they are time-consuming. It is therefore important to investigate ways to shorten the tests without affecting the quality of results. In this study, we evaluate the feasibility of decreasing testing time by increasing flow rate and decreasing equilibration time compared to the conditions specified in ISO/TS 21268-3, with equilibration periods of 48h and flow rate of 12mL/h. We tested three equilibration periods (0, 12⿿16, and 48h) and two flow rates (12 and 36mL/h) on four different soils and compared the inorganic constituent releases. For soils A and D, we observed similar values for all conditions except for the 0h⿿36mL/h case. For soil B, we observed no appreciable differences between the tested conditions, while for soil C there were no consistent trends probably due to the difference in ongoing oxidation reactions between soil samples. These results suggest that column percolation tests can be shortened from 20 to 30days to 7⿿9days by decreasing the equilibration time to 12⿿16h and increasing the flow rate to 36mL/h for inorganic substances.
The radioactive cesium (radio-Cs) released following the Fukushima Daiichi Nuclear Power Plant accident was unevenly distributed in soil, sediment, and buildings. It is therefore crucial to evaluate ...the impact of radio-Cs and to prevent its spread throughout various environments. Herein, we investigated the Cs adsorption capacity of woodchip-mixing porous mortar (WPM) as an ecologically friendly adsorbent for treating radioactively-contaminated water or soil. When the WPM was dipped into a solution containing stable-Cs for one month, the Cs adsorption to WPM was three times that of porous mortar without woodchips (PM). The WPM’s retention of Cs was assessed by examining the specimens after adsorbing Cs and regularly determining the Cs concentration leached by dipping the WPM samples in pure water or salt solution (1–100 mmol/L KCl) over one year. The amounts of Cs leached from the WPM were lower than those leached from PM or woodchips, and the quantities increased depending on the KCl concentration. The chemical forms of Cs retained in the WPM via a sequential extraction procedure mainly included the ion-exchange form and the silicate-bound form. Accordingly, the enhanced Cs adsorptivity of WPM arises because of the strong interactions between Cs ions and the woodchip and cement components.
The 2011 off the Pacific Coast of Tohoku Earthquake of March 11, 2011, caused devastating geotechnical and geo-environmental issues mainly in the coastal area of the Tohoku and North-Kanto Regions, ...Japan. As a result of the earthquake and subsequent tsunami, approximately 23,000Gg (23,000,000t) of disaster debris was generated, with more than 12 millionm3 of tsunami deposits left in the flooded area. The geotechnical utilization of the soil fraction in the disaster debris and tsunami deposits has presented a huge challenge to geotechnical engineers since (1) the clearance of debris and tsunami deposits is an urgent task which must be completed within a few years and (2) although a large amount of waste-mixed soil can be used in the construction of new embankments and levees to protect the coast from future tsunamis, their geotechnical properties have temporal and spatial variations. This paper summarizes the current status on the generation, clearance, and treatment and utilization of disaster debris and tsunami deposits from geotechnical and geo-environmental viewpoints. In addition, the environmental monitoring data on soil and groundwater quality conducted over the affected area is briefly reviewed. The results of several wide-area monitoring efforts conducted by different organizations indicate that no significant soil or groundwater contamination has occurred. However, the localized contamination near industrial plants where toxic chemicals leaked due to the earthquake and tsunami needs to be carefully taken into consideration during future revival and redevelopment works. Another serious geo-environmental issue is the management of the radioactive contamination of surface soils caused by the accident at the Fukushima First Nuclear Power Plant. This paper summarizes the distributions and expected behaviours of radioactive Caesium in soils and groundwater, and outlines the possible remediation options for dealing with this contamination.
This paper presents selected issues of geotechnical and geoenvironmental engineering in waste landfills in Japan. Due to the limited available land space, there have been efforts in constructing and ...operating the coastal and offshore landfills, which are expected to provide the opportunities of proper waste management as well as the new land space for urban facilities such as port and harbour. Regulatory aspects are summarised focusing on the future land use of closed landfills. Some technologies to expedite the land use, such as foundation over closed landfills and newly proposed waste containment system, are introduced.
In this study, FDEM (ECZM), which is the combined finite-discrete element method (FDEM) based on an extrinsic cohesive zone model (ECZM), was improved by incorporating a novel algorithm that makes it ...easier to insert the cohesive elements than the conventional adaptive remeshing and a scheme to avoid the generation of dormant cohesive element, which is generated as a result of inserting a single cohesive element within the FDEM mesh. The improved FDEM (ECZM) was implemented in a self-developed 2-dimentional code, and it was first validated against a numerical experiment assuming a virtual rock. Subsequently, the proposed FDEM was applied to model the uniaxial compression and the Brazilian tests of siliceous mudstones under quasi-static loading. The results of the proposed FDEM simulations reasonably captured the trends of fracturing and stress-strain curves observed in the experiments well. The proposed scheme can also be extended to parallel computation based on general-purpose-graphic-unit (GPGPU) and 3-dimentional FDEM (ECZM) with minimal efforts.
A reasonably less permeable compacted clay liner (CCL) is critical to the long-term safety of waste containment facilities. This study experimentally investigates a variety of factors, including ...salinity, pH, fluctuation in permeant, permeation duration and presence of microorganisms, that are found to influence the hydraulic conductivity (k) of consolidated kaolin and the fabrics of suspended kaolin. Amongst these factors, a reduction in hydraulic conductivity of up to 4 orders of magnitude is obtained from the modification of the microfabrics of kaolin; a reduction of 2 orders of magnitude is brought about by bioclogging; a reduction of 1 order of magnitude is related to the concentrated Ca solution (>10mM). The hydraulic conductivity of consolidated kaolin can obviously be changed by adjusting the fabrics of the kaolin particles, e.g., clogging the pore spaces with bioslurry, permeating them with alkaline solution, or transforming the kaolin into metakaolin. An effluent pH larger than the isoelectric point (pHIEP) leads to a rapid reduction in k until 1×10–11m/s. A 3-dimensional fabric map was established for kaolin suspension in contact with a wide range of Ca concentrations and pH levels. The fabrics of kaolin suspension are predominated by a salt concentration (C>2.0mM) and a pH solution (C<2.0mM), respectively.
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