• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.338-350
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• 2010

As existing materials for ground reinforcement, chemical grout material using cementitous materials and waterglass was used. But many problems in terms of ground reinforcement effects were implicated. In this study, for development and applicability verification of new materials, viscosity, fluidity, permeability, Self-Leveling, keeping of drilled hole, antiwashout underwater, resistance of water (groundwater dilution and minimize material eluting) and the early strength and long-term strength characteristics of developed materials was confirmed, and material standards, and establishing construction standards for the various model tests were conducted. As a result, high viscosity, flowability, permeability and keeping of drilled hole characteristics are excellent, in addition to the early strength properties, dilution does nat occur to groundwater, including groundwater is available for dealing with environmental issues. Application of basic and reinforcement method by Filler function in addition to structure can also or development of a new concept can be expected. In addition, middle and large-diameter drilled shaft, micropile, ground anchors, soil-nailing, steel pipes multi-grouting reinforcement for cement injection process could be used enough to even be considered.

• Journal of the Korean Geotechnical Society
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• v.29 no.1
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• pp.161-170
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• 2013

In this paper, numerical pile segment analysis is conducted with an advanced soil elastoplastic model to investigate the diameter effects on skin friction behaviour of a drilled shaft in sand. Ultimate skin friction and 't-z' behavior from the pile segment analyses for drilled shafts show good agreement with those from design methods. Higher ultimate skin friction for the smaller diameter pile is related to the greater increase in the effective radial stress at the interface due to the localized dilation at and near the pile interface. Stiffer t-z curve for the smaller diameter pile is related to the early occurrence of three shear stages (early, dilation, constant volume shear stages). The diameter effects on ultimate skin friction of drilled shafts are more prominent for denser sand and lower confining pressure.

• Journal of the Korean Geosynthetics Society
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• v.19 no.3
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• pp.23-33
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• 2020

The lateral bearing characteristics are important factors in the case of large diameter drilled shafts and the measures to increase this are to improve the adjacent ground of the pile to increase the rigidity and to increase the rigidity of the pile itself. There are many suggestions for increasing rigidity by reinforcing casing on the pile, but few studies have been done related to this. Therefore, in this study, the lateral bearing characteristics according to casing reinforcement length were studied for each ground condition using non-linear analysis to evaluate the appropriate casing reinforcement length of the large diameter drilled shafts depending on the ground conditions. As a result, the lateral bearing characteristics of the large diameter drilled shafts are most effective if the casing reinforcement length ratio is 1.2, and depending on the ground conditions, the more loose the ground, the greater the reinforcement effect.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.99-106
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• 2005

본 연구에서는 케이싱을 영구부재로 사용함으로써 기존의 현장타설말뚝과 비교하여 시공 성,품질균일성,경제성, 내구성 등을 검토한다. 연구결과 케이싱을 영구부재로 사용하는 경우, 케이싱의 재사용을 위한 인발작업이 불필요하게 되고,말뚝길이전체에 대하여 케이싱을 사용한다면 R.C.D공법에 서 적용하는 슬러리공벽보호공정이 불필요하므로 시공성이 향상되는 것으로 판단된다. 케이싱을 영구부 재로 사용하는 현장타설말뚝의 지지력은 일반 깊은 기초의 지지력을 산정하는 방법과 동일하게 구해질 수 있다. 대구경의 영구케이싱이 있는 현장타설말뚝을 시공한다면 공내에 간단한 장비와 인력을 투입해서 선단부를 그라우팅방법 등으로 강화시킴으로써 선단지지력을 효과적으로 증대시킬 수 있을 것이다. 또한 케이싱 내부로부터 미리제작한 구멍을 통하여 그라우팅, 전단키(shear key) 등을 주입 또는 압입 함으로써 주면마찰력도 크게 향상될 수 있을 것으로 사료된다.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.368-376
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• 2010

The bent foundation with single drilled shafts is suitable and economical in South Korea, which has good rock in a shallow depth. This foundation has been designed with an elastic design concept. To apply a plastic design concept written in Korea Bridge Design Criteria, a detail design regulation, which includes the method for a plastic hinge point to occur above the ground, rebar arrangement and soil modelling, should be defined. Soil modelling should be considered in the respect of structural engineer's practicality. In this paper, single drilled shaft piers with 1m diameter are constructed, and cyclic lateral load tests loaded at 4m above the ground are taken to examine the behavior. Reduced diameter shaft above the ground and remaining the steel casing under the ground were used to induce plastic hinge to occur above the ground. Simplified soil models such as elastic relation and p-y curve are adapted, and the prediction results are compared with test results. Prediction results of a model bridge were compared according to soil models with time domain analyses, and design criteria of soil were proposed.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.933-943
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• 2009

