Recently the introduction of performance-based design into infrastructure including pile foundation is on process. For performance-based design, it is necessary to forecast the long-term displacements of pile foundation in advance. However, because of the difficulty to clarify the influence of pile-soil-pile system to the long-term displacements, there are few examples to focus group-effect on the long-term displacements in pile foundation. In this paper, a series of numerical analyses are conducted in order to clarify group-effect on the long-term displacement, especially the influence of pile-spacing on the long-term behavior of pile foundation. As the conclusion, following aspects are clarified; 1) Larger amount of settlement occurs when the pile-spacing decreases, caused by the decreasing of frictional forces and the emphasis of the stress transmitted by pile-tip.; 2) When the piles are set in narrow intervals, the deformation of soil elements around inner pile is restrained by other piles around. The behavior follows the settlement of piles around, so that inner pile cannot obtain enough frictional force. As the result, the load allotted to inner pile decreases and at the same time the extra load which is assumed to be allotted to inner pile is re-allotted to outer pile. 3) Larger amount of excess pore water pressure occurs around the tip of inner pile and it remains longer than others around.

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In the present paper, in order to study effects of the dry density of specimen and the drainage conditions on the shear characteristics of sandy gravels in river embankments, various series of large triaxial test were performed using the original grain sandy gravels. The small size triaxial tests using the graded grain soils were also performed to compare the results of the large size triaxial tests using the original grain soils. From the results of the above tests, in the case of the high dry density of specimen, Φd obtained by CD tests is similar to Φ’ by CU test. However, in the case of low dry density of specimens, there is big difference between Φd and Φ’. From the comparison of the results between the large and small size triaxial tests using the same dry density specimens, the shear behavior of graded grain sandy gravel observed by the small size triaxial test has shown the dense tendency. In order to evaluate the shear properties of the original grain soil using by the conventional small size triaxial test, the effective mechanical stabilization method is proposed, which is replacing large grain gravels with small grain gravels.

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Compacted bentonite is planned for use as a buffer material in the geological disposal of the high-level radioactive waste. In this paper, in order to study the failure behavior of the compacted bentonite, a series of constant volume direct shear tests were performed. Developed shear bands were observed during the direct shearing using the PIV image analysis. Also, inside of the specimens were observed by using μ-focus X-ray CT scanner. Even though the process of shear bands formation in the unsaturated over-consolidated specimen was different from the process in unsaturated normally consolidated specimen, the low density region due to the shear failure was hardly observed in the center of both specimens under the relative high vertical stress condition. In the case of saturated specimens, there was no change of density at the shear band, and also, it has been confirmed that sealing performance does not change after development of shear bands.

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Local subsides or cave-in’s of the ground often occur in urban area. The complicated underground situation as well as the necessity of urgent restoration do not usually allow full investigation for the real cause. The detailed mechanism of the phenomenon has not been, therefore, well understood.
Cave-in is usually initiated by the formation of cavity in the ground due to soil loss. When the location of the cavity is deep in the ground, the detection of the cavity is not easy. Then it is possible that the hidden cavity expands for a long time to eventually cause sudden large-scale collapse. In this study, characteristics of formation/expansion of cavity and surrounding ground loosening are investigated, aiming at effectively indicating dangerous pattern of cavity and loosening.

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Granulation technique is a method which converts soft cohesive soils into high-strength particles. This is one of the soil improvement measures to make efficient use of soft dredged soils. Unimproved soft cohesive soils generally require long consolidation periods and have low shear strength, while granular treated soils have opposite characteristics. Based on this background, the authors initiated a project to spread the application fields for granular treated soils. This paper reports on the applicability of granular treated soil as backfill material for caisson-type quay walls. A series of centrifuge model tests was performed to investigate the dynamic characteristics of granular treated soil as quay-wall backfill material. The results showed that quay walls backfilled with granular treated soil had high earthquake resistance.

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In order to evaluate effects of spatial variability of ground improvement on the seismic behavior of improved ground, a series of shaking table tests in 1g gravitational field has been carried out through investigating the seismic behavior of partially improved ground. Following conclusions were obtained: (1) The increase in excess pore water pressure was restrained by the existence of improved element around un-improved element. From the test result in this study, it is suggested that the excess pore water pressure in un-improved area can be greatly reduced as long as 60% of ground is rightly improved enough not to cause liquefaction. (2) Average vertical ground displacement after seismic loading can be greatly reduced, which suggested that partial existence of un-improved area in improved ground is allowable for practical liquefaction countermeasure. (3) An additional effect for reducing ground settlement by the improved element is considered based on the percolation theory.

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Many old foundations, which required to be retrofitted because of poor in seismic performance, are still in service. Seismic performance of exist foundation can be improved by installing sheet-piles around footing and connecting together. Basing on this idea, authors proposed new seismic retrofitting method. This paper describes about seismic proving tests, both lateral loading tests and shaking table tests, to clarify the improvement effects on the seismic performance of the pile foundation utilizing the proposed method. Basing on the test results, in addition, the mechanism for improvement is discussed. Following outcomes were found. (1) Reduction in section force of exist pile is confirmed by the proposed method. This improvement is seen not only pile cap, but also the section deeper than sheet-pile depth. (2) Sub grade reaction of exist piles may be reduced because lateral resistance of the foundation mainly shared by additional sheet-piles instead of piles.

