This paper outlines a mathematical description of the stress dilatancy behaviour of granular materials which accounts for stress level and void ratio dependencies. The consideration of these aspects has important implications in the modelling of granular material behaviour. In fact, granular material mechanical response is largely dominated by the evolution of dilatancy, fabric and void ratio histories. The starting point in this study is the well established Rowe's theory which is revisited and ultimately modified by introducing a factor linked to governing state parameters in order to describe the complete behaviour of granular materials during deformation. Numerical simulations of triaxial tests on granular materials at different void ratios and stress levels are herein presented to illustrate the model.

抄録全体を表示

Static characteristics of two different structured InAlGaAs/InAlAs superlattice avalanche photodiodes (SLAPDs) cooled by liquid nitrogen were evaluated at a wavelength of 1. μm. The dark current of the SLAPD having a thick superlattice layer of 0.504 μm was ×10^-13 A. This was successively reduced by four orders of magnitude compared to that of the thin layer SLAPD of 0.231 μm at a breakdown voltage of around 20 V. The thickened layer was effective in suppressing tunneling dark current. An output current of 1.7×10^-12 A at a bias voltage of 15 V was measured for an optical input with a wavelength of 1. μm and a signal power of 1×10^-12 W. This showed a sharp distinction from the dark current.

抄録全体を表示

This paper reports deformation and strength characteristics for a geogrid-reinforced granular soil on a large-scale plane strain compression apparatus. The influence of intensity and types of geogrid reinforcement is specifically discussed. It was found that as more reinforcement layers are used, the strength of the reinforced soil increased. In cases where reinforcement is most intensely used, the reinforcement layers in the samples were eventually subject to breakage due to plane strain compression and the reinforced soil failed. In cases where reinforcement is less intensely used, the reinforced soil reached failure without any sign of reinforcement breakage. It was also found that types of reinforcement have a significant influence on the lateral deformation of the reinforced soil, where stiffer reinforcement provides more constraints on lateral deformation of the reinforced soil. It can be superceded, however, by the influence of reinforcement intensity. The small stain measurement by means of LDT observed that the stiffness of non-reinforced soil begins to decrease more rapidly at a strain level of 0.05∼0.15%, compared to the reinforced soil. The experimental results also indicate that the relationship between the apparent angle of internal friction and the geometry of the structure of the reinforced granular soil seems to exist for the geogrid reinforcement used in the tests reported in this paper.

抄録全体を表示

A new analytical method is proposed for determining the inextensible grid reinforcement pullout resistance and pullout force/pullout displacement curve by using basic backfill soil and grid reinforcement properties. The pullout skin friction resistance/pullout displacement relationship is simulated by linear elastic-perfectly plastic model. A hyperbolic model has been proposed to represent the pullout bearing resistance/pullout displacement relationship in which the maximum bearing resistance of a single bearing member is determined using a new bearing capacity equation proposed in this paper. The influences of the grid bearing member spacing ratio, S/, the bearing member deflection rigidity, and the pullout softening behavior on the mobilization of pullout bearing resistance are explicitly included in the proposed model. Good agreement has been obtained between calculated values and laboratory test results.

抄録全体を表示

The use of Paracoccus carotinifaciens-derived natural astaxanthin as an alternative to synthetic astaxanthin has attracted considerable attention from the aquaculture industry. Furthermore, to enhance the bioavailability of astaxanthin, its “Z-isomerization” has been actively studied in recent years. This study investigated the effects of feeding a diet containing astaxanthin rich in the all-

