• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2000년도 가을 학술발표회 논문집
• /
• pp.285-292
• /
• 2000

Though there has been increasing use of large diameter drilled shaft as a foundation structure of bridges, current practice for quality control is to confirm the minimum required load carrying capacity during construction stage. For economic and appropriate design of drilled shaft, it is necessary to evaluate the load transfer mechanism by pile load tests during initial stage of construction and to use the test results as a feedback to a revision of initial design. In this paper, results of load tests peformed at several domestic sites are presented to investigate the load transfer characteristics of large diameter drilled shaft. It was found that most of the load on piles is sustained by shaft friction and that only small portion of the load reaches the bottom of the drilled shaft. Some test results of drilled shaft by Pile Driving Analyzer performed at same sites are also presented to compare the load transfer characteristics interpreted from static pile load tests.

• 한국철도학회논문집
• /
• 제9권4호
• /
• pp.493-498
• /
• 2006

In this study, two large pile load tests were performed in the deep sand gravel deposit of Nakdong river basin so that the characteristics of the load transfer was identified. The fully instrumented rectangular barrette pile in the size of $1.5\times3.0m$ and the circular bored pile of the diameter 1.5 m were placed into the ground below 50 m. Under the applied loads of 2,400 tonf and 4,000 tonf, the test results of the load transfer showed the portion of 83% and 93% of the applied loads on the barrette pile and the bored pile, respectively, were supported by the skin friction along the pile shaft. It was revealed that the most of these skin friction mobilized in sand layer underlying clay layer having N-value more than 30 and that the friction per unit area of the bored pile was larger than the friction of barrette pile. However, if embedded in the stiff sand graval layer, the both piles were proven to be sufficient for using as the friction piles.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2008년도 추계 학술발표회
• /
• pp.455-465
• /
• 2008

In this study, the load distribution and deformation of rock-socketed drilled shafts subjected to axial load are investigated based on small scale model tests. In order to analyze the effects of major influencing factors of end bearing capacity, Hoek-cell triaxial tests were performed. From the test results, it was found that the initial slope of end bearing load transfer (q-w) curve was highly dependent on rock mass modulus and pile diameter, while the ultimate unit toe resistance ($q_{max}$) was influenced by rock mass modulus and the spacing of discontinuities. End bearing load transfer function of drilled shafts socketed in rock was proposed based on the Hoek-cell triaxial test results and the field loading tests which were performed on granite and gneiss in South Korea. Through the comparison with pile load tests, it is found that the load-transfer curve by the present study is in good agreement with the general trend observed by field loading tests, and thus represents a significant improvement in the prediction of load transfer of drilled shaft.

• 한국지반환경공학회 논문집
• /
• 제24권1호
• /
• pp.5-14
• /
• 2023

본 연구에서는 설계 대상인 현장타설말뚝기초에 대하여 상사율을 고려한 하중전이 대형토조 모형시험과 3차원 수치해석을 수행함으로써 현장타설말뚝 선단부와 주면부의 하중전이 특성을 분석하고 하중분담율을 산정하였다. 대형토조 모형시험 및 3차원 수치해석 결과에서 나타난 현장타설말뚝의 선형적 거동으로부터, 본 연구의 설계 조건에 대한 주면하중전이곡선은 Baquelin 등의 제안식, 선단하중전이곡선은 Baquelin 등의 제안식, 수평하중전이곡선은 Reese 등의 제안식이 적정한 것으로 확인되었다. 암반근입부에서 축하중은 시험값이 수치해석값보다 약간 크게 측정되었지만 암반 근입부에서 하중분담율은 연직하중이 증가함에 따라 평균적으로 약 27.8%의 분담율을 나타내었다. 연직재하 시에 말뚝두부의 침하량은 해석값이 시험값보다 약간 작게 평가되었으며, 모형시험 및 해석 최대 연직하중에서 말뚝두부의 최대 침하량은 시험치 10.6mm, 해석치 10.0mm 이고, 말뚝선단에서 최대 침하량은 시험치 2.0mm, 해석치 1.9mm로 나타났다. 수평재하 시에 기둥 두부(지표)와 말뚝 두부에서 수평변위는 시험값과 해석값이 비교적 잘 일치하는 것으로 나타났고, 모형토조시험 결과 최대 수평변위 38.0mm에서 측정된 수평하중은 24,713kN, 수치해석에서의 수평하중은 26,073kN으로 평가되었다.

• 한국도로학회논문집
• /
• 제10권2호
• /
• pp.229-239
• /
• 2008

콘크리트 슬래브를 공장에서 제작하여 도로포장의 신설 또는 보수에 사용하는 공법인 프리캐스트 콘크리트 포장의 하중전달 성능을 평가하기 위하여 연구를 수행하였다. 실내실험을 통해 다웰바 연결 부분의 그라우팅 효과를 측정할 수 있는 방법을 고안하였으며 이러한 실험을 위해 실험체를 제작하여 실험하였다. 실험을 수행한 결과 그리우팅을 한 다웰바의 전단강도는 콘크리트와 일체식으로 된 다웰바의 전단강도에 비해 떨어지지 않음을 알 수 있었다. 이울러 현장에서의 시험시공을 통해 설치된 보수용 프리캐스트 콘크리트 포장에 대해서도 FWD 시험을 실시하여 하중전달 성능을 평가하였다. 현장 실험 결과 기존 콘크리트 포장에 비해 슬래브 중앙부에서의 처짐은 다소 크게 나타나나, 줄눈부에서의 하중전달율은 거의 유사한 것으로 나타났다.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 1999년도 가을 학술발표회 논문집
• /
• pp.397-404
• /
• 1999

