This paper reported swelling and slaking characteristics of mudstones subjected to infiltration of water as related to geotechnical disaster such as degradation of excavated rock surface and slope failure. In this study, one-dimensional swelling pressure and strain tests, and slaking tests were severally carried out on undisturbed mudstone specimens and their reconstituted specimen, in order to investigate the effect of lime treatment on suppression of swelling and slaking. The test results showed that the maximum swelling pressure correlated linearly with the maximum swelling strain on logarithmic scale, and that the dry condition is one of affecting factors in swelling and slaking properties. Also it was shown that the maximum swelling strain of reconstituted specimen reduced by addition of 5% dry weight ratio of lime to the specimen, and simultaneously the occurrence of slaking can be suppressed.
In an attempt to examine the efficiency of plastic board drain for promoting consolidation of super-high water content clay, various kinds of in-situ measurement were carried out in a pond at Kobe airport. As expected before the ground improvement, it was manifested that the consolidation was achieved by the difference of total water head between the Plastic board drain and the clay. In addition to it, it was confirmed that the self-weight consolidation of the super-high water content clay takes place involved with no dissipation of excess pore water pressure in the clay. On the other hand, the applicability of ball-cone penetration test for estimating water content of the super-high water content clay was confirmed well by showing a good agreement with the direct measurement from the retrieved clay sample. Furthermore, it was well demonstrated that the plastic board drain even when deformed largely functioned well as the drain.
Embankment structures in Japan have been subjected to a large number of earthquakes and as a result some of them leads to the failure of embankments. Therefore it can be unavoidable to develop the evaluation of seismic performance and the seismic design to constructed embankments. At present embankment is constructed fundamentally by managing degree of compaction Dc (%) at higher water content than the optimum water content wopt (%). However, it is pointed out that the difference of water content at compaction has some effects on mechanical characteristics of compacted soil even if the same degree of compaction is obtained. Furthermore, it has been gradually revealed that the mechanical characteristics can be remarkably improved due to achieving as the high degree of compaction as possible. Keeping in view the above, a series of cyclic undrained triaxial tests was carried out on compacted and saturated sandy-silt soil, which was actually adopted as a dike material. The specimens were prepared by compaction at the different water content with various compaction energy Ec (kN/m3) in order to compare with effects of compaction condition such as the degree of compaction and water content on seismic characteristics. Experimental results show that the samples compacted at lower water content than the optimum water content wopt (%) are stronger than the samples compacted at higher water content than wopt under the same degree of compaction. It is also confirmed that the deformation due to cyclic loading develops rapidly at drier side of wopt rather than at wetter side of wopt. Thus, it is inferred that seismic performance of embankment greatly relies on some factors such as degree of compaction and water content.
Unconfined compression tests and Brazilian tests were performed on dry and wet specimens in order to investigate the relation between microstructure and fracture strength in weathered coral skeletons. In particular, we theoretically considered the distribution of internal stress in coral skeletons by introducing pore-pressure in coral skeletons. As the result of experimental and theoretical consideration, we determined that the strength of coral skeletons strongly depend on pore-size and pore-pressure. Furthermore, we described that the coral skeletons show a marked tendency to a fracture localization, and the size effect was not observed in any experiments. With these experimental phenomena, we showed that the pores distribution is closely related.
The ancient Yoshinogari burial mound (about B. C. 150) is the oldest large earth fill which is mainly constructed by Sochiku method. The construction technique of earth fill is classified as Taichiku, Sochiku and Hanchiku in the order from the lowest to the highest level. The Chinese burial mounds, namely Jiangnan burial mounds (B. C. 1, 070 - B. C. 221) and Shandong Peninsula burial mounds (B. C. 202 - A. D. 220), and Yoshinogari burial mound are compared on various actual conditions such as the application of three construction techniques to the mounds and the location of burial matters in the mounds. Considering also the roots and propagations of other cultures and techniques, it is concluded that the construction technique of Jiangnan burial mounds propagated to the Shandong Peninsula burial mounds, and that the technique of Jiangnan or Shandong Peninsula burial mounds propagated to Yoshinogari, in northern Kyushu, Japan, through the sea, not through the Korean Peninsula.
Engineered barrier made by bentonite is required to stand without settlement or lateral flow for long term in a repository of radioactive waste. Centrifuge tests which simulated radioactive disposal were executed for evaluating the bearing capacity. And actual deformation was predicted with considering centrifuge scale effect. The result are as follows. Overpack settlement is predicted 8 mm (0.8% strain) after 55 years since the construction, if a repository is constructed with a condition that the highest overpack density is 3.4 Mg/m3 and the lowest engineered barrier density is 1.2 Mg/m3. The settlement is increasing according with overpack density. Siliceous sand mixed engineered barrier effects for reducing the overpack settlement.
This paper aims at clarifying the deformation-strength properties for coastal soft cliff. A series of triaxial compression tests was performed on undisturbed specimens sampled from the coastal soft cliff in Hokkaido, Japan to obtain mechanical properties such as shear strength. From the triaxial test results, it was found that the effect of fabric anisotropy on the strength-deformation behavior could not be ignored for the coastal soft cliff. In addition to these laboratory tests, a series of 1G-model and centrifuge test to grasp the feature of slope failure due to wave erosion was conducted on the model cliff having the corresponding strength with that of the soft cliff. Based on the test results, a slope stability evaluation was discussed in detail.
