Earth pressures acting on, and deformation of, buried pipes installed in sloping-sided ditches were investigated through 24 centrifuge model tests using 1/30-scale 2-D models. The models were placed in a centrifugal acceleration field of 30 G, and a load equivalent to a design load due to several 25-ton vehicles was applied at the center of the ground surface by means of a strip loading plate. The test results fully quantified the effects of the following investigated factors, on the mechanical behavior of the buried pipes: inclination of ditch wall, roughness of ditch wall, cover height, type of backfill soil, and flexibility of pipe. The test results, measured before the surface loading and during the surface loading, were compared with results predicted in accordance with current design standards. The comparison revealed that the current design standards do not reflect the actual behavior of the buried pipes and tend to underestimate the safety of the pipes in most cases, leading to a conclusion that a new design method for the buried pipes is needed instead of the problematical current design standards.

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Rapid development of a reasonable liquefaction countermeasure for flume channels has been required for the following reasons: 1) several large earthquakes are predicted to occur throughout Japan in the near future; 2) severe damage to flume channels built in liquefiable ground is predicted as a result; 3) flume channels supplying drinking water is an important as lifeline facilities after earthquakes; and 4) tremendous amounts of money would be required to apply the countermeasures in popular use (such as those to prevent liquefaction) to the whole length of long flume channels. Therefore, the authors conducted a study on the application of a countermeasure using sheet-pile with drain to flume channels with the aim of reducing the influence of liquefaction on such structures while satisfying their performance requirements. In this study, the effectiveness of the proposed countermeasure to flume channels was initially confirmed through a series of shaking table tests (1G). This paper describes the details of the experiment and the applicability of the countermeasure to the flume structure as well as the background to this study grounded on performance-based design (PBD) concept.

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This paper describes the strength-deformation characteristics and internal structures of cement-stabilized soils mixed with bassanite and coal ash. The unconfined compressive strength of cement-stabilized soil with coal ash increases with increasing bassanite addition ratio. Based on the observation of internal structure using a scanning electron microscope (SEM), ettringite occurrence is related to the strength increase of cement-stabilized soil. Well-developed ettringite could be seen in the case of higher bassanite and higher coal ash addition ratios.

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During the Niigataken Chuetsu-oki earthquake, rather large settlemens of the backfill ground around the rigid and stable buildings were observed. In this study, two cases of centrifuge tests were conducted to reproduce the similar type of the settlements in order to examine the mechanism of the settlements. The results from those tests indicate that the settlements were suddenly increased when the backfill ground was apart from the rigid wall modeling the rigid and stable buildings, namely a sliding failure in an active state was occurred in the backfill ground near the structure. Further, these settlements were well simulated by using the elasto-plastic finite deformation FE analysis.

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This paper presents the newly developed realtime rain gauge and its application to the numerical simulations for slope stability problems. The newly developed realtime rain gauge uses the ultrasonic revel meter and can measure the torrential rainfall so called guerrilla-like rainfall with good accuracy comparing with the conventional tipping-bucket rain gauge. The measured realtime rainfall data can be used to the numerical simulations as rain intensity along the rainfall boundary. The numerical simulation results clearly show that the rapid and drastic change of the matric suction and water content around the ground surface can not be evaluated accurately by conventional method using rainfall per hour as rain intensity. Hence, the realtime measurement of rainfall is required to evaluate the impacts of the torrential rainfall on the mechanisms for rainwater infiltration into the slopes and rainfall-induced slope instability/failure correctly.

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Bio-cover soil is a capping soil applying bio-grout for landfill. Bio-grout can be produced with the materials, which can provide materials such as calcium ion and CO₂ due to microbe metabolism in the landfill and then, CaCO₃ would be precipitated in the cover soil. Bio-cover soil has lower hydraulic conductivity and greater strength than untreated capping soil. In this study, the valuable pH of leachate and organic nutrition in the landfill were focused; eventually, it was concluded that soil or solvent to produce the bio-grout should have great buffer ability and if the organic-nutrition molecular had the simple molecular structure, the chemical reaction should be finalized in 24 hours. Besides, unconfined compression stress of bio-cover soil had twenty times greater and hydraulic conductivity was at least one-tenth less than each of the untreated-cover soil.

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Soil skeleton structural concept is important for examining the mechanical characteristics of naturally deposited clay, and the laboratory test for remolded sample is necessary to describe the action of the soil skeleton structure quantitatively and qualitatively. In this study, the effects of water contents on compression curves in remolded samples are discussed, and the main conclusions obtained are as follows. (1) The sample remolded in lower water content than the liquid limit shows behavior like overconsolidated soil, because the sample is hard and needs big power for remolding. (2) The sample remolded in higher water content than the liquid limit shows behavior like bulky soil that remains its structure. (3) The most suitable water content for making remolded sample is the liquid limit in which the soil skeleton structure is lost completely.

