• Geomechanics and Engineering
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• 제13권5호
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• pp.757-774
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• 2017

The subgrade reaction modulus of a large mat foundation was investigated by using a numerical analysis and a field case study. The emphasis was on quantifying the appropriate method for determining the subgrade reaction modulus for the design of a flexible mat foundation. A series of 3D non-linear FE analyses are conducted with special attention given to the subgrade reaction modulus under various conditions, such as the mat width, mat shape, mat thickness, and soil condition. It is shown that the distribution of the subgrade reaction modulus is non-uniform and that the modulus of subgrade reaction at both the corners and edges should be stiffer than that at the center. Based on the results obtained, a simple modification factor for the subgrade reaction modulus is proposed depending on the relative positions within the foundation in weathered soil and rocks.

• Geomechanics and Engineering
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• 제28권1호
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• pp.89-105
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• 2022

The behavior of the soil subgrade is complex and irregular against loads. When modeling, the soil is often replaced by a more straightforward system called a subgrade model. The Winkler method of linear elastic springs is a popular method of soil modeling in which the spring constant shows the modulus of subgrade reaction. In this research, the factors affecting the distribution of the modulus of subgrade reaction of elastoplastic subgrades are examined. For this purpose, critical theories about the modulus of subgrade reaction were examined. A square raft foundation on a sandy soil subgrade with was analyzed at different internal friction angles and Young's modulus values using ABAQUS software. To accurately model the actual soil behavior, the elastic, perfectly plastic constitutive model was applied to investigate a foundation on discrete springs. In order to increase the accuracy of soil modeling, equations have been proposed for the distribution of the subgrade reaction modulus. The constitutive model of the springs is elastic, perfectly plastic. It was observed that the modulus of subgrade reaction under an elastic load decreased when moving from the corner to the center of the foundation. For the ultimate load, the modulus of subgrade reaction increased as it moved from the corner to the center of the foundation.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 봄 학술발표회 논문집
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• pp.255-262
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• 2000

Shaking table tests were peformed to evaluate the subgrade reaction of ground according to the build-up of pore water pressure. Model pile was installed in the sand ground. The acceleration of the model ground, the pore water pressure build-up and displacement of pile were recorded by measuring devices. Subgrade reaction approach based on Winker soil model was applied to obtain the modulus of the horizontal subgrade reaction. The results of analysis show that the reduction factor of the subgrade reaction due to pore pressure increase is about 1 and the horizontal subgrade reaction of liquefied ground is not influenced by the stiffness of pile, a ground acceleration and the intial ground density.

• 한국철도학회논문집
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• 제10권3호
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• pp.264-270
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• 2007

Two modulus, strain modulus $(E_v)$ and subgrade reaction modulus $(K_{30})$ are being used as a standard for bearing stiffness in Korea Railroad design. The first is used in Europe and the other is used in Japan. The methodologies to obtain the two modulus are similar in using plate. But testing methods are different in loading to plate. Therefore, according to soil strain range, there should be large gap in not only computations of deformation modulus but also the necessary time to test. At first, this paper focuses on the two kinds of test methods to evaluate bearing stiffness. Secondly, based on elastic theory, the theory to obtain the two coefficients are studied thoroughly. Finally, the correlations between the two coefficients were analyzed and evaluated based on the field test results more than 38 places. The matching values for subgrade and ground between $K_{30}$ and $E_{v2}$ are proposed with the consideration of the proposed strain reduction factor (1.5 for subgrade and 3 for ground) and safety factor, respectively.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2006년도 춘계 학술발표회 논문집
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• pp.1228-1236
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• 2006

In soft ground, There are many case that Bridge Abutment is constructed after soil improvement in order to reduce the Negative Friction and prevent from Lateral Soil movements of Bridge Abutment. That section of Horizontal Subgrade Reaction $Modulus(K_h)$ derivation has much important mean due to Horizontal Stability of Abutment. It is come from behavior of Pile and Soil within depth of $1/\beta$. After Soil Improvement, however, If Bridge Abutment was construction, It's not impossible to carry out Field Investigation After Ground of Improved at design stage. Therefore, It's not able to derivate Horizontal Subgrade Reaction $Modulus(K_h)$. Therefore, in this case of study compare with Field Construction Test Data in order to derivation of Horizontal Subgrade Reaction $Modulus(K_h)$ and Reliability in terms of ground of Bridge Abutment by Sand Compaction Pile(SCP) during design of The 2nd Bridge Connection Road of Incheon International Airport. In this paper determine, Soil Property(The rate of strength increase, $c_u$ so on) and Horizontal Subgrade Reaction $Modulus(K_h)$ after soil improvement at design stage.