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Multi depth pore water pressure in-situ measurement has been carried out in the Kansai international airport second phase island. MP(Multi-level Groundwater monitoring) system was installed in this site in order to observe the behavior of the upper diluvial clay (Osaka bay marine clay Ma12), which was one of the most significant clayey layers in this site due to the thickness of deposits and the large volume of landfill. This system consists of casing, packer, measuring ports and measuring prove, a pore water pressure can be measured as well as a settlement of the port. The construction of the second phase island was started in 1999, the in-situ measurement was installed in 2005. A comparative study of in-situ measurement and elasto-plastic numerical simulation employing “SYS Cam-clay model” with soil-water coupled analysis was mainly discussed in this study.
An elasto-plastic parameter for Ma13, MaDtc and Ma12, which was one of the dominating consolidated layers, was determined referring the results of laboratory tests. A comparison in-situ measurement and numerical simulation considering the landfill construction history, was carried out focusing on the pore water pressure and settlement behavior. A large settlement beyond the pre-consolidated pressure could be described as a loss of soil structure in this model. A comparison exhibited a good agreement, and an accuracy of the second phase island behavior estimated by numerical simulation was verified.

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The landslide which occurred in an expressway constructing site was turned out to be a large scale landslide with around 2.8 million cubic meters by the results of the detailed research. The ground anchors constructed as the countermeasures against this large landslide were the largest scale anchors in Japan in both length and numbers. The most important technical subject of this longer anchor was that anchor load was decreased by friction loss between sheath and tendon in the free anchor length, and that deterrent effect of anchors might not be expected. To recognize directly the friction loss in free anchor length, we carried out the test which was performed by multi-cycle loading with strain gages on tendon. As the results, we confirmed that friction loss was larger than calculated by the general empirical formula. In real works, we confirmed effects that the friction loss in free anchor length was decreased by multi-cycle loading before fixing.

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The rigid frame viaduct is used for railway structures. But it is sometimes problematic on the train-running safety in the seismic conditions because of the differential displacement with adjacent structure by its low horizontal stiffness. The batter pile is one of the measures to gain the horizontal stiffness of the viaduct and expected to secure the train-running safety. But it has not been used recently for the railway and there are many unknown matters such as characteristics of lateral resistance in the case of earthquake. In this study we clarified the characteristics of lateral resistance of batter pile based on the static and dynamic non-liner analyses and experiments. And we studied its applicability for the railway structure. We studied the relatively acute-angled batter pile and found that it can control the horizontal displacement of structures and shorten the equivalent natural period even for the batter piles with the angle of approximately 5 degrees. Furthermore, it can also have not only seismic but also economical advantage in the case that train-running safety becomes the decisive factor of the structure’s specifications.

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The present study examines the failure mechanism of shallow foundations rested on deep mixing stabilization soils to discuss the applicability of the deep mixing soil underneath highway bridge shallow foundations. Highway bridge shallow foundations undergo cyclic vertical loads because of traffic and frequent-scale earthquakes during the service life of bridge. In addition, they are subjected to severe cyclic overturning moments during rare-scale earthquakes because of “top-heavy” superstructures and they are also required to be workable even after such a strong earthquake. The present paper first shows the fatigue load test result for cement-treated soil specimens and proposes the allowable compressive stress criteria for service conditions and frequent-scale earthquake conditions. Second, the present papers shows the centrifuge load test result of pier-shallow foundation systems rested on deep mixing stabilization soils. The deep mixing soils were arranged in the two ways as follows: block type and contact column type. Monotonic vertical loads, lateral loads, and cyclic lateral loads with a constant vertical load were separately applied to the top of the pier. Although the behavior of both deep mixing stabilization soil types were similar to each other when the deep mixing stabilization soil was subjected to a vertical stress smaller than the proposed allowable stress, the failure mechanism was totally different against larger loads. The contact column type cement-treated soils subjected to cyclic overturning moments showed the remarkable residual settlement and rotation after they reached the peak strength.

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Spatial distribution of different properties of grains and density of soils would cause the local unsaturated flow in the ground. In case that heterogeneous flow was caused in cover soil layer on the landfill closed, chemical stabilization of waste layer should be also valuable spatially; besides retardated. To the issues of the case, non-woven geotextile (NWG) with water dispersivity could be used in the cover layer to regulate the local unsaturated flow and then, it was expected that the spatial variation of the chemical stabilization would be reduced in the waste layer. The objective of this research was to clarify the generation mechanism of local unsaturated flow and evaluate the water dispersivity of non-woven geotextile in the ground. In this paper, the grain and density property of soils was focused as the condition of infiltration test due to model raining and then, the model infiltration test and numerical analysis with respect to the unsaturated flow using finite element method (FEM). As the results, the local unsaturated flow was generated in the ground with less uniformity coefficient; however, the NWG cut the local path of water flow and water dispersed in the NWG. Eventually, NWG reduced the variation of permeation.