Axial loads and shaft resistances can be calculated by load transfer analysis using strain data with load level. In load transfer analysis, the elastic modulus of concrete is a one of the most important parameters to consider. The elastic modulus, $E_{50}$, suggested by ACI (American Concrete Institute), has been commonly used. However, elastic modulus of concrete shows nonlinear stress-strain characteristic, so nonlinearity should be considered in load transfer analysis. In this paper, a load transfer analysis was performed by using data obtained from bi-directional pile load tests for four cases of drilled shafts. For consideration of nonlinearity, elastic modulus was calculated by both the Fellenius method and the nonlinear method, assuming the stress-strain relation of concrete to be a quadratic function, and then, the calculated elastic modulus was applied to the estimation of shaft resistance. The calculated shaft resistances were compared with the result obtained using the constant elastic modulus of ACI code. It was found that the f-w curves are similar to each method, and elastic modulus and shaft resistances decreased as strain increased. Moreover, shaft resistances estimated from elastic modulus considering nonlinearity were 5~15% different than those obtained using the constant elastic modulus.

• Journal of the Korean Geosynthetics Society
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• v.18 no.4
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• pp.263-272
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• 2019

This paper describes the results of bearing capacity using field loading test of pile, in order to extend the applicability of drilled shaft with mid-size, and the results were compared with the prediction results of design bearing capacity by empirical formular. The static load test result showed that the allowable bearing capacity of high pile strength was about 2.4 times higher than that of low pile strength. The dynamic load test result showed that the allowable bearing capacity of high pile strength was about 1.4 times~1.5 times higher than that of low pile strength. The comparison result of allowable bearing capacity between static and dynamic load test showed that the difference of allowable load ranged from 3% to 6% under the same settlement conditions. As a result of comparing the ultimate bearing capacity by load test and design bearing capacity, it was found that the FHWA proposed equation could be more reasonable than the other proposed equation in load sharing ratios of end bearing and skin friction.

• Journal of the Korean Geotechnical Society
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• v.23 no.2
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• pp.85-92
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• 2007

As the use of drilled shafts for foundation of a large size structure increases, the evaluation of the reliable bearing capacity of the pile has become important. The purpose of this study is to verify the reliability of bearing capacity equations for drilled shafts socketed in weathered rock by comparing the bearing capacity values from static load tests with values from bearing capacity equations. In this study, twelve data from static load test were selected from four field sites, and the data of load test and the properties of weathered rock were analyzed. Three methods widely used in practice were selected for analysis, namely the AASHTO method (1996), Carter & Kulhawy method (1988), and FHWA method (1999). The comparison of the bearing capacity values from the bearing capacity equations to those obtained from load tests showed that the Carter & Kulhawy method (1988) was the most reliable in giving conservative design values and smaller COV (Coefficient Of Variation).

• Journal of the Korean GEO-environmental Society
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• v.10 no.3
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• pp.29-36
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• 2009

In this paper, a case of a high-rise building supported by a large-diameter drilled shaft socketed in a weathered ground has been studied. The design case of pile foundation presented in this paper could be a representative example of execution of pile design through three(3) design stages of "preliminary design-proof test-supplementary design". As proof test, two(2) BDH PLT (Bi-directional High Pressure Pile Load Test) were performed at the early construction stage. By following the design process of this way, the economic pile design could be carried out and a large amount of construction cost saving could be realized.

• Journal of the Korean Geotechnical Society
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• v.20 no.5
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• pp.87-98
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• 2004

In this study reinforcing effect of soil nailed-drilled shafts subjected to axial and lateral loads was evaluated. Special attention was given to the reinforcing effects of soil nails placed from the drilled shafts to surrounding weathered- and soft-rocks based on model tests, numerical analyses and field tests. The model tests and numerical analyses are conducted to analyze the reinforcing effect of various conditions of number, inclination, position and length. The results of 1/40 scale model tests and numerical analyses show that as the number of reinforcing level increases, the incremental effect of reinforcement tends to increase, whereas the reinforcing effect on relative position is negligible. In addition there is a reinforcing effect as the inclination angle increase up to 30 degrees. Based on the results of tensile load tests, soil nailed-drilled shaft has a considerably smaller settlement to reach the ultimate level compared with the result of un-reinforced drilled shafts. For compression tests, there is a reinforcing effect of about 200% measured.