In Japan, condition rating of retaining structures has been done based on visual inspection by following the maintenance standards. In this study, applicability of the percussion test for the condition rating of retaining structures is examined by conducting a series of prototype scale model tests and percussion tests at the site. It was found from these tests that the vibration characteristic of deformed retaining wall was different from the sound retaining wall; large Fourier's amplitude of the spectrum was exhibited especially at low frequency range. Two indexes, these are Spectrum area (SA) and Spectrum score (SS), are proposed to evaluate the change of the vibration characteristics of the deformed retaining wall. Relevant analyses on formerly conducted percussion tests results and prototype scale model test revealed that the proposed indexes could work well to distinguish the deformed retaining wall from the sound ones.
Clarification of mechanical characteristic of solid waste material and its evaluation method have been strongly required to prevent the collapse of illegal dumping sites, and to propose high-degree applications of landfills. Especially, Clarification of mechanical characteristics focused on compositional ratio of solid waste material is also important to establish an evaluation method of various waste grounds. In this study, the mechanical tests in both in-situ and laboratory were conducted on four waste grounds that consist of different compositional ratio of waste material. In-situ shearing response of solid waste material and shearing responses against compositional ratio were discussed from experimental results. As a result, it is clear that the shear stresses do not indicate the clear distinct peak strengths, and the stress ratios decrease with increasing normal stress levels due to containing fibrous material in solid waste material. In addition, the shear strengths of various waste material have excellent correlation with their content rate of fibrous material, thus the content rate of fibrous material has some possibility to be indicators for estimating shear strength of various waste material.
As considering the safe isolation of high level radioactive wastes, the long-term evolution of the hydraulic properties of rocks should be examined because a thermo-hydro-mechano-chemical processes are active under such conditions. In this study, a coupled THMC numerical model, especially by considering the pressure solution mechanism, has been developed to examine the long-term change of the permeability in sedimentary rocks that are assumed to be purely composed of quartz. The model predictions show a significant influence of the pressure solution on the permeability change with time. The predicted permeability decreases by one order of magnitude in 104 years when considering the pressure solution. The monotonic decrease of the permeability is congruent with the observed behavior in the literature.
A series of undrained cyclic tests were performed on sand-non plastic fines mixtures and sand-plastic fines mixtures with various fines content. The characteristics of a mixed soil depend on whether the fine grained or coarse grained material is the main constituent. The boundary of the area where coarse-grained soil formed the structural skeleton and the area where fine-grained soil composed the matrix was investigated. The consistency changed drastically on the boundary of a fines content of about Fc=20%~30%. From experimental results, the effect of the fines content Fc on the cyclic shear strength of both soils with the fine grained material forming the main constituent and soils with the coarse grained material forming the main constituent was considered. Through use of an equivalent skeletal void ratio which introduces a contribution factor b, a correction coefficient which takes the fines volume and course volume as the same, it became clear that there exists an unmistakable correspondence between the cyclic shear strength and the equivalent skeletal void ratio. Furthermore, with regards to the contribution factor b, it was found that the particle size ratio of the course and fine grained material correlated to some degree with the contribution factor b. From this, it was confirmed that the contribution factor b is important for evaluating the strength characteristics of mixed soils and an equation for predicting the contribution factor b using the particle size ratio χ is proposed.
A series of tilting tests and shaking table tests were carried out so as to develop an aseismic countermeasure for masonry retaining walls using collapse prevention net and soil nailings. Tilting tests were carried out so as to investigate into the reinforcement mechanisms and the effect of backfill stability on the reinforcement effect. Shaking table tests were carried out to understand the resistant mechanisms in dynamic field. Results from a series of model tests clarified the resistant mechanism. It was also found from the tests that collapse prevention net was highly effective in reducing horizontal displacement by restricting the blocks with soil nailings as well as preventing the collapse of masonry retaining walls. In additions to the above, a design methodology was also proposed by reflecting the resistant mechanism revealed by the model tests. Relevant analyses revealed that the proposed analysis procedure could safely evaluate the timing when the horizontal displacement began to increase in the shaking table model test.
Hakuryuko soft ground is located in the northeast end of Yonezawa Basin consisting of alternated layers of organic soft cohesive soils more than a depth 100 m. The expressway construction was planned over this soft ground by the using vacuum consolidation as a ground improvement method. The ground surface is a plow layer following by a fibrous peat and the alternating layers of organic and cohesive soils. A sand layer existing between the organic and cohesive soil layers is considered to reduce the effectiveness of vacuum consolidation. Therefore, full-scale trial embankments were placed to verify the effectiveness of vacuum consolidation. As the result, the vacuum consolidation method was found to be applicable to this kind of soft ground when using with the auxiliary construction method to improve the surface airtightness.
In the present study, in order to establish a stability evaluation method of a caisson-type breakwater against a tsunami, mechanical behaviors of the laterally loaded caisson and the reinforced embankment behind the caisson were discussed on the basis of the results in numerical simulations using the two-dimensional discrete element method. Two types of a tsunami bore and a tsunami overflow were assumed by changing the points of force. As a result, the horizontal resistance in the case of using the reinforced embankment was up to 3 times as great as that without the reinforced embankment. Moreover, it was revealed that the behavior of the caisson and the earth pressure distribution behind the caisson were entirely different under two external force conditions. Judging from the analytical results, the contact pressure beneath the caisson and the stress on the base of the reinforced embankment were postulated as a triangle distribution. The load distributions were given as external forces and a circular slip analysis was carried out. By the circular slip analysis, the bearing capacity can be evaluated under the condition of the tsunami overflow. The moment equilibrium was considered for the condition of the tsunami overflow dealing a trapezoidal distribution as the earth pressure behind the caisson. From the comparison with the DEM result, it was revealed that the stability was adequately evaluated by the moment equilibrium.
