• Journal of the Korean Geotechnical Society
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• v.40 no.1
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• pp.5-14
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• 2024

PHC piles demonstrate superior resistance to compression and bending moments, and their factory-based production enhances quality assurance and management processes. Despite these advantages that have resulted in widespread use in civil engineering and construction projects, the design process frequently relies on empirical formulas or N-values to estimate the soil-pile friction, which is crucial for bearing capacity, and this reliance underscores a significant lack of experimental validation. In addition, environmental factors, e.g., the pH levels in groundwater and the effects of seawater, are commonly not considered. Thus, this study investigates the influence of vibrating machine foundations on PHC pile models in consideration of the effects of varying pH conditions. Concrete model piles were subjected to a one-month conditioning period in different pH environments (acidic, neutral, and alkaline) and under the influence of seawater. Subsequent repeated direct shear tests were performed on the pile-soil interface, and the disturbed state concept was employed to derive parameters that effectively quantify the dynamic behavior of this interface. The results revealed a descending order of shear stress in neutral, acidic, and alkaline conditions, with the pH-influenced samples exhibiting a more pronounced reduction in shear stress than those affected by seawater.

• Journal of the Korean Geotechnical Society
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• v.21 no.1
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• pp.81-91
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• 2005

This paper is the results of experimental and numerical works on the investigating design factors influencing the bearing capacity, the ratio of stress concentration, and the failure mechanism of the clay ground improved with sand compaction piles (SCP). In order to find the behavior of the clay ground improved with SCP, extensive centrifuge model experiments were carried out for each of the SCP replacement ratio of 20, 40, and $70\%$, the non-plastic fine contents in sand of 5, 10, and $15\%$, and the ratio of the improved width to the loaded area (W/B) of 1, 2, and 3. The commertially available software of FEM, CRISP, was used to analyze test results by performing numerical estimations. In these numerical analyses the sand compaction piles and the clay ground were simulated as a linear elastic and plastic constitutive model and the modified Cam-clay model, based on Critical State Soil Mechanics, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.9
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• pp.4205-4209
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• 2011

Numerical analysis were executed in order to investigate ultimate lateral resistance of roots of vegetation. Ultimate lateral resistances of roots obtained from the assumed values of cohesions were distributed between the values of the two kinds of the existing studies. The ultimate lateral resistance values were more close to those by the bearing capacity solution than those by the cavity expansion theory. Coefficient of bearing capacity determined by the numerical analysis was 33. Yielding displacements obtained from the numerical analysis were 0.08~0.29 times of the diameter of the root and those were overall close to the value of the existing study which was undertaken for the pile diameter of 1 cm.

• Geomechanics and Engineering
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• v.13 no.6
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• pp.929-946
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• 2017

Composite foundation treated with compaction piles can eliminate collapsibility and improve the bearing capacity of foundation in loess area. However, the large number of piles in the composite foundation leads to difficulties in the analysis of such type of engineering works. This paper proposes two simplified methods to quantify the stability of composite foundation treated with a large number of compaction piles. The first method is based on the principle of making the area replacement ratios of the simplified model as the same time as the practical engineering situation. Then, discrete piles arranged in a triangular shape can be simplified in the model where the annular piles and compacted soil are arranged alternately. The second method implements equivalent continuous treatment in the pile-soil area and makes the whole treated region equivalent to a type of composite material. Both methods have been verified using treated foundation of an oil storage tank. The results have shown that the differences in the settlement values obtained from the water filled test in the field and those calculated by the two simplified methods are negligible. Using stability analysis, the difference ratios of the static and dynamic safety factors of the composite foundation treated with compaction piles calculated by these two simplified methods are found to be 3.56% and 5.32%, respectively. At the same time, both static and dynamic safety factors are larger than the general safety factor, which should be greater than or equal to 2.0 according to the provisions in civil engineering. This indicates that after being treated with compaction piles, the bearing capacity of the composite foundation is effectively improved and the foundation has enough safety reserve.

• Journal of the Korean Geotechnical Society
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• v.22 no.5
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• pp.69-81
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• 2006

The micropile, which is a kind of the in-situ manufactured pile with small diameter of $150\sim300mm$, is constructed by installing a steel bar or pipe and injecting grout into a borehole. The application fields of micropile are being gradually expanded in a limited space of down-town area, because the micropile has various advantages with low vibration and noise in method and compact size in machine, etc. Mostly, the micropile has been applied to secure the safety of structures, depending on the increment of bearing capacity and the restraint of displacement. The micropile is expected to be used in various fields due to its effectiveness and potentiality in the future. The model test, focused on the interaction between micropile and soil in this study, was carried out. The micropile is installed in a soil adjacent to footing (concept of 'soil reinforcement'). With the test results and soil deformation analysis, the reinforcement effect (relating to bearing capacity and settlement) was analysed in a qualitative and quantitative manner, respectively. Consequently, it is expected that we nay demonstrate the improvement of an efficiency and application in the design and construction of micropile.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3C
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• pp.191-200
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• 2006

The micropile, which is a kind of the in-situ manufactured pile with small diameter of 100~300mm, is constructed by installing a steel bar or pipe and injecting grout into a borehole. The application fields of micropile are being gradually expanded in a limited space of down-town area, because the micropile has various advantages with low vibration and noise in method and compact size in machine, etc. Mostly, the micropile has been applied to secure the safety of structures, depending on the increment of bearing capacity and the restraint of displacement. The micropile is expected to be used in various fields due to its effectiveness and potentiality in the future. The model test, focused on the interaction between micropile and soil in this study, was carried out. The micropile is installed under footing(concept of "structure supporting"). With the test results and soil deformation analysis, the reinforcement effect(relating to bearing capacity and settlement) was analysed in a qualitative and quantitative manner, respectively. Consequently, it is hoped to demonstrate the improvement of an efficiency and application in the design and construction of micropile.

