Kiyoshi Kishida

A coupled inversion of pressure and surface displacement

A coupled inversion of transient pressure observations and surface displacement measurements provides an efficient technique for estimating subsurface permeability variations. The methodology has the advantage of utilizing surface observations, which are typically much less expensive than measurements requiring boreholes. Furthermore, unlike many other geophysical observables, the relationship between surface deformation and reservoir pore fluid volume changes is relatively well understood. Our treatment enables us to partition the estimation problem into a sequence of three linear subproblems. An application of the approach to a set of tilt and borehole pressure data from the Raymond field site in California illustrates its efficiency and utility. The observations are associated with a well test in which fluid is withdrawn from a shallow fracture zone. During the test, 13 tiltmeters recorded the movement of the ground surface. Simultaneously, nine transducers measured pressure changes in boreholes intersecting the fracture system. We are able to image a high permeability, north trending channel located within the fracture zone. The existence and orientation of this high-permeability feature is substantiated by a semiquantitative analysis of some 4000 transient pressure curves.

Experimental study on the distribution of earth pressure and surface settlement through three-dimensional trapdoor tests

In order to clarify the mechanical behavior in tunnel excavations, the authors develop and perform three-dimensional trapdoor experiments. The influence of the excavations is considered in the experiments. Based on the results, the distribution of earth pressure is found to greatly affect the process of the excavations. It can be confirmed, therefore, that a higher level of earth pressure is working on a ground where loosened conditions occur due to previously lowered trapdoors.

Long‐term observation of permeability in sedimentary rocks under high‐temperature and stress conditions and its interpretation mediated by microstructural investigations

In this study, a series of long-term, intermittent permeability experiments utilizing Berea sandstone and Horonobe mudstone samples, with and without a single artificial fracture, is conducted for more than 1000 days to examine the evolution of rock permeability under relatively high-temperature and confining pressure conditions. Effluent element concentrations are also measured throughout the experiments. Before and after flow-through experiments, rock samples are prepared for X-ray diffraction, X-ray fluorescence, and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy to examine the mineralogical changes between pre and postexperimental samples, and also for microfocus X-ray CT to evaluate the alteration of the microstructure. Although there are exceptions, the observed, qualitative evolution of permeability is found to be generally consistent in both the intact and the fractured rock samples—the permeability in the intact rock samples increases with time after experiencing no significant changes in permeability for the first several hundred days, while that in the fractured rock samples decreases with time. An evaluation of the Damkohler number and of the net dissolution, using the measured element concentrations, reveals that the increase in permeability can most likely be attributed to the relative dominance of the mineral dissolution in the pore spaces, while the decrease can most likely be attributed to the mineral dissolution/crushing at the propping asperities within the fracture. Taking supplemental observations by microfocus X-ray CT and using the intact sandstone samples, a slight increase in relatively large pore spaces is seen. This supports the increase in permeability observed in the flow-through experiments.

Centrifuge Model Test and FEM Analysis of Dynamic Interactive Behavior between Embankments and Installed Culverts in Multiarch Culvert Embankments

A multiarch culvert embankment is a new type of filling structure for which several precast arch culverts are installed continuously in the direction of the road extension. The key points in the design are to estimate the practical, optimal spacing between installed arch culverts and to clarify the interactive seismic behavior of the filling material and the culvert structure. In the current study, first, dynamic centrifuge model tests and a numerical analysis were carried out to clarify the basal earthquake behavior of the structure and verify the numerical approach. Then, the full-scale numerical analysis was performed to investigate the influence of spacing between multiarch culverts and the mechanical behavior under seismic conditions. From the results, it is confirmed that when the unit spacing is narrow, the whole rigidity of the ground and the arch culvert increases relatively. This is because the volume in the fill part, where the rigidity is small, decreases comparatively. Hence, the section force and the deformation are controlled.

Evaluation of dynamic behavior of culverts and embankments through centrifuge model tests and a numerical analysis

In the design of culverts in Japan, the effects of earthquakes are not usually considered in the design of conventional culverts. This is because culverts are thought to follow the deformation of the surrounding soil. Due not only to the increase in construction opportunities involving high embankments, but also to the development of new forms of culverts, such as precast arch culverts, which contain hinge structures, it is becoming more and more important to clarify the seismic performance of those culvert embankments. In this study, dynamic centrifuge modeling tests and a numerical analysis were carried out to clarify both the mechanical influence of the structural shape and the height condition of the embankment. From the results, it was found that the effect of the embankment condition on the increments in bending moments varies greatly depending on the structural shape of each culvert.

Detection of gaps between land and building surface displacement by PSInSAR and SBAS analysis using L-band PALSAR data

This paper presents the potential of differential synthetic aperture radar (SAR) interferometry to detect the gaps of the displacement rate between the buildings and the land surface. We assumed that the information about building surface displacement can be extracted from single look SAR images whereas the information about land surface deformation can be extracted from multi look SAR images. The proposed method implements Persistent Scatters (PS) InSAR and Small Baseline SAR (SBAS) techniques for respective purposes. Subtraction of the two results can detect the gaps. In addition, the proposed method corrects orbital phase error to mitigate phase ramp of the interferograms without phase unwrapping that is widely known to cause errors in applying to the areas where terrain is fluctuating. We applied the proposed method to Bangkok, Thailand, and found that it succeeded in detecting areas those have severe displacement rate gaps.

Interaction between water and eocene limestone

Abstract The Great Sphinx at Giza, Egypt was carved out of Middle Eocene limestone formations. They are highly porous and cavernous showing the evidence of having been greatly affected by water erosion. To investigate possible mechanism of its deterioration, the Japanese Sphinx Monitoring Mission organized by the authors carried out monitoring the monument site by means of moisture measurement, infrared thermal scanning, electric resistivity measurement, etc. in the winter of 1995. Also, the interaction between water and limestone was tested in the laboratory from the point of view on salinization and evapotranspiration. The daily cycle of moisture content and temperature at the Sphinx site has been clarified.