To clarify the mechanism of the surface failure, the authors were measuring the relationship between shear strain and soil moisture content in a natural granite soil slope. The shear deformations were generated according to the infiltration of the rainfall. Because the depth of occurrences of shear deformation was same to the depth of increase of volumetric water content, we considered the deformation occurred according to the variation in the soil moisture content by the rainfall infiltration. Though in the summer season the shear deformation occurred in moist process according to rainfall and it returned slowly in the drying process after the rainfall, it was confirmed the transformation accumulated in the shallow layer after the second half of September. In this study we examined the influence that the soil moisture content gave shear strain using data obtained through our monitoring. As a result, we understood the shear strain was readily generated when the initial soil moisture content was high and the increasing of the soil moisture content was rapid. Thus, we showed the possibility that a large shear deformation is generated in a slope if the heavy rainfall occurred under the high soil moisture condition effected by the preceding rainfall.

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This paper describes a method for increasing the lateral resistance of a screwed steel pile in soft ground by carrying out soil improvement around the pile head. In this method, after a screwed pile is installed in the ground, a ground-improvement device is set up on the outside of the pile, and a column of cemented soil is built up around the pile head. For a cemented soil diameter that was 3.5 times that of the steel pile, field tests were conducted to measure the size and the compressive strength of the improved soil region. In-situ loading tests and a three-dimensional finite element method analysis were also performed in order to investigate the lateral resistance of the pile. The experimental results showed that the use of such a composite pile in soft ground can result in a significant reduction in pile lateral displacement and bending moment, compared to the case for a conventional screwed pile. The numerical analysis clarified the mechanism that gives rise to the improved lateral resistance of the pile. It was shown that the resistance increases due to the effects of the enhanced strength of the improved soil, and the presence of the reinforcing soil improvement device which has steel bars and prevents failure. It was also found that the use of this pile can eliminate softening of the surrounding soil.

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Capillary barrier (CB) refers to a soil layer structure composing of a sand layer over a gravel layer used as a rainwater infiltration control technique for preventing seepage. The CB effect results mainly from differences in water-holding capacity and permeability between the sand layer and the gravel layer. Experimental verification of the CB effect requires that the CB layer interface be flat. Trying to achieve flatness, however, the soil layer interface over a large area at a real construction site would not only greatly affect the construction schedule and cost but also pose a quality control challenge. In order to put the CB structure to practical use, it is very important to quantify the CB effect, or the degree of influence of nonflatness of the CB layer interface on diversion length. In view of this, this study compared the CB diversion length in the case where the CB interface is flat, which was determined in the authors' previous study, and the CB diversion length in the case where the layer interface is not completely flat, which has now been investigated through newly conducted experiments. The results thus obtained reveal that although under the limited condition of regularly shaped (sinusoidal) nonflatness, nonflatness of the interface of a sand layer and a crushed seashell layer would not affect diversion length, etc. (the CB effect would not be lost) if the nonflatness is regularly shaped and is within about 30 mm, which is likely to be encountered in practical conditions.

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The stability condition of clay under wave loading was studied. The circle slip analysis of bottom clay was carried out under the water pressure difference accompanied by the wave. The calculated safety factor for slide, in which the yield stress of clay measured by visco-meter was used as a strength of clay, showed the correlation with the responses of bottom clays in 11 cases of experiments fairly well. The safety factor of seabed was calculated in the case that a typhoon passed Tokyo Bay. The observed time when the hoisting and erosion took place at the seabed agreed to the time when the safety factor drastically reduced to less than 1.0. The range of calculated water contents of bottom clays, when the safety factor of seabed loaded by waves of the average significant wave heights is 1.0, were ranging from 1.1 to 2.1 times the liquid limit depending on the water depth, which agreed with the measured water contents at the seabed of 3 sites.

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There are many historic masonry structures which collapsed due to deformation and/or failure of their foundation ground, and then, it is demanded to investigate the deterioration mechanisms and the rational restoration methods based on the geotechnical engineering. In this paper, NMM-DDA (coupled Numerical Manifold Method and Discontinuous Deformation Analysis), one of the discontinuum based numerical methods, was enhanced and a method to simulate the deformations of the composite structures of soils and discontinuous masonry stones was developed. Firstly, formulation of the elasto-plastic NMM-DDA which incorporates elasto-plastic constitutive laws into incremental form of equation of motion was shown. Then, as a method to avoid volumetric locking in conventional NMM-DDA, which adopts constant strain triangle element, application scheme of node-based uniform strain element was also described. Finally, developed method was applied to some fundamental boundary value problems such as beam bending problem and bearing capacity problems, and the applicability of the new method was examined by comparing the simulation results with theoretical solutions.

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This paper examines, through a series of laboratory tests, the effect of the flyash improver, FAI, on liquefaction susceptible backfilling soils for underground pipes and excavatability of the improved soils. The soil material used in this study is Toyoura sand. Unconfined compression tests show that the unconfined compressive strength of soil increases with both increasing FAI additive ratio and curing time. Drop shovel test is chosen to provide material excavatability in a quantitative manner, and undrained cyclic triaxial tests are conducted for specimens with different additive ratio of FAI. It is found that the FAI additive ratio of about 2% is optimum in the light of both liquefaction resistance and excavatability, though this finding is to be verified in-situ. This paper also suggests that small strain shear moduli can serve as a good index of the in-situ improver’s effect.

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In this study, a handy and simple cone penetration test device that is able to estimate easily the strength of surface of soft ground or core sample etc. was designed. To evaluate the applicability of the designed test device, a series of cone penetration test was performed with the different conditions of apex angle and penetration length of cone tip for two kinds of clay sample consolidated various overburden pressure. The results of cone penetration tests were compared with the test results of the soil hardness tester and handy vane test device those are conventionally used. It is also examined the correlation for the unconfined compression strength. As a result, the high linear relation was obtained to cone resistance and unconfined compression strength. The correlation between the each test results was also obtained. Furthermore, the similar correlation between the each test results was also obtained to the core sample retrieved from the sea-bed, as well as the correlation for the reconstituted specimens. Therefore, it is said that the shear strength of cohesive soil can be estimated by using the designed cone penetration test device.

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