• Journal of the Korean Geotechnical Society
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• v.19 no.5
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• pp.199-210
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• 2003

The development of strain localization within shear zones is frequently observed during soil deformation. In fact, the phenomenon appears to be more often the norm rather than the exception. Conceptually, any soil condition that renders negative work increment is prone to localization. In this study, a broad range of soil and loading conditions are investigated to test this criterion, including: dilative soil subjected to drained shear (standard case), contractive soil sheared under undrained conditions, cavitation in dilative soil in undrained shear, inhomogeneous soils, particle alignment in contractive soils made of platy particles, soils that experience particle crushing, and the shear of low-moisture and/or lightly cemented loose soils. Unique specimens and test procedures are designed to separately test each of these soil conditions in the laboratory According to experimental test results, soil specimens with post-peak strain softening behavior are prone to progressive failure, localization of deformations, and shear banding. The state of stress, the soil density, inherent mechanical and geometrical properties of soil particles, low water content, and heterogeneity can contribute to triggering strain localization. Considering all possible cases of localization, the best method to obtain the critical state line in the laboratory is to use contractive homogeneous specimens subjected to drained shear.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.41-48
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• 2002

The fact that nonlinearity and anisotropy of soil should be considered for the proper estimation of soil deformation has been recongnized for a long time. In this study, a new stiffness model which can reflect both nonlinearity and anisotropy is proposed. Nonlinearity is simulated by Ramberg-Osgood model and anisotropy is modeled with the cross-anisotropic elasticity. Analysis results with the developed model compared with those from analyses using linear isotropic model, linear anisotropic model, and nonlinear isotropic model. In the triaxial compression like condition, the effects of nonlinearity on the vertical strain are significant, but soil anisotropy does not affect the vertical strain. In 1-dimensional deformation condition, however, both nonlinearity and anisotropy of soil influence the final magnitude of the vertical strain. Also the increase of poisson's ratio magnifies the effect of anisotropy on the vertical strain in this condition.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.95-100
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• 2000

When compared with conventional retaining wall system, there are many advantages to reinforced soil such as cost effectiveness, flexibility and so on. The use of reinforced soil have been increased in the last 17 years in Korea. In this study, a full-scale reinforced soil with rigid facing were constructed to investigate the behavior of reinforcing system. The results of soil pressure and strain of reinforcement during construction are described. The influence of compaction on soil pressure and strain of reinforcement is addressed. The results show that lateral earth pressures on the wall are active state during backfill. It is obtained that the lateral soil pressure depends on the installation condition of pressure cell and construction condition. It is also observed that maximum tensile strains of reinforcement are located on 50cm to 150cm from the wall. Long-term measurement will be followed to verify the design assumptions with respect to the distribution of lateral stress in the reinforcement

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.96-102
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• 2006

Because of the increasing need to use clayey soil as the backfill in reinforced soil structures and embankment material, nonwoven geotextiles with the drain capability have been receiving much attention. However, there are few studies of the deformation behavior of nonwoven geotextiles at geosynthetics reinforced soil structures in the field because the nonwoven geotextile, which has low tensile stiffness and higher deformability than geogrids and woven geotextiles, is difficult to measure its deformation by strain gauges and to prevent the water from infiltrating. This study proposes a new, more convenient method to measure the deformation behaviour of nonwoven geotextile by using a strain gauge; and examines the availability of the method by conducting laboratory tests and by applying it on two geosynthetics reinforced soil (GRS) walls in the field. A wide-width tensile test conducted under confining pressure of 7kPa showed that the local deformation of nonwoven geotextile measured with strain gauges has a similar pattern to the total deformation measured with LVDT. In the field GRS walls, nonwoven geotextile showed a larger deformation range than the woven geotextile and geogrid; however, the deformation patterns of these three reinforcement materials were similar. The function of strain gauges attached to nonwoven geotextile in the walls works normally for 16 months. Therefore, the method proposed in this study for measuring nonwoven geotextile deformation by using a strain gauge proved useful.

• Magazine of the Korean Society of Agricultural Engineers
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• v.41 no.2
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• pp.70-79
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• 1999

The lower ground of structure, in which the strip loads, such as earth dams and embankments , are signiificantly working on , is required to be interpreted as a state of plane strain where the strain of intermediated principal stress direction is put '0' . The plane strain state is frquently observed in actural soil engineering case. For those case, drained stress-strain and strength behavior of Iksan weathered granite soil prepared in cubical specimens with cross-anisotropic fabric was studied by conventional triaxial compression, plane strain and cubial triaxial tests with independent control of the three principal stress. All specimens were loaded under conditions of principl stress directions fixed and aligned with the directions of the material axes. As a result of research , when a ground condition is analyzed under plane strain state, the shear strength obtained from the conventional triaxial compression test can be understimated.

