Some technical difficulties caused by the rock pressure are firstly reported in late 19th century in German coal field. In the field of tunneling, the technical problem concerned with heavy load of tunnel support are observed and discussed in the last decade of 19th century. However, from the scientific point of view, it had been difficult to explain the remarkable difference between the overburden pressure and the load of tunnel support as well as the increasing convergence of drift with time elapsed. In early 20th century, it was recognized that the zone of loose, fractured or/and yield rock around the drift plays some important roles on the convergence and support load, both of which increase generally with time elapsed. In 1930's, the theory of elasticity and plasticity was applied to make clear phenomena caused by the rock pressure. However, the theory did not succeed to explain the time-dependent behaviour concerned with rock pressure. Then, the theory of linear visco-elasticity was applied to explain the time-dependent behaviour of rock mass around the drift. In early 1960's, a new theory called as NATM was proposed and applied for tunneling. This theory explicitly indicated the load bearing ability of rock mass around the drift and the dependence of the final support load on the setting time of support. In late 1960's, a method of numerical analysis called as FEM was applied to various problems concerned with the rock pressure. Application of this method made possible to analyze the stress concentration and yield zone in the rock mass around various cross-sections of the drift. In 1970's, furthermore, FEM was applied to analyze such three dimensional problems as the convergence in the vicinity of the driving face of drift.
Methane hydrate (MH) is one of the potential resources of natural gas in the near future, because large amount of MH exists in marine sediments or in permafrost regions worldwide. Depressurization process is regarded as the most effective process for gas recovery from the viewpoints of gas productivity and economical efficiency, compared with the other in-situ dissociation processes of MH. However, increase of effective stress during depressurization causes consolidation of MH sediments and permeability reduction. As a result, decrease of gas productivity is also supposed. Therefore, it is very important to understand the behavior in MH reservoir, especially in developing the extraction system for MH, and when considering the environmental impacts due to the development. In this study, we conducted an experimental study on consolidation and gas production behavior during MH dissociation by depressurization, using the special type apparatus. To reproduce the real flow condition of gas and water, we used disc shape samples as simulated MH sediment. Horizontal radial flow in porous media during MH dissociation was constructed whereas vertical load system was used to simulate rock pressure conditions in real MH sediment. From an experimental observation, it was found that dissociation and gas production during depressurization consisted of the following three stages depending on temperature and pressure conditions, such as 1) expansion of methane gas in pore space by depressurization, 2) dissociation due to the latent heat of sand grain and each phases and 3) dissociation due to thermal conduction from outer temperature boundary. In addition, we confirmed that increase of effective stress at the initial stage of depressurization was dominant factor on compaction behavior, and deformation after constant effective stress condition was primarily dependent on the creep effect rather than MH dissociation. Then, dissociation pressure, sand grain size, MH saturation and initial temperature was changed as experimental parameters, we discussed the effect of these parameters on MH dissociation, consolidation, and dissociated gas production.
The wear generated in grinding balls having a ball size distribution in a tumbling mill was investigated using a laboratory-scale mill for both dry and wet grinding. The balls were divided into five diameters with the same mass fractions. The weight loss of grinding balls with a diameter Db, Mb appeared to have a non-linear relationship with the time of milling t in the ball mill. The kinetics of wear could be expressed as a power law of the type Mb=Atb, where the coefficient A is a function of the ball diameter Db, and the exponent b is a constant. The coefficient A obtained for each ball diameter, with the exception of the maximum diameter, followed the power law A ∝Dbn-3, based on the formulation of the weight loss of a grinding ball mb as mb∝Dbn. The exponent n indicates the ball wear mechanism in ball mill grinding. A value of n = 2 fits the surface theory which indicates that the intensity of the abrasive interactions in ball milling can be improved, while a value of n = 3 is in accord with the volume theory which shows that the intensity of the impactive interactions can be increased. In this study, the ball wear mechanism for dry milling changed from the volume theory to the surface theory with an increase of the milling time, while the mechanism of wet milling was consistent with the volume theory irrespective of the milling time.
