Noriyuki Yasufuku

Microbial fuel cell (MFC) for bioelectricity generation from organic wastes.

Microbial fuel cells (MFCs) have gained a lot of attention recently as a mode of converting organic matter into electricity. In this study, a compost-based microbial fuel cell that generates bioelectricity by biodegradation of organic matter is developed. Grass cuttings, along with leaf mold, rice bran, oil cake (from mustard plants) and chicken droppings (waste from chickens) were used as organic waste. The electric properties of the MFC under anaerobic fermentation condition were investigated along with the influence of different types of membranes, the mixing of fly ash, and different types of electrode materials. It is observed that the maximum voltage was increased by mixing fly ash. Cellophane showed the highest value of voltage (around 350mV). Bamboo charcoal is good for anode material; however carbon fiber is better for the cathode material in terms of optimization of power generated. This developed MFC is a simple cell to generate electricity from organic waste.

Bioelectricity from kitchen and bamboo waste in a microbial fuel cell

This study evaluated bioelectricity generation by using kitchen garbage (KG) and bamboo waste (BW) as a solid waste management option by a microbial fuel cell (MFC) method. The nutrient content [nitrogen, phosphorus and potassium (NPK)] of the by-products of bioelectricity were also analyzed and assessed for their potential use as a soil amendment. A one-chamber MFC was used for bioelectricity generation in laboratory experiments using both KG and BW. A data-logger recorded voltage every 20 mins at a constant room temperature of 25°C over 45 days. The trend of voltage generation was different for the two organic wastes. In the case of KG, the voltage at the initial stage (0–5 days) increased rapidly and then gradually to a peak of 620 mV. In contrast, the voltage increased gradually to a peak of 540 mV in the case of BW. The by-products of bioelectricity can be used as soil conditioner as its NPK content was in the range of soil conditioner mentioned in other literature. Thus, the MFC has emerged as an efficient and eco-friendly solution for organic waste management, especially in developing and technologically less sophisticated countries, and can provide green and safe electricity from organic waste.

Risk assessment of water inrush in karst tunnels based on two-class fuzzy comprehensive evaluation method

A feasible and accurate method named two-class fuzzy comprehensive evaluation is put forward to assess the risk of water inrush in karst tunnels. In view of regarding tunnel face as the evaluation object, 12 influencing factors of water inrush are selected as the evaluation index system consisting of 4 first-class and 12 second-class indices. Based on fuzzy mathematics theory and expert evaluation method, all the indices are quantitatively graded according to five risk grades. The weights of indices affecting water inrush are rationally distributed by using analytic hierarchy process. Membership functions and weights of indices are utilized to stepwise compute the membership degree of indices corresponding to risk grade, and the principle of maximum membership degree is carried out to discern the risk grade of water inrush. The tunnel faces in seven segments of Qiyueshan tunnel are chosen as the case studies. Evaluation results are derived from the proposed method, and they are generally consistent with the actual results through comparisons. This method provides a cogent way for evaluating the risk of water inrush in karst tunnels.

Analytical solution for soil water redistribution during evaporation process

Simulating the dynamics of soil water content and modeling soil water evaporation are critical for many environmental and agricultural strategies. The present study aims to develop an analytical solution to simulate soil water redistribution during the evaporation process. This analytical solution was derived utilizing an exponential function to describe the relation of hydraulic conductivity and water content on pressure head. The solution was obtained based on the initial condition of saturation and an exponential function to model the change of surface water content. Also, the evaporation experiments were conducted under a climate control apparatus to validate the theoretical development. Comparisons between the proposed analytical solution and experimental result are presented from the aspects of soil water redistribution, evaporative rate and cumulative evaporation. Their good agreement indicates that this analytical solution provides a reliable way to investigate the interaction of evaporation and soil water profile.

Discrete Element Modelling of Geogrid Pullout Test

The pullout test was effective in order to study the interaction behavior between soil and geogrid in the reinforced zone. Therefore its resulting properties had important implications on the reinforced soil structure practice. It had been demonstrated by experimental studies that several parameters (geotechnical properties of soil, geogrid properties, applied vertical effective stress) influenced on the pullout behavior and pullout resistance. As a micro-mechanics study is difficult to carry out in traditional study, a discrete element modelling of pullout test was employed here to investigate the pullout behavior of geogrid embedded in a compacted granular soil. The discrete element modelling was used to investigate the interaction between the geogrid and compacted granular soil paying attention to the properties of geogrid, taking into account the compaction effect linked with porosity. Compared with the experimental results, the discrete modelling was favourable. The discrete element modelling was capable of evaluating the interaction between soil and reinforcement.

