• Geomechanics and Engineering
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• v.13 no.5
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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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• v.28 no.1
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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.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.03b
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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.

• Journal of the Korean Society for Railway
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• v.10 no.3 s.40
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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.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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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.

• Journal of the Korean Geotechnical Society
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• v.24 no.6
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• pp.57-67
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• 2008

Two test methods, nonrepetitive plate loading test (NPLT) and repetitive plate loading test (RPLT) are being used to control the quality of compaction through the evaluation of the stiffness of subgrade soils in the Korea railway industry. Subgrade reaction modulus ($k_{30}$) from the NPLT and strain modulus ($E_v$) from the RPLT are the index values to check them. The methods have similar aspects, but they differ in the modulus evaluation method, the numbers of loading stage, termination procedures, etc. This paper analyses the differences of the two test methods and evaluates the relationship between subgrade reaction modulus and strain modulus. In order to develop the relationship, total 22 tests were performed including the NPLT and the RPLT at the 6 original grounds, and 5 upper or lower subgrades in Kyungbu High Speed Railway II stage construction sites. According to the soil conditions, the relationship between subgrade reaction modulus and strain modulus was proposed with corrections by considering strain states, mean confining pressures, and Poisson's ratio.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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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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• v.7 no.6
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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.

• Journal of the Korean GEO-environmental Society
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• v.17 no.4
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• pp.5-15
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• 2016

For achieving stability and economic construction at a retaining wall construction site, quantitative parameters of soil properties with excavation steps coincides with the actual field site. The main parameters of retaining wall design such as deformation modulus and modulus of horizontal subgrade reaction are common with N value of standard penetration test. Therefore, this study is compared and analyzed about the mutual relationship which is SPT, PBT and PMT for overcoming inconsistency of the existing retaining wall design generalized. In addition, modulus of horizontal subgrade reaction and reduction factor with excavation steps are proposed through back analysis of elasto-plasticity and finite element method with actual field monitoring data. Finally, it is purpose that parameter errors are reduced for applying effective retaining wall design at a construction small and medium-sized.

• International Journal of Highway Engineering
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• v.16 no.6
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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.