• Geomechanics and Engineering
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• 제12권4호
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• pp.611-626
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• 2017

The research reported herein is concerned with the model testing of piles socketed in soft rock which was simulated by cement, plaster, sand, water and concrete hardening accelerator. Model tests on a single pile socketed in simulated soft rock under axial cyclic loading were conducted and the bearing capacity and accumulated deformation characteristics under different static, and cyclic loads were studied by using a device which combined oneself-designed test apparatus with a dynamic triaxial system. The accumulated deformation of the pile head, and the axial force, were measured by LVDT and strain gauges, respectively. Test results show that the static load ratio (SLR), cyclic load ratio (CLR), and the number of cycles affect the accumulated deformation, cyclic secant modulus of pile head, and ultimate bearing capacity. The accumulated deformation increases with increasing numbers of cycles, however, its rate of growth decreases and is asymptotic to zero. The cyclic secant modulus of pile head increases and then decreases with the growth in the number of cycles, and finally remains stable after 50 cycles. The ultimate bearing capacity of the pile is increased by about 30% because of the cyclic loading thereon, and the axial force is changed due to the applied cyclic shear stress. According to the test results, the development of accumulated settlement is analysed. Finally, an empirical formula for accumulated settlement, considering the effects of the number of cycles, the static load ratio, the cyclic load ratio and the uniaxial compressive strength, is proposed which can be used for feasibility studies or preliminary design of pile foundations on soft rock subjected to cyclic loading.

• 한국해양공학회지
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• 제25권6호
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• pp.35-41
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• 2011

Recently, as large structures, which should support large design loads have been constructed, the study on the large diameter composite pile becomes necessary. The large diameter composite pile has the diameter over 700mm and consists of two parts of the upper steel pipe pile and the lower PHC pile by a mechanical joint. In this research, to analyze the bearing capacity and the material strength of the composite pile, three dimensional numerical analyses were performed. First, the numerical modeling method was verified by comparing the calculated load-movement curves of the pile with those of the field pile load tests. Then, a total of twelve analyses were performed by varying pile diameter and loading direction for three pile types of PHC, steel pipe and composite piles. The results showed that the vertical and the horizontal load-movement curves of the composite pile were identical with those of the steel pipe pile and the horizontal material strength of the composite pile was 60-80% larger than that of the PHC pile.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.708-712
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• 2008

Piles and pile foundations have been in common use since very early times. Usually function of piles is to carry load to a depth at which adequate support is available. Another important use of piles is to furnish lateral support and nowadays it is getting highlighted due to the wind load, lateral action of earthquake, and so on. After Broms (1964), many researchers have been suggested methods for estimating lateral capacity of pile. But each method assumes different earth pressure distribution and lateral earth pressure coefficient and it gives confusion to pile designers. Lateral earth pressure, essential in lateral capacity estimation, influenced by pile's behavior under lateral load. Prasad and Chari (1999) assumed the rotation point of pile and suggested an equation of ultimate lateral load capacity. In this study, we investigate the depth of rotation point in both homogeneous soil and multi layered soil, and compare to the estimation value by previous research. To model the pile set up in the sand, we use the chamber and small scale steel pile, and rain drop method. Test results show the rotation point is formed where the Prasad and Chari's estimation value, and they also show multi layered condition affects to location of rotation point to be scattered.

• 한국지반신소재학회논문집
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• 제19권1호
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• pp.65-73
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• 2020

본 연구에서는 현장타설말뚝이 사질토 지반에서 지지되는 경우에 대하여, 설계지지력 산정을 위해 적용되고 있는 다양한 제안식을 이용하여 말뚝의 길이비와 N값이 지지력에 미치는 영향을 평가하였다. 그 결과, Meyerhof 제안식은 전체 지지력에 있어서 선단지지력과 주면마찰력의 분담률은 동일하게 평가하고, 지지력 분담률은 길이비에 의해서만 영향을 받는 것으로 분석되었다. NAVFAC DM-7 제안식은 말뚝의 길이가 주면마찰력과 선단지지력 모두 영향을 미치기는 하지만, 선단지지력에 더욱 큰 영향인자로 작용하는 것을 알 수 있었다. 특히, N값과 말뚝의 직경에 의한 영향보다는 말뚝 길이요소에 의한 영향이 가장 큰 것을 알 수 있었다. FHWA의 제안식은 말뚝의 지지력 산정 시, 주면마찰력에 의한 영향요소를 다른 제안식에 비해 적극적으로 반영하는 것으로 평가되었으며, 극한지지력 평가 시에 주면마찰력의 영향을 더 크게 반영하는 것을 알 수 있었다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2006년도 추계 학술발표회
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• pp.603-608
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• 2006

