• Journal of the Korean Geotechnical Society
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• v.35 no.11
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• pp.75-95
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• 2019

The numerical analysis on PHC piles socketed into weathered rocks through sandy soil layers was conducted to propose the table solution or the chart solution to obtain the mobilization capacity. The mobilization capacity was determined at the settlement of 5% pile diameter and applied a safety factor of 3.0. In order to utilize the excellent compressive strength of the PHC pile effectively, it is recommended that the allowable bearing capacity of ground would be designed to be more than the long-term allowable compressive pile load. A procedure for determining an allowable pile capacity for PHC piles socketed into weathered rocks through sandy soil layers is given by the sum of the allowable skin friction of the sandy soil layer and the weathered rock layer and the allowable end bearing capacity of the weathered rock layer. The design efficiency of the PHC pile is about 85% at the reasonable design stage in the verification of the newly proposed method. Thus, long-term allowable compressive load (P_all) level of PHC piles can be utilized in the optimal design stage.

• Proceedings of the Korean Geotechical Society Conference
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• 1996.10a
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• pp.351-356
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• 1996

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.376-387
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• 2009

Piled raft foundation is a geotechnical composite construction to support the superstructure by pile-soil-raft interaction. General conventional design for piled raft doesn't consider the contribution of a raft. This is very conservative and requires more piles to satisfy the factor of safety. It is important to evaluate the load sharing features of piled raft. In this research, this characteristics of piled raft evaluated using both centrifuge and numerical modelings. The ultimate bearing capacity of piled raft foundation was also evaluated and predicted through comparisons of ultimate bearing capacity of single pile (SP), unpiled raft (UR), freestanding pile group (FPG) and piled raft (PR). $\xi_{pr}$ and $\eta$ were determined by centrifuge model tests to simply evaluate the ultimate bearing capacity of piled raft and bearing capacity of piled raft was predicted using the calibrated numerical model based on the centrifuge tests and laboratory tests data.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.5
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• pp.523-531
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• 2021

In general, the foundation refers to a group pile with several single piles connected by an upper structure. However, when a load is applied to pile groups, the range of stress applied to the ground is expanded and overlapped compared with the single pile, so the overall bearing capacity may decrease. This reduction ratio of bearing capacity is referred to as the efficiency of pile groups. Therefore, in this study, the soil composition, the arrangement and spacing of group piles, and the contact characteristics between the ground and piles were set as analysis variables, and the group pile efficiency and individual pile behavior were analyzed. As a result of the analysis, the efficiency of pile groups tends to converge or decrease when the friction coefficients are increased with ground type. Through this, the optimal efficiency of pile groups can be derived. In addition, through the analysis of individual piles, the load ratio of each pile was analyzed when an upper load was applied. In the case of piles located inside group piles, the load was relatively low, and this is considered to have an influence on the internal ground.

• Journal of the Korean Geosynthetics Society
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• v.18 no.3
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• pp.89-100
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• 2019

The purpose of this study is to analyze the characteristics of bearing capacity of pre-bored super strength PHC (SSPHC) piles socketed in rocks based on dynamic load test results. Because the SSPHC piles have high compressive concrete strengths compared with those of regular high strength PHC piles, the allowable structural strengths of the SSPHC piles were increased. For optimal design of the super strength PHC piles, the geotechnical bearing capacity of the SSPHC piles should also increased to balance the increased allowable structural strength of the SSPHC piles. Current practices of pile installation apply the same amount of driving energy on both SSPHC and high strength PHC piles. As results of analyzing factors that influence bearing strength of SSPHC piles using dynamic load test, there was no relationship between SPT-N value at pile toe and end bearing capacity. But driving energy effects on end bearing capacity. In case of skin friction, driving energy had no effects. And reasonable method verifying design bearing strength is necessary because end bearing capacity is not considered sufficiently in restrike test results.

• Journal of the Korean Geotechnical Society
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• v.24 no.5
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• pp.37-54
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• 2008

The standard construction manual of the SDA (Separated Doughnut Auger) piling method was proposed so that the resisting capacity of the augered piles could work effectively. 438 dynamic pile load tests were performed on 379 test piles, which were installed at 36 sites in Korea by the SDA piling method with application of various water-cement ratio of cement milks. The dynamic pile load test results showed that the bearing capacity of the SDA augered piles depended on the water-cement ratio of cement milks. And couple of the formulas were presented according to water-cement ratio and various grounds to estimate quantitatively both the unit end bearing and the unit frictional capacity of the SDA augered piles. It was also considered that the water-cement ratio of cement milks exerts an influence on the bearing capacity of the SDA augered piles. The presented formulas were compared with the existing formulas, which were presented by several standard design codes to design the augered piles.

