In the case of application of the mountain tunneling method in the urban areas, the method which the shotcrete and steel rib are installed at the invert to perform the early crosssection closure is mainly adopted in some tunnels to restrain the occurrence of ground surface settlement.
In this paper, the effect of the invert closure distance from tunnel face on ground surface settlement is examined based on the three dimensional numerical analyses, focused on the small ground covering tunnels. The results of investigation show that the invert closure distance from tunnel face has a remarkable impact on the restraint of occurrence of ground surface settlement due to excavations in the soft ground conditions and in the comparatively stable ground conditions. It is clear that the restraint effect on the ground surface settlement is very great if the invert closure distance from the upper half face is within 20m. Furthermore, comparing analysis results with measurement results of two tunnels which adopted the early invert closure method, the validity of the proposed numerical analysis approach is verified, and it is also confirmed that the early invert closure could restrain significantly the occurrence of ground surface settlement.

View full abstract

To apply to soil improving method using horizontal directional drilling (HDD), smaller grouting pipes are desirable for installing into curving boring hole. In this study, the self-packers are newly equipped on grout pipes, that is more simplified than conventional packer system.
Feasibility of the new systems were examined through field tests. The grout pipes were installed into the ground successfully and its applicability to HDD was found satisfactory. Furthermore the improved soil bodies were directly observed and effectiveness of grouting were confirmed through compressive strength tests.

View full abstract

A magnetic sensor built on the principle of the magneto-strictive effect in which changes in magnetic permeability due to deformation of a ferromagnetic material was used to measure stresses on the surface of steel members in a nondestructive manner. This technique was applied in the tunnel fields to measure stresses of steel ribs, used as tunnel support structures, to confirm expected measurement accuracy. The results of stress measurements conducted on multiple occasions show that this method could be one of the promising technologies for non-destructive stress measurement for safety management during and after the construction of underground structures.

View full abstract

In this study, we have proposed the method to control blast vibrations due to secondary tunnel excavation in the twin tunnel constructions. Generally, it is difficult to keep the closest distance between the face of construction tunnel and the vibration monitoring points along pre-existing serviced tunnel. In the pro-posed method, a peak particle velocity (PPV) is controlled on the basis of the attenuation curve between the distance and monitored PPV, which has been compiled and updated based on the vibration monitoring measurements. Moreover, the practicability and utilization of the attenuation curve have been studied in the view of the factors for measured PPV.

View full abstract

Many binocular tunnels have been constructed under the difficult surface conditions such buildings or lifelines. While excavating a binocular tunnel, more than three cutting faces pass through an identical section and the settlement of ground surface increases in every heading. Therefore it is very important to estimate and forecast the final surface settlement by using field measurement. In this research, the authors paid attention to the ratio of surface settlement occurs in every excavation stage (primary and secondary tunnel) of binocular tunnels, and we analyzed the ratio of the surface settlement of primary side to secondary side by using the measurement result of past cases. From this analysis, we propose a simple forecast method, which estimates the final settelement from the early settlement occurs in primary excavation side.

View full abstract

Recently, it is required to investigate the spatial distribution of vegetation in urban areas on a regional scale for not only the improvement of urban environment but also the conservation of ecosystem. The purpose of this study is to develop the analysis method of the spatial distribution of vegetation on a regional scale. We defined the NDVI calculated from Landsat ETM+ data as the potential of vegetation abundance. The spatial analysis method consisted of local spatial autocorrelation and hydrological analysis for extracting the core of the vegetation-covered areas and uncovered areas, and the two kinds of lines regarding the spatial continuity of vegetation distribution.

View full abstract

On the RCD (roller-compacted dam-concrete) method, very stiff concrete is compacted by vibration rollers after spread in either 75cm or 100cm in thickness. In this method, compressive strengths of upper part and lower part in a lift are sometimes observed to be different, namely strength of upper part is lower than that of lower parts. In this study, compressive strength test and ultrasonic pulse velocity test were carried out for the core samples drilled from the RCD trial embankment. At the same time, X-ray CT (Computed Tomography) method was applied to the core samples to investigate the vertical distribution of material properties such as coarse aggregate ratio, void ratio and mortar density. It is shown that coarse aggregate ratio is uniformly distributed in vertical direction, but voids and average mortar CT value are different between upper part and lower part in the core samples. Furthermore, analyzing the CT images, voids are found on the boundary between coarse aggregate and mortar in upper part. Then it is considered that those voids mainly influence the heterogeneity of the compressive strength of the RCD core samples.

View full abstract

This paper illustrates issues on practical applications of slope stability evaluation models, and has proposed an ambiguity index for evaluating results derived from these models. Quantitative models generally construct the relationship between past slope failures and causal factors, and “hazardous or non-hazardous” areas are delineated on the slope stability evaluation map, respectively. Based on those classified results, Quantity of Acquired information (QA) has been formulated based on the concept of “conditional entropy.” Through the statistical measure of correlation ratio, we conclude that the proposed index of QA is superior, for selecting the models, to the general index of “success rate” with respect to training data sets (i.e. outside variables).

View full abstract

Ground settlement advances over time, steadily increasing the stress in the buried pipeline. A rational method of identifying problem locations has been proposed. If such locations can be identified, measures to reduce the stress are planned. Typical method is removing the earth pressure, adjusting the pipeline elevation, and then restoring the backfill. This paper proposes an analytical model for FEM analysis to evaluate the stress in the pipeline during such stress releasing process. Tests have confirmed that the proposed methods are fully practical and capable of evaluating stress in exposed pipeline on uneven elastic foundation with sufficient precision.

View full abstract

In this paper, a dynamic fault analysis model of large-scaled information systems is formulated to investigate the impacts of the system service inoperability upon social systems. The renewal processes of the components of the systems are described by use of rondom Weibull hazard models, and the fault tree model is formulated to analyze the magnitude of the system inoperability. The reliability of the information systems and the expected repair/maintenancce cost estimated by Monte Carlo simulation models. The practical availability of the methodology presented in this paper is investigated by a case study dealing with the traffic control systems for an expressway.

View full abstract

Full-scale tunnel model tests under a few kinds of load conditions have been performed to clarify the collapse mechanism of tunnel lining and the effect of reinforcing material on the load-bearing capacity of tunnel lining. It is found that tunnel lining reaches the state of entire structure collapse when the cross-sectional failure by compressive stress due to bending or development of tensile cracks at three locations on a tunnel cross section, or the shear failure by axial compressive stress at a location on a tunnel cross section occurs depending on the load conditions. Furthermore, it is verified that steel-fiber-reinforced concrete and reinforced concrete have the effect of improving the load-bearing capacity of cross section or entire tunnel lining structure depending on the collapse patterns.

View full abstract