• Journal of the Korean GEO-environmental Society
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• v.18 no.2
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• pp.29-37
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• 2017

As the behavior of the debris flow due to the torrential rains in mountain is affected by shear strength and rheological properties of the fine fraction in the ground, the evaluation of both properties is necessary to estimate the behavior of the debris flow. The objective of this study is to evaluate the shear strength and rheological properties using the direct shear apparatus. The direct shear tests are conducted for two kinds of fine-grained soil specimens, which are in dry state and liquid limit state. From the direct shear tests, shear strengths are measured according to the normal stresses applied on the specimens to evaluate the cohesion and internal friction angle. In addition, reversal shear tests are performed for the fine-grained soil specimens in liquid limit state according to the shear rate to evaluate the residual shear strength. The results of direct shear tests show that the specimen at the liquid limit state has lower internal friction angle and higher cohesion compared to the dry stated, and the residual friction angle and cohesion at the residual state are lower than those at the peak state. In the result of reversal shear test, the residual shear strength is directly proportional to the shear rate and viscosity is calculated as $73.60Pa{\cdot}s$. This study demonstrates that the direct shear apparatus can be effectively used for the evaluation of the shear strength and rheological properties of the fine-grained soils related with the debris flow.

• The Journal of Engineering Geology
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• v.19 no.2
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• pp.177-189
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• 2009

The shear strength has been managed as an important factor in soil mechanics. The shear strength estimation model was developed to evaluate the shear strength using only a few soil properties by the linear regression analysis model which is one of the statistical methods. The shear strength is divided into two part; one is the internal friction angle (${\phi}$) and the other is the cohesion (c). Therefore, some valid soil factors among the results of soil tests are selected through the correlation analysis using SPSS and then the model are formulated by the linear regression analysis based on the relationship between factors. Also, the developed model is compared with the result of direct shear test to prove the rationality of model. As the results of analysis about relationship between soil properties and shear strength, the internal friction angle is highly influenced by the void ratio and the dry unit weight and the cohesion is mainly influenced by the void ratio, the dry unit weight and the plastic index. Meanwhile, the shear strength estimated by the developed model is similar with that of the direct shear test. Therefore, the developed model may be used to estimate the shear strength of soils in the same condition of study area.

• Geomechanics and Engineering
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• v.14 no.4
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• pp.307-314
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• 2018

Strength of loess that experienced cyclic freeze and thaw is of great significance for evaluating stability of slopes and foundations in loess regions. This paper takes the frequently encountered loess in the Northwestern China as the study object and carried out three kinds of laboratory tests including freeze-thaw test, direct shear test and SEM test to investigate the strength behaviors of loess after cyclic freeze and thaw, and the correlation with meso-level changes in soil structure. Results show that for loess specimens at four dry densities, the cohesion decreases with freeze-thaw cycles until a residual value is reached and thus an exponential equation is proposed. Besides, little change in the angle of internal friction was observed as freeze-thaw proceeds. This may depend on the varying of soil structure, based on which a clue can be found from the surface morphology and mesoscopic scanning of loess specimens. Clearly we observed significant changes in surface morphology of loess and it tends to aggravate at higher water contents or more cycles of freeze and thaw. Moreover, freeze-thaw cycling leads to obvious changes in the meso-structure of loess including lowering the particle aggregates and increasing both the proportion of fine particles and porosity area ratio. A damage variable dependent on the ratio of porosity area is introduced based on the continuum damage mechanics and its correlation with cohesion is discussed.

• Geomechanics and Engineering
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• v.12 no.5
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• pp.831-847
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• 2017

Conventional geotechnical engineering soil binders such as ordinary cement or lime have environmental issues in terms of sustainable development. Thus, environmentally friendly materials have attracted considerable interest in modern geotechnical engineering. Microbial biopolymers are being actively developed in order to improve geotechnical engineering properties such as aggregate stability, strength, and hydraulic conductivity of various soil types. This study evaluates the geotechnical engineering shear behavior of sand treated with xanthan gum biopolymer through laboratory direct shear testing. Xanthan gum-sand mixtures with various xanthan gum content (percent to the mass of sand) and gel phases (initial, dried, and re-submerged) were considered. Xanthan gum content of 1.0% sufficiently improves the inter-particle cohesion of cohesionless sands 3.8 times and more (up to 14 times for dried state) than in the untreated (natural) condition, regardless of the xanthan gum gel condition. In general, the strength of xanthan gum-treated sand shows dependency with the rheology and phase of xanthan gum gels in inter-granular pores, which decreases in order as dried (biofilm state), initial (uniform hydrogel), and re-submerged (swollen hydrogel after drying) states. As xanthan gum hydrogels are pseudo-plastic, both inter-particle friction angle and cohesion of xanthan gum-treated sand decrease with water adsorbed swelling at large strain levels. However, for 2% xanthan gum-treated sands, the re-submerged state shows a higher strength than the initial state due to the gradual and non-uniform swelling behavior of highly concentrated biofilms.