• Journal of the Korean GEO-environmental Society
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• v.8 no.6
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• pp.5-12
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• 2007

Mudstone has characteristics that it has high enough strength and stiffness in a dry condition, but the strength and stiffness decrease in a wet condition with groundwater infiltration. The sliding of cut slope frequently encountered in Pohang area has been reported due to the rapid reduction of shear strength in mudstone after being exposed to the air. The study in this paper shows that mudstone having enough strength in a boring stage has lost the strength after installing PRD (percussion rotary drill) steel pipe pile inducing an insufficient bearing capacity. Field test has been performed to investigate the most favorable method for increasing a pile bearing capacity in mudstone with various methods such as MSG (Micro Silica Grouting) around the tip and side of a pile, the perimeter grouting combined with Micro pile reinforcement, and concrete filling after tip reinforcing grouting. MSG has been turned out to be the most favorable method for increasing a pile bearing capacity in mudstone, confirmed by the static load test.

• Journal of the Korean Geotechnical Society
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• v.29 no.12
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• pp.105-111
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• 2013

The standard penetration test (SPT) has been widely used because of its usability, economy, and many correlations with soil properties among other factors. In SPT, hammer energy is an important factor to evaluate and calibrate N values. To measure hammer energy, an instrumented SPT rod was developed considering that stress waves transferring on rods during SPT driving are the same as stress waves transferring on piles due to pile driving. Using this idea, an instrumented SPT rod with a pile driving analyzer was applied as a pile capacity prediction tool in this study. In order to evaluate this method, SPT and dynamic cone tests with the instrumented SPT rod were conducted and also 2 pile load tests were performed on pre-bored steel pipe piles at the same test site. End bearings were predicted by CAPWAP analysis on force and velocity waves from dynamic cone penetration tests and SPT. Comparing these predicted end bearings with static pile load tests, a new prediction method of the end bearing capacity using the instrumented SPT rod was proposed.

• Journal of the Korean GEO-environmental Society
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• v.14 no.6
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• pp.5-11
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• 2013

Because the regulation for a noise and a vibration in our country has been being reinforced more and more, a more environment-friendly pile construction method than a current low-noise and low-vibration method was needed for the close construction in the downtown area. In this study, the characteristics of a screw concrete pile method for noise and vibration-free method was explained, and it's vertical bearing capacity was studied in the base of the static pile load test data of the screw concrete piles. Constructed by two methody; a pre-digging shoe type construction method and a toe-jetting shoe type construction method. The vertical load bearing capacity of a screw pile constructed by the former was more about 70% than that of a screw pile constructed by the latter.

• Geomechanics and Engineering
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• v.31 no.2
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• pp.129-147
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• 2022

The properties of soil are naturally highly variable and thus, to ensure proper safety and reliability, we need to test a large number of samples across the length and depth. In pile foundations, conducting field tests are highly expensive and the traditional empirical relations too have been proven to be poor in performance. The study proposes a state-of-art Particle Swarm Optimization (PSO) hybridized Artificial Neural Network (ANN), Extreme Learning Machine (ELM) and Adaptive Neuro Fuzzy Inference System (ANFIS); and comparative analysis of metaheuristic models (ANN-PSO, ELM-PSO, ANFIS-PSO) for prediction of bearing capacity of pile foundation trained and tested on dataset of nearly 300 dynamic pile tests from the literature. A novel ensemble model of three hybrid models is constructed to combine and enhance the predictions of the individual models effectively. The authenticity of the dataset is confirmed using descriptive statistics, correlation matrix and sensitivity analysis. Ram weight and diameter of pile are found to be most influential input parameter. The comparative analysis reveals that ANFIS-PSO is the best performing model in testing phase (R² = 0.85, RMSE = 0.01) while ELM-PSO performs best in training phase (R² = 0.88, RMSE = 0.08); while the ensemble provided overall best performance based on the rank score. The performance of ANN-PSO is least satisfactory compared to the other two models. The findings were confirmed using Taylor diagram, error matrix and uncertainty analysis. Based on the results ELM-PSO and ANFIS-PSO is proposed to be used for the prediction of bearing capacity of piles and ensemble learning method of joining the outputs of individual models should be encouraged. The study possesses the potential to assist geotechnical engineers in the design phase of civil engineering projects.