현장시험을 통한 파형 마이크로파일의 시공성 및 거동 평가

한진태,장영은 한국지반공학회 2016 한국지반공학회논문집 Vol.32 No.10

Waveform micropile is an advanced construction method that combined the concept of conventional micropile with jet grouting method. This new form of micropile was developed to improve frictional resistance, which consequently leads to achieving higher bearing capacity and cost efficiency. Two field tests were conducted to examine the field applicability as well as to verify the effects of bearing capacity enhancement. In particular, waveform micropile construction using jet grouting method was performed to evaluate the viability of waveform micropile installation. After testing, the surrounding ground was excavated to check the accomplishment on the shape of waveform micropile. The result showed that waveform micropile can be installed by adjusting the grouting time and pressure. In the loading tests, waveform micropile’s bearing capacity increased by 1.4 to 2.3 times depending on their shapes when compared with conventional micropile. Overall results clearly demonstrated that waveform micropile is an enhanced construction method that can improve bearing capacity.

Numerical Analysis of Effect of Waveform Micropile on Foundation Underpinning During Building Vertical Extension Remodeling

Wang, Cheng-Can(왕성찬),Jang, Youngeun(장영은),Kim, Seok-Jung(김석중),Han, Jin-Tae(한진태) 대한토목학회 2019 대한토목학회논문집 Vol.39 No.2

기존건물의 수직증축시, 추가되는 증축하중을 지지하기 위해서 기초를 보강하는 것은 필수적이다. 일반적으로 기초의 지지력을 증대시키고 침하를 감소시키기 위하여 마이크로파일공법이 널리 활용되고 있다. 본 연구에서는 기존의 마이크로파일에 전단키가 추가된 새로운 형식의 파형마이크로파일을 활용하여 연구를 수행하였다. 유한요소해석법(FEM)을 통해 기초보강시 파형마이크로파일의 하중침하거동과 하중분담율을 평가하였으며, 3가지 길이 다른 일반적인 마이크로파일들의 지지거동과 비교를 통해 보강효과를 확인하였다. 해석 결과, 파형마이크로파일의 지지력과 축강성이 일반 마이크로파일보다 크게 나타났으며, 이는 파형 마이크로파일의 전단키에 의한 효과인 것으로 판단된다. 또한, 수직증축 리모델링 시, 기존하중 대비 20 %의 증축하중이 재하될 때, 파형마이크로파일의 하중분담율이 동일한 길이의 일반 마이크로파일에 비해 약 40 % 증가하였으며, 보강효과는 길이 1~1.5배의 일반적인 마이크로파일보다 우수한 것으로 나타냈다. 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.

사질토 지반에 설치된 마이크로파일의 설치간격 및 설치각도에 따른 압축거동특성

경두현,김가람,김대홍,신주호,이준환 한국지반공학회 2013 한국지반공학회논문집 Vol.29 No.12

Micropile technology has evolved continuously since its instruction by Fernando Lizzi in the 1950s. The effectsof group micropile have been researched by many researchers. The effects of group micropile differ and changewith pile length, pile spacing (S), pile angle (θ) and pile embedded conditions. In the present study, the effectsof 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 variouspile 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-raftwere 20% (S=3D, θ=45°) to 70% (7D,θ=15°) of settlement of mat foundation.

수치해석을 이용한 파형 마이크로파일의 지지거동 분석

한진태(Han, Jin-Tae),김성렬(Kim, Sung-Ryul),장영은(Jang, Young-Eun),이승현(Lee Seung-Hyun) 한국산학기술학회 2013 한국산학기술학회논문지 Vol.14 No.11

