• 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 Soil and Groundwater Environment
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• v.26 no.1
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• pp.17-23
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• 2021

In order to investigate change of shear strength of coastal muddy sediment by mixing pretreated oyster shells with different pyrolysis temperatures and particle sizes, a vane shear test was carried out. The shear strength of the sediment with oyster shells pyrolyzed at 800℃ was twice higher than that of the control, with a maximum shear strength of ca. 0.2 kPa. The Ca2+ concentration in the pore water was the highest at sediment with oyster shells pyrolyzed at 800℃ with a concentration of ca. 790 mg/L. From the above results, it is concluded that the application of the oyster shells pyrolyzed at 800℃ can affect the increase in shear strength of coastal sediments through the aggregation of clay particles and pozzolanic reactions with sediments.

• Geomechanics and Engineering
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• v.11 no.6
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• pp.739-756
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• 2016

The shear strength reduction finite element method (SSRFEM) is a powerful tool for slope stability analysis. The factor of safety (FOS) of the slope can be easily calculated only through reducing effective cohesion (c′) and tangent of effective friction angle ($tan{\varphi}^{\prime}$) in equal proportion. However, this method may not be applicable to soil slope under wetting-drying cycles (WDCs), because the influence of WDCs on c′ and $tan{\varphi}^{\prime}$ may be different. To research the method of estimating FOS of soil slopes under WDCs, this paper presents an experimental study firstly to investigate the effects of WDCs on the parameters of shear strength and stiffness. Twelve silty clay samples were subjected to different number of WDCs and then tested with triaxial test equipment. The test results show that WDCs have a degradation effect on shear strength (${\sigma}_1-{\sigma}_3)_f$, secant modulus of elasticity ($E_s$) and c′ while little influence on ${\varphi}^{\prime}$. Hence, conventional SSRFEM which reduces c′ and $tan{\varphi}^{\prime}$ in equal proportion cannot be adopted to compute the FOS of slope under conditions of WDCs. The SSRFEM should be modified. In detail, c′ is merely reduced among shear strength parameters, and elasticity modulus is reduced correspondingly. Besides, a new approach based on sudden substantial changes in the displacement of marked nodes is proposed to identify the slope failure in SSRFEM. Finally, the modified SSRFEM is applied to compute the FOS of a slope example.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2002.10a
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• pp.333-336
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• 2002

Traditional methods of earth reinforcement consist of introducing strips, fabrics, or grids into an earth mass. Recently, discrete fibers are simply added and mixed with the soil, much the same as cement, lime or other additives. The advantages of randomly distributed fibers is the maintenance of strength isotropy, low decrease in post-peak shear strength and high stability at failure. In this study, new composite reinforcement structures which consist of geotextile and randomly distributed discrete fibers were examined their engineering properties, such as shear strength of the composite reinforced soil. The increments of shear strength of composite reinforced soils were the sum of increments by fiber and woven geotextile respectively.

• Geomechanics and Engineering
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• v.22 no.3
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• pp.237-244
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• 2020

To achieve a wide suction range, the low suction was imposed on compacted silt specimens by the axis translation technique and the high suction was imposed by the vapor equilibrium technique with saturated salt solutions. Firstly, the results of soil water retention tests on compacted silt show that the soil water retention curves in terms of gravimetric water content versus suction relation are independent of the dry density or void ratio in a high suction range. Therefore, triaxial tests on compacted silt with constant water content at high suctions can be considered as that with constant suction. Secondly, the results of triaxial shear tests on unsaturated compacted silt with the initial void ratio of about 0.75 show a strain-hardening behavior with a slightly shear contraction and then strain-softening behavior with an obviously dilation. As the imposed suction increases, the shear strength increases up to a peak value and then decreases when the suction is beyond a special value corresponding to the peak shear strength. The residual strength increases to fair value and those at high suctions are almost independent of imposed suctions. In addition, the contribution of suction to the strength of compacted silt would not diminish even in a high suction range.

• Geomechanics and Engineering
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• v.20 no.3
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• pp.191-205
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• 2020

Soil shear strength parameters play a remarkable role in designing geotechnical structures such as retaining wall and dam. This study puts an effort to propose two accurate and practical predictive models of soil shear strength parameters via hybrid artificial neural network (ANN)-based models namely genetic algorithm (GA)-ANN and particle swarm optimization (PSO)-ANN. To reach the aim of this study, a series of consolidated undrained Triaxial tests were conducted to survey inherent strength increase due to addition of polypropylene fibers to sandy soil. Fiber material with different lengths and percentages were considered to be mixed with sandy soil to evaluate cohesion (as one of shear strength parameter) values. The obtained results from laboratory tests showed that fiber percentage, fiber length, deviator stress and pore water pressure have a significant impact on cohesion values and due to that, these parameters were selected as model inputs. Many GA-ANN and PSO-ANN models were constructed based on the most effective parameters of these models. Based on the simulation results and the computed indices' values, it is observed that the developed GA-ANN model with training and testing coefficient of determination values of 0.957 and 0.950, respectively, performs better than the proposed PSO-ANN model giving coefficient of determination values of 0.938 and 0.943 for training and testing sets, respectively. Therefore, GA-ANN can provide a new applicable model to effectively predict cohesion of fiber-reinforced sandy soil.

