• Journal of the Korean Geotechnical Society
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• v.36 no.11
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• pp.35-49
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• 2020

The lateral bearing capacity of the micropile depends on the installed conditions such as number, installation angle and spacing of the pile. Existing research on micropile has been limited to the evaluation of vertical bearing characteristics and suggestion of effective installation methods, and there are few studies on failure mechanisms such as failure mode. And most of the studies on the lateral bearing capacity of micropile are also on the 1-row micropile. Therefore, in this study, a model test was performed to evaluate the behavior and lateral bearing characteristics of a 2-row micropile when the installed conditions such as the installation length, angle, and spacing of the pile were different. As a result of the model test, when the installation angle is θ > 0° (Not cross installation), the lateral bearing capacity of 2-row micropile depends on the spacing of the piles, and the installation angle θ = +30° was the most effective for increasing the bearing capacity. In addition, when the installation angle is θ < 0° (Overlap installation), it depends on the spacing and angle of the pile, and the condition of installation angle θ = -15° was found to be the most effective for increasing the bearing capacity.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.2
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• pp.335-344
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• 2019

Micropiles are widely used for foundation underpinning to enhance bearing capacity and reduce settlement of existing foundation. In this study, the main objective is to evaluate underpinning performance of a newly developed micropile called waveform micropile for foundation underpinning during vertical extension. Finite element method (FEM) was used to evaluate the underpinning performance of waveform micropile in terms of load-settlement response of underpinned foundation and load sharing behavior. For comparison, underpinning effects of three conventional micropiles with different lengths were also discussed in this study. Numerical results of load-settlement response for single pile demonstrated that bearing capacity and axial stiffness of waveform micropiles were higher than those of conventional micropiles because of the effect of shear keys of waveform micropiles. When additional loads 20 %, which is according to design loads of the vertical extension, were applied to the underpinned foundation, load sharing capacity of waveform micropile was 40 % higher than conventional micropile at the same size. The waveform micropile also showed better underpinning performance than the conventional micropile of length 1~1.5 times of waveform micropile.

• Journal of the Korean GEO-environmental Society
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• v.22 no.4
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• pp.15-23
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• 2021

Various micropiles have been developed through research related to micropiles, which have been carried out with the increased use of micropiles. Among the micropile construction methods being developed, the triaxial micropile (tmp), which is recently developed for the purpose of increasing the horizontal bearing capacity (seismic resistance), is representative. The three-axis micropile has the advantage of a method that can resist horizontal load more effectively because three micropiles installed inclined on each axis resist horizontal load. However, there is a problem in effectively using this pile method due to insufficient research on the support characteristics of the triaxial group micropile. In order to effectively utilize the triaxial group micropile (tmp), it is required to evaluate the bearing capacity for the factors that affect the horizontal bearing capacity of the pile. Therefore, in this study, field horizontal loading Tests were performed for each load direction, field loading Tests were verified through three-dimensional finite element analysis, behavioral characteristics of triaxial micropiles were evaluated, and appropriate horizontal bearing capacity was analyzed in consideration of horizontal load directions.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.03a
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• pp.177-184
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• 1999

In soft ground tunneling, shield method is very good for safety of neighboring structures. Although shield tunnel method has the merits to minimize the deformation of ground around tunnel, ground deformations occurred until the material grouted in tail void hardens are inevitable. In this study, the effects of micropile used as one method to restrain the settlement of neighboring structures by the tail void are studied by laboratory model tests. As a basic test result, the effective direction of micropile and the restraint rate of settlement by micropile reinforcement are known.

• Structural Engineering and Mechanics
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• v.63 no.3
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• pp.417-428
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• 2017

The micropile has been mainly used under the concept of supplementing structural support or reinforcing soft ground. For the micropiled-raft system which uses a micropile and a raft in combination in particular, it is generally considered as ground reinforcement rather than foundation components considering the bearing capacity of the micropile in many cases. In this study, the bearing capacity mechanism of the micropiled-raft system is investigated through a physical model test and numerical method. The numerical results have shown that not only the slender-pile-effect of the micropile, but also the ground reinforcement effect, increase the bearing capacity considerably. The bearing capacity formula of the micropiled-raft system is derived based on the failure mechanism obtained through model tests. The formula is verified and proposed as a design chart.