Recently, in urban cities of Japan, water hazards termed as ‘urban flooding’ have been frequently experienced when the city was attacked by heavy rainfall. In cope with such flooding, infiltration facilities are often installed, with which the seepage of rainwater into ground is promoted. However, areas being suitable (or not suitable) for mounting infiltration facilities should be manifested at the stage of planning by considering two facets; i.e., cost and safety. In this paper, case study as such is described for a model city in Hyogo Prefecture. First, a 3-D stratigraphy model near ground surface was established based on the existing borehole data, a total of 432. Second, the water-retention characteristics of unsaturated surface soil above the ground water level were measured by performing in-situ infiltration test. Third, the 3D seepage flow analysis by considering these characteristics was carried out, and the results were evaluated by comparing the predicted ground water level against the field observation. Finally, a map for rainwater infiltration is proposed. It was manifested that the accuracy and reliability when predicting the fluctuation of ground water level were greatly enhanced by considering water retention characteristics of surface ground. Furthermore, any risk for secondary geo-hazards will be greatly reduced by installing seepage facilities based on the proposed map.
The countermeasure method against liquefaction by decreasing the saturation degree of soil has the features of low cost, simple procedure and environment friendly. Although it is well known that the soil resistance to liquefaction increases as the saturation degree of soil decreases, it has been difficult to lower the saturation degree of ground homogeneously. A technique using micro-bubbles can be expected to solve these problems because the micro-bubbles can easily permeate into the voids among sand particles. A series of tests for saturated sand injected with the water mixed with micro-bubbles was conducted. Based on these test results, factors influencing on decreasing the saturation degree of ground were examined and the feasibility of the micro-bubble injection method was studied in this paper.
In a regional seepage flow analysis employing the finite element method, boreholes and wells are generally approximated by nodal point sources. Such a well model often yields inaccurate results. This study proposes a new simple well model using revision functions, which are based on theoretical solutions, for enhancing solution accuracy. This present well model modifies the permeability of elements surrounding the nodal point source. Several numerical verifications were carried out to confirm the solution accuracy of the present model. The solutions of the present model show excellent agreement with the theoretical solutions, irrespective of element size.
Expanded glass material is made of waste crushed bottle foamed by calcination (900 to 1000 degree Celsius). The material includes innumerable air bubbles, so the expanded glass aggregate is much weaker than gravels and crushed stones which are used at the construction works. In this paper, in order to clarify the physical and mechanical characteristics (size and shape of the air bubbles, crushability, permeability) of expanded glass aggregate, the aggregate is investigated with a series of laboratory tests (soaking, crushing and permeability tests) at different air content. The following conclusions are obtained from the present study: (1) The air content of the expanded glass material is almost occupied with discontinuous air bubbles. (2) The size of the discontinuous air bubbles and density of the material affect crushability of the expanded glass aggregate directly. (3) The crushability of expanded glass aggregate which has relatively small air bubbles is similar to that of lapilli. (4) Even if the expanded glass aggregate is crushed remarkably, its permeability can be kept sufficiently.
The New Waste Disposal Area in Tokyo Bay is the last place available in the region where the wastes including municipal/industrial wastes, construction waste soil, dredged soil and others can be disposed. This disposal area is required to be available for a long period. A work for bulk compression of disposed clayey soils was carried out with the vacuum consolidation method at the block C of the area to prolong its service life. In this project, the prefabricated vertical drains (PVD) with a width of 150 mm and a thickness of 3.9 mm were used. The PVD were installed in a square placement of 1.8 m to the clay layers of +1.5 to -33.8 m in average elevations, to which the vacuum pressure of -65 kN/m2 was applied for 310 days. After a trial execution in 2005, full-scale work started in 2007 and ended in 2015. The vacuum consolidation method was applied to the area of 383,000 m2 and the average consolidation settlement observed was 5.13 m. As a result, the estimated amount of bulk compression attains a value of 2,167,000 m3 which corresponds approximately to the amount of soils dredged in Tokyo Bay for 2.3 years. This paper describes the general overview of this project in terms of geotechnical engineering.
This study investigates the feasibility of a new recycling technology for on-site solidification of the peaty soil generated by construction. The technology utilizes microbes inhabiting construction sites to solidify peat by capitalizing on their ability to precipitate calcium carbonate. Feasibility tests using peat specimens from multiple sites in Hokkaido showed some of the microbes to be urease-positive. Thus, laboratory tests of peat solidification were conducted for two cases: 1) microbes from the construction sites alone were used and 2) an enzyme (urease) was added to microbes from the construction site in expectation of the enzyme's ability to increase the strength of the peat at an early stage. At six months of curing, the target uniaxial compressive strength of 50 kN/m2 was attained. Thus, the technology proposed in this study demonstrated its potential for application.
In the present study, in order to confirm pH decreasing effect of steel making slag under aging process, we performed aging experiments in the laboratory up to one year and measured water content, pH, electric conductivity and carbonate content of steel making slag with elapsed day. Now, we investigated the influence of the conditions at adding water and mixing on carbonate progress during the aging term. From the results obtained, it was found that pH and electric conductivity of steel making slag with aging treatments gradually decreased with elapsed aging day and height of water content influenced on the tendency. Moreover, it was shown that the carbonate content of steel making slag gradually decreased with elapse aging day.