In this paper, principal concepts on bi-directional pile load test(BD PLT) specification were explained. These main concepts are kinds of BD PLT, loading capacity, reporting the test results to relevant association etc.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.1607-1614
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• 2011

As the connection between spread footing and pile is very important structural connection, it acts as the inter-loading medium to transfer the rail loads applied by superstructure to ground through the body pile of foundation. The experimental study is the method how to reinforce the pile cap between steel pile and footing utilizing perfobond plate with protruding keys. It were experimented on the compression punching tests and bending moment tests against the vertical loading and horizontal loadings acting on head of steel tube pipe. As a result, the tension capacity of the perfobond plate exhibited the superior performance due to the interlocking or dowel effects by the sheared keys of perfobond plate, and there were showing the sufficient strength and ductile capacity against the bending moment of horizontal loading tests. Therefore, it is judged that "the embedded method of perfobond plate in pile cap and footing" which is utilizing the shear connection of perfobond plate with protruding keys has a sufficient structural stability enough to be replaced with the current specification of reinforced method of pile cap with vertically deformed rebar against the vertical compression loads and bending moments that are able to occur in the combination structure of steel pile and the footing foundation.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.748-753
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• 2008

Bi-directional load test is one of O-cell tests. The O-cell test is a system which may be used for performing static load tests on cast in situ reinforced concrete bored piles. The technique was devised and developed by Osterberg of Northwestern University(USA) and has been in use around the world. The principle of the method is that an O-cell is installed in a cast in situ bored pile base. Once the pile concrete reaches its design strength the cell is connected to an hydraulic pump and pressured. Pressurisation causes the cell to expand, developing an upward force on the section of pile above the cell loads, pile movements and strains within the pile then enable the capacity of the pile and its load settlement curves to be ascertained. Bi-directional load tests using O-cell are now becoming common practice around the world, particularly where the loads to be applied are high or where it is not convenient to perform top-down loading tests. In the study, calculate ultimate capacity of bi-directional load test using FEM and beam on elasto-plastic foundation theory.

• 한국지반공학회지:지반
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• 제8권3호
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• pp.13-22
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• 1992

Model pile tests using calibration chamber are performed in !his paper in order to clarify the effect of the fundamental differences between the newly developed SPLT(Simple Pile Loading Test)and the conventional pile loading test on the pile bearing capacity. They are : (1) the direction of the applied load to mobilize the skin friction ; and (2) the use of reduced sifted sliding core. The conclusions obtained from the model pile tests are as follows : (1) The skin friction in tension loading is found to be somewhat smaller than that in compression loading. The average ration is 0.73 with the coefficient of variation (COV) of 0.18. (2) The ratio of the tip resistance rosin연 the reduced sized sliding core to that using the whole shoe shows wide scattering ; its average is 0.99 and the COV is 0.28. The aver - age of 0.99 means that there is no considerable difference in the tip resistance whether the reduced sized sliding core or the whole shoe is used, on condition that penetration depth ratio is larger than 4 : if the boundary effect of the chamber test is considered, the resistance of the whole shoe might be even larger.

• 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.

• 대한토목학회논문집
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• 제29권6C호
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• pp.267-275
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• 2009

강관합성말뚝은 외부 강관의 합성 구속효과에 의해 말뚝강도가 커지고, 연성파괴 거동이 발생한다. 본 연구에서는 해상 지반에 근입된 말뚝에 대하여 말뚝재료의 항복거동 및 지반의 탄소성 거동을 함께 고려할 수 있는 3차원 수치해석을 수행하여 하중-변위 거동 및 강관합성말뚝의 보강효과를 분석하였다. 이를 위하여 강관, 콘크리트, 강관합성말뚝에 대하여 각각 말뚝직경과 재하방향에 따른 변수연구를 수행하였다. 그 결과, 수직방향 극한지지력의 경우 강관합성말뚝은 강관말뚝과 비교하여 평균 1.90배, 콘크리트 말뚝에 대하여는 평균적으로 동일한 지지력을 보여주었다. 허용변위 기준에서의 수평방향 지지력의 경우 강관합성말뚝은 강관말뚝에 비하여 평균 1.46배, 콘크리트 말뚝에 비하여 평균 1.25배 큰 것으로 나타났다. 그리고, 허용변위 기준에서의 강관합성말뚝의 말뚝두부 변위는 평균적으로 강관말뚝의 약 78%, 콘크리트 말뚝의 약 53%로 나타나 강관합성말뚝의 변위억제 효과가 큰 것으로 나타났다. 본 해석조건에서 강관합성말뚝의 수직방향 극한지지력 증가효과는 작았지만 수평방향 재하시의 강관합성말뚝의 변위억제 효과에 의해 현장타설말뚝의 경제적인 설계가 가능할 것으로 판단된다.