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The long-term mechanical property of cement-treated sands by the cement stabilization has not been investigated and cleared enough. To leverage cement-treated ground as structural foundation ground in a positive way, there is a need to understand the long-term mechanical property of cement-treated ground. This study is related to the evaluation method concerning about the long-term mechanical property of cement-treated sands by the cement stabilization. The unconfined compression tests were performed on the cement-treated sands which aged about 10 years. And the method of predicting unconfined compression strength ‘q_u’ of aging cement-treated sands was proposed by using the relation between the ‘q_u’ and the stabilizing material-to-water ratio based on test results in short-term. The hollow cylindrical torsional shear tests were performed under drainage conditions to specimen which cured by about ten years. The results show that its shear strength and residual strength are related with its unconfined compression strength ‘q_u’, which is shown as the failure criterion of the power function type. Finally, we propose the evaluation method of shear strength and residual strength of aging cement-treated sands using the failure criterion of the power function type and the method of predicting ‘q_u’.

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Local subsides or cave-in’s in the road often occur in urban areas. The complicated underground situation as well as the necessity of urgent road restoration does not usually allow full investigation for the real cause. The detailed mechanism of the phenomenon has not been, therefore, well understood. On the other hand, in many cases, the loss of soil through the defects of old sewage pipes is thought to be one of the most important factors. In order to understand the possible influence of old/damaged buried pipes on the surrounding backfill, a survey on cave-in’s in the road and sewer pipes under the location was conducted in seven cities. In this paper, some typical patterns of pipe defects found in the survey are reported and the potential properties of pipes and surrounding soil causing a cave-in are discussed. Furthermore, in order to understand the mechanism and governing factors of cavity formation/expansion in the ground, a series of model tests simulating flowout of soil through a crack/gap in a damaged sewer pipe was conducted. It was found that a cavity and surrounding loosening in the ground can extend rapidly upward when the ground consists of poorly graded sand, especially when it is fully saturated. Quantitative evaluation was also given to the loosening around a cavity.

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The tube penetration speed, the effect of sample disturbance on cone penetration prior to tube sampling and applicability of the cone sampler for highly organic and clayey soils are examined through unconfined compression tests, triaxial compression tests under unconsolidated undrained conditions and incremental loading oedometer test for samples obtained from various type of samplers. The penetration distance of the cone sampler does not affect the sample quality within the tube. The quality of samples obtained from the cone sampler was similar to those of other Japanese samplers. The cone sampler can be used as the technique classified Category A in Eurocode 7, CEN/TC341.

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Penetration resistance results of the Swedish weight sounding test are known to vary at housing sites where demolition waste or crushable soft rock is mixed. This study investigated a housing site at a coastal area reclaimed using well-graded gravelly soil. To estimate the liquefaction characteristics and the applicability of existing methods for predicting liquefaction at housing sites with gravelly soils, in-situ investigations and laboratory tests were conducted. Results revealed that the penetration resistance increased concomitantly with gravel content, but the liquefaction strength increased only slightly. Based on the study results, an investigation method was demonstrated, as described herein.

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A suite of undrained cyclic triaxial tests was performed to clarify the effects of calcium carbonate precipitation on liquefaction resistance of sand. For the tests Toyoura sand was utilized with relative density of ca.50%. Two kinds of soil samples were prepared by mixing 1-3 wt.% precipitated calcium carbonate into Toyoura sand, and the difference of liquefaction resistances evolved under the two different initial conditions was examined. Triaxial tests results and the corresponding examinations elucidate that 1) liquefaction resistances of calcium carbonated precipitated sand increase with increase of the amount of the mineral precipitated (at maximum threefold), 2) the augmentation may be attributed mainly to improvement of deformation characteristics due to intergranular cohesion evolved by the mineral precipitation, and 3) the liquefaction resistance can be evaluated via a simple relation between normalized shear modulus and liquefaction resistance of bare sand.

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A series of stability analyses of soil slopes were conducted by means of limit equilibrium method to clarify the three-dimensional effects of slope shape on the slope stability and the critical sliding surface. In this paper, slopes consisting of frictionless soil were considered; the slopes have a corner, and their toe and shoulder lines run straight from the corner and are parallel each other. In the analyses two potential sliding directions were considered; one is the direction of symmetry through the corner, and the other is the perpendicular direction to the formation of side linear slope. The stability of the slopes was evaluated in those two potential sliding directions. Through the analytical investigation some important features of three-dimensional slope stability were found. If the slope slides in the slope symmetry direction, the critical sliding width is determined depending on the corner angle. In addition, the critical stability factor and the corresponding maximum shape of sliding surface are also obtained as a function of the corner angle. It was also found that the critical sliding direction varies depending on the slope angle, corner angle and possible sliding width; thus when evaluating the stability of cornered slopes, we must consider the slope stability in both sliding directions.

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