About high-level radioactive waste disposal, the general invitation in a voluntary approach for selection of “preliminary investigation areas” which is the 1st step of the stepwise site selection by Nuclear Waste Management Organization of Japan is started. On the other hand, about low-level radioactive waste disposal, several kinds of investigation for the burial disposal approach of the underground tunnel facility system in about 50-100 m depth below ground surface have been performed for disposing of high βγ radioactive wastes. For carrying forward each disposal project of these radioactive wastes, the integration of the state-of-the-art technology in an interdisciplinary broad research field is indispensable. Especially the role that civil engineering can play in fields, such as investigation, design, development of new materials and performance assessment for underground disposal facility is very large.
In this paper, the role and expectation of civil engineering, and the latest trend in the disposal techniques to need an argument to the order of very-long term of longer than 1,000 to 10,000 years which civil engineering have not experienced until now, are described.

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The author investigated into the flow characteristics of liquefied sand by flow tests of model grounds under 1 g and centrifuge conditions. The following results were obtained : 1) The liquefied sand behaves as a non-Newtonian flow (non-linear viscous flow, psedo-plastic flow or Bingham flow). The viscosity of the liquefied sand decreases with an increase of the shear strain velocity. 2) It was found from the 1 g condition test, that the viscosity of the liquefied sand increases in proportion with 1.27-1.63 exponents of the thickness of the model ground. 3) The viscosity was found to be proportional with 1.56-1.74 exponents of the overburden pressure.

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In recent years, the mountain construction method of tunneling in urban areas is being widely applied in Japan. In order to prevent damage to adjacent environment due to excavation in difficult geological conditions, ground improvement and reinforcement techniques are required. The steel pipe-reinforced multi-step grouting method has been applied to tunnel sites as an auxiliary construction technique for reinforcement. However, this technique has been usually employed empirically without much understanding with regard to its effect on the ground movement prevention. In this study, the three dimension simulations have been carried out for evaluating the displacement restraint effect of the steel pipe-reinforced multi-step grouting by changing its design pattern. As a result, a subsidence restraint rate became significant if the tunnel being excavated in soft ground conditions. In addition, the propriety of the proposed analysis is verified based on the field measurements of Nagasaki Oranda Slope tunnel and the future prediction of surface subsidence in the unexcavated region and the reinforcement effect of the reexamined auxiliary technique have also been investigated.

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A series of 3-D centrifuge model tests on buried pipelines generated detailed data of both distribution of earth pressure along the pipe long axis and non-linear change in the pipeline response (earth pressure and deflection) due to increase in differential ground settlement. The tests also quantified the effects, on the pipeline response, of several critical factors such as ground conditions, burial dimensions of pipelines, and pipe flexibilities. It was found that a pair of 3-D ground arch, produced by the differential ground settlement, generated high earth pressure concentration onto the pipelines. The test results were compared with predictions according to a current Japanese design standard based on beam theory on an elastic foundation, confirming that the design standard involves several basic defects.

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In the existing design codes/standards on the evaluation of liquefaction potential, the uncertainty of soil properties and the expected loss are not taken into account. This paper proposes a new procedure for risk analysis to evaluate the potential risk of liquefaction quantitatively. Monte Carlo simulation is introduced in the proposed method to assess the uncertainty of soil properties. Risk analysis is made as a case study for a model liquefiable ground on the basis of the methods stated in the seven different design codes/standards in Japan. The result indicated that the new method enables to evaluate the probability of liquefaction and anticipated loss by constituting the hazard curve, fragility curve and risk curve.

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Interactive shear strength and displacement between geosynthetics and geomaterials are important factors to assess the stability of the multi-liner systems installed in the slope as a sideliner for coastal landfill sites. In the present study, direct shear tests on multi-layered models were firstly conducted by using a new testing apparatus that could measure tensile forces induced in each component of the liner system when the top layer was suffered from the shear forces caused by the self-weight of the cover soil. The corresponding numerical simulations by elasto-plastic FEM were secondly conducted to clarify the effects of interaction between layers. It can be well understood that the interactive behaviours of layers in the multi-liner are governed by a) the interface shear strength between the layers that depends on the materials and b) the tensile stiffness of each geosynthetic component that depends on both the consisting materials and the structural conditions.

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A series of shaking table tests was conducted to investigate the performance of the cut-off sheet pile method as a liquefaction-countermeasure for underground structures. This method was found to be effective to reduce the uplift displacement of the structures. Especially, application of steel sheet piles with drain remarkably improved its effect. The mechanism of the uplift displacement under placement of the sheet piles was also demonstrated through test results. Simplified procedures were presented to estimate the deformation of the sheet pile wall and the uplift of the structure. Applicability of the proposed methods was discussed through comparison with results of the shaking table tests and centrifuge model tests.