• 한국지반공학회논문집
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• 제24권6호
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• pp.57-67
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• 2008

철도노반의 다짐 후 품질을 관리하기 위하여 비반복 평판재하시험(nonrepetitive plate loading test)으로부터 얻어지는 지반반력계수(subgrade reaction modulus, $k_{30}$)와 반복평판재하시험(repetitive plate loading test)으로부터 획득하는 변형률계수(strain modulus, $E_v$)의 두 계수를 혼용하고 있다. 평판을 이용한 재하시험을 수행한다는 점에서 두 시험법은 동일하나, 설계정수 획득방법, 반복재하 횟수, 각 하중 단계에서의 시험 종료방법 등 시험방법에는 큰 차이가 있다. 본 논문에서는 두 시험의 차이를 비교 분석하고 두 계수에 대한 상관성을 평가하였다. 이를 위하여 경부고속철도 2단계 공사구간의 원지반 6개소와 쌓기지반 5개소에 대한 총 22회의 현장시험을 실시하였다. 현장 시험 시의 응력조건, 변형률 조건 및 포아송비 조건을 고려한 보정을 수행하여 두 계수의 상관성을 높였으며, 현장에서 사용이 가능하도록 지반종류에 따른 상관계수를 제시하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2001년도 봄 학술발표회 논문집
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• pp.525-532
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• 2001

In this study, performance of reinforced railroad roadbeds with the crushed stones was investigated through the real scale railroad roadbed tests. Several real scale reinforced railroad roadbeds were constructed in the laboratory with different subgrade conditions and were tested with the estimated actual train loads including the impact loading of train. The affecting factors such as settlement, earth pressure and stress change at the surface of reinforced roadbed, subgrade layers as well as surface of rails were measured. It was found through the actual testing that for the roadbed with the same thickness, the settlement and vibration level (velocity) of reinforced roadbed decreases with the increase of reaction modulus of subgrade. The settlement of reinforced roadbed with the same reaction modulus of subgrade also decreases with the increase of thickness of the reinforced roadbed.

• Geomechanics and Engineering
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• 제7권6호
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• pp.679-703
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• 2014

This paper investigates nonlinear response of 51 laterally loaded rigid piles in sand. Measured response of each pile test was used to deduce input parameters of modulus of subgrade reaction and the gradient of the linear limiting force profile using elastic-plastic solutions. Normalised load - displacement and/or moment - rotation curves and in some cases bending moment and displacement distributions with depth are provided for all the pile tests, to show the effect of load eccentricity on the nonlinear pile response and pile capacity. The values of modulus of subgrade reaction and the gradient of the linear limiting force profile may be used in the design of laterally loaded rigid piles in sand.

• 한국지반환경공학회 논문집
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• 제17권4호
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• pp.5-15
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• 2016

흙막이 현장에서 안정성 및 경제적 시공이 이루어지기 위해서는 굴착단계별 토질특성을 반영한 정량적인 정수들이 실제 현장과 일치되어야 한다. 그중 흙막이 설계 시 가장 중요한 매개 변수인 변형계수 및 수평지반반력계수는 현장여건에 따라 표준관입시험의 N값으로 산출하는 것이 일반화되어 있다. 따라서 본 연구에서는 기존의 일반화된 흙막이 설계법의 모순을 극복하고, 실제 현장에 부합하는 수평지반반력계수 산정을 위하여 표준관입시험, 평판재하시험 및 공내재하시험을 실시하고 상호관계성을 비교 분석하였다. 또한, 현장의 실제 계측데이터를 통한 유한요소해석법과 탄소성해석법의 역해석을 통하여 수평지반반력계수와 굴착에 따른 저감계수를 추정하였으며, 궁극적으로 중 소형 및 일반현장에서도 흙막이 벽체 설계 시 합리적인 설계적용을 위한 정수의 오류를 줄이고자 한다.

• 한국도로학회논문집
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• 제16권6호
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• pp.69-78
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• 2014

PURPOSES : The purpose of this paper is showing that the state of pavement sublayers can be evaluated differently according to direction of FWD. METHODS : The concrete pavement slabs above subgrade without anything, subgrade with cavity, and box culvert were modeled by finite element method(FEM). The modeled pavements were analyzed by changing the direction of falling weight deflectometer(FWD). The deflection results obtained from FEM were used to calculate radius of relative stiffness and composite modulus of subgrade reaction using AREA method. Then, the analyzed results were compared to the results of the test performed at the Korea Expressway Corporation(KEC) test road. RESULTS : The composite modulus of subgrade reaction increased with subgrade elastic modulus, while radius of relative stiffness decreased. The pavement sections of pure earth showed the consistent results regardless of FWD direction. In case there was cavity, the radius of relative stiffness was larger and composite modulus of subgrade reaction was smaller when FWD was leaving the cavity than when approaching the cavity. This pattern became clear when the cavity got larger. In case of the section with box culvert, the pattern was opposite to the case of cavity. When the soil cover depth increased, the effect of box culvert got smaller. When the load was applied far from the cavity and box culvert, the effect was also declined. The test performed at the KEC test road showed identical results to those of finite element analysis. CONCLUSIONS : The direction of FWD should be considered in evaluation of the state of pavement sublayers because it can be evaluated differently even under identical condition.