Seismic refraction method has been used as one of the important geological surveys in the civil engineering widely so far, and it has been applied as an important technology about the tunnel construction in particular. However, there was a difference between the results of the geological situation in the tunnel construction and previous studies. In addition, the support pattern of the tunnel under construction did not correspond to the pattern of design. It is considered that the issue of the differences was caused by various processes such as measurement of survey, geological interpretation, design and construction. For the present situation, various problems facing in the survey have been responded by the experience and knowledge and know-how which each service company is possessing. On the basis of such a background and the recent innovation of the instruments of exploration and the analysis technology, Japan Railway Construction Transport and Technology Agency and Society of Exploration Geophysicists of Japan established the draft manual for seismic survey during 2009-2011. The draft manual is relating seismic survey method, and which determines a series of standard procedure of the survey from the planning to the reporting for mountain tunnels.
  In this report, the actual exploration for mountain railroad tunnel (Kyushu Shinkansen, Nishi Kyushu route) is mentioned as the case study which applied this manual to a real survey.

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　During a scenario earthquake with M_W 9.0 along the Nankai Trough, not only strong motion but also huge tsunami is predicted in Kushimoto Town, Wakayama Prefecture, Japan. In this study, first, microtremor measurements with high density were carried out at 525 sites in the tsunami attack area in Kushimoto Town. The ground shaking characteristics were then evaluated using the microtremor H/V spectra. Finally, based on the empirical relationship between microtremor H/V spectrum and site amplification factor, the site amplification factors from seismic bedrock (Vs=3km/s) to ground surface at the 525 sites were evaluated. The evaluated site amplification factors will be useful in the strong motion estimation in the tsunami attack area.

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　In case that strong ground force affects railway facilities during earthquakes, the reduction of the safety performance of railway structures and running vehicle is concerned. When strong ground motions are observed, railway operators stop trains as soon as possible to secure the safety of trains. After the operator stop trains, a cautious inspection patrol along the railway section following the rule decided in advance is implemented. After the safety of railway facilities are ensured, the train operation is resumed. To confirm visually the damage of railway facilities and deformation of railway tracks in the inspection, it may take a lot of time. To comprehend exactly the characteristics of earthquake ground motions along the railway line, therefore, the rapid evaluation of the earthquake ground motions are strongly required not only at the points where the seismographs are installed but also at the other points on the railway line.
　We proposed the method for estimating the subsurface velocity structures and earthquake ground motions along a railway line. In this study, we tried to apply the method to a railway embankment section in the closed Takachiho railway line, of which length is approximately 600m. The adopted section consists of an embankment in a valley, ridge in an excavation and other embankment in a valley. We installed the seismographs at two embankment sites and an excavation site. At first, we estimated S-wave velocity structures at two embankment sites, using the geophysical exploration such as surface wave exploration and array microtremor survey. Secondly, we estimated the S-wave velocity structures along the railway section using the H/V spectral ratios obtained by the high-dense microtremor measurement based on the S-wave velocity structures estimated. Finally, we estimated the earthquake ground motions along the closed Takachiho railway section by the one-dimensional multiple reflection theory using an observed seismic motion at site of the excavation section. We confirmed the validity of the S-wave velocity structures and earthquake ground motions estimated by the proposed method, through the agreements of the observations and estimations along the railway section.

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　Earth fill is one of the most standard and cheap construction method in civil engineering field and it is often used for road construction and river dike construction. The stability of earth fill is considered to increase with ages, due to the consolidation of the foundation etc. However, the failure of constructed earth fill due to heavy rainfall is reported such as the failure in Sanyo Express Way in Typhoon 14, 2005. At the failure of earth fill at Tohmei Express Way in 2009 off Suruga-bay Earthquake, it was pointed out that the rainfall before the earthquake increases the water level in the earth fill and the earth fill was shaken in the unstable condition. From these failure experiences, it is understood that the periodic assessment of the condition (health monitoring) for earth fill is necessary. In this research, as a possible periodic condition assessment method, non-destructive method to evaluate the variation of the ground condition under the effect of ground water is examined.
　First, bender element test is carried out to evaluate the relationship between the ground conditions and shear wave velocity of the ground. The test results indicate the variation of water content in the ground and flow out of small size particles in the ground causes the variation in the measured shear wave velocity. Second, the variation in the natural frequency of retaining wall for earth fill is examined by dynamic FEM analysis and microtremor measurement in the field. FEM analysis indicate the increase in the ground water level behind the wall decrease the natural frequency of the wall, however, the observed data in the field come out the opposite of analysis. Third, field observation of surface wave (Rayleigh wave) exploration at a quay wall under the tidal effect and earth fill were conducted. The field observation results at the quay wall indicate the water level variation due to the tidal action can be observed by the variation in Rayleigh wave. However, field observation at an earth fill indicates the importance of the consideration of the irregular shape of the fill.

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　We proposed an efficient detection method of the peak frequencies of microtremor H/V spectral ratio by using a low-pass filter. It was revealed that the proposed method can detect the peak frequencies that are essentially important for the earthquake response of the ground. It was also revealed that the proposed method was more advantageous than the window processing in cases where the peak frequencies were low or the peak values of the H/V spectral ratio were relatively small. Applicability of the proposed method was further investigated using the microtremor H/V spectral ratios in the Kanto region.

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　Design of underground power transmission lines requires simple and cost effective techniques for estimating soil specific thermal resistance which is one of the most important engineering properties to determine the transmission capacity of power lines. Specific thermal resistance and electrical resistivity vary with water saturation and porosity. This suggests that there is a correlation between these two parameters and specific thermal resistance can be estimated by electrical resistivity. We have conducted laboratory experiments of specific thermal resistance and electrical resistivity to evaluate the effectiveness of the estimation method of specific thermal resistance by using electrical resistivity. The results demonstrated that specific thermal resistance varied with water saturation, porosity, quartz content, and so on. Calculated specific thermal resistance by using Johansen’s equation was consistent with measured one. Electrical resistivity varied with water saturation, porosity, electrical resistivity of pore water, and so on. It could be calculated by using Archie’s equation. We developed an empirical equation based on Johansen’s equation and Archie’s equation to estimate specific thermal resistance by using electrical resistivity. Estimated specific thermal resistance by the equation using measured electrical resistivity was consistent with measured specific thermal resistance. Hereby, it is concluded that soil specific thermal resistance can be estimated by the results of the electrical resistivity method.

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[in Japanese]

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