• Journal of Bio-Environment Control
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• v.29 no.4
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• pp.440-447
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• 2020

The demand for large-scale horticultural complexes utilizing reclaimed lands is increasing, and one of the pending issues for the construction of large-scale facilities is to establish foundation design criteria. In this paper, we tried to review previous studies on the method of reinforcing the foundation of soft ground. Target construction methods are spiral piles, wood piles, crushed stone piles and PF (point foundation) method. In order to evaluate the performance according to the basic construction method, pull-out resistance, bearing capacity, and settlement amount were measured. At the same diameter, pull-out resistance increased with increasing penetration depth. Simplified comparison is difficult due to the difference in reinforcement method, diameter, and penetration depth, but it showed high bearing capacity in the order of crushed stone pile, PF method, and wood pile foundation. In the case of wood piles, the increase in uplift resistance was different depending on the slenderness ratio. Wood, crushed stone pile and PF construction methods, which are foundation reinforcement works with a bearing capacity of 105 kN/㎡ to 826 kN/㎡, are considered sufficient methods to be applied to the greenhouse foundation. There was a limitation in grasping the consistent trend of each foundation reinforcement method through existing studies. If these data are supplemented through additional empirical tests, it is judged that a basic design guideline that can satisfy the structure and economic efficiency of the greenhouse can be presented.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.6
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• pp.2411-2425
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• 2013

In the design of pile foundation on the rock layer in the stratified structure with sedimentary and rock layers, the structural analysis of the stratified rock layer is required to determine the failure modes (flexural failure, punching shear failure or end bearing failure) and the bearing capacity of the rock layer. However, the existing usable Elastic Plate Analysis Method (EPAM) suggested by ACI committee 436 and Korean Code Requirements for Structural Foundation Design is very complex, and engineers have many difficulties in using it. Therefore, in this research, we proposed the relatively simple Circular Foundation Analysis Method (CFAM) with the concept and the equation of the equivalent effective width (radius) instead of the complex EPM, and the related equations of bending moment and shear force to be equal to the analysis results of EPAM. As a result, the proposed CFAM using the equivalent effective width (radius) is simple and convenient to use, and the analysis results of it are very good in their accuracies comparing those of EPAM and Finite Element Method.

• Journal of the Korean Geotechnical Society
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• v.35 no.6
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• pp.39-48
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• 2019

This study investigated the lateral behavior of monopile embedded in the dry sand through cyclic lateral loading test using a centrifuge test. The sand sample for the experiment was the dry Jumunjin standard sand at 80% relative density and the friction angle of $38^{\circ}$. In the experimental procedure, firstly, it was determined the static lateral bearing capacity by performing the static lateral loading test to decide the cyclic load. This derived static lateral bearing capacity values of 30%, 50%, 80%, 120% were determined as the cyclic lateral load, and the number of cycle was performed 100 times. Through the results, the experiment cyclic p-y curve was calculated, and the cyclic p-y backbone curve by depth was derived using the derived maximum soil resistance point by the load. The initial slope at the same depth was underestimated than API (1987) p-y curves, and the ultimate soil resistance was overestimated than API (1987) p-y curves. In addition, the result of the comparison with the suggested dynamic p-y curve was that the suggested dynamic p-y curve was overestimated than the cyclic p-y backbone curve on the initial slope and soil resistance at the same depth. It is considered that the p-y curve should be applied differently depending on the loading conditions of the pile.

• Journal of the Korean Geotechnical Society
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• v.27 no.10
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• pp.13-23
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• 2011

Bearing capacity of pile foundations in cold region is dominated by adfreeze bond strength between surrounding soil and pile perimeter. It denotes that adfreeze bond strength is the most important design parameter for foundations in cold region. Adfreeze bond strength is affected by various factors like 'soil type', 'frozen temperature', 'normal stress acting on soil/pile interface', 'loading rate', 'roughness of pile surface', etc. Several methods have already been proposed to estimate adfreeze bond strength during past 50 years. However, most methods have not considered the effect of normal stress for adfreeze bond strength. In this study, both freezing temperature and normal stress have been controlled as primary factors affecting adfreeze bond strength. A direct shear box was used to measure adfreeze bond strength between sand and aluminum under different temperature conditions. Based on the test results, the relation between shear strength of frozen sand and adfreeze bond strength have been investigated. The test results showed that both of shear strength and adfreeze bond strength tend to increase with decreasing frozen temperature or increasing confining pressure. The ratio of shear strength and adfreeze bond strength, expressed as $r_s$, decreased initially frozen section but increased at much lower frozen temperature and there were uniform intervals under the different normal stress conditions. A method for predicting adfreeze bond strength using $r_s$ has finally been proposed in this study.