The pipe-jacking method which use the tunnelling machine have often been adopted in the construction for the pipe of gas and sewage. The performance of a tunneling machine in rock mass is usually evaluated based on the intact rock strength and the rock mass property including the crack. However, the performance is affected by not only its compressive strength but also the comprehensive characteristics including the type and properties of rock-forming minerals. In this study, mechanical properties of rock-forming minerals contained in some granite were evaluated by depth sensing indentation test (DSI test). The relationship between these properties and difficultly of excavation was also discussed. As a result, the intact rock strength of the granite in which the excavation trouble occurred was smaller than that of other granites, and the mechanical properties of feldspar grains contained in the granite were remarkably different from those of other granites. These test results suggest that the mechanical characteristic of minerals greatly influence the performance of excavation with a tunnelling machine, and DSI test is useful to clarify these properties.
Arsenic has been frequently detected with more than the Japanese environmental standard (0.01mg/L) in groundwater in south of Seino Basins, which locates in western part of Nobi Plain. Total content and chemical speciation of arsenic was evaluated by use of drilling samples of these area. The mechanisms of arsenic releasing to groundwater was investigated by some kinds of leaching experiments response to redox condition and pH. The water soluble arsenic concentration was higher in the Nobi formation distributed at south-west part of the plain than in the Nan-yo formation of north-west. Dominant arsenic speciation in Nobi layer was As sorbed Fe- and/or Mn-oxides. Total arsenic content in the profile was correlated with total carbon and total ferric content in this part of the plane. These results suggested that As sorbed on to Fe- and/or Mnoxides in Nobi layer was the one of the origin of the arsenic dissolution to groundwater. The arsenic leaching experiments suggested that slightly high pH value of groundwater and dissolved organic carbon leaching from Nobi layer enhance arsenic release to groundwater.
The objective of this study was to investigate the effects of fine fraction content, initial specimen density and residual shear strain after undrained cyclic shear in regard to the reconsolidation behavior of sandy soil at the post-cyclic shear stage. To this end, multiple stress-controlled cyclic shear torsional tests were conducted in undrained conditions. The results revealed that volumetric strain after sandy soil liquefaction is dependent on the history of shear strain hysteresis during cyclic shear regardless of the fine fraction content of the specimen. Higher values of volumetric strain at the postliquefaction stage corresponded to higher values of cyclic shear strain history. Conversely, lower values of volumetric strain at the post-liquefaction stage corresponded to higher values of initial relative density. Furthermore, when residual shear strain was seen after cyclic shear, lower values of volumetric strain corresponded to higher values of residual shear strain. These results indicated that the history of shear strain hysteresis during cyclic shear is an effective index for evaluating volumetric strain at the post-liquefaction stage. In this study, model tests using a shaking table were also performed to verify the results of the element tests. The outcomes showed that the above-mentioned index is suitable not only for use in elementary tests but also for use in shaking table tests to evaluate reconsolidation volumetric strain.
The strength of soil treated by cement deep mixing is highly variable, even at a single column, due to variability of in-situ soils, variability of mixing effectiveness, and other factors. Therefore the variability of strength has been considered in the design procedures of the improved ground. Normal or lognormal distributions have been adopted for the variability of the strength of the cement-treated soils so far. In several Japanese design procedures, the normal distribution is applied for the probability distribution of the cored-sample strength of the improved ground. However, there is little study in which the effect of the probability distribution of the cored-sample strength on full scale column strength is investigated. This paper presents the numerical study which investigates the compression behavior of full scale cement-treated column with the strength field following normal and lognormal distributions. Firstly, the goodness of fit for normal and lognormal distributions against the cored-sample strength was evaluated using K-S test and AIC. Secondly, the finite element analysis was conducted to investigate the overall compression behaviors of the columns with the strength field following normal and lognormal distributions. The influence of the probability density function of the cored-sample strength on the overall compression strength was discussed. The numerical results indicated that the normal distribution fits the calculated overall strength of the column with the normal random strength field and the lognormal distribution fits that with the lognormal random strength field.
The cut slope reinforced earth method is a restraining technique used to stabilize slopes by constructing bar reinforcements in the natural ground to form an earth reinforcement structure. As materials for this method can be procured easily and the work is simple, the self-supporting ability of slopes may be improved in a short period. But there are concerns that the deterioration of grout and erosion of steel bar cores in the ground will gradually lower the performance of the reinforcement structure. Up to now, the true state of the deterioration has not been clarified, and neither has the long-term durability of cut slopes strengthened by the reinforced earth method (hereinafter, reinforced cut slope). A number of reinforced cut slopes on expressways were selected to carry out studies to find answers to these issues. This document reports on the degree of corrosion of the steel reinforcement bars and the effectiveness of galvanization for rust-proofing, found in the studies, and suggests maintenance methods to achieve long-term durability of reinforced cut slopes.
The necessity of earthquake-resistant reinforcement for underground structure in large-scale earthquakes is rising. This paper shows a model test of the reinforcement method using the ground solidification body and its FEM analyses that were conducted to examine deformation characteristics of the reinforced underground structure and the effect of the reinforcement. Target underground structure is RC onebox culvert and the loading tests were performed by using the 1/3 scale RC model. The reinforcement body made with cement and clay was situated on both sides of the structure. The effect of the reinforcement was confirmed by comparing the results of the experiments with the earthquake resistant reinforcement and without it. And elasto-plastic FEM analyses could reproduce the behaviors of the underground structure in the loading test.
In case of application of magnesium oxide (MgO) for field of soil improvement, it is experientially known that the manufacturing process of MgO has serious influence on its performance and engineering properties of improved soil. In this study, for investigating the function of MgO in soil improvement field, typical MgO samples which have two different manufacturing process were applied to three soil samples of loamy soil, decompose granite soil and alluvial soil. Consequently, From the results, it is found that the difference in chemical reaction rate due to the variation of specific surface of MgO samples remarkably effects on the improved soil strength, and carbon dioxide in the air may not affect the increasing of improved soil strength.