• Geotechnical Engineering
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• v.7 no.3
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• pp.33-42
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• 1991

Increasing demand of rational analysis of dynamic soil behavior subjected to repetitive loading has evolved soil dynamics which is essential for proper design and/or analysis of dynamically loaded soil structure. In this paper, the stress-strain behavior of weathered granite soil under cyclic loading is stud- ied by measuring the strength and the strain before and after application of at least 11, 000 cycles of repetitive load. Relationships are suggested for predicting results of soil dynamics from those of soil statics.

• The Plant Pathology Journal
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• v.21 no.3
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• pp.244-251
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• 2005

The induction of growth promotion on numerous crops by rhizobacteria is a well documented phenomenon. In case of tomato (Lycopersicon esculentum), fruit yield is higher in replant soil than that in fresh soil. To investigate what kind of rhizobacterium is involved, microbial community in rhizosphere and on rhizoplane of tomato plants from each soil was analyzed by dilution plating on selective media. Many Gram-negative bacteria and actinomycetes were isolated from tomato in replant soil. One Gram-negative rhizobacterium isolated was identified as Pseudomonas putida based on its biochemical characteristics, fatty acid methyl ester analysis and 16S rDNA sequence. This bacterium designated strain 17 inhibited the growth of Pseudomonas corrugata, and increased growth of tomato seedlings. In addition, its culture filtrate inhibited conidial germination of plant-pathogenic fungi such as Fusarium oxysporum f. sp. radicis-lycopersici, F. oxysporum f. sp. cucumerinum, and Nectria radicicola. Scanning electron microscopy revealed strain 17 colonized and persisted on the epidermal surfaces of tomato radicles and roots. These results suggest that P. putida strain 17 may serve as a biological control agent to suppress multiple soil-borne diseases for tomato plants. Increased microbial populations that suppress deleterious microorganisms including pathogens could be one of the major factors in increased tomato yield in replant soil.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.139-146
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• 2001

Undrained triaxial tests were peformed for a weathered soil, which includes local measurement using LVDT The behavior from small In large strain conditions could be evaluated consistently through a triaxial test, The stress-strain relationship of undisturbed samples were compared with the disturbed and the shear moduli in the small strain level had the almost same values. Especially the shear moduli were mostly affected by the initial condition of water contents. An anisotropic hardening model based on the total stress concept could predict the stress-strain relationship accurately, which makes it possible to analyze the geotechnical problem reasonably for the weathered soil.

• Geomechanics and Engineering
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• v.38 no.3
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• pp.249-260
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• 2024

In order to study the mechanical propertied and change rules of undrained shear behavior of saline soil under the freeze-thaw cycles, an improved constitutive model reflecting the effects of freeze-thaw cycles was proposed based on the traditional Duncan-Chang model. The saline soil in Qian'an County, western Jilin Province, was selected as the experimental object. Then, a set of freeze-thaw cycles (0, 1, 10, 30, 60, 90, 120) tests were conducted on the saline soil specimens, and conventional consolidated undrained triaxial shear tests were conducted on the saline soil specimens that underwent freeze-thaw cycles. The stress-strain relationship was obtained by the triaxial shear test. The model parameters have a corresponding regression relationship with the number of freeze-thaw cycles. Finally, based on the function expression of the model parameters, the modified Duncan-Chang model with the number of freeze-thaw cycles as the influence factor was established, whilst the calculation program of the modified model is compiled. Based on the test results, the stress-strain relationship of the saline soil specimen shows strain hardening. The shear strength gradually decreases with the increase of freeze-thaw cycle. The 10 freeze-thaw cycles are the turning point in the trend of changes of the mechanical properties of saline soils. The calculated and experimental stress-strain relationship are compared, and the comparison between the calculated value of the model and the experimental value showed that the two had a good consistency, which verified the validity of the modified Duncan-Chang model in reflecting the effects of the freeze-thaw cycle.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.315-322
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• 2001

Underground flexible pipes for electric cables are subject to external loads and surrounding soil pressure. Particularly, strain of flexible pipes is of great concern in terms of safety and maintenance for electric cables. In this paper, stress and strain of flexible pipes with various depth are calculated using traditional formula and FEM analysis. The results show that theoretical values are more conservative in strain whereas FEM analysis gives larger stress. Considering the strain criteria - 3.5 %, maximum, flexible pipes can be buried at the range of 50cm to 5m in depth without additional soil improvement.