원심모형 실험을 이용한 반복하중을 받는 모노파일 거동 평가

이명재,유민택,박정준,민경찬,Lee, Myungjae,Yoo, Mintaek,Park, Jeongjun,Min, Kyungchan 한국지반공학회 2019 한국지반공학회논문집 Vol.35 No.6

본 연구는 원심모형실험을 이용해 건조 사질토 지반에 근입된 모노파일의 수평 반복하중에 대한 거동을 연구하였다. 실험에 사용된 지반 시료는 상대밀도 80%에서 마찰각이 $38^{\circ}$인 건조 주문진 표준사를 사용했다. 실험 과정은 우선 반복하중의 크기를 결정하기 위해 정적 하중 실험을 수행하여 극한하중을 결정하였다. 이를 통해 도출된 극한 하중 값의 30%, 50%, 80%, 120%을 반복하중의 값으로 결정하였고, 반복횟수는 100회로 수행되었다. 이 결과를 통해 실험 반복하중 p-y 곡선을 산정하였고 도출된 하중 별 최대 지반반력점들을 이용하여 깊이 별 반복하중 p-y 중추곡선을 도출하였다. 이를 기존 p-y 곡선과 비교 결과, 동일 깊이에서 초기기울기가 API(1987) p-y 곡선보다 과소평가 되었으며, 극한지반반력은 과대평가되었다. 또한, 동적 p-y 곡선과 비교하였을 때, 동일 깊이에서의 반복하중 p-y 중추곡선의 초기기울기와 지반반력이 작게 평가되었다. 이는 말뚝이 받는 하중 조건에 따라 p-y 곡선을 다르게 적용해야 할 것으로 판단된다. 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.

진동대 시험을 활용한 구조물의 모드 형상에 따른 동적 p-y 곡선 특성 분석

한재혁(Han, Jae-hyeok),안성노(Ahn, Seongnoh),윤형철(Yoon, Hyungchul),정종원(Jung, Jongwon) 한국방재학회 2021 한국방재학회논문집 Vol.21 No.5

말뚝기초의 내진설계 시, 지진의 동적 하중을 고려한 지반의 비선형적 거동을 나타내는 p-y 곡선이 필요하다. 최근 지반-구조물 상호작용을 고려한 p-y 곡선 분석이 이루어지고 있으나, 다층 구조물을 활용한 연구는 부족한 실정이다. 이에 본 연구에서는 진동대 실험을 통해 구조물 모드형상(구조물이 부재, 단층 구조물, 3층 구조물)에 따른 지반-구조물 상호작용 영향을 고려한 p-y 곡선 특성을 분석하였다. 그 결과, (1) 입력가속도의 증가에 따른 휨모멘트 및 말뚝 변위의 증가, (2) 각 구조물의 고유진동수에서 최대 지반 반력 및 말뚝 변위 발생을 관찰하였다. 또한, 본 연구에서 사용된 3층 구조물에 비해 단층 구조물의 경우 휨모멘트, 지반 반력 및 p-y 곡성의 기울기가 크게 나타났다. 이는, 단층 구조물로 모사한 내진설계가 보수적인 설계임을 나타낸다. In the seismic design of pile foundations, a p-y curve representing the nonlinear behavior of the ground considering the dynamic load of the earthquake is required. Recently, p-y curve analyses reflecting the soil-structure interaction have been conducted, but studies on multilayer structures have not been investigated extensively. In this study, the p-y curve characteristics were analyzed, considering the influence of the ground-structure interaction based on the mode shape of the structure (no structure, single-story structure, and three-story structure) through shake table tests. It was found that (1) the bending moment and pile displacement increased with input acceleration, and (2) the maximum soil resistance and pile displacement occurred at the natural frequencies of each structure were observed. In addition, the bending moment, soil resistance, and p-y curve slope were higher in the single-story structure than in the three-story structure. The findings indicate that the seismic design simulated for a single-story structure is conservative.

3차원 수치해석을 이용한 점성토 지반의 p-y 곡선 산정

이시훈,김성렬,이주형,정문경 한국지반공학회 2011 한국지반공학회논문집 Vol.27 No.7

The p-y curve has been used to design pile foundations subjected to lateral loading. Although the p-y curve has a large influence on the pile lateral behavior, p-y curves have not been clearly suggested. In this study, the p-y curve of clay was evaluated for drilled shafts in marine deposits by using 3-dimensional numerical analyses. First, the optimization study was performed to properly determine boundary extent, mesh size, and interface stiffness. The numerical modeling in the study was verified by comparing the calculated and the pile loading test results. Then, the p-y curves of single and group piles were evaluated from the parametric study. The selected parameters were pile diameter, pile Young's modulus and pile head fixed condition for a single pile, and pile spacing for group piles. Finally, the p-multiplier was evaluated by comparing the p-y curves of a single pile and group piles. As a result, the p-multiplier at pile spacing of 3D was 0.83, 0.67 and 0.78 for the front, middle, and back row piles, respectively, and showed values similar to those of O’Neill and Reese (1999). For the pile group with pile spacing larger than 6D, the group effect can be ignorable.

