• Journal of the Korean Geotechnical Society
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• v.21 no.8
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• pp.95-105
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• 2005

Generally, a modified version of limit equilibrium method can be used to evaluate a slope stability of the geosynthetic reinforced soil slopes. In most cases, resisting effects of geosynthetic reinforcement are dealt with considering an increased shear strength on the potential slip surface. However, it is not clear that the methods satisfy all three equilibrium equations. As we know, the pattern of normal stress distribution along the slip surface is the key factor in calculating the safety factor of slopes. In this study, the new slope stability analysis method in which not only reinforcing effects of geosynthetics can be considered but also all three equilibrium equations can be satisfied was proposed with assuming the normal stress distribution along the slip surface as quadratic curve with horizontal $\chi-coordinate$. A number of illustrative examples, including published slope stability analysis examples for the reinforced and unreinforced soil slopes, loading test of large scale reinforced earth wall and centrifuge model tests on the geotextile reinforced soil slopes, were analyzed. As a result, it is shown that the newly suggested method yields a relatively accurate factor of safety for the reinforced and unreinforced soil slopes.

• Journal of the Korean Geotechnical Society
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• v.32 no.11
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• pp.43-50
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• 2016

A reinforcement is required to ensure the structural safety in case of railway embankment excavation under railway load. A large diameter soil nailing with concrete wall is applied as the reinforcement method instead of the conventional soil nailing system. In this study, a series of 3 dimensional numerical analyses are performed to investigate the optimum reinforcement considering 15 different conditions based on the length, lateral spacing, diameter, and inclination of the reinforcement. The interface between soil nail and perimetric grout is considered by means of cohesion, stiffness and perimeter of the grout. 0.3 m of reinforcement diameter is assessed as the most appropriate based on the economical viewpoint though ground displacement decreases with the increase of diameter, however the difference of displacement is negligible between 0.4 m and 0.3 m of diameter. Surface settlement, lateral displacement of wall, and stress of reinforcement are calculated and economic viewpoint to reinforce embankment considered. Consequently, the optimum reinforcement conditions considering those factors are evaluated as 3 m in length, 0.3 m in diameter, 1.5 m in lateral spacing, and 10 degree of inclination angle in the case of 3 m of excavation depth. Additionally, inclined potential failure surface occurs with approximately 60 degrees from the end of nails and the surface settlement and wall lateral displacement are restrained successfully by the large diameter soil nailing, based on the result of shear strain rate.

• Journal of the Korean Geosynthetics Society
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• v.20 no.3
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• pp.1-10
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• 2021

The purpose of this study is to present the possibility a utilization of the tertiary mudstone in Pohang as road subsoil material through pilot experiments on the road embankment structure. This mudstone is an unconsolidated rock that is distributed in the soft rock sedimentary layer, the tertiary layer of the Cenozoic, and causes physical problems such as slaking, swelling, and reduced shear strength and chemical problem like acid drainage. In order to solve various complex problems, an laboratory mixing test was conducted, and the optimal mixing conditions of the tertiary mudstone (90%), composite slag (steel making 70%, blast furnace 30%), and neutralization and coating agent treatment were derived. In order to prove its utilization, a real-scale road embankment structure was constructed and tests were conducted for each section. The pre-processing section is stable due to the design of optimal mixing conditions, while in post-processing section, natural weathering proceeded rapidly, and structural problems were concerned. Since the effect of neutralizing and coating agents was confirmed in temporary-staking section, the neutralizing and coating agents can be applied during the temporary storage period.

• Journal of the Korean Geotechnical Society
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• v.36 no.12
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• pp.45-56
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• 2020

In this paper, intelligent compaction (IC) technology and the earthwork quality control specifications based on IC were analyzed, and the field study was conducted to investigate the relationship between the representative IC value CMV (Compaction Meter Value) and spot test results (plate bearing test and field density test). As the number of roller passes increased, both the CMV and spot test results increased. However, point-by-point comparison between CMV and spot test results yielded poor quality correlations; this is because the ununiform stiffness of the underlying layer and the moisture content of the lift layer affected the CMV and spot test results, respectively. Most international specifications related to IC requires knowledge of the IC values and their relationships with the soil properties obtained by the traditional spot tests. Therefore, for the successful implementation of intelligent compaction technology into earthwork construction practice, the number of roller passes as well as the lift thickness and the moisture content of the soil should be carefully considered.

• Journal of the Korean Geosynthetics Society
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• v.22 no.3
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• pp.1-10
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• 2023

Recently, numerous structures have been constructed near the Nakdong river estuary, with pile foundations embedded in sand and gravel layers. In this study, the side resistance for six drilled shafts embedded in that region was evaluated based on the results of bi-directional and static axial compressive pile load tests. Subsequently, these results were compared with the side resistance calculated using domestic and foreign design codes such as FHWA (1999), KDS (2021), and AIJ (2004). Based on the test results, the evaluated side resistances ranged from 120 to 444kPa. However, the estimated values obtained from the design codes ranged from 69.3 to 170kPa, which were less than 50% of the evaluated values. It was observed that the empirical methods and correlations used in design codes provide a conservative estimation of the side resistance for drilled shafts embedded in sand and gravel layers. It implies that a suitable domestic approach should be developed to accurately estimate the side resistance of pile in sandy gravel and gravel layers near the Nakdong river estuary.

