• Proceedings of the Korean Geotechical Society Conference
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• 2003.03a
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• pp.411-416
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• 2003

As rapid industrialization continues in these days, construction in the down town areas increases. Since constructions are performed around old and existing structures, the need to provide reinforcements to protect the existing structures from collapse and damage arises. Furthermore, if the construction is to take place in the down town area, difficult work space and damage caused by noise, vibration and collapse of structure can't be ignored. Among the remedial measures available today, micropile reinforcement is considered the best method to remedy these problems. But up to the present the characteristics of micropiles and ground behaviour has not been proven and no standard design is not yet available. Therefore, most design are performed based on previous experiences. In this study, the difference in the bearing capacity with changing reinforcement angle, space and sphere around foundation was monitored. These results were induced to broaden heighten the limits of micropile application.

• Journal of the Korean GEO-environmental Society
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• v.10 no.6
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• pp.117-123
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• 2009

The mechanical behavior of a micropile due to horizontal load has not yet clearly identified in Korea. It has generally estimated from that of a traditional pile because there is no standard method even though it has shorter length. To tell the truth, its behavior is very different from a traditional pile's. Specifically, it is general fact that horizontal resistance of earth is one of the main factors to control the mechanical behavior of micropile. To this reason, a laboratory model has been made in this study to estimate the behavior of a micropile which loaded increasingly horizontally. The laboratory model has been designed to estimate both the behavior of load to displacement and skin friction to displacement. And the analysis of the latter was compared with the solution of strain wedge model. In the end, it was proved that the mechanical behavior of a micropile should be estimated from considering the horizontal resistance of earth.

• Journal of the Korean GEO-environmental Society
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• v.21 no.6
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• pp.19-25
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• 2020

In the recent downtown works, there are frequent cases where the work on existing piles is impossible due to the influence from lack of space and surrounding environment. In such cases, there has been growing cases of using the micropile method that is available to work with the small equipment and asserts the bearing capacity of the existing piles. The micropile method is a type of drilled shaft with the diameter of a pile to be around 75 mm~300 mm that, even for a case where it has certain surrounding structure, foundation and spatial obstacle, there is almost no work difficulty and the work is feasible under all types of soil conditions. In addition, the work can be done in places where the ceiling of the building is low with less vibration and noise in the work process that such method is significantly used for foundation reinforcement of existing buildings. With respect to the motion characteristics that are changed depending on the foundational characteristics or when the micropile is applied with compression or tensile force, there is very few studies conducted. Therefore, under this study, through the data analysis of the field loading test regarding the micropile worked in the fields, it clarifies the settlement and characteristics of bearing capacity following the embedded condition of the ingredients and piles that consist the foundation if the compression and tensile force are applied to the micropile, and by facilitating the statistical analysis program, SAS, to carry out the analysis on the main elements influencing on settlement of the micropile and bearing capacity.

• Journal of the Korean Geotechnical Society
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• v.34 no.3
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• pp.67-75
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• 2018

In this study, we developed a micropile equipped with ground fixing wedge device which is able to ensure the bearing capacity early before grouting by expanding the tip and exerting the tip surface friction while compressing and expanding the tip of the micropile during loading. The purpose of this study is to verify the applicability of the developed micropile to the ground with various kinds of strength and to compare its characteristics with those of the simple tip expansion micropile. A new test system including a model soil box which can measure the tip resistance and the tip skin friction separately was devised. The loading test was carried out according to the changes of the ground strength and the tip cross section using the devised test systems. As a result of the test, it was found that the developed micropile increased the tip skin friction due to the wedge horizontal force as the soil strength increased and could be applied more effectively to the ground with the strength not lower than the strength of the weathered rock. In addition, it was found that additional bearing capacity could be obtained due to the tip cross section expansion and the wedge horizontal force exertion even in the ground with the strength below the weathered rock strength.

• Journal of the Korean Geotechnical Society
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• v.29 no.12
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• pp.57-67
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• 2013

Micropile technology has evolved continuously since its instruction by Fernando Lizzi in the 1950s. The effects of group micropile have been researched by many researchers. The effects of group micropile differ and change with pile length, pile spacing (S), pile angle (${\theta}$) and pile embedded conditions. In the present study, the effects of resistance increase and settlement reduction from micropiles were investigated through a series of axial load tests. For the study, axial load tests were performed using mat, group micropiles and micropiled-raft (MPR) in various pile spacing and pile angle conditions. As the result, the effects of resistance of micropiled-raft were 80% (3D) to 110% (7D) of the total resistance of mat and group micropile. The effects of settlement restraint of micropiled-raft were 20% (S=3D, ${\theta}=45^{\circ}$) to 70% (7D, ${\theta}=15^{\circ}$) of settlement of mat foundation.

