The objective of this paper is to evaluate the performance of coal ash based barriers subjected to continuous differential settlements in a geotechnical centrifuge. Motor based differential settlement simulator was used to induce differential settlements with a distortion level up to 0.125 at 40 gravities in a 4.5 m radius large beam centrifuge facility available at Indian Institute of Technology Bombay, India. A short series of centrifuge model tests were conducted by varying the thickness of coal ash based barriers. All the developed coal ash-based barriers were subjected to an overburden of 25 kN/m² equivalent to that of in landfill cap covers. All the models were thoroughly instrumented with Linearly Variable Differential Transformers (LVDTs) and Pore Water Pressure Transducers (PPTs) to measure vertical settlements and pore water pressure. Digital Image Cross-correlation (DIC) technique was adopted to arrive at deformation profiles of coal ash-based barriers and strain distribution along the top-most surface of the tested barrier during all settlement stages. The water sealing efficiency was assessed in terms of limiting distortion level and strain at water breakthrough. A 0.6 m thick coal ash based barrier with an overburden of 25 kN/m² was observed to experience a limiting distortion level of 0.068 and a strain at breakthrough of 0.98%. In comparison, a 1.6 m thick coal ash based barrier was not registered any water breakthrough and noted to sustain large deformations. This centrifuge study demonstrates that coal ash based barriers of an adequate thickness can be used to as impervious barriers of landfill cap covers.

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Municipal solid waste is a specific type of a soil-like material. Waste landfills are always placed near urban settlements and occupy sizeable territories, which are irretrievably withdrawn from circulation. As a result of the permanent process of waste generation, landfill areas are steadily growing. There has been a tendency of a landfill capacity increase in waste storage types of 20 and more meters in height lately. This height increment is accompanied by both the increase of loads applied to the subsoil and stresses and deformations in a waste massif. As a result, the evaluation of stability becomes necessary, for which physical-mechanical properties of waste, as well as prediction of their changes in time are required. The application of modern nondestructive methods of field determination of mechanical properties of waste has significant advantages over the traditional approaches. One of these nondestructive methods is a multichannel analysis of surface waves (MASW). This method allows measurements in the weathering zone of the near-surface part of the profile during the field testing of soils and soli-like materials, when it is practically unrealizable to select and restore undisturbed samples. When applying the MASW-method, the data along the geological cross-section are usually obtained as mean values along the defined depth, which is suitable for the investigations of homogeneous massifs of municipal solid waste.

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Landfill stability and deformation analysis is one of the most important concerns in the municipal solid waste (MSW) landfill design and operation. Estimation of landfilling capacities based on deformation characterization of MSW assumes considerable significance in the estimation of additional landfilling capacity before closure. In the analysis, it is important to consider mechanisms such as primary compression, time dependent mechanical creep and biodegradation effects occurring in the MSW system. In this paper, a simple landfill cell is considered and stability and deformation analysis is performed based on the constitutive modeling approach. The implications on the slope stability and deformation response of MSW for a 5m high landfill cell are explained in terms of vertical and horizontal deformations, volume changes, factors of safety considering the effects of loading, effects of mechanical and biodegradation. The effects of time on the strength and stability of the landfill cell are studied. The study shows that the analysis using constitutive modeling approach provides useful insights in the land-filling operations.

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In the northwest of China, loess is widely distributed, and the climate is mainly arid and semi arid. The use of loess as soil cover material for landfills is promising. In this paper, water balance analyses were carried out to evaluate the technical feasibility with a consideration of the climate characteristics and the hydraulic properties of the loesses. The analyses demonstrate that the loess, having a considerable water storage capacity and relatively low conductivity for water and gas flow, is a good cover material for the arid and semi arid regions. The required thickness of monolithic soil cover, depending on the climate condition and the type of loess, ranges from 0.5 to 2.0 m. For a given region, the designed thickness for the silty loess is the least, and that for the sandy loess is the largest. It is deserved to do more research and engineering practice on this topic.

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This paper presents the results of an experimental investigation on gas leakage through a geomembrane (GMB)/geosynthetic clay liner (GCL) composite liner where the GMB contained a circular defect and the GCL was partially hydrated. The results indicate that gas leakage rate increased with increasing gas differential pressure and increase of the GCL total suction. It was also observed that gas leakage rate reduced with the increase of the gravimetric water content of the GCL.

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Nowadays groundwater contamination widely spreads in China. Organic pollutants are of the public concern since they are toxic and with long cycle, causing considerable remediation cost. The innovative remediation technologies are urgently needed. In this paper, the micro-nano bubbles (MNBs) technology with the ozone oxidation method was proposed, and laboratory tests were conducted for both surface water and groundwater remediation to degrade methyl orange, which was selected as the representative pollutant. In the test, deionized water was used to configure methyl orange solution of certain concentration, then the concentrations of methyl orange were monitored during the treatment process of ozone macro bubbles, oxygen MNBs, and ozone MNBs. Glass beads with the diameter of 4.0-4.5 mm were selected to simulate highly permeable soil, and the concentrations of both methyl orange and the dissolved ozone were measured during groundwater remediation by ozone MNBs. The results indicated that oxygen MNBs did not degrade methyl orange, while the degradation effect of ozone bubbles was obvious. The degradation effect of ozone MNBs can even be 41 times greater than ozone macro bubbles for polluted surface water. The groundwater remediation tests further verified that ozone MNBs have significant capability in the remediation of organic contaminated subsurface.

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Japan was severely impacted by the 2011 off the Pacific coast of Tohoku earthquake, and radiation from the subsequent accident at the nuclear power plant in Fukushima continues to pose problems for the region. This paper describes efforts that are underway to remediate the area based on civil engineering and environmental geotechnic principles. Specifically, this paper describes recommendations from a special task force that was organized by the Japanese Geotechnical Society (JGS) in response to the accident. The task force has identified several areas where new environmental geotechnic technologies are needed and has put forth ideas for educational initiatives that will be necessary to train future engineers to work on the project. Research efforts on behalf of the authors and collaborators to develop new radiation shielding geo-materials are also presented. Preliminary data show that heavy bentonite based mud water has exceptional shielding properties, and this geo-material may be useful for radiation shielding near and inside of the nuclear reactors. Lastly, some ideas regarding the design of intermediary repositories for contaminated soil are presented. Such repositories will be used to store contaminated soil for a period of 30 years.

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