The high-pressure injection mixing method is extensively used to improve the ground to have a high seismic stability, including the prevention works of soil liquefaction. The uniformity of the strength and stiffness of cement-mixed grounds improved by this technology is relatively low. Based on a comprehensive series of studies in the laboratory and in the field, it is proposed to evaluate the unconfined compression strength q_u in such grounds rapidly and continuously from field shear wave velocities V_s measured based on the relationship between V_s and q_u obtained by using specimens prepared in the laboratory under respective field ground improvement conditions. A typical case in which this method was applied is described.

View full abstract

 The compacting performance of light weight compactors, which are often employed for soil compaction at narrow areas such as backfilling for underground pipes or around concrete structures, was discussed theoretically with computation for underground stress. The discussion suggested an index which quantitatively indicates the performance of the light weight compactors in soil compaction and its reliability was examined through test pits experiments with 5 types of small compactors. A practical method is suggested, based on those results, for determining the construction conditions of the sort of compactors and the lift thickness which are suitable for the in-situ soil conditions.

View full abstract

 The evaluation of the advection-dispersion in fractures and diffusion into the matrix from fractures is important to describe the mass transport processes in fractured porous media such as sedimentary rocks. However, it is often difficult to uniquely determine a number of parameters relevant to these phenomena, such as fracture aperture, dispersivity coefficient, and matrix diffusion coefficient, from a data set of a single tracer test. In this paper, a one-dimensional multiple tracer test for single fracture in a sedimentary rock block was conducted under the condition of injection rate for the unique parameter estimation suggested by authors. And the new efficient test procedure using both multiple tracer and multiple flow rate tests was suggested.

View full abstract

 The authors have tried to develop a practical and a simplified reliability analysis procedure for geotechnical structures. Since the reliability analysis has been developed basically by the structural engineers, there remain a number of points that need to be developed for geotechnical reliability analysis. In this paper, basic works done by the authors are integrated to show the full picture of a proposed procedure called GRASP, which stands for Geotechnical Reliability Analysis by a Simplified Procedure. In the latter half of the paper, the proposed procedure is applied to the reliability analysis of shallow foundations to demonstrate its effectiveness and usefulness in engineering practice. The calculated results show some weaknesses to be improved in the current design practice.

View full abstract

 The improved strength by the permeation grouting is reported to be influenced by soil density, grain-size distribution, grouting concentration, age of improved soil and so on. The strength of improved soil varies in wider ranges compared with that created by the Deep Mixing Method. In this study, the mechanism of strength variation of treated sand was theoretically and experimentally investigated. The advection-dispersion equation was used for analyzing the dilution of injected grout which would reflect the strength variation of improved sand. In addition, model injection tests and field test were carried out to clarify the causes of variety in strength of improved sand. The result reveals that the main cause of strength deviation of sand improved by permeation grouting can not be attributed to dilution of injected grout due to diffusion, but can be attributed to the submergence of grouting material, which is caused by the difference of density between pore water and injected chemical grout, after finishing injection and solidification process.

View full abstract

 In this paper, the numerical analysis focused on the dynamic behavior of unsaturated embankment was performed with the three-phase (soil, water, and air) coupled analysis based on porous media theory. In this analysis, we employed the conventional constitutive model for unsaturated sandy soil considering the suction-dependent plastic volumetric strain under cyclic loading. The proposed model was validated by the simulation of the cyclic unsaturated tri-axial tests of sandy soil. Furthermore, the simulation of shaking table tests of model embankment affected by seepage water and rainfall confirmed the applicability of the numerical method.

View full abstract

 The authors have been conducting seismic and resistivity tomography surveys in a gallery of the Horonobe Underground Research Laboratory in order to investigate an extent of an Excavation Damaged Zone (EDZ) along time. The objective of this paper is to discuss an influence of fracture distribution and water saturation of a rock mass on variations in seismic velocity and the value of apparent resistivity in an EDZ. Based on the result of seismic tomography survey, the extent of a layer which has low seismic velocity was about 1.0 m from the gallery wall after excavation of the tomography area. From the results of resistivity tomography survey, the value of apparent resistivity has not changed remarkably along time. To investigate a relationship between variations in seismic velocity and density of fracture in the survey area, the authors built a three dimensional fracture model around the tomography area. From the comparison of seismic velocity with density of fracture, seismic velocity decreased almost linearly as the density of fracture increased. Also, it was found that density of fracture in the layer of low seismic velocity could be estimated using a simple numeric model. From this result, seismic tomography survey and investigation of density of fracture are suitable method for evaluation of an EDZ.

View full abstract

 A new method for granulating liquid muds is proposed in this study. The method includes the process which crumbles partially-cemented muds. Laboratory experiments showed that granulation could not be achieved if cement-mud mixtures were stirred just after the cement was poured to the liquid muds of marine clays. However, the mixtures could be granulated if they were restirred after they had been primary cured for the period from a few hours to about one day. The particle size of the granulated materials could be changed by adjusting the primary curing periods. Laboratory experiments revealed that the cone indices of the cement-mud mixtures just after primary cured can control the possibility of the granulation and the size of particles, regardless of the water content and the primary curing period of the muds. It was also found that the compressive strength of single particles of the granulated materials which were secondary cured could not be affected by the primary curing time.

View full abstract

 During the 2011 off the Pacific Coast of Tohoku Earthquake, a lot of houses were suffered severe damage due to the open crack of ground and the differential ground settlement around the boundary area of cut-and-fill in the filled-valley residential site. The ground deformation around the boundary area of cut-and-fill in the filled-valley residential site is influenced by the shape of old ground surface. Then, the measurement of 3-D residual displacement in the model ground is necessary to study the soil deformation mechanism in the filled-valley residential site. In this note, the measurement method of 3-D residual deformation by using the multi-layered color sand grid is proposed. This method made it possible to indicate the internal 3-D residual displacement in the model ground.

View full abstract