• Journal of Ocean Engineering and Technology
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• v.21 no.5
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• pp.25-32
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• 2007

The piled-raft foundation, a new design concept, is one of the most effective kinds of foundation for reducing settlement of structures. An alternative piled-raft system with disconnection cap and a sand cushion between the pile and raft was also investigated to compare the influence of ultimate bearing capacity and settlement. Load-settlement relation curves were used to evaluate the ultimate bearing capacity. In the numerical analyses, a plane strain elasto-plastic finite element model (Mohr-Coulomb model) was used to present the response of the piled-raft foundation.

• Geomechanics and Engineering
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• v.21 no.6
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• pp.503-511
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• 2020

This study evaluated the side resistance of drilled shafts socketed into rock sections. Commonly used analysis methods for side resistance of piles in rocks are examined by utilizing a large number of load test data. The analysis of the unit side resistance of pile foundations embedded into rock sections is based on an empirical coefficient (α) and the uniaxial compressive strength (q_u) or its root (${\sqrt{q_u}}$). The Davisson criterion was used to interpret the resistance capacity from the load test results to acquire the computed relationships. The α-${\sqrt{q_u}}$ relationship is proven to be reliable in the prediction of friction resistance. This study further analyzed the relationship by including the effect of rock quality designation (RQD) on the results. Analysis results showed that the analysis model of α-${\sqrt{q_u}}$-RQD provided better prediction and reliability considering the RQD classification. Based on these analyses, the side resistance of drilled shafts socked into rocks is provided with statistical data to support the analysis.

• Journal of the Korean Geotechnical Society
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• v.20 no.5
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• pp.117-126
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• 2004

Recently, the top ＆ down method with drilled shafts as a foundation of high rise building is often adopted for the purpose of construction period reduction and construction cost effectiveness. It is common to omit the loading test as a quality assurance on account of the high capacity of drilled shafts for the top ＆ down method. It seems that the capacity of drilled shaft in recent top ＆ down method is beyond that of conventional loading test method. However, the quality assurance for the drilled shaft as foundation of high rise building becomes much more important since the drilled shaft should bear much higher working load. A small scale test pile can be an alternative as a quality assurance for the drilled shaft with hish capacities. Through a case study, this paper gives an idea for solving the limitation of the conventional loading test method for the quality assurance of drilled shaft with high capacities. In particular, this paper analyzed the scale effect for a small drilled shaft installed into bedrock, which could be used for an alternative.

• Journal of the Korean Geotechnical Society
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• v.24 no.10
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• pp.121-129
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• 2008

Numerical analysis for the in-situ top base foundation (In-situ TBF) was carried out in order to investigate the effect of bearing capacity and the load delivering mechanisms in granular soil. The input data for the numerical model was prepared from the result obtained from the plate load test and full size in-situ TBF field tests. According to the result of numerical analysis, the behavior of in-situ TBF showed that bearing capacity of the foundation increased by $50{\sim}100%$ and settlement was reduced up to $1/2{\sim}1/3$ comparing to other types foundation. The effect of cone-shaped part of the in-situ TBF was as important as pile part for the improvement of foundation stability. The variation of the length of pile part indicated that the present length was proved satisfactory in terms of effectiveness.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.223-233
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• 2003

Sand compaction pile (SCP) is one of the ground improvement techniques which are being used for not only accelerating consolidation but also increasing bearing capacity of loose sands or soft clay grounds. In this study, laboratory model tests and 3-D finite element analyses were performed to investigate the interaction between sand compaction piles and surrounding soft soils. Based on the results obtained, as the area replacement ratio increases, the stress concentration ratio increases at the pile point, the settlement decreases, and the relative displacement between column and soil also decreases. It is also found that numerical study is illustrated by good comparison with model test results, and the numerical analysis revealed slip effects which could not be specifically identified in the model tests.