1g 진동대 실험을 이용한 연약 점성토 지반에서의 동적 p-y 곡선 연구

한진태,유민택,최정인,김명모 한국지반공학회 2010 한국지반공학회논문집 Vol.26 No.8

In this study, a series of 1 g shaking table tests were carried out for a single pile in soft clay with various input acceleration amplitudes and frequencies. Based on the results, dynamic p-y curves were drawn and, in turn, the dynamic p-y backbone curve was formed by connecting the peak points, corresponding to the maximum soil resistance, of the dynamic p-y curves. In order to represent the p-y backbone curve numerically, Matlock’s p-y formulations for clay was used to find the initial stiffness (kini) and the ultimate capacity (pu) of the clay, both of which are required to formulate the p-y backbone curve as a hyperbolic function. The suggested p-y backbone curve was verified through comparisons with currently available p-y curves as well as other researchers' centrifuge test results and numerical analysis results.

3차원 수치해석을 통한 점성토 지반의 군말뚝 p-y 곡선 산정

정재우(Jung,Jaewoo),최용진(Choi,Yongjin),안재훈(Ahn,Jaehun) 한국방재학회 2021 한국방재학회논문집 Vol.21 No.6

말뚝기초로 지지된 구조물에 지진;강풍 및 해류가 작용할 경우 큰 수평하중이 발생할 수 있다. 수평하중을 받는 무리말뚝의 거동은 p-y 곡선과 무리말뚝효과를 고려하기 위한 계수인 “p-multiplier (Pₘ)”을 이용하여 해석한다. 본 연구에서는 3차원 유한요소해석 프로그램인 Plaxis 3D를 활용하여 점성토 지반에 설치된 단일말뚝과 3행 × 3열로 배치된 무리말뚝을 해석하여 p-y 곡선과 Pₘ을 산정하였다. p-y 곡선의 해석 결과;지반저항력은 지반의 비배수 전단강도가 증가할수록;말뚝중심간 간격(S/D)이 멀어질수록 증가하였다. 무리말뚝효과인 Pₘ의 경우;무리말뚝 중심에 위치할수록;말뚝중심간 간격이 가까울수록;인접한 개별말뚝의 간섭효과로 인해 Pₘ은 감소하였다. 이를 통해 Pₘ은 개별말뚝 위치와 말뚝중심간 간격에 따라 크게 영향을 받는다는 것을 알 수 있다. The pile foundation supported on a structure can generate large horizontal loads due to earthquakes;high winds;and wave actions. The behavior of piles when subjected to horizontal load is generally analyzed using the p-y curve and “p-multiplier (Pₘ),” which is the coefficient of the group pile effect. In this study;the p-y curves and Pₘ were calculated by analyzing a single pile and group of piles arranged in 3 × 3 installed in cohesive soil using the finite element analysis program;Plaxis 3D. The soil resistance (p) increased as the undrained shear strength of the clay increased and the distance between the pile centers (S/D) increased. In the case of the group pile effect;when Pₘ was closer to the center of the group pile;the distance between the pile centers was smaller;and Pₘ was less due to the interference effect of the adjacent individual piles. In conclusion;it was observed that Pₘ is affected by the location of the individual piles and the distance between the pile centers.