Experimental evaluation and parameterization of evaporation from soil surface

Abstract Surface evaporation is one of the main processes in the soil–atmosphere interaction. Since it is highly related to meteorological factors and soil properties, determination of evaporation rate from soil surface remains a challenge. To investigate the evaporation from unsaturated soil, a climate control apparatus has been newly developed, which has a feature of completely controlling air temperature, relative humidity and wind speed. Twelve climatic conditions are applied to three kinds of soil specimens to carry out the evaporation tests. The results show that only water content cannot allow an accurate estimation, additional variables accounting for soil texture and wind speed must be included as well. Moreover, a simple approach to parameterize evaporation is presented by the soil moisture θ of top 1-cm layer with considering the effect of soil texture and wind speed. It is found that the new approach is able to accurately estimate the evaporation from unsaturated soil.

Advanced Direct Shear Testing for Collapsible Soils with Water Content and Matric Suction Measurement

At natural, in-situ water content, collapsible soils have high strength and relatively high void-ratio with low compressibility. These soils could easily collapse when wet. If the differential deformations and slope stability effects have been neglected in the design and construction processes, they could cause damage to constructions. Ther efore, the identification of collapsible soils with estimation of the collapse potential and shear strength become major components in appropriate engineering for these moisturesensitive soil sites . To deal with shear strength of unsaturated soil or collapsible soil, the direct shear box apparatus for measuring in water content with matric suction must be modified. The electrical sensors for water content measurement are installed near the shear plane. Due to low friction material, Teflon sheets are then used as a spacer to control the water content of the specimen during testing.

Estimation of lateral force acting on piles to stabilize landslides

The lateral force on stabilizing piles due to the movement of the landslide has been studied by many researchers. One of the most widely used methods was proposed by Ito and Matsui in 1975 based on the plastic deformation theory. This paper aims to extend the approach of Ito and Matsui by considering the soil arching effects along the height of the sliding layer between two neighboring piles. The analysis is carried out in two stages. First stage involves the plastic deformation of soil adjacent to piles. In this stage, considering the arching effects along the height of the sliding layer, a typical cross section of the soil is employed to analyze the soil stress in the rear of piles. In the second stage, the plastic deformation theory proposed by Ito and Matsui is adopted to analyze the squeezing effects between two neighboring piles. Moreover, the parametric analysis is performed to investigate the susceptibility of the governing factors, which include the geometric and mechanical parameters. The results show that both the geometric and mechanical parameters impart the significant influence on the lateral force. Finally, both the numerical simulation results and the field experiment data from the literatures are introduced to validate the proposed approach. The comparison charts illustrate that the predictions by the proposed approach are consistent with the experimental results.

Bimodal and multimodal descriptions of soil-water characteristic curves for structural soils

In the last decades several approaches have been developed to describe bimodal or multimodal soil-water characteristic curves (SWCCs). Unfortunately, most of these models were derived empirically. In the presented study, physically based bimodal and multimodal SWCC functions have been developed for structural soils. The model involved two or more continual pore series; the probability density functions for each pore series were assumed to be lognormal distribution and can be superposed to obtain the overall probability density function of the structural soils. The proposed functions were capable of simulating bimodal or multimodal SWCCs using parameters which can be related to physical properties of the structural soils. The experimental SWCC data were used to verify the proposed method. The fitting results showed that the proposed approaches resulted in good agreement between measurement and simulation. These functions can potentially be used as effective tools for indentifying hydraulic porosities in the structural mediums.

Characterization and Effective Utilization of Volcanic Ash for Soil Improvement

Volcanic ash becomes environmental important issues as waste material if it is not effectively reduced or reused. In engineering practice, utilization of volcanic ash as substitution material is limited. Indonesia has a large road on soft soil and volcanic ash. The objectives of this paper are focused to study the characterization, classification and utilization of volcanic ash as soil stabilization material which give benefit in engineering practice and also be environmental friendly material. Engineering properties, mineral composition and soil mixture characteristics involve physical and mechanical properties are discussed. Result shows that the effect of addition of volcanic ash after curing time 14 days can improve the engineering properties of soft soil, decrease liquid limit, change curve of grain size distribution, increase bearing capacity, and decrease swelling potential. The soil-volcanic ash mixture with 35% of volcanic ash and 5% of lime is obtained as optimum mixture design. This result is still early stage and need further study.