• Geotechnical Engineering
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• v.13 no.5
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• pp.145-154
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• 1997

Though the static pile load tests gives the mosts accurate estimation on the load carrying capacity of tested pile, it appears time-consuming and not economical. Many test methods using equipments, such as Pile Driving Analyzer(PDA), STATNAMIC, and Osterberg cell, have been introduced in Korea, and pile best using PDA has been gaining popularity because of iris fast and simple operation. Static and dynamic tests results on the piles installed in the granular coils were analyzed to investigate the effect of geometrical damping on the estimated load carrying capacity. It was found that the CAPWAP analysis without considering geometrical damping effect underestimates the pile capacity by 30~60% under certain conditions. It was observed that the underestimation of pile capacity by CAPWAP occurs on the piles installed in the water-borne granular boils by SIP methods. When Smith skin damping value(SSkn) greater than 1.0 sec/m is obtained in CAPWAP analysis, it may reflect the large possibility of underestimation of pile capacity. The introduction of the geometircal damping option in CAPWAP analysis gives reasonable pile capacity, compared with the static pile load test results, and reduces the SSb value under 0.7 sec/m.

• Journal of the Korean Geotechnical Society
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• v.23 no.8
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• pp.35-45
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• 2007

It is known that the response of piles is affected by the shape of pile as well as soil conditions. In order to investigate the characteristics of the axial responses and bearing capacities of non-displacement tapered and cylindrical piles in sands, 12 model pile load tests using a calibration chamber were conducted on model tapered and cylindrical piles, which were specially manufactured to measure the base and shaft load capacities independently. Results of the model tests showed that the shaft load of tapered piles continuously increased with pile settlement, whereas the shaft load of cylindrical piles reached ultimate values at a settlement equal to 4% of pile diameter. Therefore, taper piles have greater shaft loads than cylindrical one at the same settlement. It is also observed that the total load capacity of tapered piles is lower than cylindrical piles for dense sand but is greater than that of cylindrical piles for medium sand. The ultimate unit base resistance of tapered piles was greater than that of cylindrical piles for lateral earth pressure ratio greater than 0.4, and the shaft resistance was greater than that of cylindrical piles irrespective of lateral earth pressure ratio.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.387-395
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• 2003

Model tests were conducted to study the behavior of the piled raft foundation system on sands. Especially in this study, the method using the triaxial compression apparatus was devised and used to apply the confining pressure which is considered difficult in the existing model test on the soil. Steel rods (6mm dia.) and aluminum plates (8mm thickness, 50mm dia.) were used to simulate piles and rafts respectively. Jumunjin standard sands were used to ensure the homogeneity of the sample. After the sample with the piled raft model was laid inside the triaxial cell, the confining pressure was applied and then the compressive force was applied. The increase and/or decrease ratio of the bearing capacity, the load distribution ratio between raft and piles and the effect of settlements decrease depending on the confining pressure, the number of piles and the length of piles were analyzed and the bearing capacity and skin friction of the pile was calculated. By the results of these experiments, the bearing capacity increased and the settlement decreased with this piled raft foundation system. Especially the effect was larger with the increase of the number of piles than with the increase of length of piles. Hereafter, the study of the load transfer mechanism of piles under confining pressure would be made possible using these small model tester like triaxial compression apparatus.

• Journal of the Korean Geotechnical Society
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• v.20 no.7
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• pp.25-32
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• 2004

This paper examines the results of full-scale field tests on micropiles and side resistance is evaluated with respect to axial displacements and soil properties. Both cohesive and cohesionless soils are included in this evaluation. For all practical purposes, the developed load-displacement relationship and the geotechnical soil properties for each micropile and soil type can be used to represent the available data well through normalized average values and empirical correlations. There is a significant difference in load-carrying capacity between micropiles and drilled shafts that results primarily from the micropile pressure-grouting installation effects on the state of stress in the ground. The results show that micropiles can have a significant increase of capacity over larger-diameter drilled shafts at shallower depths with D/B < 100 or so. In cohesive soils, the typical increase is on the order of 1.5 with values as high as 2.5. For cohesionless soils, the typical increases are in the range of 1.5 to 2.5 with values as high as 6.