3차원 수치해석을 통한 사질토 물성에 따른 무리말뚝 p-y 곡선과 p-multiplier 평가

최용진,안재훈 한국방재학회 2020 한국방재학회논문집 Vol.20 No.4

The p-y curve method and p-multiplier (Pₘ), which implies a group effect, are widely used to analyze the nonlinear behaviors of laterally loaded pile groups. Factors affecting Pₘ includes soil properties as well as group pile geometry and configuration. However, research on the change in Pₘ corresponding to soil properties has not been conducted well. In this study, in order to evaluate the effect of soil properties on the group effect in a laterally-loaded pile group installed in sandy soil, numerical analysis for a single pile and 3×3 pile group installed in loose, medium, and dense sand, was performed using the 3D numerical analysis program, Plaxis 3D. Among the factors considered in this study, the column location of the pile was the most dominant factor for Pm. The effect of the sand property change on Pₘ was not as significant as that of the column location of the pile. However, as the sand became denser and the friction angle increased, the group effect increased, leading to a decrease in Pₘ of approximately 0.1. This trend was similar to the result reported in a previous laboratory-scale experimental study. 무리말뚝의 수평방향 비선형 거동 해석에는 p-y 곡선과 무리말뚝 효과를 나타내는 p-multiplier (Pₘ)을 사용한 방법이 보편적으로사용된다. Pₘ은 무리말뚝의 기하형상뿐만 아니라 지반 물성의 영향도 받는다. 하지만 지반 물성에 따른 Pₘ의 변화에 대한연구는 부족한 실정이다. 본 연구에서는 사질토지반에서 수평방향 하중을 받는 무리말뚝의 지반 물성 변화에 따른 무리말뚝효과차이를 평가하기 위해, 3차원 수치해석 프로그램인 Plaxis 3D를 활용하여 느슨, 중간, 조밀한 사질토지반에 설치된 단일말뚝과 3행×3열 무리말뚝에 대한 해석을 수행하고 p-y 곡선과 Pₘ을 산정하였다. 본 연구의 해석조건인 말뚝 중심간격, 무리말뚝내 개별말뚝의 행과 열 위치, p-y 곡선 산정 깊이, 사질토지반 물성 중에는 말뚝이 위치한 열이 Pₘ에 가장 지배적인 영향을미쳤다. 사질토지반의 물성변화가 Pₘ에 미치는 영향은 말뚝이 위치한 열의 영향에 비해 크진 않았지만, 지반이 조밀해지고내부마찰각이 증가함에 따라 무리말뚝 효과가 커져, Pₘ이 감소하는 경향을 나타내었으며, 이는 기존 실내실험 결과와 유사하였다.

조밀한 포화 실트질 모래지반에서 횡방향 반복하중을 받는 말뚝의 p-y 거동 평가

백성하,최창호,조진우,정충기 한국지반공학회 2019 한국지반공학회논문집 Vol.35 No.11

Piles that support offshore wind turbine structures are dominantly subjected to cyclic lateral loads of wind, waves, and tidal forces. For a successful design, it is imperative to investigate the behavior of the cyclic laterally loaded piles; the p-y curve method, in which the pile and soil are characterized as an elastic beam and nonlinear springs, respectively, has been typically utilized. In this study, model pile tests were performed in a 1 g gravitational field so as to investigate the p-y behaviors of cyclic laterally loaded piles installed in saturated dense silty sand. Test results showed that cyclic lateral loads gradually reduced the overall stiffness of the p-y curves (initial stiffness and ultimate soil reaction). This is because the cyclic lateral loads disturbed the surrounding soil, which led to the decrement of the soil resistance. The decrement effects of the overall stiffness of the p-y curves became more apparent as the magnitude of cyclic lateral load increased and approached the soil surface. From the test results, the cyclic p-y curve was developed using a p-y backbone curve method. Pseudo-static analysis was also performed with the developed cyclic p-y curve, confirming that it was able to properly predict the behaviors of cyclic laterally loaded pile installed in saturated dense silty sand.

제주 연근해 해저암반의 p-y 곡선 모델에 관한 연구

장영은(Jang, Young-Eun),이준용(Lee, Joonyong),조삼덕(Cho, Samdeok),유동우(Yoo, Dong-Woo),최창호(Choi, Changho) 한국지반환경공학회 2012 한국지반환경공학회논문집 Vol.13 No.6

