Yoshitada Mito

Evaluation of the geological condition ahead of the tunnel face by geostatistical techniques using TBM driving data

In tunnel excavation by Tunnel Boring Machine (TBM), it is difficult to grasp the ground condition ahead of and surrounding the tunnel face because the face cannot be observed during tunnel driving. This is the reason why it has not been possible to make the best use of high-speed excavation capability of the TBM, especially in ground under complex conditions. Thus, the TBM Excavation Control System was developed to realize the accurate prediction of the geological condition ahead of and surrounding the tunnel face simultaneously with excavation. The special feature of this system is that geostatistical techniques are introduced into the data analysis using both drill logging data from pilot boring and TBM driving data obtained during excavation, in order to improve the precision of the ground mapping.

In situ experimental studies on improvement of rock masses by grouting treatment

Abstract One of the purposes of consolidation grouting for dam foundation is to improve mechanical properties of rock masses. In this paper, we would like to discuss in situ experiment carried out in order to explore the grouting effects of rock masses on mechanical properties. This experiment is mainly consisted of operating, electromagnetic and elastic wave prediction and borehole expansion test. The results obtained through this study are listed as follows. o 1. The change of permeability zone can be identified by change of electromagnetic wave amplitude. 2. Further injection steps may help rock masses to become uniform in terms of electric characteristics. 3. The change of elastic wave velocity by grouting injection also explains uniformity of rock masses. 4. Grouting injection can improve deformability of rock masses. 5. For more deformable rock masses before grouting injection, the more mechanical improvement will be expected. 6. The rheological model explaining grouting injection effects can be verified. This model shows a tendency that poor rock masses which have lower mechanical properties, can be well expressed the experiment results.

Stochastic block theory for initial support decision of large slope

Abstract Stochastic Block Theory is suggested as the management tool for the decision for initial support of key block before every discontinuity trace of the block has not appeared on slope surface, in other word, in the moment some of the discontinuity traces of the block have appeared. The probability of forming a removable block by the next excavation can be calculated by taking rock joint distribution into account. The applicability of the theory is examined using the joint trace maps.

Multivariate Auto-regressive Model for Groundwater Flow around Dam Site

Time series analysis is carried out using multivariate auto-regressive model for the monitoring of temporal variations of groundwater behavior around the fill dam site. The filtered time series referring atmospheric temperature is suggested as the main manipulated variables in order to take the melting snow, which causes a sudden rise in the level of the river, into account. Its effectiveness is verified through analyzing the power contribution. The results of the regression show that the multivariate auto-regressive model using the proposed variables is very effective tool for the estimation of the groundwater behavior of the dam site.

Study on Improvement of Dam Foundation by Grouting Treatment.

The purpose of consolidation grouting for dam foundation is to improve the permeability and mechanical properties of rock masses. For permeability, the grouting effect is usually confirmed by the permeability test at check holes. But for the change of mechanical properties, it has been difficult of confirmation. So, the mechanical improvement of foundation by grouting, like the changes of elasticity and strength, has not been considered in dam foundation design. In this study, an in situ experiment has been made in order to examine the grouting effect on mechanical properties of rock masses. The testing yard where the experiment was performed was 10m square, and 13 boreholes for grouting, divided into four (4) stages, were laid out. These boreholes had the length of 7m each, and the injection material was cement mixed with water. The experiments mainly consisted of elastic wave prediction and borehole expansion tests. As the results, the followings were obtained.(1) The change of distribution of elastic wave velocity by grouting represents the uniformity of rock masses.(2) Grouting can improve the deformability of rock masses.(3) For more deformable rock masses before grouting, the more mechanical improvement is achieved.(4) The reological model can be used to explain the grouting effect. By this model, the experiment results of poor rock. masses, which have lower mechanical properties, can be well expressed.

Stochastic Block Theory for the Observational Construction of Large Rock Slope.

For the excavation and the supporting of large rock slope, the observational construction method is becoming increasingly important in order to carry out the support decision immediately, by taking discontinuity distribution into account, because of the difficulty of supporting after some benches have already cut.It is well known that slope stability is strongly controlled by discontinuity distribution in the case of the hard rock masses. Goodman and Shi (1982) proposed “Block Theory” for the estimation of slope stability considering discontinuity distribution. Key block, however, can be found out after all the discontinuity traces of the block appeare on the slope surface. In that moment, the key block is unstable and can move out of the slope.Considering the above, the authors developed “Stochastic Block Theory” for the prediction of the key block before all the discontinuity traces of the block have not appeared on the slope, in other word, in the moment some of the discontinuity traces of the key block have appeared.Using Stochastic Block Theory, the probability of becoming a key block can be estimated concerning the block surrounding some discontinuity traces and bench.