• Journal of the Korean Geotechnical Society
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• v.24 no.6
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• pp.85-93
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• 2008

For long piles driven in deep clay deposits, it is difficult to estimate the ultimate bearing capacity due to large resistance induced by long embedded depth, and also the load transfer curve due to large residual load induced by negative skin friction, even with the performance of pile load tests. In this research, a hi-directional load test on a PHC pile driven in deep soft deposit was performed in order to evaluate the tip and shaft resistances separately, which are feasible to estimate the ultimate bearing capacity of the pile. Residual load of the pile was determined by continuous monitoring of pile strains after the pile installation. The true resistance and true load-movement curve of the pile were properly estimated by taking account of the residual load. A model far behavior of the shaft resistance vs. movement was also proposed, which includes the effects of residual load based on the experiment. Consequently, it was proved that the residual load should be taken into consideration for correctly analyzing load test results of piles in deep clay deposits.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.95-105
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• 2003

The existing design criteria f3r the estimation of ultimate bearing capacity of drilled shaft socketed into rock masses are mainly obtained from the ultimate pile load capacities, which are determined by inconsistent failure criteria. Therefore, these design criteria generally produce difffrent predictions even for drilled shaft in the same condition. In this paper, the accuracies of the existing design criteria are investigated to develop an optimized design process for drilled shaft socketed into rock masses. Reasonable and consistent ultimate capacities of drilled shafts socked into rock masses, necessary far the check of accuracies of predictions, are determined by applying a specific failure criterion to a total of 11 pile load test results. A comparison between the predicted and the measured load capacities shows that ultimate base load capacities calculated from Zhang and Einstein's equation and NAVFAC are close to the measured values. Rosenberg and Journeaux's equation produces satisfactory prediction f3r ultimate side load capacity.

• Journal of the Korean Geotechnical Society
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• v.20 no.6
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• pp.29-40
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• 2004

The bearing capacity of drilled shaft is affected by several factors, such as shaft length, shape, surface roughness, young's modulus of geomaterials and shaft, soil strength, confining stress and so on. However, there has been no design method of drilled shaft considering all factors mentioned above. Moreover, since geomaterials are simply classified as sand, clay and rock, there was no design criterion for IGM (Intermediate Geomaterials). Therefore, the rigorous design approach of drilled shaft was not possible by classical design method. However, since these characteristics were not considered in classical theories, bearing capacity was generally different ken practical value. In this study, the bearing capacity of drilled shaft with the IGM's theory was compared with those of classical theories. The results showed that classical method showed smaller values of bearing capacity than those of field load transfer data. Moreover, the evaluated value of bearing capacity with IGM theory corresponded fairly well with those of field data.

• Journal of the Korean Geotechnical Society
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• v.33 no.6
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• pp.27-36
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• 2017

Gravel compaction pile method has been widely used to improve the soft ground on the land or sea as one of the soft ground improvement technique. The ultimate bearing capacity of the ground reinforced by gravel compaction piles is affected by the soil strength, the replacement ratio of pile, construction conditions, and so on, and various prediction equations have been proposed to predict this. However, the prediction of the ultimate bearing capacity using the existing models has a very large error and variation, and it is not suitable for practical design. In this study, multiple regression analysis was performed using field loading test results to predict the ultimate bearing capacity of ground reinforced by gravel compaction pile, and the most efficient input variables are selected through evaluation of error by leave one out cross validation, and a multiple regression equation for the prediction of ultimate bearing capacity was proposed. In addition, the prediction error was evaluated by applying artificial neural network using the selected input variables, and the results were compared with those of the existing model.

• Journal of the Korean Geotechnical Society
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• v.32 no.11
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• pp.61-72
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• 2016

For the construction of high-rise structures and the optimized foundation design, the use of the large-diameter PHC pile has increased. Especially, the use of the 600 mm diameter PHC pile has significantly increased. In this study, for the evaluation of the suitability of the current design practice, the 46 dynamic pile load tests, which were carried out in the 600 mm diameter preboring PHC pile, are analyzed. The end bearing capacity is obtained from the end of initial driving test and the shaft capacity is estimated from the restrike test. The allowable capacities estimated by the dynamic load test are compared with those based on the current design practice. The analyses show that the allowable end bearing capacity evaluated by the dynamic pile load test is greater than the design practice in most piles. The allowable shaft capacity, however, is smaller than the design practice in many piles. The higher end bearing capacity and the smaller shaft capacity may result from the improvement of the drilling equipment and the increase in the penetration depth. Thus, the portion of the end bearing capacity in the total capacity increases.

• Journal of the Korean GEO-environmental Society
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• v.4 no.2
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• pp.65-76
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• 2003

Stone column is a soil improvement method and can be applicable for loose sand or weak cohesive soil. Since the lack of sand, stone column seems one of the most adaptable approach for poor ground as a soil improvement technique. However, this method was not studied for practical application. In this paper, the bearing capacity of single stone column at the Gaduk, Ulsan and Gwangyang under the bulging and general shear failure mode were compared with those of the suggested formulas. Especially, a test result of single stone column at the Busan area by static load was compared with the bearing capacity of suggested formulas. The analysis results showed that there were not much bearing capacity differences among those suggested bearing capacity formulas. However, the bearing capacity by static load test was almost double of those with suggested formula. The result also showed that the undrained shear strength was the most important parameter for the bearing capacity estimation of stone column.