The “high-standard micro-piles method” which is also possible at a narrow space, low altitude head condition and low cost has been developed as a new construction method for reinforcing existing foundation structures. Micro-piles are constructed with double tube excavation using by boring machine. After inserting a steel pipe into the hole, grouts are filled both inside and outside of pile. This paper describes the results of bending load test of pile and horizontal load test of constructed pile. By these load test results, the following things could be confirmed. 1) The joint of steel pipe of bending load and flexural rigidity have higher performances than only steel pipe of those, 2) It was confirmed that the lateral ground reaction coefficient in ground lateral displacement exceeds that coefficient calculated from deformation coefficient of investigation and test results indicating by specifications for highway bridges and building foundation design guidance.
Prediction of the permeability of freeze-thawed soils is significantly important in the case that a final disposal site is being constructed in a cold region or a large-scale frozen earth wall is operating for a long period. Although a large number of knowledge has been obtained, it still is difficult to predict the permeability of freeze-thawed soils in a practical level. This study proposes a permeability prediction method of freeze-thawed soils based on the experimental findings. In this study, freeze-thaw experiments were conducted with saturated fine-grained soils with different pre-consolidation pressures and overburden loads in order to predict the permeability of freeze-thawed soil. Two types of freeze-thawed experiments were carried out with the artificial ground freezing on-site construction condition considered, one is one-dimensional freeze-thaw test, and the other is horizontal displacement restrained freeze-thaw and vertical permeability test, which enables horizontal freezing under restricted horizontal displacement. The result has revealed that the permeability of freeze-thawed soil is obviously influenced by overburden test pressure rather than pre-consolidation pressure, over-consolidation ratio and frost heave ratio. The result suggests that the permeability of freeze-thawed soil can be predicted by the freeze-thaw test for which the effective overburden pressure is considered, rather than strength or hardness of the ground materials and other freezing conditions are. Moreover, void ratio and permeability after freeze-thaw tended to approach the value of unfrozen soils with an increases of pressure. Furthermore, it has been suggested that the permeability of freeze-thawed soils in an actual artificial ground freezing method might be increased by non uniformity in distribution of void ratio due to frost heave.
It is becoming progressively important to predict occurrence of slope failures induced by heavy rainfall because torrential rain and localized heavy rainfall are recently showing an increasing trend of occurrence. Prediction methods of slope failures are now required to make assessments from perspectives of not only for issuing warnings but also for canceling the warnings. In this study, an estimation method of in-slopes pore water pressure was considered as a quantitative criterion to determine when to cancel the warnings. The method first calculates Soil Water Index (SWI) from rainfall data using 3-series tank motels, and then applies a linear function to the calculated index in order to fit it equal to the maximum pore water pressure observed in field monitoring, and eventually estimates pore water pressure at which slopes start to collapse, on the basis of the fitting function used in the second process. The estimation method was applied to past rainfall histories recorded around several slope failure events in Izu Oshima Island for verification. The method successfully estimated and reproduced occurrence of surface failures which triggered debris flows in 1958 Typhoon Ida (the 22nd twenty of the year, also known as Kanogawa Typhoon) and 2013 Typhoon Wipha (26th typhoon of the year).
When short fibers reutilized waste PET bottles is added to liquefied stabilized soil, the flow value and bleeding rate of mortar are affected by the length and diameter of the short fibers and decrease with the increase of its additive rate. The unconfined compressive strength was recognized to have correlations with the diameter and additive rate of short fibers and the density of adjusted slurry. Therefore, an experimental equation with the variables of these factors was proposed. Failure strain or deformation modulus was not recognized to have any correlation with the diameter, length, additive rate of short fibers and the density of adjusted slurry. On the other hand, because the strength ratio (the ratio between compression stress at 15% strain and unconfined compressive strength) showed to have a correlation with the diameter, length and additive rate of short fibers; an experimental equation with the variables of these factors was proposed.
A large scale shaking table model test was carried out so as to investigate into the resistant mechanism of aseismic countermeasure for existing railway masonry walls using failure prevention net and soil nailing. Model of reinforced masonry wall with its height of about 2.7m was subjected to the horizontal shaking using the design Level 2 seismic load in Railway seismic design standards in Japan. It was found from the model test that the proposed method showed sufficient seismic performance against Level 2 Earthquake. Combined resistant mechanism exhibited by the net and the soil reinforcement was also clarified by the comprehensive investigation on the dynamic response of the model masonry wall, backfill, net and soil reinforcement. Relevant pseudo static analysis revealed that the evaluated yield seismic coefficient (Kh=0.433) corresponded well with the acceleration level when the wall displacement started to accumulate in the shaking table model test (Kh≈0.5).