최근 국내에서 철도부지 상부에 인공지반을 구축하고, 인공지반 위에 복합주거타운을 건설하는 정책이 추진 되고 있다. 이에 상부 구조물 및 인공지반을 지지할 수 있는 적합한 기초형식이 요구되는데, 철로와 철로 사이의 좁 은 공간에 급속 시공 가능한 기초 형식 중 가장 대표적인 방법은 마이크로파일로 알려져 있다. 그러나 주기초로 마이 크로파일이 사용될 경우 기초 시공비가 크게 증가하게 된다. 따라서 본 연구에서는 마이크로파일의 경제성 및 지지력 을 향상시키면서 철도상부 인공지반에 적합한 신개념 마이크로파일을 제안하였다. 신개념 마이크로파일은 지반을 Jet Grouting 공법을 이용하여 지반의 일정 영역을 고결시킨 뒤 강봉을 시공하는 방법에 Jet Grouting 시 말뚝체를 파형 (waveform)의 형상으로 시공하여 지지력을 향상시키고 기존 마이크로파일 대비 말뚝의 전체 길이를 줄여 경제성을 높이고자 한 방법이다. 본 연구에서는 2차원 축대칭 유한요소해석을 수행하여 이러한 파형 마이크로 파일의 지지거동 을 분석하였다. 해석 결과 파형 마이크로파일은 일반 마이크로파일에 비해 길이가 15% 정도 감소하였음에도 불구하 고 동일한 설계하중에서 변위가 감소하여 지지력 및 경제성 측면에서 효과가 있는 것으로 나타났다. 또한, 파형 마이 크로파일의 요철에 의한 주면 마찰력 증가효과는 상대적으로 연약한 토층에서 큰 것으로 나타났다. Recently in Korea, the policy is being proceeded to build a intergenerational housing on artificial ground of railroad site for utilizing rental house. Due to narrow space of rail road site, suitable method have to be developed such as micropiles which is known as a method of a fast construction. However, If micropile is used as foundations for the super structure, construction cost is increases compared with other pile. Consequently, new concept micropile proposed to improve both bearing capacity and cost efficiency of general micropile. New concept micropile consists of waveform cement grout surrounding tread bar that formed by grouting the soil layer with jet grouting method as control the grout pressure and flow. The micropile with waveform is expected to decrease the construction cost by cut down pile length of general micropile. This paper examined the behavior of the new concept micropile with waveform subjected to axial load using two-dimensional axisymmetric numerical analyses method. According to the numerical result, there will cost effectiveness as the pile displacement decreased despite the length of waveform micropile is down about 5% from a general micropile under the same loading condition. Also, the effect of skin friction force which mobilized from the waveform of micropile appeared at relatively soft ground.

조밀한 모래지반의 기초하부에 설치된 마이크로파일 보강효과에 관한 실험적 연구

이태형(Lee Tae-Hyung),임종철(Im Jong-Chul) 대한토목학회 2006 대한토목학회논문집 C Vol.26 No.3

직경 100~300㎜ 정도의 보링공에 강봉 또는 강관을 삽입하여 그라우팅 재료로 주입ㆍ압력을 가하는 소구경 현장 타설 말뚝의 일종인 마이크로파일 공법은 기계의 소형화, 저진동, 저소음 등의 장점으로 도심지의 협소한 공간에서의 적용 범위가 점차 확대되고 있다. 마이크로파일은 지지력 증가, 지반 변위억제를 통한 구조물 안정성 확보 등에 주로 적용되어져 왔고, 향후 공법의 유효성과 잠재성으로 다양한 방면에 활용될 것으로 예상된다. 본 연구에서는 마이크로파일과 지반과의 상호작용에 초점을 두고 기초의 하부지반(구조물 지지개념) 보강을 실시하였으며, 모형실험 결과 및 지반 변형 분석을 통해서 보강 효과(지지력 증가효과 및 침하억제 효과)를 정성적ㆍ정량적으로 분석하여 설계 및 시공에서의 효율성과 적용성을 높이고자 한다. The micropile, which is a kind of the in-situ manufactured pile with small diameter of 100~300㎜, 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.

Prediction of Uplift Capacity of a Micropile Embedded in Soil

홍원표,Neatha Chim 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.1

An analytical approach was performed to predict the uplift capacity of a micropile embedded in soil on the basis of the failuresurface generated inside the soil mass around a micropile. The failure surface rises from the critical embedded depth of the micropileand has an angle equal to half of the internal friction angle of soil to the vertical. To investigate the failure surface, image of soildeformation was captured from a model test on a panel embedded in soil. The analytical approach to uplift capacity could evaluatethe effect of parameters related to the properties of both the micropile and soil such as the embedded length, the diameter and surfaceroughness of the micropile, and the shear strength parameters of the soil. A series of model tests were conducted on a micropile toverify the applicability of the analytical approach in actual practice. Furthermore, to increase the reliability of the analytical approach,the predicted uplift capacity was compared with experimental results previously presented in the literature. The predicted upliftcapacity of the micropile shows practically good agreement with the experimental results of the model tests. Moreover, the predicteduplift capacity has good agreement with previous experimental results.

원심모형실험을 통한 파형 마이크로파일의 연직 지지력 평가

장영은,한진태,김재현,박헌준,김상환 한국지반공학회 2015 한국지반공학회논문집 Vol.31 No.8

In this study, a series of centrifuge tests were performed in order to observe the bearing capacity of waveform micropile, a new concept of micropile that uses a modified jet grouting process. A total of six models were considered,conventional micropile, jet grouted pile, and four different shapes of waveform micropiles. The test results indicated that the waveform micropile effectively contributes to the increase of the bearing capacity compared to the micropilewithout the shear keys. Among the waveform micropiles, the model that has a relatively small space between the shear keys showed the most significant improvement of load capacity. Additionally, the ultimate load capacities of all pileswere compared using well-known estimation method. As a result, P-S curve method and total settlement method with 25.4 mm were considered suitable to account ultimate load for the waveform micropile.

