• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2003년도 봄 학술발표회 논문집
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• pp.431-438
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• 2003

The domestic design method for the shaft resistance of drilled shafts into a bedrock Is based on the empirical method, where the uniaxial compressive strength of rock specimen is utilized for calculation of the shaft resistance. This method has uncertainties in prediction of capacity of drilled shafts and result in uneconomic engineering design. Recently a new improved design method was suggested, which reflects important factors that affect the strength of pile sockets. Socket roughness is one of significant factors influencing the shaft resistance of drilled shaft socketed into rock In this paper roughness information for the shaft resistance design of socket pile was suggested on the basis of statistical analysis of data measured from wall surface In the bore holes of drilled shafts.

• Geomechanics and Engineering
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• 제33권5호
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• pp.519-528
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• 2023

In this paper, we present the results of an experimental study on the effect of polymer support fluid on shaft resistance of offshore bored piles. A series of pullout tests were performed on bored piles installed under various boundary conditions considering different types of grounds and support fluids, and a range of support fluid exposure times. Contrary to previous studies concerning onshore bored piles, a time dependent effect of polymer fluid on shaft resistance was observed in all ground types. The adverse effect of polymer support fluid on the shaft resistance, however, was considerably less than bentonite support fluid for a given exposure time. No significant reduction in shaft resistance was evident when limiting the exposure time of the polymer support fluid to the side wall of the borehole within 2-3 hours. The degree to which the polymer fluid affects shaft resistance seemed to vary with the ground type. A proper consideration should be given to the time dependent effect of polymer fluid on shaft resistance of bored piles installed in offshore construction environment to limit its adverse effect on the pile performance. The practical implications of the findings are discussed.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2006년도 추계 학술발표회
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• pp.409-429
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• 2006

In designing rock-socketed drilled shaft, bearing capacity evaluation is very important because the maximum values of base and side resistance are not generally mobilized at the same value of displacement, FHWA and AASHTO code suggest different ultimate bearing capacity formular according to rock type and shaft settlement. In domestic code suggest base resistance and side resistance can be added on condition that after confirming the result of field load test with axial load transfer test. This paper shows that static load test and hi-directional load test result analysis of deep rock-socketed drilled shaft in three different sites. Load-settlement curve, t-z, and q-w curve in rock-socketed part were calculated and compared. t-z curve in weathered and soft rock showed no deflection softening behavior in pretty large strain (about 2-3% of diameter). Ultimate resistance could be the summation of side resistance and base resistance in rock-socketed drilled shaft in domestic sites.

• Geomechanics and Engineering
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• 제5권2호
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• pp.119-142
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• 2013

Pile load tests using Osterberg cells (O-cell) were conducted on cast-in-place concrete piles founded in oil sand fill and in situ oil sand at an industrial plant site in Fort McMurray, Alberta, Canada. Interpreted pile test results show that very high pile shaft resistance (with the Bjerrum-Burland or Beta coefficient of 2.5-4.5) against oil sand could be mobilized at small relative displacements of 2-3% of shaft diameter. Finite element simulations based on linear elastic and elasto-plastic models for oil sand materials were used to analyze the pile load test measurements. Two constitutive models yield comparable top-down load versus pile head displacement curves, but very different behaviour in mobilization of pile shaft and end bearing resistances. The elasto-plastic model produces more consistent matching in both pile shaft and end bearing resistances whereas the linear elastic under- and over-predicts the shaft and end bearing resistances, respectively. The mobilization of high shaft resistance in oil sand under pile load is attributed to the very dense and interlocked structure of oil sand which results in high matrix stiffness, high friction angle, and high shear dilation.

• Smart Structures and Systems
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• 제30권2호
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• pp.209-219
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• 2022

The determination for bearing capacity of precast nodular piles is conventionally time-consuming and high-cost by using numerous experiments and empirical methods. This study proposes an intelligent method to evaluate the bearing capacity and shaft resistance of the nodular piles with high efficiency based on long short-term memory (LSTM) approach. A series of field tests are first designed to measure the axial force, shaft resistance and displacement of the combined nodular piles under different loadings, in comparison with the single pre-stressed high-strength concrete piles. The test results confirm that the combined nodular piles could provide larger ultimate bearing capacity (more than 100%) than the single pre-stressed high-strength concrete piles. Both the LSTM-based method and empirical methods are used to calculate the shift resistance of the combined nodular piles. The results show that the LSTM-based method has a high-precision estimation on shaft resistance, not only for the ultimate load but also for the working load.

• 한국지반환경공학회 논문집
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• 제4권2호
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• pp.5-13
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• 2003

국내의 경우 암반에 근입된 현장타설말뚝의 지지력을 계산하는데 있어 일축압축강도를 이용하는 경험적인 방법으로 설계를 수행하고 있다. 이러한 경험적인 설계방법들은 설계시 상당한 불확실성을 내포하는 것으로 나타났다. 최근에는 암반에 근입된 현장타설말뚝의 주면저항에 영향을 주는 모든 인자를 고려하는 설계법도 제안되었다. 암반에 근입된 현장타설말뚝의 지지력에 영향을 미치는 인자에는 여러 가지가 있는데 이중 굴착면의 거칠기는 암반에 근입된 말뚝의 전단거동에 중요한 역할을 하는 것으로 알려졌다. 따라서 본 연구에서는 국내 현장타설말뚝의 암반부 굴착벽면의 거칠기 특성을 조사, 분석하여 설계에 적용할 수 있는 거칠기 정수를 제안하였다.

