On the 19th January in 2011, a phreatomagmatic eruption occurred at Mt. Shinmoedake in the Kirishima volcanoes group of Kyushu Island. Large amount of volcanic ashes were falling in the surrounding areas. It was reported that over 40 million tons volcanic ashes were deposited on the surrounding city. In this paper, a series of soil tests are carried out a volcanic ash deposit originating from Mt. Shinmoedake. The approach employed in these soil tests was as follows: 1) physical properties tests, 2) compaction test, 3) undrained cyclic shear test and 4) slaking test. In addition, this paper compares the geotechnical properties of volcanic ash deposits originating from Mt. Shinmoedake with those of other volcanic ash deposits and typical silica sand. As a result, geotechnical characteristics of volcanic ash deposits originating from Mt. Shinmoedake were similar to those of sandy soil in practice. However, it is predicted that geotechnical characteristics of this volcanic ash deposits will change due to the influence of physical weathering.

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Significant number of subsurface cavities was found in the liquefied ground after the Great East Japan earthquake. Using the results of the radar exploration conducted in Urayasu-city, Shinkiba-area and Narashino-city, all of those suffered from damage by the ground liquefaction, characteristics of sub-surface cavities are investigated. It was found that cavities tended to form near man-holes and joints in pavement. Size/shape of the cavities is larger and thinner compared to those of cavities observed in the non-liquefied ground.
A series of model tests was also conducted in order to understand the mechanism of underground cavity formation when liquefaction occurs. Liquefaction and sand boiling was simulated in the model test. Sand grains initially moved horizontally and then vertically, causing disturbance and loosening in the ground. Gaps and voids near the ground surface were eventually generated at the location of the boiled sand.

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Under the situation that frequency of flooding and landslide disaster due to short-period, high rainfall intensity is increasing, this study investigates mechanism of run-off and moisture infiltration into subsoil based on results of field monitoring in two sites comprising different geological condition, and analysis by one-stage tank model. The results made it clear that rainfall downpour are divided into run-off, infiltration and surface retention, and ratio of each component changes, depending on soil properties such as permeability and porosity.

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Japan has large areas covered by volcanic ash sediments. Volcanic coarse soils of their sediments are used in earth structure well. However, most of such soils are classified in problematic soil. Their constituent particles are very porous. Therefore, it is anticipated that measurements of soil tests using volcanic soil are spread, especially physical property tests, when soil tests are conducted under JIS/JGS methods. In this study, a series of density tests of soil particle and grain size analyses was performed on a few volcanic coarse soils with intra-particle void to consider the influence factors on spread of experimental results. As a result, the physical properties of volcanic coarse soils were affected remarkably by the sample preparation and experimental method rather than the uncertainly of test process or measurement. Hence, it is necessary for the quality evaluation in such materials to consider the homogeneity and preparations situation of the sample enough.

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Highways in Japan have played important roles as emergency traffic routes after earthquakes. Although highway embankments often damaged due mostly to soil liquefaction or related phenomena, however, any liquefaction countermeasure is not implemented. This is largely due to the fact that damaged embankments had been fixed in relatively short time. But this may not be the case if huge earthquake such as the Nankai earthquake occur. In this study, an innovative liquefaction countermeasure technique, desaturation by air injection, is focused on which is inexpensive and applicable to foundation soil below existing structures. Effectiveness of the technique to embankments on liquefiable soils were studied through a series of centrifuge tests.
Three models were tested including the benchmark model without desaturated zone and two models with partly saturated foundation soils. In the later models, fully saturated foundation soils were prepared first and air was injected in flight. The resultant degree of saturation in the desaturated zones after the air injection was halted was some 88%. All the models were horizontally shaken at 40g field and model responses were observed in detail.
The foundation soil of the benchmark model was liquefied during shaking and embankment crest settled as much as about 20% of the embankment height. While for desaturated model, observed excess pore pressures in the desaturated zones were considerably low and significant reduction in crest settlement was observed.
In this study an attempt was made to simulate the centrifuge models using a numerical code, ALID. In the simulation, liquefaction resistances of sand in the desaturated zone were estimated based on the formula proposed by Okamura and Soga (2006). In addition, influence of ridged boundary imposed by the rigid container side walls were taken into account. The simulations captured fairly well the overall figure of experimental observations that crest settlement and deformation of foundation soil decrease with increasing the width of desaturated zone.