삼축 마이크로파일(TMP)의 현장수평재하시험과 3차원 수치해석을 통한 거동 분석

김태현(Taehyun Kim),안광국(Kwangkuk Ahn),안성율(Sungyul An) 한국지반환경공학회 2021 한국지반환경공학회논문집 Vol.22 No.4

마이크로파일의 활용증가로 수행되었던 마이크로파일의 관련연구를 통해 다양한 마이크로파일이 개발되어왔다. 개발되고 있는 마이크로파일 공법들 중 최근 수평지지력(내진저항력)의 증가를 위한 목적으로 개발된 삼축 마이크로파일(Triaxial micropile, TMP)이 대표적이라 할 수 있다. 삼축 마이크로파일은 각축에 경사지게 설치된 3개의 마이크로파일이 수평하중에 저항하므로 좀 더 효과적으로 수평하중에 저항할 수 있는 공법의 장점이 있다. 그러나 삼축 마이크로파일에 대한 지지특성에 대한 연구가 부족하여 이 파일공법을 효과적으로 활용하는데 문제가 있다. 즉, 삼축 마이크로파일(TMP)의 효과적인 활용을 위해서는 파일의 수평지지력에 영향을 주는 요인에 대한 지지력 평가가 요구된다. 이에 본 연구에서는 하중 방향별 현장수평재하시험을 수행하고 3차원 유한요소해석을 통해 현장 재하시험을 검증하고 거동 특성을 고찰하였으며, 수평하중의 방향을 고려한 적정한 수평지지력을 분석하였다. 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.

Characterizing Optimum Casing Configuration for Laterally Loaded Micropiles with Inclined Condition

홍성철,김가람,김인철,이지영,이준환 대한토목학회 2022 KSCE Journal of Civil Engineering Vol.26 No.9

Micropile is vulnerable to lateral load due to the small diameter configuration. Inclusion of a steel casing can be an effective option to enhance the lateral load capacity of micropile, yet not quantified in detail. In this study, the reinforcing effect of casing for laterally loaded micropile is investigated considering the inclined condition of micropile. A series of the finite element analysis were performed to simulate laterally loaded micropiles for various configurationconditions. The maximum bending moment (Mmax) and its location (Zmax) became smaller and shallower, respectively, when micropile was inclined at an angle of θ, which is advantageous in design. For micropile with a casing, the lateral load capacity (Hu) increased as casing length (Lc) increased, and the effect of θ was similar for all cases with different length ratios of casing and micropile (i.e., Lc/Lp). Hu increased by 50% to 60% for Lc/Lp of 0 to 0.3, respectively. For Lc/Lp > 0.3, the values of both Hu and Mmax did not change significantly for all θs. Therefore, Lc/Lp = 0.3 was proposed as an optimum casing length that yields the most economical yet most enhanced stability condition. A design equation was proposed to estimate the lateral load capacity of inclined micropiles with a casing.

인발력을 받는 팩마이크로파일의 주면마찰력

홍원표,조삼덕,최창호,이충민 한국지반공학회 2012 한국지반공학회논문집 Vol.28 No.6

Pack micropiles were recently developed to improve pile capacity of general micropiles. Pack micropiles were made by warping thread bar or steel pipe of general micropile by geotexlile pack and grouting inside the pack with pressure. According to the pressure, the boring hole could be enlarged. A series of pile uplift tests were performed on three micropiles. Two out of the three piles were the pack micropiles and the other was the general micropile, in which a thread bar was used in the boring hole. According to the pressure applied to the pack micropiles, the diameter of boring hole was enlarged from 152 mm to 220 mm. Unit skin friction mobilized on side surfaces of micropiles increased with displacement of pile head and reached on a constant value, which represents that the relative displacement between piles (or thread bar) and soils was reached on critical state. And the uplift resistance of pack micropile was higher than that of general micropile. Two reasons can be considered: One is that the frictional surface increases due to enlarging diameter of boring holes and the other is that the unit skin friction could increase due to compressing effect of surrounding soils by soil displacement as much as the enlarging volume of boring hole. The compression effect appeared at deeper layer rather than surface layer. The unit skin friction mobilized on micropiles with small diameter was higher than the ones on large bored piles.