• Journal of the Korean Geotechnical Society
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• v.24 no.1
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• pp.101-110
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• 2008

This paper investigates the mechanical characteristics of monofilament-reinforced bottom ash mixtures for recycling dredged soil. Reinforced bottom ash mixture is a lightweight soil added with monofilament in order to increase its shear strength. Test specimens were fabricated by various mixing conditions including monofilament content, its length and its diameter. Then several series of unconfined compression tests and direct shear tests were performed to investigate mechanical characteristics of reinforced lightweight soil. The experimental results indicated that stress-strain behaviors of reinforced lightweight soil were strongly influenced by mixing conditions of monofilament content, its length and diameter. The compressive strength of reinforced lightweight soil generally increased by adding monofilament. In this test, the maximum increase in compressive strength was obtained at 0.5% content and 4cm length of monofilament. These results were similar to those of direct shear tests. The unconfined compressive strength of reinforced lightweight soil with monofilament of 0.25mm in diameter was greater than that of reinforced lightweight soil with monofilament of 0.5mm in diameter.

• Geomechanics and Engineering
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• v.38 no.3
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• pp.307-317
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• 2024

To get a better understanding of the effect of drying-wetting cycles (DWC) on the mechanical behaviors of silty clay hiving different initial moisture content (IMC), the direct shear tests were performed on sliding band soil taken from a reservoirinduced landslide at the Three Gorges Reservoir area. The results indicated that, as the increasing number of DWC, the shear stress-displacement curves type changed from strain-hardening to strain-softening, and both the soil peak strengths and strength parameters reduced first and then nearly remain unchanged after a certain number of DWC. The effects of DWC on the cohesion were predominated that on the internal friction angle. The IMC of 17% is regarding as the critical moisture content, and the evolution laws of both peak shear strength and strength parameters presented a reversed 'U' type with the rising of the IMC. Based on it, a strength deterioration evolution model incorporating the influence of IMC and DWC was developed to describe the total degradation degree and degradation rate of strength parameters, and the degradation of strength parameters caused by DWC could be counterbalanced to some extent as the soil IMC close to critical moisture content. The microscopic mechanism for the soil strength caused by the IMC and DWC were discussed separately. The research results are of great significance for further understanding the water-weakening mechanicals of the silty clay subjected to the water absorption/desorption.

• Journal of the Korean GEO-environmental Society
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• v.12 no.7
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• pp.13-21
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• 2011

In seasonal frozen areas with climatic features, which have a temperature difference in the winter and thawing season, changes of mechanical properties of the soil in the zone could be seen between the freezing and thawing surface. In particular, in soil with many fine particles, a softening of the roadbed usually occurs from frost and thawing actions. The lower bearing capacity is a rapidly progressive the softening of roadbed, and occurred a mud-pumping by repeated loading. In this study, the three kind of sandy soil with contents of fine particles were conducted by directly shear box test with the number of cyclic in freeze-thawing and the water content of soil. Subsequently, the relationship between the shear strength and freeze-thaw cycling time was obtained. The shear strength was decreased with the increase of the freeze-thaw cycling time. A shear stress deterioration of the soil with power function modal is proposal.

• Journal of Ocean Engineering and Technology
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• v.25 no.3
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• pp.34-39
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• 2011

This study investigated the shear and CBR characteristics of dredge soil-bottom ash-waste tire powder-mixed lightweight soil, which was developed to recycle dredged soil, bottom ash, and waste tire powder. Test specimens were prepared with various contents of waste tire powder ranging from 0 to 100% at 50% intervals by the weight of the dry dredged soil. Several series of triaxial compression tests and CBR tests were conducted. The shear strength characteristics of the lightweight soil were compared using two different shear tests (triaxial compression test and direct shear test). The experimental results indicated that the internal friction angle of the lightweight soil obtained by the direct shear tests was greater than that by the triaxial shear tests. However, the cohesion value obtained by the triaxial shear tests was greater than that by the direct shear tests. The CBR value of the lightweight soil decreased from 35% to 15% as waste tire powder content increased.