• Journal of the Korean Geotechnical Society
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• v.37 no.11
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• pp.37-49
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• 2021

Micropiles are widely used in construction field to enhance bearing capacity and reduce settlement of existing foundation. It has various benefits such as low construction expense, simple installation process, and small construction equipment. Recently, new microple equipped with the base expansion structure at the end has been developed to improve the foundation bearing capacity. The improvement of load capacity can be conceptually achieved by expanding the base expansion structure when a load is applied to the micropile. However, the expansion mechanism of the base expansion structure and the improvement of load capacity of the micropile were not yet experimentally validated. Therefore, in this study, a series of centrifuge model tests was performed to evaluate the effect of the base expansion structure on the improvement of load capacity. Two types of soil, sand and weathered rock, were prepared and the loading tests were performed using the real micropile with the base expansion structure. During the tests, the earth pressures surrounding the base expansion structure were monitored. As a result, when a load of 30 kN was applied to the micropile, the increase in the ratio of the horizontal to vertical pressure increment (∆σ_h/∆σ_𝜈) ranged from 0.4 to 0.58 in sand and ∆σ_h/∆σ_𝜈 = 0.19 in weathered rock, respectively. Therefore, it can be concluded that the increase in the horizontal earth pressure adjacent to the base expansion structure will improve the bearing capacity of the micropile.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.514-519
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• 2006

The purpose of this study is to evaluate the performance of existing bridge foundation reinforced by battered micropiles. In order to do numerical method using a Finite element program was used to predict the micropile behavior and quantify their reinforcing effect to existing bridge foundations. In addition, effect of battered micropiles on existing foundations was compared with vertically reinforced bridge foundations. Based on the study performed, it was found that the use of battered micropile is more efficiently reducing displacement of existing foundation than vertically installed micropiles under vertical and horizontal loadings respectively. The batter angle of micropile was also found effective about $15^{\circ}\sim20^{\circ}$ to reduce the vortical displacement. The horizontal reinforcement effect is continuously larger with an increase in batter angle. So, it is believed that the results presented could give an idea to enhance in-service performance of existing bridge foundations reinforced by micropiles.

• Journal of the Korean Geotechnical Society
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• v.31 no.6
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• pp.5-13
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• 2015

Micropile was mainly used as one of underpinnig methods, and recently has been used for the various purposes such as foundation for new structure or slope stability etc. However, despite of the increase of the usage of micropile, studies about the horizontal bearing characteristic of micropile are insufficient. Thus the model test has been conducted to investigate the horizontal bearing characteristics of micropile with the length ratio and installation angle of pile. Consequently, micropiles at the installation angle of $+30^{\circ}$ and $-30^{\circ}$ effectively increase the horizontal bearing capacity, respectively for L/d ${\leq}25$ and L/d > 50.

• Journal of the Korean Geotechnical Society
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• v.23 no.1
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• pp.5-11
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• 2007

Micropiles have been used for underpinning or rehabilitation of existing foundations, and direct structural support system as well. However, relatively few studies have been done on the load-transfer mechanism of micropile systems in Korea. In addition to that, only the limited information is available for estimating the side friction values on micropiles installed in weathered soils. In this study, a full-scale test on an instrumented micropile is performed in order to establish the load-transfer curves based on a hyperbolic function. Then, an empirically derived equation that correlates the load-transfer curve of micropiles with the N values from field standard penetration tests is proposed. The results from all procedures are presented in this paper. Finally, back analysis using a finite difference method and the published field data are adopted for examination of a developed skin friction equation of micropile in weathered soils respectively.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.538-543
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• 2004

Micropile has been widely used for reinforcing general grounds, improving slope stability and structural foundations. However, a need still exists for evaluating the effects of inclined micropiles on shallow foundations in Korea. In this paper, numerical analyses were presented to evaluate settlement characteristics on shallow foundations reinforced by micropiles and the effects of inclined micropiles under various conditions such as the installation position, installation angle, hardness(diameter), and grouting type. In addition, this paper reports trends of effectiveness and efficiency of using inclined micropiles on shallow foundations under specified conditions.