It is essential to measure load transfer mechanism of pile to check the appropriateness of assumptions made for design purpose and to continuously monitor the behavior of pile foundation. Through many attempts to monitor the behavior of super-structure in civil engineering area using several optical fiber sensors have been made, application of optical fiber sensor technology on pile foundation has not been tried up to now. Load transfer of model piles during compression loading was measured by optical fiber sensors and compared with the measurement by strain gauges. Fiber Bragg Grating(FBG) sensor system was used since it has many advantages, such as easy multiplexing, high sensitivity, and simple fabrication. Besides the model pile tests, uniaxial tension test of steel bar and compression tests of mortar specimen were carried out to evaluate the performance of FBG sensors in embedded environments. The shift of refilming wavelength due to the strain in FBG sensor is converted to the strain at sensor location and the dependence between them is 1.28 pm/${\mu}$ strain. FBG sensors embedded in model pile showed a better survivability than strain gauges. Measured results of load transfer by both FBG sensors and strain gauges were similar, but FBG sensors showed a smoother trend than those by strain gauge. Based on the results of model pile test, it was concluded that the use of FBG sensor for strain measurement in pile has a great potential for the analysis of pile load transfer.

• Structural Engineering and Mechanics
• /
• 제20권5호
• /
• pp.575-587
• /
• 2005

Using the nonlinear load transfer function for pile side soil and the linear load transfer function for pile end soil, a combined approach of the incremental load transfer matrix method and the approximate differential equation solution method is presented for the nonlinear analysis of interaction between flexible pile group and soil. The proposed method provides an effective approach for the solution of the nonlinear interaction between flexible pile group under rigid platform and surrounding soil. To verify the accuracy of the proposed method, a static load test for a nine-pile group under a rigid platform is carried out. The finite element analysis is also conducted for comparison purposes. It is found that the results from the proposed method match very well with those from the experimental test and are better in comparison with the finite element method.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2000년도 말뚝기초 학술발표회
• /
• pp.85-106
• /
• 2000

The load distribution and deformation of drilled shafts subjected to axial loads were evaluated by a load transfer approach. The emphasis was on quantifying the load transfer mechanism at the interface between the shafts and surrounding highly weathered rocks based on a numerical analysis and small-scale tension load tests performed on nine instrumented piles. An analytical method that takes into account the soil coupling effect was developed using a modified Mindlin's point load solution. Based on the analysis, a single-modified hyperbolic model is proposed for the shear transfer function of drilled shafts in highly weathered rocks. Through comparisons with field case studies, it is found that the prediction by the present approach is in good agreement with the general trend observed by in-situ measurements.

• Smart Structures and Systems
• /
• 제7권4호
• /
• pp.303-317
• /
• 2011

A specially designed tendon, which is proposed by embedding an FBG sensor into the center king cable of a 7-wire strand tendon, was applied to monitor the prestress force and load transfer of ground anchor. A series of tensile tests and a model pullout test were performed to verify the feasibility of the proposed smart tendon as a measuring sensor of tension force and load transfer along the tendon. The smart tendon has proven to be very effective for monitoring prestress force and load transfer by measuring the strain change of the tendon at the free part and the fixed part of ground anchor, respectively. Two 11.5 m long proto-type ground anchors were made simply by replacing a tendon with the proposed smart tendon and prestress forces of each anchor were monitored during the loading-unloading step using both FBG sensor embedded in the smart tendon and the conventional load cell. By comparing the prestress forces measured by the smart tendon and load cell, it was found that the prestress force monitored from the FBG sensor located at the free part is comparable to that measured from the conventional load cell. Furthermore, the load transfer of prestressing force at the tendon-grout interface was clearly measured from the FBGs distributed along the fixed part. From these pullout tests, the proposed smart tendon is not only expected to be an alternative monitoring tool for measuring prestress force from the introducing stage to the long-term period for health monitoring of the ground anchor but also can be used to improve design practice through determining the economic fixed length by practically measuring the load transfer depth.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 1999년도 봄 학술발표회 논문집
• /
• pp.249-258
• /
• 1999

Dynamic load and static load tests are performed on steel pipe piles and concrete piles at five construction sites in highway to compare the difference of load bearing mechanisms. At each site, one steel pile is instrumented with electric strain gages and dynamic tests are performed on the pile during installation. Damages of strain gages due to the installation are checked and static test is performed upon the same pile after two or seven days as well. It shows that load transfer from side friction to base resistance behaves somewhat differently according to the results of load-settlement analysis obtained from PDA and static load test. Initial elastic stage of load settlement curves of two load tests is almost similar. But after the yielding point, dynamic resistance of pile behaves more stiffer than static resistance, thus, dynamic load test result might overestimate the real pile capacity compared with static result. Analysis of gage readings shows that unit skin friction increases exponentially with depth. The skin friction is mobilized at the 1∼2m above the pile tip and contributes to the considerable side resistance. Comparison of side and base resistances between the measured value and the calculated value by Meyerhof's bearing capacity equation using SPT N value shows that the calculated base resistance is higher than the measured. Therefore, contribution of side resistance to total capacity shouldn't be ignored or underestimated. Finally, based upon the overall test results, a construction control procedure is suggested.