Recently it has been found that frost heave phenomena can be seen not also in soil but also in rock. It is obvious, however, that the number of researches on frost heaving in rock is much less than that of researches on frost heaving in soil. In the present research, we newly developed test equipment in which a pressure transducer is incorporated into a device for testing frost heave in rock. Frost heaving tests were performed using three types of rocks (Ohya tuff, which is soft rock with high frost susceptibility; Kimachi sandstone, which is medium-hard rock with low frost susceptibility; and Sapporo soft rock, which is non-frost-heaving soft rock) to measure the suction pressure generated in the process of frost heaving. In these tests, we obtained fairly large negative pressures for Ohya tuff and Kimachi sandstone. In mediumhard Kimachi sandstone, negative pressure was generated before frost heaving displacement started. On the other hand, negative pressure was not generated in non-frost-heaving Sapporo soft rock. Therefore we considered that frost heaving in rock might be caused by negative pressure generated in the process of frost heaving.
Depressurization process is regarded as the most effective process for gas recovery method from the viewpoints of gas productivity and economic efficiency among in-situ dissociation processes of Methane Hydrate (MH) existing in marine sediments. However, it is supposed that the stratum deformation occurs due to MH dissociation and increase of effective stress in the stratum during operation of depressurization. When stratum consolidation is progressed, the occurrences of damage on production well and destabilization of seabed in addition to decrease of gas productivity are concerned. Therefore, for optimization of gas production process by depressurization, it is necessary to perform numerical simulation in consideration of a series of phenomenon during MH dissociation in porous media and predict the behavior of stratum deformation quantitatively. In this study, using the geo-mechanical simulator named as COTHMA developed under MH21 research consortium, we carried out the field-scale numerical simulation to clarify a series of behaviors during MH dissociation process by depressurization. On the basis of field data for Nankai Trough area, reservoir model was constructed as alternation strata consisting of sand and mud layers. From calculation results, it was found that consolidation process during depressurization consisted of three stages such as stage-1: consolidation only due to decrease of water pressure in pore space, stage-2: consolidation due to both MH dissociation and decrease of water pressure and stage-3: consolidation only due to MH dissociation under a constant pressure condition. The second stage involving increase of effective stress by depressurization and decrease of elastic modulus due to MH dissociation has large effect on consolidation behavior of each layer. In addition, larger vertical stress was applied to the casing and cementing of production well corresponding to the interval of depressurization. Furthermore we discussed the effects of degree of depressurization, MH saturation and absolute permeability on the behavior of stratum deformation and the integrity of the production well during depressurization process.
In the construction of a deep underground facility, the hydromechanical properties of the rock mass around an underground opening are changed significantly due to stress redistribution. This zone is called an excavation damaged zone (EDZ). In high-level radioactive waste disposal, EDZs can provide a shortcut for the escape of radionuclides to the surface environment. Therefore, it is important to develop a method for predicting the detailed characteristics of EDZs. For prediction of the EDZ in the Horonobe Underground Research Laboratory of Japan, we conducted borehole televiewer surveys, rock core analyses, and repeated hydraulic conductivity measurements. We observed that niche excavation resulted in the formation of extension fractures within 0.2 to 1.0 m into the niche wall, i.e., the extent of the EDZ is within 0.2 to 1.0 m into the niche wall. These results are largely consistent with the results of a finite element analysis implemented with the failure criteria considering failure mode. The hydraulic conductivity in the EDZ was increased by 3 to 5 orders of magnitude compared with the outer zone. The hydraulic conductivity in and around the EDZ has not changed significantly in the two years following excavation of the niche. These results show that short-term unloading due to excavation of the niche created a highly permeable EDZ.
This is an essay on the methodology and practical process of the research work in the field of engineering science. In this paper, firstly the philosophy and concept of scientific research is discussed. Secondly, the author describes the present procedure of the publishing of research papers in the journal of some academic or professional societies, as well as the review system which is indispensable for certification of the academic quality of research papers. Thirdly, some processes of study and academic training from the graduate student up to the professional researcher are concretely explained.
Furthermore, the author indicates the important role of technical abilities of each researcher, which include mathematical analysis and designing of experimental equipments applied for the research works.
Next, the author describes the practical process of research works, which starts from the search and decision of research theme, through the evaluation of its expected contributions as well as possibility of success, the theoretical analysis and/or experimental work on the decided research theme, and the examination of test results or the verification of test run of theoretical analysis, attains to the publishing of results of the research work.
Finally, the process and measure of evaluation of the quality of research papers are discussed from academic and industrial points of view, and some features of the excellent research paper are described.