- or Z-isomers derived from P. carotinifaciens on the pigmentation and astaxanthin concentration in rainbow trout (Oncorhynchus mykiss) flesh. Z-Isomer-rich astaxanthin was prepared from the P. carotinifaciens-derived all--isomer by thermal treatment in fish oil, and the prepared all--isomer-rich astaxanthin diet (-AST-; total Z-isomerratio = .1%) and Z-isomer-rich astaxanthin diet (Z-AST-; total Z-isomer ratio of astaxanthin = 56.%) were fed to rainbow trout for 8 weeks. The feeding of Z-AST- resulted in greater pigmentation and astaxanthin accumulation efficiency in the flesh than those fed -AST-. Specifically, when -AST- was fed to rainbow trout, the SalmoFan score and astaxanthin concentration of the flesh were .1±1.4 and 1.36±0.71 μg/g wet weight, respectively, whereas when Z-AST- was fed, their values were 26.0±2. and .33±1. μg/g wet weight, respectively. These results suggest that P. carotinifaciens-derived astaxanthin Z- isomers prepared by thermal isomerization are more bioavailable to rainbow trout than the all--isomer.

抄録全体を表示

In this study the field feasibility of an innovative thermal technique to improve the performance of prefabricated vertical drains (PVD) used in conjunction with the preloading ground improvement method is investigated. For this purpose, two identical .0 m high full-scale test embankments for preloading were constructed over the soft Bangkok clay where a conventional PVD system was installed underneath one embankment and a novel prefabricated vertical thermo-drain (PVTD) system was utilized for the other. The PVTD unit consists of a U-tube made of cross-linked polyethylene plastic (PEX) that is attached to a conventional PVD unit. Preheated water at about 90°C is circulated through the attached U-tube to raise the soil temperature underneath the PVTD embankment. The behavior of the two test embankments were compared in terms of excess pore water pressure and consolidation results. The comparison shows the advantage of a PVTD system over a conventional PVD system. The rate of consolidation increases significantly in the PVTD system due to the temperature effect on the hydraulic conductivity. Moreover, the embankment with the PVTD system generates more settlement due to the thermally induced irreversible contraction of saturated normally consolidated soft Bangkok clay.

抄録全体を表示

An empirical equation in use for estimating the pseudo-elastic shear modulus, G_f, of subsoil, associated with shear strains less than 0.001% is proposed in this paper. In a series of in-situ seismic cone tests performed nationwide, the profiles of both G_f and the in-situ void ratio, , with depth were successfully characterised at five sites, each comprising a soft clay layer deposited in the Holocene era. The database which comprised the original data from the field and laboratory tests, coupled with similar information on well-documented Holocene clay deposits in Europe, was statistically analyzed in attempts to determine a generalised relationship with which G_f of soft clay may be reasonably estimated only from routinely available borehole data; that is and the current geostatic effective overburden pressure, σ'_v. An empirical relationship, G_f=, 000 -√(σ'_v) (kPa), was derived from the statistical analysis applied to data from seven different clays worldwide, for which extended over a range between 1 and , and the overconsolidation ratio ranged roughly between 1 and 2. The applicability of the proposed relationship was evaluated for two case records, each in which the clay exhibited unusual behavior; i.., the undrained shear strength remained more or less constant with depth due to the existence of artesian pressure at one site, and, at the other, G_f decreased, whereas increased, with depth. It was demonstrated that even in these clay deposits exhibiting exceptional profiles, the proposed relationship was capable of predicting G_f with a reasonable accuracy by determining the profiles of and σ'_v with depth. In addition, the prediction when compared to G_max from carefully performed laboratory cyclic tests, yielded a better estimate of G_f from the in-situ seismic survey. Despite the fact that the empirical relationship was initially designated to estimate G_f of soft clays, it may be equally applicable to sandy deposits. This was verified by comparing it to similar, and well-established, relationships developed for sands. A case record as such is also described for a loose sand deposit at Higashi-Ohgishima in Tokyo Bay which was placed in 1960's by land reclamation.

