• Journal of Ocean Engineering and Technology
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• v.25 no.2
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• pp.47-54
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• 2011

A piled raft foundation is one of the systems used to reduce the settlement of structures. However, the general design method for a piled raft foundation system assumes that the piles only support external loads, which exclude the bearing capacity of the raft itself. In this study, an experimental model test was performed to evaluate the raft capacity for the external load on the sand. Additionally, a part of the sandy ground under the raft was replaced with a gravel mat to reinforce the piled raft foundation system and increase the bearing capacity. Then, parametric studies of the reinforced ground were performed to determine the displacement and load-sharing ratio of the piled raft foundation system.

• Geomechanics and Engineering
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• v.16 no.6
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• pp.589-597
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• 2018

Centrifuge model tests were used to simulate pile-raft composite foundation and pile-geogrid composite foundation with different pile spacing for researching the time effect of negative skin friction of rigid piles in high-speed railways. The research results show that the negative skin friction has a significant impact on the bearing capacity of composite foundation. Pile-raft composite foundation has higher bearing capacity compared to pile-geogrid composite foundation to reduce the effect of negative skin friction on piles. Both the foundation settlement and negative skin friction have significant time effect. The distribution of skin friction can be simplified as a triangle along the pile. The neutral point position moves deeper in the postconstruction stage at larger pile spacing. For pile-geogrid composite foundation, the setting of pile-cap affects the position of neutral point in the post-construction stage. Reinforced cushion with geotextile may promote the better performance of cushion for transmitting the loads to piles and surrounding soils. Arching effect in the cushion of the composite foundation is a progressive process. The compression of the rigid piles contributes less than 20% to 25% of the total settlement while the penetration of the piles and the compression of the bearing stratum below the pile tips contribute more than 70% of the total settlement. Some effective measures to reduce the settlement of soils need to be taken into consideration to improve the bearing capacity of pile foundation.

• Journal of the Korean Society of Safety
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• v.18 no.1
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• pp.81-88
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• 2003

Recently, pile foundations were constructed in rough or soft ground than ground of well condition thus it is important that prediction of ultimate bearing capacity and calculation of proper safety factor applied pile foundation design. This study were performed to dynamic loading tests for the thirty two piles at four different construction sites and selected pile at three site were performed to static loading tests and then compare with measured value and value of static and dynamic loading tests. The load-settlement curve form the dynamic loading tests by CAPWAP was very similar to the results obtained from the static load tests. Based on dynamic and static loading tests, the reliability of pile-driving formula were analyzed and then suggested with proper safety factor for prediction of allowable bearing capacity in this paper.

• Journal of the Korean Geotechnical Society
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• v.16 no.3
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• pp.57-65
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• 2000

다층의 지오그리드로 보강된 사질토 지반에 축조된 줄기초의 극한 지지력을 결정하기 위하여 실내모형실험을 실시하였다. 한가지 종류의 사진토와 지오그리드를 사용하였으며, 시험은 기초의 근입깊이(Df)가 없을 때와 근입깊이(Df)가 있을 때로 분류하여 시행되었다. 기초의 근입깊이(Df)는 기초의 폭(B)보다 작도록 제한되었다. 시험결과, 주어진 보강깊이의 두께에 대하여 지지력비(BCR)는 기초의 근입깊이(Df)가 0보다 클 때 증가하였다.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.544-551
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• 2004

Piles are structural elements made of steel, concrete or timber, and utilize as pile foundation which is one of deep foundations. Driven pile among them, which drives pile into the ground, is fast-constructable, less expensive and it supplies much bearing capacity. For these reasons, its demand is steady. In this study, by selecting the cases which reached ultimate failure during in-situ static loading tests, bearing capacities acquired from these tests were compared with those computed by existing theories and formula. As the results of the analysis, ultimate bearing capacity computed by theoretic formula were less or similar to those of test results in most cases, but lower ground water level and more dense layer where end of piles were reached remarkably high bearing capacity in theoretical methods. ${\beta}-method$ and Korean structure foundation design standard were sensitive to ground physical properties. Meyerhof metbod and API code were relatively independent from site condition.

