In this research, a series of centrifuge model tests and effective stress analyses was carried out in order to clarify the effect of desaturation on the seismic behavior of horizontally layered ground. In the model tests, unsaturated model ground with the degree of saturation of 90% was created by controlling the water injection speed from the bottom of a rigid box during the saturation process. While the rise in excess pore water pressure in the unsaturated ground was suppressed compared to that in the saturated ground, the excess pore water pressure in the unsaturated ground took more time to be dissipated. In the effective stress analyses, simplified three-phase analyses, where equivalent bulk modulus is used for a mixture of liquid (or pore water) and gas (or pore air) assuming that suction is zero, were also performed in addition to three-phase analyses strictly considering pore water and pore air pressures. The simulation has clarified that the simplified three-phase analyses can be applied to the seismic behavior of unsaturated sandy ground when the degree of saturation is relatively high.
Slope measurement system of negative pore-water pressure using wireless sensor network was developed and the details of the measurement system were described in this paper. Long-term performances of the developed measurement system by in-situ and laboratory experiments were verified and problems of the long-term measurement using the wireless measurement system were described based on the measurement data. The problems on batteries of wireless nodes, tensiometers and so on were discussed based on the measurement results. The problems on resistance to climatic condition of the devices were explored by in-situ and laboratory experiments and improvement plans were also discussed.
It is pointed out that the shear strength of cemented soil improved with calcium carbonate (CaCO3) crystal is enhanced by decrease in saturation degree during precipitation. In this study, improvement efficiency of liquefaction resistance enhanced through controlling saturation degree (from 20 to 100%) and CaCO3 content (from 0 to 1%) was investigated by undrained cyclic triaxial tests for coarse and fine sand specimens. Enzymatically Mediated Calcite Precipitation (EMCP) technique was employed to precipitate CaCO3. SEM-EDX was utilized to observe calcium carbonate crystal on the sand grain surface and to identify the crystal. It was found that, in EMCP with controlling saturation degree during precipitation, high efficiency in liquefaction mitigation was provided to finer sand including larger crystal.
The paper describes a method of regional landslide susceptibility maps with permanent seismic displacement obtained from the Newmark method including a strong-motion accelerogram with a corresponding slope azimuth. To validate the proposed method, the newly created regional landslide susceptibility map was compared to an official landslide inventory map that was produced following the 2004 Mid Niigata prefecture earthquake. This study also proposed a calculation method for the prediction rate and determined the strength parameters of the geomaterials based on the prediction rate. The proposed regional landslide susceptibility map could be useful for early understanding of slope failure locations, for estimating the magnitude of damage, for planning first investigations after earthquakes, and for preventing secondary disasters immediately after earthquakes.
Crushed concrete aggregate (CCA) is one of the major construction byproducts. It is currently widely recycled as a road base material but it might be also considered as a good potential fill or backfill material for typical soil structures such as embankments. To examine the above, its physical, mechanical and chemical properties were investigated by performing of a comprehensive series of laboratory tests, including compaction and consolidated-drained triaxial compression tests. Two types of CCA materials retrieved from two concrete structures of different periods were used and their grain size distribution were relevantly adjusted. CCA comprises composite particles made from cement paste, fine and course aggregates. Cement paste is responsible for solidification of particles after compaction but may also cause elution of hexavalent chromium Cr(VI). As far as mechanical properties are concerned, strength of compacted CCA was found to be equivalent to that of a natural well-graded gravelly soil. Compacted CCA with unhydrated cement particles remaining showed further increase in strength while curing, under the conditions of compaction realised in the present study.
Engineering behaviors such as soil compaction behaviors and strength-deformation properties after compaction of two types of gravelly soils that has similar grain size distribution and particle shapes were compared based on the results of a comprehensive series of laboratory tests. The parent rocks of the tested soils are sandstone and andesite, respectively. While the values of maximum dry density and optimum water content of those gravelly soils obtained from the compaction test using a rammer were similar, there was a large difference in roller compaction behavior and strength-deformation properties. One of main factor affecting the engineering behaviors of gravelly soils are the difference of the plasticity of the fine fractions. Because the parent rocks of the tested materials are respectively identical, difference of the plasticity of the fine fractions are derived from the characteristics of those parent rocks. The results obtained in this study indicate that, therefore, the characteristics of mother rock have influence on the engineering behaviors of gravelly soil even if the fine fraction content is low. When the value of plasticity index of the fine fraction becomes smaller, the compaction efficiency and strength-deformation characteristics of the gravelly soil were improved.
This paper proposes an evaluation method for the spatial variability of the strength distribution derived from cone penetration test (CPT) results inside an earth-fill dam composed of mixed materials with different particle size distributions. The in-situ data from the studied site contain outlying data which can cause the mis-estimation of the statistical parameters. Therefore, the outliers should be separated from the original data. In order to reduce the effects of outliers in modeling the random field of the studied site, the N-values converted from the CPT results are divided into three groups, namely, high, middle, and low. The root mean squared error (RMSE) in the middle group is calculated from the residual error between the variogram values and the regression function and depends on the threshold values for separating the N-values into the three groups. The threshold values between the high and low groups are determined so that the RMSE is minimized. From among the many candidates of threshold values, a pair of values that corresponds to the minimum case of the RMSE is finally determined as the optimal case. The three groups are modeled and simulated through the use of a geostatistical method. By combining the simulated values of the three groups, the original spatial distribution of strength can be evaluated. To validate the proposed method, part of the data is intentionally removed from the measured data. The remaining data are applied to the simulation. The simulated value and the removed data are compared at the same location to verify the correlation between them. As a result, the random field was simulated reasonably. Thus, it has been verified that the proposed method can be used to reasonably simulate the distribution of in-situ strength including outliers.
In this study, the grouting material composed of silica micro-particles and fine calcium hydroxide was suggested and the effect of liquefaction countermeasure were investigated using this combined grouting material. First, the fundamental properties, the appropriate mix conditions and the permeation conditions of the grouting material were confirmed. In order to consider the strength change by curing time and permeation distance, unconfined compression tests were carried out. As a result, the unconfined compression strength has not decreased by one month curing but increased in the injection point by clogging of the grouting material. On the other hand, under appropriate permeation conditions, the grouting material was able to be permeated uniformly into a sand specimen. Finally, through cyclic consolidated undrained shear tests, it was revealed that the grouting material not only provided the specimens with high toughness but also improved the liquefaction strength and the reconsolidation characteristic.
A series of uniaxial tensile tests and Brazilian tests were conducted on six kinds of softrocks to study fundamental characteristics of uniaxial tensile strength. The sizes of the specimens were varied to study the influence of scale effect. Moreover, the orientations of specimens and loading directions were varied to study the influence of anisotropy. The test results demonstrated that the tensile strengths obtained by uniaxial tensile tests and Brazilian tests were comparable but may depend on the rock types. The scale effect was found insignificant for a small range of diameters of specimens, from 50mm to 200mm. Moreover, the anisotropic nature of tensile strengths was not significant for some kinds of softrocks.