• Journal of the Korean Geotechnical Society
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• v.35 no.12
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• pp.35-44
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• 2019

In this study, the axial stiffness of reinforcing piles (K_vr) for the vertical extension remodeling structures was estimated through 3D finite element analysis. In the computation of the minimum required axial stiffness of reinforcing piles, proposed maximum axial stiffness of old and deteriorated existing piles (K_ve) based on theoretical and experimental approaches will be applied. Through this, the required increase rate of axial stiffness of reinforcing piles in order to support the increased structural loading was proposed for end-bearing and friction piles by different slenderness ratio (L/D). The numerical model was validated by comparing the computed results with actual field measurements. Based on the computed results, it was concluded that the end-bearing reinforcing pile needs 44% - 67% increase in axial stiffness to deal with the deterioration of existing piles and support the additional structural load due to vertical extension remodeling.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.3
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• pp.545-550
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• 2016

The main purpose of this study is to analyze and evaluate the feasibility of ligthweight pavement system with pile foundation on soft soil by laboratory small chamber test. In order to verify the stability of lightweight pavement system, the 1/30 scaled downed model system was tested at lab. The soft soil condition was simulated and group piles for skin friction resistance were used. Within the limited lab test, the settlements of pavement system were 0.86 mm for Case A, 0.70 mm for Case B, and 0.50 mm for Case C. The converted maximum settlement differential settlement were 25.8 mm and 10.8 mm. These values meet the inside of specification of Bridge Design Guide in Korea. The use of lightweight pavement systems on soft soils could be an alternative construction method on soft soils to reduce the challenges of conventional design and constructions.

• Journal of the Korean GEO-environmental Society
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• v.2 no.1
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• pp.91-101
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• 2001

This paper investigates the effectiveness of quick lime piles for soft ground improvement. The field tests based on the results of the laboratory test were performed, and the results of field tests were compared with those of numerical analyses(FEM). The results of the field test showed that the domestic quick lime was very effective in reducing the water contents of the surrounding ground quickly due to its characteristics such as digestion, absorption, and exothermic reactions. Accordingly, consolidation occurred without any additional load increment and the shear strength of surrounding ground was increased more than twice. Therefore the quick lime pile method could be considered as an excellent improvement technique reducing the improvement period for soft ground. For the practical applications of the quick lime pile method, issues such as hydration heat, particulation and equipment enhancement should be solved through continuous research and development.

• Geomechanics and Engineering
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• v.32 no.4
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• pp.427-443
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• 2023

Across the globe, rapid urbanization demands the construction of basements for car parking and sub way station within the vicinity of high-rise buildings supported on piled raft foundations. As a consequence, ground movements caused by such excavations could interfere with the serviceability of the building and the piled raft as well. Hence, the prediction of the building responses to the adjacent excavations is of utmost importance. This study used three-dimensional numerical modelling to capture the effects of twin excavations (final depth of each excavation, H_e=24 m) on a 20-storey building resting on (4×4) piled raft. Because the considered structure, pile foundation, and soil deposit are three-dimensional in nature, the adopted three-dimensional numerical modelling can provide a more realistic simulation to capture responses of the system. The hypoplastic constitutive model was used to capture soil behaviour. The concrete damaged plasticity (CDP) model was used to capture the cracking behaviour in the concrete beams, columns and piles. The computed results revealed that the first excavation- induced substantial differential settlement (i.e., tilting) in the adjacent high-rise building while second excavation caused the building tilt back with smaller rate. As a result, the building remains tilted towards the first excavation with final value of tilting of 0.28%. Consequently, the most severe tensile cracking damage at the bottom of two middle columns. At the end of twin excavations, the building load resisted by the raft reduced to half of that the load before the excavations. The reduced load transferred to the piles resulting in increment of the axial load along the entire length of piles.

• Geotechnical Engineering
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• v.12 no.2
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• pp.71-84
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• 1996

In order to investigate the influence of slanting angle of reticulated root piles(RRP) on their bearing capacities, model tests of compressive and uplift loads on RRP with different slanting angles, which were installed in sandy soils with a relative density of 47%, were carried out. Each pile which is made of a steel bar of 5mm in diameter and 300mm in length, is coated with sand to be 6.5mm in diameter. One set of RRP consists of 8 piles which are installed in circular patterns forming two concentric circles, each of which has 4 piles. Slanting angles of RRP for load tests are 0$^{\circ}$, 5$^{\circ}$, 10$^{\circ}$, 15$^{\circ}$, 20$^{\circ}$, and 25$^{\circ}$. In addition, compressive load tests on circular footing whose diameter is the same as the outer circle of RRP were carried out. Test results show that maximum load bearing capacities of RRP by regression analysis are obtained at about 12$^{\circ}$ and 13$^{\circ}$ of slanting angles for compressive and uplift load tests, respectively. Maximum compressive bearing capacity is estimated to be 13oA bigger than that of the vertical RRP and 95% bigger than that of surface footing. Maximum uplift capacity is estimated to be 21% bigger than that of the vertical RRP. And it can be appreciated that increasing the slanting angle makes the load -Settlement behavior more ductile.