• Geotechnical Engineering
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• v.10 no.3
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• pp.5-16
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• 1994

This paper presents a new method to improve the bearing capacity of a square shallow foundation placed on a sand layer reinforced with geogrids which shows promise for further field work. The geogrid reinforcement will be necessary in the case of machine foundation, embankments for railroads, and foundations of structures in earthquake-prone areas. The ultimate bearing capacity (UBC) for the unreinforced sand and reinforced sand has been compared. Also, the effect of length, spacing, width of reinforcement on increasing the UBC have been evaluated. Based on the present model test results, it appears that significant improvement in the UBC of medium sand can be achieved by geogrid reinforcement.

• Geotechnical Engineering
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• v.12 no.4
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• pp.33-46
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• 1996

When structures are constructed in ground with poor bearing capacity, deformation of ground may induce foundation settlements and cracks of structures. Recently, high pressure jet grouting is widely used to improve the engineering properties of such foundation. Sometimes, the grouting columns are built in the ground by jet grouting method. They are used as in -situ piles to increase the bearing capacity of existing foundation. In this paper, as for the grouting columns built in ground by high pressure jet grouting with double tube rod, the effects on reinforcement and bearing capacity of ground are investigated. A series of laboratory tests has been performed on the specimens sampled from the grouting columns and a pile load test has been performed on a grouting column. The test results show that high pressure jet grouting has a sufficient effect on reinforcement of ground and restraint of settlement of structure.

• Earthquakes and Structures
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• v.19 no.2
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• pp.103-117
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• 2020

The effect of the foundation size on the efficiency of seismic base isolation using a layer of stone pebbles is experimentally investigated. Four scaled models of buildings with different stiffnesses (from very stiff to soft) were tested, each with the so-called small and large foundation, and exposed to four different accelerograms (different predominant periods and durations). Tests were conducted so that the strains in the model remained elastic and afterwards the models were tested until collapse. Each model was tested for the case of the foundation being supported on a rigid base and on an aseismic layer. Compared to the smaller foundation, the larger foundation results in a reduced rocking effect, higher earthquake forces and lower bearing capacity of the tested models, with respectable efficiency (reduced strain/stress, displacement and increase of the ultimate bearing capacity of the model) for the considered seismic base isolation compared to the foundation on a rigid base.

• Journal of the Korean Geotechnical Society
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• v.20 no.7
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• pp.107-117
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• 2004

A series of model tests were conducted to investigate how the number of reinforcement layers, stiffnesses, types of reinforcement material and buried depth of a flexible pipe can affect bearing capacity-settlement curve at a loose sand foundation. In the test results, whereas the type of failure in unreinforced sand was local shear, the type of failure, for model tests with more than 2 reinforcement layers in loose sand, was general shear: The number of the optimum reinforcement layers was found to be two: Stiffness and type of reinforcement were more important than the maximum tensile strength of reinforcement in improving bearing capacity. When the depth of buried pipe from the sand surface was less than the width of the footing, test results showed that both bearing capacity and ultimate bearing capacity of buried pipe in unreinforced sand significantly decreased, and the type of failure in the reinforced sand changed from general shear to local shear.

• Earthquakes and Structures
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• v.22 no.6
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• pp.597-608
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• 2022

One of the most important parameters affecting nonlinearsoil-structure interaction, especially rocking foundation, is the vertical factor of safety (F.S_v). In this research, the effect of F.S_v on the behavior of rocking foundations was experimentally investigated. A set of slow, cyclic, horizontal loading tests was conducted on elastic SDOF structures with different shallow foundations. Vertical bearing capacity tests also were conducted to determine the F.S_v more precisely. Furthermore, 10% silt was mixed with the dry sand at a 5% moisture content to reach the minimum apparent cohesion. The results of the vertical bearing capacity tests showed that the bearing capacity coefficients (N_c and N_γ) were influenced by the scaling effect. The results of horizontal cyclic loading tests showed that the trend of increase in capacity was substantially related to the source of nonlinearity and it varied by changing F.S_v. Stiffness degradation was found to occur in the final cycles of loading. The results indicated that the moment capacity and damping ratio of the system in models with lower F.S_v values depended on soil specifications such cohesiveness or non-cohesiveness and were not just a function of F.S_v.