抄録全体を表示

A simple method based on theoretical and experimental considerations is presented to predict the pile end bearing capacity and load-settlement curve in sands in relation to soil compressibility. The key to the method is in the assumption of a failure mode with a spherical cavity expansion pressure given as a function of the soil compressibility, shear stiffness and friction angle. The practical prediction of pile end-bearing capacity in sandy ground is discussed in terms of a compressibility factor, friction angle and shear stiffness. Further, the pile tip settlement behaviour is also discussed based on an empirical model incorporating the pile end bearing capacity from a cavity expansion analysis with a Kondner type hyperbolic function. The applicability of the proposed method is verified by comparing the predicted results with the results from a series of model pile load tests and a database for in-situ pile load tests in sands.

抄録全体を表示

Some existing analytical methods which have been used in geotechnical engineering are modified to handle the shear strength reduction with time due to softening in fissured, over-consolidated clays and mudstones. These are limit equilibrium analysis of slope stability, calculation of earth pressure and calculation of stress and displacement around a tunnel. The softening effect is incorporated in these analyses using the failure criterion and the time-dependent strength parameters proposed previously by the authors. Examples are presented which emphasize the importance of appreciating the softening effect in analyses and further illustrate that the effect of shear strength reduction with time due to softening could easily be captured with existing analytical methods.

抄録全体を表示

The paper analyses the mechanical behaviour of a silty sand, as it was measured in laboratory tests on samples prepared with different density and moisture contents. After a description of the physical characteristics of the material, the methods used to prepare compacted and slurry-consolidated soil samples are reported, followed by a description of the apparatus and experimental procedures adopted. The compressibility characteristics were analysed by isotropic tests at ordinary stress levels (p'<1 MPa) and by oedometer tests at stress levels up to 40 MPa. The shear behaviour was investigated by means of triaxial compression tests following conventional undrained or drained paths with variable directions ; also, the initial shear stiffness was measured by resonant column tests. The basic behaviour of the slurry-consolidated silty sand appeared consistent with the theoretical framework of Critical State Soil Mechanics ; this soil could therefore be used as a reference material to which the mechanical properties of the compacted samples were compared throughout the paper. Two volumetric state loci were taken as reference curves to investigate the behaviour of the compacted material : (i) the isotropic compression line of the remoulded soil, and (ii) the critical state line, which proved to be independent of the soil preparation procedure. Whatever the preparation technique, the mechanical behaviour of the silty sand under triaxial compression was found to be stress-path dependent from the very beginning of the stress-strain curve. The net effect of the compaction could be assessed by comparing the stress-strain behaviour of dynamically compacted soil to that of remoulded material brought to comparable density through a mechanical overconsolidation process. The stress-strain behaviour of the compacted silty sand proved to be more fragile and showed lower initial stiffness than the remoulded soil. It was therefore observed that, even though the compaction may be considerably beneficial to compression behaviour, it does not necessarily optimise the stress-strain response under shear loads.

抄録全体を表示

In Osaka Bay of Japan, a number of large-scale reclamations have been executed. The settlement due to those reclamations has been serious enough to provoke investigation. The compression of the stiff Pleistocene clay deposits has caused the half of this settlement, and it makes the quality control of the reclaimed lands very difficult. According to the geological history, the Pleistocene clays in Osaka Bay are thought to be normally consolidated aged clays that exhibit seemingly overconsolidated behavior due to the nature of quasi-overconsolidation. This makes the problem of settlement more complex. In this paper, characteristics of the long-term settlement of the reclaimed islands in Osaka Port are discussed based on the in-situ measured data. Long-term compression is found to occur even in the deeper Pleistocene clay layers, stress conditions of which remain close to or less than p_c. Discussion is extended to the applicability of conventional procedure in terms of elasto-viscoplastic finite element method to the long-term settlement measured in the Maishima Reclaimed Island in Osaka Port. The conventional procedure to assess the settlement is found to function well for normally consolidated clays, however, serious limitation exists for describing the timedependent behavior of the Pleistocene clays, in which stress states remain close to or less than p_c. A series of long-term consolidation tests is done to assess the property of the quasi-overconsolidated Pleistocene clays. Laboratory experimental results also provide remarkable time-dependent behavior even in the region less than p_c. It is found that the rational modeling for compression in the region of close to and less than p_c is indispensable to describe the actual time-dependent behavior of the quasi-overconsolidated Pleistocene clays in Osaka Bay.