• Geomechanics and Engineering
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• 제29권4호
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• pp.407-420
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• 2022

Embedded piles, which are typically used in Korea, are precast piles inserted into prebored ground with cement paste. Dynamic pile tests tend to underestimate the bearing capacity of embedded piles because of the undeveloped shaft resistance prior to the curing of the cement paste and the insufficient energy transferred after the curing. In this study, a resistance combination method using the base resistance before the cement paste is cured and the shaft resistance after the cement paste is cured is proposed to obtain a combined load-settlement curve from dynamic pile tests. Two pairs of embedded piles with diameters of 600 and 500 mm are installed. Each pair comprises one pile for the dynamic pile test and another pile for the static load test. The shape of the load-settlement curve obtained using the proposed method is similar to that obtained from the static load test. Thus, the resistances evaluated using the proposed method at selected settlements are similar to those obtained from the static load test. This study shows that the resistance combination method may be used effectively in dynamic pile tests to accurately evaluate the bearing capacity of embedded piles.

• 한국지반공학회지:지반
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• 제14권1호
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• pp.71-80
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• 1998

서해안에 위치한 서산지역에서 연구용 prestressed concrete 말뚝을 3본을 설치하고 주변에서 콘관입시험을 수행하여 말뚝의 주면마찰력을 추정하는 연구를 수행했다. 본 연구에서 이용한 말뚝 지지력 산정식은 세계적으로 많이 이용하고 있는 Schmertmann방법, Tumay & Fakroo방법 및 프랑스의 LCPC방법을 이용하였다. 콘관입시험의 측정결과를 이용하여 3가지 방법으로 예측한 말뚝 의 주면마찰력과 현장에서 수행한 정역학적 재하시험 및 동재하시험에서 산정된 주면마찰력과의 비교하여 3가지 예측방법들에 대한 신뢰성을 평가했다. CPT를 이용한 3가지 예측식으로 산정한 말뚝의 주면마찰력은 전체적으로 25일과 42일이 지난후 수행한 정재하시험에 의한 주면마찰력을 상당히 과소평가했으나, 항타시좌 말뚝설치후 2주가 지난 시점에 수행한 동재하시험결과와는 유사한 말뚝의 주면마찰력을 예측했다.

• 대한토목학회논문집
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• 제26권1C호
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• pp.25-31
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• 2006

대부분의 설계지침서에서는 암반에 근입된 현장타설말뚝의 주면저항력을 산출하기 위하여 암석의 일축압축강도를 사용한다. 그러나 최근에 도로교 설계기준 해설(대한토목학회, 2001)과 AASHTO 설계지침서(2000)에서는 현장조건을 보다 잘 반영할 수 있도록 RQD를 적용하여 산출한 암반의 일축압축강도를 사용하도록 개정되었다. 그런데 RQD를 이용하여 암반의 일축압축강도를 산정하는 식을 국내의 주요 기반암에 적용하는 데에 문제가 제기되었고, 여기에는 RQD 자체의 문제점, 즉 지하수, 절리면 상태 등을 반영하지 못한다는 점도 포함되었다. 결국 도로교 설계기준 해설(2001)은 암석의 일축압축강도를 이용하여 주면저항력을 산정하는 방법으로 다시 개정되었다(한국도로공사, 2002). 본 연구에서는 암석의 일축압축강도와 현장 암반의 일축압축강도를 연관시키는 수단으로 제시되어 있는 기존의 여러 방법을 비교 검토하였으며, 이 가운데 신뢰도가 있는 것으로 평가되고 있는 Hoek-Brown 파괴 규준을 이용하여 암반의 일축압축강도 추정식을 제시하였다. 또한 이를 이용하여 암반에 근입된 현장타설말뚝의 주면저항력 예측 방법을 제안하였다. 제안된 방법은 현장타설말뚝의 재하시험 데이터를 이용하여 기존의 여러 방법으로 구한 주면저항력과 비교한 결과 신뢰도가 있음을 알 수 있었다.

• 한국지반공학회논문집
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• 제23권9호
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• pp.51-63
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• 2007

암반에 근입된 현장타설말뚝의 주면거동특성을 분석하고자, 편마암질의 풍화암/연암지역에서 현장 말뚝재하시험(압축재하 4회, 인발시험 5회)을 수행하였다. 이를 통해 암반 풍화, 굴착면 거칠기, 말뚝 직경, 재하방향 등의 요소들이 암반 근입 현장타설말뚝의 주면 전단거동을 결정짓는 주요요소임을 확인할 수 있었다. 본 연구에서는 국내에서 수행된 암반 근입 현장타설말뚝의 재하시험 사례를 토대로 국내 암반조건을 반영한 극한주면마찰력($f_{max}$)을 제안하였다.