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In order to evaluate the safety of residential areas on artificial fill for a landslide triggered by earthquakes, delineating geological features, such as thickness and stiffness of the fill, is very important. It is also well-known that seismic amplification characteristics of artificial fill are influenced by fill thickness, its resistance to shear, and its contrast with the underlying bedrock. This paper demonstrates a geographical analysis of artificial fill in terms of a Swedish weighted sounding test and a surface-wave method at residential area in Sendai City. A 3D representation of artificial fill estimated from the soundings and the surface-wave method is compared with old topographic maps and reliability and resolution are discussed.

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Slope failure/collapse due to heavy rain occurs frequently and causes serious damages and losses of infrastructures. For the slope stability analysis, porewater pressure and its distribution along the potential sliding planes as well as their time evolution will be the most sensitive and important factors. To evaluate the porewater pressure distribution properly, a new technique combining the tank model and saturated-unsaturated flow simulations was proposed in this paper. Using this technique, the field condition can be represented more realistic by adjusting time-dependent hydraulic head boundary conditions as well as the infiltration of the rain water. The tank model was applied at both sides of modeling area to predict groundwater level variations due to rainfall intensity pulse. The groundwater level was derived from the components affecting water entering and leaving the system. The numerical flow simulations were carried out to estimate groundwater level within the modeling area controlled by physical characteristics of the system such as unsaturated soil properties. This proposed method was also implemented into the real field slope stability problem in Japan. Verification was carried out by comparing estimated groundwater level with a set of observed data. The flow simulation results show a good agreement with the observed ones.

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Static and dynamic centrifuge model tests, conducted to investigate mechanical behavior of buried pipes installed in sloping-sided ditches, revealed that the safety of the pipe is critical under vehicle loading applied in the static tests rather than seismic loading applied in the dynamic tests. The static tests were analyzed by using FEM, in which the soil and pipe were assumed to be linear elastic. Small frictional resistance was allowed at the interface between the pipe and the soil by introducing joint elements. Separation, slip failure, and frictional resistance were also allowed at ditch walls by introducing similar joint elements. The analysis generated results that conformed well to the test results, while the current design standards tend to underestimate the safety of the pipes. Thus, design charts for predicting the vertical deflections and the maximum bending moments of the pipes that are buried in sloping-sided ditches with different inclinations of the ditch walls were constructed by using the FEM. A thorough examination showed that the charts can be applied reasonably to any pipe (regardless of different weights, dimensions and materials), any backfill soil (regardless of different soil types, elastic coefficients and weights), and any cover height, leading to the conclusion that the charts can be used instead of the problematical current design methods.

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The case record is reported, each in which the landslide took place along the fissured zone of Osaka soft rock group in the residential land development area at Sakai city of Osaka. A series of investigation including in-situ and laboratory direct shear tests, the analysis of diatom content etc. was carried out in order to examine the failure mechanism by considering the geological background. It was manifested that i) the basic properties were significantly different between the marine clay and the fresh-water formed clay, ii) the shear strength of marine clay was smaller than that of the fresh-water formed clay, iii) the fissured zone in the marine clay is likely to be formed, and iv) the shear strength of the fissured clay subjected to cyclic shear in direct shear box test was close to the back-analyzed shear strength of the slope.

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Groundwater contamination by organoarsenic compounds in Kamisu City, Ibaraki Prefecture was examined based on the findings of field investigations. The field investigations revealed that the primary contaminant, diphenylarsinic acid (DPAA), was mainly detected in the deep layer of the aquifer in the study area. However, the subsequent discovery of buried, concrete-like blocks just below the ground surface 90 m southeast of the well where the contamination was first detected, revealed that the blocks had remarkably higher DPAA concentrations than was observed deep within the aquifer. These blocks were thought to the most probable source of the well contamination. Moreover, the groundwater contamination has spread about 3 km downstream from the contaminant source.

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Although there has been an increase in the number of slope disasters occurring along roads every year, there have been reports of slope disasters occurring in many places along roads that were judged as safe as a result of preventive measures carried out in 1996, 2001, and 2006. Further, considering the recent increase in the amount of local rainfall, it has become crucial to assess the risk of slope failure by taking into account the effects of rainfall on slope failure. In this study, our objective is to assess the risk of slope failure by taking into account rainfall characteristics and each slope feature along expressways. We attempt to achieve this by using a qualification theory. The factors contributing to slope failure are determined for every cut slope and natural slope. Then, on the basis of heavy rainfall data of 2004, the Soil Water Index for grids of 2.5 km each are calculated. The contributing factors and the Soil Water Index are analyzed by using a qualification theory, and the areas at risk of slope failure are determined. As a result of this approach, i.e., the classification accuracy to extract the unstable slops in natural slopes has risen compared with classification accuracy by using only slope features.

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The new mechanical joint of the small size pipe piles applied to the foundation of residential structures was proposed. Investigating the strength of the mechanical joint, loading tests (compression test and torsion test) and FEM analysis were carried out. As a result of these investigations, the mechanical joint has grater compression and torsion strength than that of required value. In consequence, it is confirmed that the proposed joint satisfy the required performance as a major conclusion.

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