• Journal of the Korean Society of Safety
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• v.29 no.5
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• pp.74-81
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• 2014

This study proposes an advanced type of a micropile system. The proposed micropile system consists of perfobond ribs installed steel rod to improve shear capacity between the thread and the grout, and partially expanded drill holes to increase resistance capacity between the grout and the ground. This study contains experimental evaluations on the proposed micropile system to verify the shear capacity of perfobond rib installed on the steel rod and the load-carrying capacity of shear key created by the partially expanded drill hole. Push-out tests were conducted on a rolled screw thread and steel rods which perfobond ribs are installed instead of rolled screw, in order to compare their load-carrying capacity and behavioral characteristics. As a result, it was confirmed that the perfobond-rib steel rods show much superior structural behavior in terms of initial stiffness, ultimate load, and ductile behavior.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.368-375
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• 2009

This paper describes field installation and load test results performed for three types of micropiles in the process of developing a new micropiling method. Field tests were performed for two conventional types(i.e., micropile reinforced with steel bar and gravity grouting, micropile reinforced with steel bar and steel casing and gravity grouting) and a proposed type(i.e., micropile reinforced with hollow steel pipe wrapped with geotextile-pack and pressurized grouting). The load test results subjected to axial compression and tension and lateral loading conditions are described in this paper. The micropiles were exposed in the air in order to verify the installation quality and curing condition of grouting material via ground excavation. Axial compression and tension test results indicate that the new micropile type provide at least 40% higher bearing capacity than that of conventional types. Based on the examination of exposed piles, it is induced that the proposed method, packed micropile, provides better interlocking between grouts and surrounding soils and increases higher frictional resistance comparing to conventional types.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.6
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• pp.687-695
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• 2020

Micropile is used to improve the stability of existing structures as well as solve various geotechnical problems, such as suppressing slope activity and shearing keys of retaining walls. The existing micropile method has a significantly less capacity to resist a horizontal force than a vertical force0355 Therefore, it is necessary to develop and study an umbrella-type micropile method with excellent seismic performance that can secure seismic performance economically while minimizing structures and ground disturbance areas in the limited space of existing structures. In this study, numerical analysis was performed on the umbrella-type micropile, in which the sloped pile and vertical pile were combined, and the horizontal behavior in soft clay ground during earthquakes was analyzed. Numerical analysis showed that umbrella-type micropile suppresses horizontal displacement in soft ground, and the effect of reducing the horizontal displacement was more pronounced when the embedded depth of the slope pile was 15 m or more. The embedded depth of the micropile and horizontal displacement suppression effect was proportional. Therefore, the umbrella-type micropile has an excellent effect of suppressing horizontal displacement during earthquakes on soft clay ground.

• Geomechanics and Engineering
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• v.31 no.2
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• pp.197-208
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• 2022

Micropiles consisting of steel bars and grouts are commonly used in underpinning methods to reinforce supports or to suppress the subsidence of existing structures. Recently, applications in the field of geotechnical engineering have expanded. Despite the increasing use of micropiles are used, the PHC or steel pile formula is still applied for the settlement amount of micropiles. Compared with field test results, the amount of micropile subsidence obtained from the existing method may result in a very large error in the displacement of the micropile. Therefore, it is difficult to utilize micropiles effectively. Hence, to solve this problem, this study evaluated the behaviors and support characteristics of micropiles through field compression and tensile tests, and proposed a method for predicting the amounts of their subsidence. To confirm the appropriateness of the proposed method, field test results and the results obtained using the proposed method were compared. It was found that the settlement amounts of the micropiles as predicted through the existing method were significantly overestimated (error ≈ 50-80%) relative to the field test results, whereas the settlement errors of the piles predicted through the proposed method decreased (error ≈6-32%). Thus, it is possible to reduce the previously overestimated amount of settlement, and the modified method of this study allows more efficient design than the conventional method.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.11a
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• pp.1-26
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• 2002

This study addresses preliminary design and construction specification for micropiles. Especially several design methods for micropiles in sands, clays or mixed soil layers are described. The bearing capacity of micropiles are mainly depended upon the shaft resistance. Therefore, the pressure of grouting is one of the most important design parameters for the bearing capacity evaluation of micropile. There is no theoretical way to evaluate the shaft resistance of micropile up to now because grouting method is another key parameter for micropile design approach. Because of above reasons, the present design approaches of the micropile are based on the collected field data The bearing capacities of designed micropiles should be verified by static load tests before and after construction at the planned site.