The more accurate understanding and appropriate control of unsaturated area around tunnel excavated in deep rock-mass are required, for the geological isolation of radioactive waste project and also under-ground rock cavern storage project of liquefied petroleum gas. The numerical simulation of seepage flow is usually conducted to understand and evaluate the unsaturated zone around tunnel. The unsaturated parameters (such as moisture characteristic curve and relative permeability) and appropriate control of boundary condition are indispensable for the simulation. Authors developed methodology to measure unsaturated parameters utilizing the measuring method conventionally applied to soils and showed the efficiency of the method via a laboratory experiment. The idea of combining seepage face condition and flow rate fixed condition was derived, and the efficiency was shown in an model simulation. The two developments enabled the accurate estimation and understanding the evolution of unsaturated zone around tunnel.
In order to identify saturated hydraulic conductivity and longitudinal dispersivity, saltwater tracer tests using dual boreholes were performed for an unconfined and an underlying confined aquifer at Nagano-Wakasato campus of Shinshu University. The data of electrical conductivity monitored at injection and observation borehole were used to inversely identify the parameters by combining a three-dimensional numerical model, SIFEC3dp, for solving coupled problems of density-dependent, saturated-unsaturated flow and convective-dispersive transport of conservative tracer in an aquifer system, and Powell's optimization method. The developed method was first validated by applying to arbitrary test cases with given parameters. Furthermore, application of the inverse method to the site generated reasonable results while numerical simulations using identified parameters satisfactory reproduced measured salt concentrations.
We proposed the bridge column integrated by multiple steel pipes and connected directly to piles with and without a footing in order to design a rational foundation of the proposed column. We compared a seismic response characteristic of the conventional substructure with a footing and proposed substructures, to reveal their characteristics and feasibility. As result of a case study by a pushover analysis and seismic response analysis, proposed substructures have advantages of a strain reduction of piles by a strain decentration at footing point. In addition, reduction in footing weight contributes to decrease pile strain in case of no footing. On the other hand the proposed substructure has the disadvantage of an increase in a strain of a pile and a displacement of piles. But it was revealed that a strain of piles decrease by using the beam in the ground. At the end, this study showed the proposed substructure has a sufficient seismic performance against lateral soil movement.
A large scale model test was carried out in this study to investigate relationship between an increase of the potential risk of slope failure and the shear strain in the shallow section. A simplified shear strainmeter (MPS) was developed to measure the shear strain. MPS comprises a screw at the lower end of the compact body of 0.6m in length and 10mm in diameter so that easy installation without pre-borings. Moreover, lateral compression by installation in the surrounding soil makes strong contact, thereby resulting in high sensitivity. A model slope was composed of soft deposit by Kanto-loam and 45 degrees of inclination and 3.5m of height. Several sets of MPS and conventional sensors of inclinometers and displacement transducers were set to compare the reactions in the test. Seven steps of cuttings were carried out from the toe of slopes to make unstable. The model slope did not fail immediately after a completion of final cut, and 7 minutes of a time lag existed prior to the failure. Clear increases in the responses of shear strains (θ) were measured with the progress of slope cuttings in the tests. The relationship between θ and the displacement shows good agreement in the reactions. Similar reactions to the creep strain curve were observed in θ. A couple of minutes' time could be provided for escape by identifying either a 2nd creep or a 3rd creep. Accordingly, the relationship between the increase of the potential risk of slope failure and the increment of shear strain in the shallow section of slope was confirmed. It was clarified that this simplified monitoring can save worker's lives by escape prior to failure.
The application of bamboo charcoal to cement soil stabilization was investigated in present study. A series of the unconfirmed compression tests was performed on cement-treated soil with bamboo charcoal to clarify the improvement effects. Both normal Portland cement and Blast-furnace Slag cement B were used in these experiments. In addition, Japanese leaching tests No. 46 and a tank leaching tests were conducted to evaluate the effects of bamboo charcoal on leaching characteristics of hexavalent chromium (Cr(VI)) contained in the cement-treated soil. As a result, the unconfirmed compression strength of the cement-treated soil mixing with bamboo charcoal increased remarkably. For each leaching tests, it was indicated that the leaching amount of Cr(VI) was inhibited to some extent due to mixture of the bamboo charcoal in cement cement-treated soil. Moreover, it was found that the unconfirmed compression strength of the cement-treated soil mixing with bamboo charcoal didn't decrease under submerged curing for a long term.
This paper deals with a rational design method of contact pressure distribution and displacement at the bottom of faulting footings on slope. The faulting footings are well used for effective enlargement of development area, but the design of faulting footings is sometimes problematic. We have already published a rational design method of contact pressure distribution and displacement at the bottom of flat footings. We showed that this design method was applicable to the cases of faulting footings by carrying out some numerical simulations based on new design method for some concrete structures of faulting footings.
The fractures or crustal faults have complete control over hydrological property of each fractured rock mass. This paper proposed the multi-scale numerical mass-transfer simulation model in fractured rock mass by using the discrete fracture network model , random walk model and generalized finite element approximation. In this numerical simulation, the Logistic regression model and Weibull distribution was employed as the space distribution of permeability coefficients. As a numerical result, the bleeding channel flow in fractured rock mass model was revealed numerically.
Understanding the relationship among water saturation, water matric potential, and air permeability is important for accurately simulating the behavior of toxic gases at the polluted site and optimizing remediation technologies. In this study, air permeability (ka) was measured on sands with different particle sizes and shapes during drying and wetting cycles. The hysteresis in soil-water retention highly affected gas transport, showing higher ka for the wetting processes than for the drying processes at the same air content for all sand samples. This suggests that the existence of more continuous air-filled pore networks for the wetting processes enhanced advective gas transport. A power-law type ka model was applied to the measured data, demonstrating a clear relation between the pore network tortuosity factor in the ka model and model parameters for describing water retention characteristics. In addition, it is indicated that for sands with rough particle shape the continuity in larger-pore network is obstructed by the soil water filled in smaller pores as compared to sands with round shape.
Numerical simulations of unsaturated soil cyclic shear tests were performed using the three-phase porous media theory and a simplified elasto-plastic constitutive model for sand. As a result, the simulations provided a satisfactory reproduction of the cyclic test results in the cases where the initial suction was low volume regardless of the degree of saturation. In this study, Furthermore influence of the pore air pressure in the analysis was examined by two methods the previously described three-phase analysis and two-phase analysis with the same pore air pressure and pore water pressure. It was the result the two-phase analysis results would overestimate the volumetric compression compared to the three-phase analysis results due to the influence of the pore air.