Uniaxial compression tests and multi-stage stress relaxation tests for specially prepared young-age tunnel shotcrete were carried out. Comparing to previous studies, clip gauges were determined to be the best to evaluate elastic moduli of young-age tunnel shotcrete. Uniaxial compressive strength and 33% secant modulus were larger than those of base concrete till 1 day, however, they became less than those of base concrete after then. Uniaxial compressive strength and 33% secant modulus till 1day showed a linear relationship. This means that 33% secant modulus could be determined from uniaxial compressive strength which is routinely determined at tunnel construction sites. In the multi-stage stress relaxation test, displacing rate significantly affected 33% secant modulus. This will result in significant change in support response to rock mass deformation. Stress decrease by yielding and stress increase with curing time even after the yielding were observed for slow loading multi-stage tests. The above findings will help to design reasonable tunnel supports through precise stress analyses around tunnel faces.
Based on the viscoelastic behavior of grain boundaries, we proposed a new mechanism for rock damage induced by stress relief. In this mechanism, the normal and shear stiffnesses of grain boundaries change with geological time so that the state of stress becomes more uniform, and elastic response of the grain boundaries during stress relief produces tensile residual stress that induces damages in rock. The residual stress was determined with finite element method for three specimen models of polycrystalline rock in a general state of compressive stress, and the degree of damage and the crack density were estimated according to the extended Coulomb criterion to compare the results with the assumptions in the differential strain curve analysis (DSCA) for determining rock stress. The damages are induced only for the grain boundaries having a normal direction that is not much deviated from the directions of the principal stresses with the maximum value. As a result, the maximum crack density increases with the maximum principal stress, while the intermediate crack density does not always increase with the intermediate principal stress and furthermore, the minimum crack density decreases with the minimum principal stress, which does not agree to the assumptions in DSCA. However, the directions of all the principal crack densities approximately coincide with those of the principal stresses for about half of all possible regime of compressive rock stress when the mean stress is large, since the principal crack densities are indirectly determined from the principal strains that are determined by the contribution of all intergranular cracks including those inclined from the principal stresses. Although the assumptions in DSCA are not supported by the mechanism proposed in this study, there is a stress region for which both the magnitudes and directions of the principal stresses can be accurately estimated from those of the principal crack densities and this region becomes wider as the mean stress increases with depth.
The stress state around rock structures, such as underground opening and rock slope, is changed as their construction progresses and the time proceeds. The monitoring of the stress change is important to verify the design, control the construction and estimate the long term stability of rock structures. In order to measure two dimensional stress changes in a plane perpendicular to a borehole axis, we developed the Cross-sectional Borehole Deformation Method (CBDM) and made clear the influence of factors on estimated stress change theoretically. In this paper, the applicability of CBDM to measure stress change in laboratory and in situ experiment. Firstly, the prototype instrument with a laser displacement sensor is described in detail. Secondly, the instrument is applied to estimate the stress change in a laboratory experiment. Then it is made clear that a non-linear least square method and a non-linear programming for optimization with the technique of golden section search is effective for estimating rock stress change. Finally, applying the CBDM to measure rock stress change within the immediate sidewall of underground opening under its construction, the stress changes for six months can be estimated successfully. As a result, it is concluded that the CBDM is available for estimating rock stress change in two dimension.
The paper describes the resource potential for waste electric and electronic equipments which is not a target to be recycled in Japanese regulation, through some experimental trials of comminution and separation. The test samples were electric cleaner, fan, rice cooker, radio cassette recorder, telephone, radio, audio player, printer, fax machine, and video tape recorder, which were collected from citizens in Akita prefecture, and also collected from municipal waste disposal facilities in some municipalities in Akita prefecture. After sorting the samples into eight groups, comminution and separation (magnetic separation, eddy current separation and hand picking) was conducted for each group weighing approximately 1 ton. At the result, the mass balance of construction materials such as ferrous materials, nonferrous materials, motors, cables and PCBs was clarified. The resource potential for the samples was analyzed and found that the recoverable quantities of Fe, Al and Cu from e-scraps (aimed on the paper) hoarded in the house for ten years corresponded to 135 %, 380 %, 9 % recovered from house hold appliances which is presently collected and recycled in the regulation. Prices of ferrous materials, aluminum parts and copper parts (mainly copper wire) were plotted as a function of separative work units, and suggested that it is effective for Cu recovery to separate copper wire from motors and/or residual materials of magnetic and eddy current separations.
The effect of Al2O3 on glass transition temperature Tg and thermal expansion coefficient α is studied for CaO-Al2O3-SiO2 glasses including 45, 50, 55, and 60 mol% SiO2 with a molar ratio of CaO/Al2O3 > 1. Tg increases and α decreases monotonically with increasing Al2O3 concentration. The result of infrared spectra suggests the formation of ring-type mixed anions of SiO4 and AlO4 due to Al2O3 addition. The measured values of α are related to a parameter calculated from the coulomb force between cation and oxide anion based on chemical composition.
A continuous glue dissolution and addition system has been developed to reduce consumption of glue and electric power at the Tamano Refinery. In an aqueous glue solution, the molecular weight of the glue gradually decreases with time, depending on the solution temperature and acidity. The molecular weight is reduced 40% for 24 hours after it's dissolution in the addition tank, which is caused by the addition of hydrochloric acid about pH 2 and the retention temperature with atmosphere cooling from the dissolution temperature at 50°C. In the proposed system, a single tank is designed for both glue dissolution and addition, and the solution is directly supplied to the electrolyte head tank during dissolution. It was placed in operation in April 2010 and, as reported here, has reduced both the quantity of glue addition and the rate of electric power consumption.