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There are a lot of difficulties in ground water survey in developing country, especially, when the survey targets ground water quality. The water quality issues in water resource development become important notably. In the case of contaminant in the water has no taste, color or smell, chemical analysis is only one way of examination, however, the reliability of laboratory testing is difficult to guarantee. In this paper, the possibility of practical use of field kit in survey is examined on the basis of the experience in developing countries. When the field kit is used under control and appropriate quality management, it should be powerful tool.

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In the literature, research dealing with geotechnical engineering properties of scoria is scarce. Therefore, it involves some difficulty in discussing the adequacy of scoria to use as a fill material. In this paper, the engineering properties of scoria sampled in areas around Mt. Fuji were in detail examined by in-situ and laboratory tests. Bearing in mind the use of it for fill material, the scoria around Mt. Fuji could be equivalent to, even superior to, natural sandy/gravelly soils in terms of permeability, residual settlement on wetting and the shear strength. For example, when using the scoria as a fill material, we see no problems in terms of not only the stability but also the residual subsidence of the embankment. Since the scoria is light in weight at around 1.0Mg/m3 by showing significant crushability, care should be taken against the control of compaction work. The quality of embankment may be degraded when over-compaction is seen.

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As the increasing demand for housing, the house built on cut earth or embankment has been increasing. In order to effectively use the land for housing, houses in the vicinity of the retaining wall are often built during reclamation. A problem sometimes occurs in the vicinity of the existing retaining wall due to the displacement. However, because the mechanism is not clear, it is difficult to carry out the suitable countermeasure to the displacement of the retaining wall.
In order to make clear the mechanism of deformations of the retaining wall, we carried out the in-situ construction of the soil-cement column near the retaining wall of the real size, and measured the earth pressure and displacement of the retaining wall. In addition, based on the results measured by the in-situ experiment, two dimensional elastic FEM analysis was also carried out and influence of the distance between the retaining wall and soil-cement column was numerically simulated.

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A constitutive model extended from the modified Cam Clay model is proposed to predict more accurately the far-field deformation that occurs in peaty soft ground. The model considers the large initial stiffness developed at initial consolidation stresses and its degradation as function of shear deformation over a small to medium strain range. The initial stiffness values were sought by means of field sounding tests. A parameter controlling the elastic shear stiffness degradation can be determined through fitting the model to monotonic shear test results. This study also proposes its representative values that can be used as first estimates in practice. A simulation of a field embankment test with the proposed model demonstrated that the model can predict the far-field ground displacement in both the vertical and horizontal directions with better accuracy than the existing model.

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Because of risk of small earth dams’collapses induced by earthquakes and heavy rainfalls, the safety diagnoses of the embankments are necessary urgently. The authors developed an in-situ shear test method (BST; the Borehole Shear Test; BST) for measuring the shear strength of embankment soil easily by using a sounding borehole. Test method is 1) to install a balloon with shear blades into 42mm test hole in the embankment ground, 2) to expand the balloon at specific pressure and consolidate soil around the test hole, 3) to shear soil around the test hole by rotating the balloon and measure the torque, and 4) calculate shear strength using the Coulomb criteria by plotting peak shear stress calculated from torque to normal stress on the test hole calculated from balloon pressure. We performed large scale model tests and field investigations, and compared the shear strengths by BST to those by tri-axial shear tests. As a result, both strengths well coincided under unsaturated conditions while variation in the data of soil materials with gravel were little-bit large. In saturated soil, strengths of permeable soils by BST were close to CD-test strength, while those of impermeable soils were to CU-test strength.

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The impermeable coating treatment is an original technology which coats solid wastes by a particle unit with the impermeable material containing water-absorbing polymers. The elution of attached substances on the surface of soil particles such as heavy metals will be suppressed, because each particle of soils is coated with impermeable materials uniformly. Furthermore, since the swollen impermeable coating material by absorbing the pore water can fill the void space of solid wastes, the treated soils will be expected to improve their water interception performance. In order to utilize solid wastes as soil improvement materials, impermeable treatment materials and so on, this study evaluated the key properties such as the elution of heavy metals and alkaline, a water permeability, and the relationship between swelling and upheaval of treated soils with the impermeable coating by laboratorial experiments.

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The following correction should be made to the original paper, Vol.8, No.4, pp.579-595, “Proposal of the Simple Simulation Method to Estimate the Stability of Slope Surface Layer under Rainfall Condition”:
Page 592, Fig. 29 should be replaced the new one
Page 593, Fig. 30, Fig. 31 and Fig. 32 should be replaced the new one
Page 593, left-hand side, 11th, 18th, 20th, 22th and 47th line should be replaced the new one

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