There are some soil-structure sections of the Tokaido Shinkansen that, although mud pumping is not usually observed at these sections, require more frequent track maintenance work than other soil sections annually. The cause for this issue was not well understood yet, and therefore, the ground and the trackbed of the Tokaido Shinkansen civil-engineering structures were investigated to identify the soil related factors that might lead to locally frequent track maintenance work. As a result, such locations, when compared with other sections with a fair track state, were found to generally have thinner ballast layers or retain water in the track, in spite of minor difference observed in ground properties.
The deformation properties of soft ground caused by the embankment construction for widening the existing single railway embankment have not been understood in detail. In this study, therefore, a centrifuge model test was performed to grasp deformation properties of soft ground for such construction mentioned above. We established suitable model preparation techniques for centrifuge tests to realize real condition at site, such as stress path of soft ground below embankment and construction procedure of the widening embankment and so on. The experiments revealed that large horizontal and vertical deformation occurred around bottom edge of the existing embankment, which induced the uplift of ground surface in front of the widening embankment and subsidence of existing embankment at the crest. Furthermore, shaking table model tests were also performed after the complete consolidation of the soft ground. Large deformation of the soft ground around bottom edge and in front of the widening embankment was observed. Based on these tests results, new countermeasure using wall type improvement method in combination with cement-mixed gravely soil slab is proposed.
Even if no outstanding collapse factors are observed, a cut-slope face is considered to lose its stability over time after it goes into service, exposed to weathering and other factors. The burden of maintaining the cut-slope face can be reduced if measures such as making the slope gentler or carrying out slope protection works are taken, considering the effects of slope gradient and rock type on the long-term stability of the cut-slope face. On expressways, cut-slope observation and elastic wave exploration have been carried out continuously on 96 cut slopes, selected nationwide, since their construction. This paper evaluates some 40 years' worth of measured data taken at 16 cut-slope sites on the Tohoku Expressway to see the effects of different slope angles and rock types on the long-term stability of cut slope faces.
A procedure to evaluate earthquake induced residual displacement of the slope reinforced with ground anchors is proposed based on the results form relevant dynamic centrifuge model test. It was found from the analysis on the model test that seismic behavior of the slope reinforced with ground anchors is strongly affected by stepwise increase and loss of the mobilized tensile force of ground anchors. The authors proposed a procedure to evaluate residual displacement of the slope using Newmark method with considering change of the tensile force of the anchors, which are evaluated by nonlinear FEM analysis. The evaluated residual displacement of the slope showed reasonable agreement with the measured one in the model test because the change of the yield acceleration of the slope due to the change of the tensile force of the ground anchors can be considered in proposed analysis. As a result of the calculation on prototype scale slope using the proposed method, it is also confirmed that it is possible to reduce the amount of anchor reinforcement compared to the ones calculated from the conventional method based on the pseudo static limit equilibrium approach.
In this paper, in order to clarify the mechanical properties of lime-stabilized soil subjected to normal and over-consolidation histories, a series of laboratory tests at different mixture ratio of lime-stabilizer were carried out. The experiments involve isotropic consolidation test and consolidated undrained compression (CU) test. The following conclusions are obtained from this study: (1) Even if the lime-stabilized soil is in early curing period, its compressibility and swelling can be suppressed. 2) The shear strength of the stabilized soil increases according to the increase of mixture rate of lime-stabilizer. Its improvement effect of the soil appears remarkably in over-consolidation ratio. 3) During shear process, the lime- stabilized soil subjected to heavily over-consolidation histories is shown positive dilatancy and the soil subjected to normal-consolidation histories is exhibited negative dilatancy. Frictional resistance of soil particles of the lime-stabilized soil at the critical state becomes large gradually by increasing mixture ratio of lime-stabilizer. (4) The internal friction angle φ′ of lime-stabilized soil is not much affected by the amount of lime-stabilizer, and is within the range of 30 to 32 degree. In contrast, mixing much lime-stabilizer with soil, the apparent cohesion c′ increases higher.
In the design of ground anchors, it is considered that the pull-out resistance force of the anchor body is directly proportional to the length and outer diameter. However, since the frictional stress generated in the anchor body is not uniformly distributed, the pull-out resistance force is not directly proportional to the length, and the transmission length of frictional stress is limited. Further, since the anchor body itself is irregularly deformed by a change in load, it is conceivable that there may not be a linear relationship between the outer diameter of the anchor body and the pull-out resistance force. Here, we studied the relationship between the outer diameter of the anchor body and the pull-out resistance force with a pull-out experiment and tensile experiment in the field. Furthermore, we measured the strain of the anchor body due to the change in load, and considered the stress transmission length of the rock anchor and the mechanism of the pull-out resistance force of the anchor body.
To keep the seismic stability and durability of existing sheet pile quay walls, the method using geocell layer was proposed in this paper. Geocell layer filled with gravelly soil was located on the upper parts of the existing tie rods, and its end was fixed to the sheet pile. The factor of stabilization with the proposed method is the frictional resistance acting on the top and bottom interface of the geocell layer. In this study, a series of shaking table tests was performed to investigate the effects of the proposed method. As the results, it was confirmed that the seismic stability of the quay wall applied the proposed method became higher than that of the conventional sheet pile quay wall. The excess pore water pressure around the geocell layer dissipated rapidly during and after shaking because the permeability of the geocell layer was high compared with that of the backfill material. The frictional resistance acting on the geocell layer was not lost during shaking due to the rapid dissipation of the excess pore water pressure, which was assumed to be the reason for the improvement of the seismic stability of the sheet pile quay wall.
Urgent safety inspections of hazardous reservoirs have been conducted in Japan. The undrained cyclic triaxial test is used to evaluate the dynamic strength of embankment soils during earthquakes. In general, the initial static shear stress acts on the slope of an embankment. Furthermore, the embankment soil of a reservoir is subjected to various effects such as initial shear stress, seepage flow, deterioration, and cementation due to aging. Although it is important to consider these factors when evaluating the dynamic strength characteristics of embankment soils, these effects have not yet been examined in detail. This study used the undrained cyclic triaxial test to elucidate the effect of initial shear stress on the undrained cyclic behavior and strength characteristics of three types of embankment soils. In addition, cyclic triaxial tests were conducted under different confining stress conditions. The soil samples used were sand and silt with plastic or non-plastic fine fractions. The main conclusions of the study are as follows: 1) For an embankment soil consisting of non-plastic fine fractions, liquefaction occurred under isotropic confining stress conditions. 2) For all types of embankment soils, liquefaction did not occur under initial shear stress conditions and the effective stress path reached a steady state. 3) The cyclic shear strength of embankment soils slightly increased with increasing confining stress. 4) The fine fraction content is an important parameter for evaluating the cyclic shear strength characteristics of embankment soils subjected to initial shear stress.
The existence of a fault fracture zone closely related to lineament is known as one of the topographical conditions. The existence is recognized as an important factor for collapsing phenomenon to induce an elevation of higher groundwater level. However, the quantitative relation between the location of faults and the rise of groundwater level is not fully investigated. So, an in-situ investigation for groundwater level measurement was performed over six years at three places of debris flow generated and dangerous mountain streams with faults. From the measurement data, the characteristic of the groundwater level fluctuation subjected to the influence of faults was examined. The obtained data gave quantitatively the elevating amount and section of the groundwater level affected by existence of faults. Moreover, it was found clearly that the fluctuation of the groundwater level was differed at upper or lower section of faults.