Authors have developed a technique, called the cement-mixing and mechanical dehydration (CMD), as one of recycling techniques for dredged soils. In order to investigate the long-term strength property and the adaptability for marine environment, unconfined compression test and a series of ecology observation were performed for the CMD soil blocks exposed on the costal environment around Hakata Bay. The main conclusions obtained from this study are as follows; 1) the CMD technology can created soil blocks having the unconfined compressive strength of more than 10 MPa. 2) the water cement ratio is a practical index to evaluate the strength of CMD soil block instead of density and cement content. 3) the CMD soil blocks have high durability during exposure test against marine environment for 41 months. 4) since the coverage and number of animals and plants on the CMD soil block exposed in tidal zone and sea water are similar trend indicating the seasonal change as nearby concrete wall, the CMD soil block have sufficient adaptability for marine environment.
The earth pressure calculation formula based on Coulomb's earth pressure theory that are currently used in the design of retaining wall cannot be used if cohesion is included. Also, the calculation formula applicable to the actual slopes, such as case where the gradient of slope changes variously, does not exist. In this paper, a new earth pressure calculation formula based on Coulomb's earth pressure theory is proposed for resolving this kind of issue. In addition, in order to verify the validity of the proposed this formula, the calculation results obtained according to conventional formula and Trial Wedge Method were compared with the results from this new formula. Also, the conventional formula during earthquake based on Rankine's earth pressure theory is complex. In this paper, this formula is simplified and formula of angle of slip line during earthquake is proposed. Furthermore, in order to confirm the effectiveness of this new formula was verified in comparison with conventional method.
This research aims to clarify the mechanical characteristics of waste ground including plastics and propose methods to assess these characteristics. Mechanical characteristics of waste grounds including plastics have not been studied in sufficiently in Japan, because such grounds have been considered to be very elastic and difficult to use as land. However, in the previous research, it has been reported that waste grounds including plastics have high slope stabilities. The authors investigate characteristics of the waste ground including plastics such as slope stability, bearing capacity, subsidence, etc. Sizes of individual solid waste pieces in landfill ground including plastic are fairly large compared with that of the soil particles. It would require a huge and expensive test facility to accurately reproduce such actual sites indoors. Accordingly, the tests were conducted primarily on site such as plate loading test, box shear test in 19 sites (29 places) of landfills inside and outside of Japan. For simplified on site-test, impact bearing test, repose angle test and void test are proposed. The results of plate loading test indicate that the solid waste ground of the landfills with plastics has sufficient strength to permit construction of a heavyweight structure (for example, wind power generation). And bearing capacity could be estimated from the proposed impact bearing test and repose angle test. In addition, differential settlement is found to be unlikely to occur by the demonstration experiment on a landfill in central Japan. It is believed to be due to the transfer in the horizontal direction of the vertical force due to connection of the fibers. By proposed strength evaluation, it is expected that the waste ground is used as land.
When chemical stabilized soil is exposed to seawater, white color sediments may be observed at boundary between seawater and the soil. In this study, in order to investigate difference of calcium leaching behavior and mechanical deterioration degree of stabilized soil due to presence of the sediments on the surface of lime stabilized clay, an immersion test which was simulated marine environment was conducted. As a result, white color sediments were generated on the surface of the lime stabilized clay specimen with relatively high stabilizer content. The sediments were estimated spherical magnesium hydroxide by scanning electron microscopy observation and elemental analysis, and it is verified that calcium leaching and mechanical deterioration of stabilized clay were suppressed due to fine structure of the sediments.
It is well known that partially saturated soils show higher strength and stiffness due to suction which works at meniscus water, however, they also exhibit more brittle failure with relatively large strain softening as well as clear shear bands than fully saturated soils and dry soils. It is important to understand the mechanism of brittle failure of partially saturated soils by investigating relation between macroscopic mechanical behavior and three-phase microstructural change such as progressive changes in suction and distribution of meniscus water with development of shear bands. In the present study, shear bands region generated in triaxial compression test of partially saturated sand specimen was observed by x-ray computed tomography. Image analysis provided the curvature, retention states and the number of pore water in order to evaluate the contributions of suction and meniscus water to the deviator stress. It was found that variation in suction due to the development of shear bands is very small. It was also found that relatively large number of meniscus water exists during strain hardening, while the decrease in the number of meniscus water seems to be one of the reason to cause strain softening. It seemed that lower number of meniscus water exists inside shear band so that the contribution to deviator stress is smaller than outside shear bands.