• Journal of the Korean GEO-environmental Society
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• v.17 no.7
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• pp.15-25
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• 2016

In the present work, a number of advanced three-dimensional (3D) parametric finite element numerical analyses have been conducted to study the behaviour of single piles and pile groups in consolidating ground from coupled consolidation analyses. Single piles, $4{\times}4$ and $6{\times}6$ piles inside groups with a spacing of 2.5D were considered, where D is the pile diameter. It has been found that dragload and downdrag on the piles developed rather quickly at the early stage of consolidation. However, when the degree of consolidation was more than 50~75%, only little increases of dragload and downdrag were induced on the pile. Negative Skin Friction (NSF) on the pile in the fill layer was mobilised quickly and remained constant throughout further consolidation. The development of NSF is influenced both by the relative shear displacements at the pile-soil interface and the vertical effective soil stresses during consolidation. The former governed the early stage of consolidation and the latter affected the later stage of consolidation. The vertical effective soil stresses adjacent to the piles were reduced due to the shear stress transfer at the pile-soil interface, in particular for piles inside the pile groups. The range of NSF influence zone concerning the reductions of the effective vertical soil stresses was about 20D measured from the piles in the horizontal direction. On the contrary, the effective horizontal soil stresses acting on the piles were similar to those at the far field.

• Journal of the Korean GEO-environmental Society
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• v.17 no.12
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• pp.27-34
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• 2016

Many steepened slopes have become increasingly advantageous because of the desire to increase land usage and decrease site development costs. The proven concept of tensile reinforcement allows construction of slopes with far steeper face angles than the soils natural angle. Steepened slope face reinforced with improved soil can increase land usage substantially while providing a natural appearance. The paper presents composite reinforced earth with improved soil surface and geogrid-reinforced backfill. For the stability of the steepened slope, the behavior of the composite reinforced earth are validated and verified by case study and numerical analysis. The case study has performed to investigate the deformation of reinforce soil slope for 14 months. Its horizontal behavior by general vertical load shows within the safe range (0.5% of structure height). As a result of numerical analysis and case study, the reinforcement effect of the steepened slope technique using improved soil is sufficient to be constructed as reinforced soil slope.

• Geotechnical Engineering
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• v.13 no.4
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• pp.37-54
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• 1997

This paper is to investigate the bearing capacity and the failure mechanism of slope subjected to strip surcharges adjassent to embankment slope of sandy soil. Parametric model tests under plain strain condition were performed by changing width of footing, relative density of slope materials, and position of footing from the crest of slopes. For model tests, Jumunjin standard sand was used as the slope material and its relative density was 45% and 70%, respectively. The angle of slope was formed with 1 : 1.5 and 1 2. Rigid model footings, made of aluminuu were used with their widths of 4, 7, 10 and 12cm. For the position of model footing, position ratios, distance of model footing from the crest of slope divided by footing width, were 0, 0.5, 1, 2, 3, 4, 5. Failure mechanism was observed by using ink colored sands and markers inserted in model slopes. Ultimate bearing capacity obtained from tests was analyzed and compared with limit equilibrium method, limit analysis method and empirical equation. Characteristics of load-settlement curves and failure mechanism were also analyzed and compared with the existing theories. Thus, their effects on ultimate bearing capacity of model footing adjacent to slope were assessed.

• Journal of the Korean Geosynthetics Society
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• v.22 no.1
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• pp.87-96
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• 2023

There are a lot of difference between the surface settlement and the differential settlement measured at the Busan New Port, where the dredged and reclaimed clay layer exists and below the clay is originally thickly distributed. To find the cause and solution of this, the actual conditions of each differential settlement used for the soft ground improvement, characteristics, installation method, measurement frequency, measurement data management, and data analysis of each type were considered. In the deep soft ground improvement work where large deformation occurs, the bending deformation of the screw-type differential settlement gauge is less than that of other types of measuring instruments, so there is less risk of loss, and the reliability of data is relatively high as the instruments are installed by drilling for each stratum. Since the greater the amount of high-precision settlement measurement data, the higher the settlement analysis precision. It is necessary to manage with higher criteria than the measurement frequency suggested in the standard specification. For the data management of the differential settlement gauge, it is desirable to create graphs of the settlement and embankment height of the relevant section over time, such as surface, differential, and settlement of pore water pressure gauge for each point. In the case of multi-layered ground with different compression characteristics, it is more appropriate to perform settlement analysis by calculating the consolidation characteristics of each stratum using a differential settlement data.

• Journal of the Korean Geotechnical Society
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• v.26 no.7
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• pp.147-159
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• 2010

The settlement prediction is very important in preloading method for a construction site on the soft ground. At the design stage, however, it is hard to predict the settlement exactly due to limitations of the site survey. Most of the settlement prediction is performed by a regression settlement curve based on the field data during construction. In Korea, hyperbolic method has been most commonly used to align the settlement curve with the field data, because of its simplicity and many application cases. The results from hyperbolic method, however, may differ by data selections or data fitting methods. In this study, the analyses using hyperbolic method were performed about the field data of $\bigcirc\bigcirc$ site in Pusan. Two data fitting methods, using an axis transformation or an alternative method which is a direct regression method, were applied with various data groups. If data was used only after the ground water level being stabilized, fitting results using both methods were in good agreement with the measured data. Regardless of the information about the ground water level, the alternative method gives better results with the field data than the method using an axis transformation.