We propose a method for profiling soil permeability on a river embankment with integrated geophysical data. In this method, the unconsolidated sand model and the Glover's equation are employed for modelling seismic velocity - porosity and resistivity - porosity relationships, respectively, in order to obtain a seismic velocity – resistivity model. The clay content as a control parameter for elastic and electric properties of the soil in these two models is used for soil classification with the seismic velocity and resistivity. The effective grain size for the soil type derived as above and porosity estimated from resistivity by the Glover's equation are substituted into the Kozeny-Carman equation for estimating permeability of the soil. The proposed method is applied to an S-wave velocity profile obtained by refraction tomography and a resistivity profile from a 3D electric survey on a river embankment for estimating its soil permeability profile. Comparison of the estimated permeability with actual measurements in the laboratory permeability test of soils sampled on an excavated levee body shows that permeability can be estimated in accuracy less than one order of magnitude. This result indicates that the proposed method is promising for profiling permeability on a river embankment using integrated geophysical data.

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　Design of underground power transmission lines requires simple and effective techniques for estimating soil thermal resistance which is one of the important factors to determine the capacity of power lines. At first, we have performed the heat conduction numerical simulation in the underground containing of the power transmission line. As a result, it is enough to set the range of geophysical exploration to a radius of 3m around a power transmission line. Then we have tried the several geophysical explorations, the electrical, electromagnetic (the slingram), S-wave refraction, and surface wave methods, at the reclaimed land site where underground power transmission lines were buried and have examined the applicability of each exploration. Particularly, the electromagnetic method was performed by using both horizontal and vertical loops. As the results, it was confirmed that the electromagnetic method can explore the resistivity structure with the precision that is approximately equal to the electrical method. In addition, it is identified that the surface wave method is approximately equal precision as the S wave refraction method. Because the ground surface over the underground power transmission lines is almost a paved road, it is practical to use the electromagnetic and the surface wave methods. Furthermore, we have calculated the thermal resistance structure by combining the electrical resistivity with the S-wave velocity structures based on the empirical equations estimated from the laboratory tests with the artificial soil samples. Consequently, the calculated thermal resistance values quite matched to the measured values from the collected soils. However, this technique is based on the empirical equations that the reliability is insufficient, it is important to plan practical use of the new technique using the Johansson’s equation, for example. In addition, it is necessary to correct the influence caused by the resistivity of the pore water in soil samples collected from the site.

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　Recently, the accidental collapse of structures due to natural disasters such as large earthquakes and large-scale typhoons, or local torrential rain as a result of global warming, has been regarded as a serious problem for effective and precise management of infrastructure safety. Particularly, dams as large-scale structures should be evaluated for the safety of their water sealing performance after transformation of the dam structure by strong earthquake vibrations. It is very important to establish monitoring techniques to visualize the penetration during filling of the dam for the long term. The authors conducted an electrical exploration during the first filling of a rock-fill dam site, as well as laboratory tests using samples of the materials which constitute the dam. As a result, a greatly decreased zone of resistivity (-75%) was confirmed in the rock material in the upstream side after filling. In addition, a decreased zone of resistivity (-40%) appeared in the core material area, but the zone of the resistivity change from -20 to -5% was widely distributed in the core material area and the rock material in the downstream side, except for the shallow zone. Furthermore, the resistivity of the samples of dam materials decreased to -80% when the water saturation was increased from 20% to 100% in the laboratory tests, so we can infer that water saturation is the most dominant factor affecting the resistivity of the dam materials. These results suggest that water saturation in the dam during filling can be visualized by utilizing the resistivity change. In conclusion, electrical exploration is an effective method to monitor penetration during filling of the dam, and to evaluate the safety of the dam’s water sealing performance in the event of large earthquakes in the near future.

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　Recently the collapse accidents of the existing steel towers, due to natural disasters such as large earthquakes and large-scale typhoons, are regarded as the important problems for the safety managements of the infrastructures. Particularly, the steel tower facilities, built before the 1970s, should be reinforced for prevention of the deterioration. Practical use of the non-destructive exploration of their foundation with easy handling and low coat is expected for maintenance and management of the facilities effectively and properly. We performed the laboratory tests simulating the electrical exploration of foundations of steel tower and the field experiments of real-scale foundations made of steel reinforced concrete by using the electrical exploration. As a result, it was confirmed that we can distinguish the reversed T-shaped foundations from the mat-type foundations by using the 2D electrical exploration while the size of the foundation is indistinct. On the other hand, the size of the foundation (5.2m×5.2m×1.5m) can be estimated more clearly as the low resistivity zone with approximate accuracy of 25cm (5% of the foundation size) by using the 3D electrical exploration. The large low resistivity zone can be seen as a false image on the apparent resistivity section, because the current flows through a part of the steel tower above the ground surface at some electrode arrays. It is necessary to use the electrode array such as the dipole-dipole to evade the influence. As a future problem, we examine the applicability for the foundation of plain concrete.

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　In observations at Akita-Komagatake volcano, considerable changes of gravity accompanied with variation of thermal activity were noted. This paper proposes a thermal expansion model to explain this phenomenon. The model is based upon elastic deformation due to the nucleus of dilatation (ND) in the semi-infinite homogeneous isotropic solid which corresponds to a minute region of high temperature. A high-temperature region can be regarded as continuous distribution of NDs. Effects of the high-temperature region can be obtained by integrating those of the NDs throughout its whole region. These effects include displacement and gravity change on the free plane surface (the ground surface). The high-temperature region with arbitrary shape does not cause gravity change except the free-air effect. As a modification of the model, the ground is assumed to be a water saturated porous medium with open pore. In this case, effects of pore water mass are added to the gravity change. Thermal expansion coefficient of water is considerably larger than that of solid skeleton. Thermal expansion decreases mass of pore water in the high-temperature region and causes negative gravity change. This effect is added to the free air effect and somewhat enhances the total (negative) gravity change. Gravity changes are estimated assuming simplified models, to evaluate actual significance of the thermal expansion model.

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[in Japanese]

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[in Japanese]

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