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One of the authors has been developing a soil-cement pile that consists of a thin-wall steel pipe with soil cement. The newly developed soil-cement pile is more economical and ductile. The mechanical behavior of the soil-cement composite materials, however, has not been studied yet. Therefore, it is rather difficult to reflect the above-mentioned advantages in design. In this paper, in order to clarify the compressive strength-deformation characteristics of steel pipe-soil cement composite structure, triaxial tests on the cemented soil have been carried out. Then, an elastic model for thin steel pile and a constitutive model for the composite structure has been developed based on an elasto-plastic model with strain softening proposed by Adachi and Oka. Finally, FEM analysis of the thin-wall steel pile-soil cement has been performed. From the numerical analysis, the compressive strength-deformation characteristics of the composite

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Strength characteristics of soil and reinforcement have potentially variabilities. It is important task for design to evaluate such variabilities quantitatively. However, the current design method using conventional safety factor can not show how safe the structure is. Several reliability analyses to take into account the uncertainties associated with the input parameters were applied to reinforced soil retaining walls with various heights in static condition for sliding and overturning modes. Consequently, the most seinsitive parameter on the limit state exceedance probability was the friction angle, and the second is the tensile strength of reinforcement. The safety average values of friction angle and tensile strength of reinforcement were clearly shown.

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The instantaneous profile method is favorable for measuring hydraulic conductivity of unsaturated soils. However, it requires the use many expensive measuring sensors and a large amount of soils, and in the case of fine grain soils, it is difficult to set up the specimen. Therefore, an experiment method has been development in Chubu University. It is an improved type of the original instantaneous profile method, and characterized by linear approximation of soil moisture distribution. Application of this experiment method is discussed in comparison with other steady state methods. From the experimental results, it is clarified that hydraulic conductivity of unsaturated sandy soil with large grain size and with narrow grain size distribution is decreased by orders of magnitude in higher degree of saturation.

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Steel sheet piles with holes to permeate pore water have been applied to preserve the flow of ground water and to prevent structures from damage by dissipating excess pore water pressure of liquefiable sand deposits during earthquake. A series of laboratory tests and numerical analyses were conducted to study the seepage flow through steel plates with holes. The permeability evaluation method of them was derived and then the influence of the steel sheet pile wall with holes to the groundwater flow was discussed. The application procedure of the proposed method to the seepage analysis of the liquefiable sand layer around the sheet piles with drain was also demonstrated and examined by shaking table tests.

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Hydraulic characteristics of rock masses depend strongly on the aperture conditions of discontinuities in rock masses. The shear behaviors of the discontinuities that lead to fracture and dilation also affect the aperture conditions of discontinuities. The paper presents a new apparatus for shear-flow coupling tests to describe the relationship between the shear behaviors and the hydraulic characteristics of rock joints. Experimental results show the changes of hydraulic conductivities of a single joint with various surface roughnesses under the shear processes.

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Main object of this study is to clarify the mechanical behavior of the surrounding ground of cylindrical cavity when a section contracts in a shallow ground. There is little clear quantitative definition of estimating the stress changes and/or extension of plastic zone around a cavity in a shallow ground caused by contraction. The authors try to represent these values around a cavity in a shallow ground by the extended cavity expansion theory presented in this study, and apply this extended cavity expansion theory to evaluate the influence of neighboring construction. As a result, it is described that the behavior of stress changes with cavity contraction can be estimated by using the presented method.

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Attenuation properties of subway-induced ground vibration were experimentally investigated to improve the accuracy of empirical prediction methods for the Vibration Level and bone noise level in buildings. Vibration accelerations both in the tunnels and on the ground were measured at 17 locations in and around the Tokyo area. This paper presents distributed levels of measured acceleration in the tunnels and ground. Dependency of attenuation properties on frequency is examined, and internal damping in every 1/3 octave band are calculated based on the Bornitz formula. Variations of internal damping and damping factors with ground conditions are discussed, and also variations of Vibration Level are estimated.

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Buckling analysis of tunnel lining is made by proposing a simple mechanical model. The tunnel lining may buckle when its rigidity is small. This paper shows the buckling load and buckling mode of a tunnel lining which is modeled by elastic bars and rotation springs. The buckling analysis is first carried out on a circular arch under uniform external pressure; the analytical results are then compared with theoretical results in order to check the validity of the method of analysis. Furthermore, an analysis model which considers ground reaction is constructed to study the interaction between the ground and a tunnel lining and to investigate buckling behavior of tunnel lining when its thickness and shape is varied.

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An in-situ cement stabilized soil is subjected to overburden pressure under the drained condition, and the magnitude of the overburden pressure varies progressively with stage construction. This paper reviews the strength characteristics of cement stabilized soil cured under different loading conditions, based on unconfined compression tests. The main conclusions are as follows. The unconfined compressive strength declines with elapsed time up to the subsequent loading. When the total overburden pressure is constant, the unconfined compressive strength cured under step loading is lower than that under monotonic loading. Also, an increase in overburden pressure scarcely damages a specimen and its existing cementation properties are preserved.

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