抄録全体を表示

The elasto-plastic finite element method based on the modified Cam-clay theory was used in numerical experiments to investigate the settlement behavior of an improved ground where vertical drains had been installed in a portion of the ground area. The numerical experiments were performed taking into account the effect of changes in the loading width and the width of the area improved by vertical drains. As a result, the authors have clarified the following facts : the rate of settlement of a ground which is partially improved by installation of vertical drains lags behind the rate predicted by design theory ; the degree of lag becomes more noticeable in the areas closer to the edges' of the improved area and in the later stage of consolidation due to the influence of the adjacent non-improved area. In order for any ground improvement work to be completely effective within a limited period of time, it is necessary to install drains over an area somewhat larger than the designated improvement area. In this paper, a method for the determination of the size of the additional drain-installation area required to properly complete the improvement process is proposed using the results of the numerical experiments.

抄録全体を表示

Two types of consolidation tests using a large consolidometer equipped with Linear Vertical Displacement Trans-ducers (LVDT), pore pressure transducers and total earth pressure cells were carried out. With these instruments, deformation behavior as well as pore pressure responses were monitored throughout the tests. The first type used two-step high pressure loading at 100 and 190 kPa. The second type used incremental step loading starting from an applied pressure of 12 kPa. In the high pressure loading test with 100 and 190 kPa, there was no pore pressure dissipation noted from half a day to more than 10 days, depending on the locations of the pore pressure transducers. However vertical displacement was measured during this period with no pore pressure dissipation. In the low pressure step loading test, the slurry continued to compress without any noticeable dissipation of excess pore pressure. The gain in effective stress was much lower than the applied pressure although large settlement had occurred. The lower bound values of undrained shear strengths measured by laboratory vane and fall cone were in direct proportion to the gain in effective stress. In addition, particle migration was evident from the laboratory measurements.

抄録全体を表示

The behavior of the self-weight consolidation of suspension has been studied by the Oxford group (Been and Sills, 1981). However the deformation behavior of slurry-like soil upon additional load is not well understood. Due to the high demand for land in coastal areas and surrounding city areas, reclamation or remediation of land on ultra soft soil like waste ponds and mine tailing ponds has become necessary. Materials in such waste ponds and mine tailing ponds are extremely soft, and high water content which is usually above the liquid limit. In addition to this, these materials are in an underconsolidated condition and are still undergoing self-weight consolidation. A laboratory study with a large diameter consolidation cell equipped with pore water pressure transducers was carried out to find out the deformation behavior of slurry-like soil under a one dimensional vertical load. It was noted that before commencing Terzaghi's consolidation process, the slurry was deformed solely due to the expelling of water from the slurry. This deformation was as high as 19% strain and no pore water pressure dissipation was detected during this period. The behavior in the laboratory results was confirmed by a case study carried out with a trail embankment on slurry-like soil contained in the containment bund.

抄録全体を表示

In this paper, consideration is given as to how to characterize depth-variation for the small-strain shear modulus of natural clay sedimentation, in a state of normal consolidation. A case study was carried out for a relatively uniform clay layer deposited in the Holocene era. Initially, the effects of both strain and in-situ stress levels on secant shear modulus were carefully examined in cyclic torsion shear tests using undisturbed samples, which were recovered at different depths in a test borehole. The range of shear strain examined was between 0.001% and 1%. Similar examination was made for a silty clay using reconstituted samples that were isotropically consolidated at different stress levels. On the basis of the results of these laboratory tests, together with the shear modulus from an in-situ seismic survey, the small-strain shear modulus was formulated in terms of the stress and strain levels, and linked also to undrained shear strength. Interactions of the small strain stiffness between in-situ and laboratory are discussed in depth with an attention paid to the existing aging effect in the original subsurface condition.

抄録全体を表示