In order to examine soil adsorption behavior of fluorescein, adsorption-equilibrium experiments were carried out. The soil samples used in this study are Kuroboku soil, Yellow brown forest soil, Kanuma soil and Peat. The parameters on the experiments were the initial concentration of sodium fluorescein (0.1, 1, 10 mg/l) and the mass ratio of soil to liquid (0.001, 0.01, 0.1). When the mass ratio were 0.001 and 0.1, the quantity of fluorescein adsorbed on soils was Kuroboku ≒ Yellow brown forest > Peat >> Kanuma. However, the adsorbed amount on Kanuma was remarkably small and there was not so different among the adsorbed amounts on the other soils. The particle size of soils did not affect the absorbed amount. The BET specific surface area was ranged as Kanuma > Yellow brown forest > Kuroboku > Peat. The absorbed amount on Kanuma having the largest BET specific surface area was the least. Therefore the number of the pore effectively utilized for the adsorption of fluorescein seems to be dependent on the type of soil. The clear correlation could not be found between absorbed amount of fluorescein and each chemical composition which constitutes the soils. It is found that the soil adsorption behavior of fluorescein can be prescribed in the Freundlich's adsorption equation. The adsorption behaviors on Kuroboku, Yellow brown forest and Peat are independent of the initial concentration of fluorescein and the mass ratio of soil to liquid. Although the adsorption behavior on Kanuma is dependent on the mass ratio of soil to liquid, the behavior could be represented by one Freundlich's adsorption equation if the mass ratio is constant.
The acid mine drainages (AMD) are treated by neutralization with the two problems: (1) an enormous expenditure; and (2) a discharge of neutralization sludge. In this context, as a case study, a novel remediation method was applied for AMD at Horobetsu mine. The schwertmannite is generated by iron-oxidizing bacteria with Fe2+ and SO42- in acidic mine waters. Its efficiency in As uptake through sorption has been documented in the natural attenuation in Nishinomaki. This study demonstrates the advantages and feasibility of utilizing schwertmannite as a novel remediation method for AMD. At first, the drainage and sludge in Horobetsu mine were characterized to investigate the current method. Secondly, the synthesis of schwertmannite and arsenic removal from the drainage were examined. Results of the characterization indicated that the sludge contained much residual calcite and arsenic by adsorption to the ferrihydrite. The calcite, however, may be dissolved with rainwater. After the reaction, pH of the sludge should be increased and then, which presumably causes the desorption of arsenic from the ferrihydrite. On the contrary, schwertmannite, successfully synthesized from Horobetsu mine drainage by pH adjustment to pH 3.5, removed As almost completely from the drainage. A novel processing method proposed based on the above results consists of the following procedure: (1) arsenic in AMD is removed by the schwertmannite, process, (2) As-free schwertmannite is spontaneously synthesized from the drainage by pH adjustment to pH 3.5 and iron-oxidizing bacteria, and supplied to (1), and (3) the drainage is neutralized in order to remove sulfate by using the waste concrete. In the above procedure, As-bearing schwertmannite, As-free schwertmannite and gypsum are produced as byproduct. This novel processing method is therefore defined as combination system including the removal of arsenic, iron, and sulfate and the resource recovery from AMD.
Adsorption treatment by chelate resin is widely used to remove toxic heavy metal ions from waste water. However, chelate resin is expensive and also disposed after use. Thus, alternative low-cost heavy metal adsorbent is required. On the other hand, hydroclassification technique is a conventional preliminary treatment to treat contaminated soil, which separates heavily contaminated fine particles from the site and reduces the amount of soil to be treated. But separated fine soil is disposed to landfill site in many cases because it is difficult to remove heavy metals from fine soil particles, which strongly adsorb heavy metals. Thus, by utilizing separated fine soil as heavy metal adsorbent, it is expected to promote reuse of soil wastes and reduce cost of waste water treatment. In this paper, adsorption of lead and cadmium ions on hydroclassified lead contaminated soil was investigated. The effect of treatment procedure and co-existing cations on removal of heavy metal ions was examined. It was clarified that calcium ion and low pH obstruct heavy metal adsorption. Residual lead concentration was reduced below environmental standard despite high concentration of obstructive cations. Cadmium concentration was also reduced, but environmental standard was cleared only when concentration of obstructive cations was low.
In the previous study, the authors have investigated the mechanism and the optimum condition of lead removal from contaminated soil by application of sequential treatment of chlorination and warm water extraction. Lead was successfully removed from soil at lower temperature than conventional heat treatment on soil. However, relatively large amount of mixed chloride was required. In this paper, new soil remediation technique was investigated to overcome the disadvantage of the sequential treatment. In the new method, stable lead complex in soil was chlorinated to be PbCl2 by HCl gas emitted by reaction between SiO2 and MgCl2-CaCl2-KCl mixed chloride. Because of high vapor pressure of PbCl2, lead was eliminated from soil by chlorination volatilization. Lead removal was promoted by enhancing volatilization of PbCl2 by introducing carrier gas and by optimizing mixed chloride composition. Residual lead content was reduced more effectively with small amount of mixed chloride than the sequential treatment.