• Journal of the Society of Disaster Information
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• v.3 no.2
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• pp.23-35
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• 2007

Recently, for places with poor vegetating environment, such as slopes made of weathered soil or rocks, erosion tranquilizers, coverings and composite fertilizers have been mixed with seeds and sprinkled onto soil. Also, these plant revegetations have been mixed with nets and used to strengthen cohesion. However, this technique often obstructed plant growth and caused pollution because of not decomposing nets. This study has tested influence on plant revegetation B for slope of weathered soil and rocks and decomposition of naturally decomposing polyester filament yarn. In result, it was showed that plant revegetation B does not harm environment in case of applying it to soil slope and enhance protection capacity of slopes as time goes by. Also, naturally decomposing polyester filament yam was analyzed its physical properties with the passage of time and was known that naturally decomposing polyester filament yarn transformed into a structure easy to decompose by hardening. Thus it is considered that the revegetation method used this study was very effective method for plant establishment and stability of slope.

• Structural Engineering and Mechanics
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• v.83 no.3
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• pp.377-386
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• 2022

This paper considers dynamic impedance functions and presents a detailed analysis of the soil plasticity influence on the pile-group foundation dynamic response. A three-dimensional finite element model is proposed, and a calculation method considering the time domain is detailed for the nonlinear dynamic impedance functions. The soil mass is modeled as continuum elastoplastic solid using the Mohr-Coulomb shear failure criterion. The piles are modeled as continuum solids and the slab as a structural plate-type element. Quiet boundaries are implemented to avoid wave reflection on the boundaries. The model and method of analysis are validated by comparison with those published on literature. Numerical results are presented in terms of horizontal and vertical nonlinear dynamic impedances as a function of the shear soil parameters (cohesion and internal friction angle), pile spacing ratio and frequencies of the dynamic signal.

• Geomechanics and Engineering
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• v.10 no.2
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• pp.125-135
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• 2016

Adhesion in geotechnical engineering is the interaction between cohesive soil and a solid surface which can cause clogging in mechanized tunnelling through clayey formations. Normal piston pull out and modified direct shear tests were performed on clayey soil samples to determine which type of adhesion stress, normal or tangential, could be most effectively measured. Measured values for normal adhesion ranged from 0.9 to 18 kPa. The range of tangential adhesion was 2.4 to 10 kPa. The results indicate normal adhesion results were more accurate than those for the modified direct shear test that measure tangential adhesion. Direct shear test on identical samples did not show any correlation between measured cohesion and normal adhesion values. Normal adhesion values have shown significantly meaningful variation with consistency index and so are compatible with the base of field clogging assessment criteria. But tangential adhesion and cohesion were not compatible with these assessment criteria.

• Geomechanics and Engineering
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• v.35 no.1
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• pp.95-108
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• 2023

Soft soil ground is a crucial factor limiting the development of the construction of transportation infrastructure in coastal areas. Soft soil is characterized by low strength, low permeability and high compressibility. However, the ordinary treatment method uses Portland cement to solidify the soft soil, which has low early strength and requires a long curing time. Microbially induced carbonate precipitation (MICP) is an emerging method to address geo-environmental problems associated with geotechnical materials. In this study, a method of bio-cementitious mortars consisting of MICP and cement was proposed to stabilize the soft soil. A series of laboratory tests were conducted on MICP-treated and cement-MICP-treated (C-MICP-treated) soft soils to improve mechanical properties. Microscale observations were also undertaken to reveal the underlying mechanism of cement-soil treated by MICP. The results showed that cohesion and internal friction angles of MICP-treated soft soil were greater than those of remolded soft soil. The UCS, elastic modulus and toughness of C-MICP-treated soft soil with high moisture content (50%, 60%, 70%, 80%) were improved compared to traditional cement-soil. A remarkable difference was observed that the MICP process mainly played a role in the early curing stage (i.e., within 14 days) while cement hydration continued during the whole process. Micro-characterization revealed that the calcium carbonate filling the pores enhanced the soft soil.

• Proceedings of the KSR Conference
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• 2003.10b
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• pp.73-78
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• 2003

As a fundamental study to develop the retaining wall of new type, short-fibers are mixed with soils and a series of compaction tests and triaxial compression tests for short-fiber reinforced soils are performed. From the results of compaction tests, optimum moisture content is increased and maximum dry unit weight is decreased with fiber mixing ratio. When 60mm fibrillated fiber of 0.2$\%$ mixing ratio is added to SM soil, strength increment of short-fiber reinforced soil is above 1.2 times compared to soil only. Strength increment shows maximum value for composite reinforced soil, namely, soil+short-fiber+planar reinforcement. But in case of mixing with ML soil and short-fiber, the strength of short-fiber reinforced soil is nearly the same as soil only. Internal angle of short-fiber reinforced soil is increased about $2\~3$ degrees and cohesion is also increased above 10kPa compared to soil only. Therefore, it is judged that short-fiber is a good material to strengthen the soil.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.4
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• pp.89-98
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• 2010

Recently, many researches on bottom ash which is produced in the burning process of power plant are actively performed for its utilization for soil-subbase materials. In this paper, bottom ashes from 5 different power plants are prepared and several tests including compaction, CBR, and tri-axial compression are carried out for mixed bottom ash and weathered soil considering 3 replacement ratio of 30%, 50%, and 70%. Through the tests, CBR result over 20 are evaluated without plastic property, which shows availability of subbase material. With higher increase in replacement ratio of bottom ash, CBR of mixed soil increases due to the higher mechanical performance of bottom ash. However, replacement effects of bottom ash on friction angle and cohesion are evaluated to be little since bottom ash plays a little role in rearrangement of mixed soil. Bottom ash with a good mechanical property is evaluated to have reasonable bearing capacity which shows a good property for subbase materials.