해상풍력시스템의 규모가 점차적으로 증가하고 있는 추세에 따라 상부구조물을 지지하는 기초구조물 안정성 확보의 중요성이 대두되고 있다. 이에 따라, 지반공학적 측면에서 기초구조물과 지반의 상호작용이 전체 시스템에 미치는 영향을 파악하기 위한 해석방안이 요구되고 있으며, p-y 곡선 모델의 적용이 대표적인 방법이다. 본 연구에서는 풍황이 우수하여 해상풍력발전 시스템 운영을 위한 대상지로써 적합하다고 알려져 있는 제주도 해저지반(현무암)의 공학적 특성을 현재까지 제안된 암반 p-y 곡선 모델에 적용하였다. 이를 통해 제주도 및 국내 암반 분포 지역에 대한 해상풍력시스템 기초구조물과 해저암반 간의 상호작용 해석 과정을 정리하고 향후 연구 방향을 제안하였다. 전반적으로 암반 p-y 곡선 산정결과는 지표면에 근접할수록 지반반력이 증가하는 경향을 나타냈으며, 말뚝에 작용하는 모멘트, 전단력 등을 분석한 결과 암반의 공학적 특성을 적절히 모사할 수 있음을 확인하였다. Safety issue for offshore wind-turbine foundation becomes a crucial factor as offshore wind turbines have been scaled up. Correspondingly, there is a demand to understand the effect of soil-structure interaction on to system behavior in geotechnical engineering point of view. The p-y curve method researched in past few decades is one of the most appropriate methodology to analyze the problem. In this study, recently proposed p-y curve models for various rocks are calibrated to analyze the engineering characteristics of seabed of Jeju Island where it is known to be most suitable area for offshore wind energy farm. Step by step calibration process for p-y models is presented. Analysis results show that subgrade reaction generally increases as closer to seabed. It is also shown that the behavioral characteristics of foundation reflect well rock properties in terms of resultant moment, shear force, etc.

원심모형 실험을 이용한 지반-말뚝 상호작용의 정적 및 동적 거동 평가

유민택,권선용 한국지반공학회 2018 한국지반공학회논문집 Vol.34 No.7

In this study a series of centrifuge tests were carried out in dry sand to analyze the comparison of lateral pile behavior for static loading and dynamic loading condition. In case of static loading condition, the lateral displacement was applied up to 50% of pile diameter by deflection control method. And the input sine wave of 0.1 g~0.4 g amplitude and 1 Hz frequency was applied at the base of the soil box using shaking table for dynamic loading condition. From comparison of experimental static p-y curve obtained from static loading tests with API p-y curves, API p-y curves can predict well within 20% error the ultimate subgrade reaction force of static loading condition. The ultimate subgrade reaction force of experimental dynamic p-y curve is 5 times larger than that of API p-y curves and experimental static p-y curves. Therefore, pseudo-static analysis applied to existing p-y curve for seismic design could greatly underestimate the soil resistance at non-linear domain and cause overly conservative design.

장변위공내재하시험기를 이용한 철도교 기초의 p-y곡선에 관한 연구

김종칠,조국환 한국방재학회 2016 한국방재학회논문집 Vol.16 No.1

Applied lateral load and moment on railway bridge foundation are usually larger than other transportation bridge foundation. Therefore, high strength steel pipe piles are used for Honam high speed railway bridges to resist lateral load and moment, even though those are much more expensive than concrete piles. It is very important to measure soil characteristic under lateral load from piles in order for economical design. A large displacement borehole testmeter (LDBT) is developed to measure nonlinear characteristics of the soil applied bored pile in this study. Most in-situ borehole test devices to estimate p-y curves can measure low displacement range in soil, which is usually in elastic range. Non-linear characteristics of the soil which is one of the most important characteristics of the soil cannot be obtained. The research result shows that the measured p-y curves using LDBT can be properly matched with back-calculated p-y curves from field tests by applying scale effects for sand. The developed technique using LDBT is verified lateral load test comparing with pile head deflection under field. 철도교 기초는 상당한 수평하중과 모멘트가 발생된다. 호남고속철도에서는 콘크리트 말뚝보다 비싼 고강도 강관말뚝을 사용하여 수평하중과 모멘트에 대한 저항성을 가지도록 하였다. 따라서 보다 경제적인 설계를 위하여 지반의 수평하중에 대한 거동특성을 정확하게파악하는 것이 매우 중요하다고 할 수 있다. 본 연구에서는 장변위공내재하시험기를 개발하였으며 이를 이용하여 매입말뚝이 건설된지반에 대하여 지반의 비선형 특성을 측정하였다. 현재까지 주로 사용되어 지고 있는 공내재하시험기는 장비의 특성상 제한된 변위에대한 지반의 반력을 측정함으로 인하여 주로 탄성 범위에 해당하는 응력-변위 관계만을 측정하고 있는 실정이다. 이러한 경우 지반의가장 중요한 특징인 비선형 특성을 측정하지 못함으로 인하여 응력-변위의 정확한 예측은 어렵게 된다. 이에 따라 개발된 장변위공내재하시험기를 이용하여 p-y 곡선을 측정하였다. 이를 수평재하시험을 실시하여 얻어진 휨모멘트를 적용한 p-y 곡선과 비교하였다. 개발된 장비를 사용하여 얻어진 측정결과와 수평재하시험 결과를 이용하여 크기영향(Scale effect)를 제안하였으며, 두부변위 시험을 실시하여 검증하였다.