• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.387-395
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• 2003

Model tests were conducted to study the behavior of the piled raft foundation system on sands. Especially in this study, the method using the triaxial compression apparatus was devised and used to apply the confining pressure which is considered difficult in the existing model test on the soil. Steel rods (6mm dia.) and aluminum plates (8mm thickness, 50mm dia.) were used to simulate piles and rafts respectively. Jumunjin standard sands were used to ensure the homogeneity of the sample. After the sample with the piled raft model was laid inside the triaxial cell, the confining pressure was applied and then the compressive force was applied. The increase and/or decrease ratio of the bearing capacity, the load distribution ratio between raft and piles and the effect of settlements decrease depending on the confining pressure, the number of piles and the length of piles were analyzed and the bearing capacity and skin friction of the pile was calculated. By the results of these experiments, the bearing capacity increased and the settlement decreased with this piled raft foundation system. Especially the effect was larger with the increase of the number of piles than with the increase of length of piles. Hereafter, the study of the load transfer mechanism of piles under confining pressure would be made possible using these small model tester like triaxial compression apparatus.

• Earthquakes and Structures
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• v.26 no.2
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• pp.97-115
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• 2024

In this paper, a database consisting of the dynamic shear modulus ratio and damping ratio test data of clay obtained from 406 groups of triaxial tests is constructed with the starting area of Xiong'an New Area as the research background. The aim is to study the nonlinear dynamic properties of clay in this area under cyclic loading. The study found that the effective confining pressure and plasticity index have certain influences on the dynamic shear modulus ratio and damping ratio of clay in this area. Through data analysis, it was found that there was a certain correlation between effective confining pressure and plasticity index and dynamic shear modulus ratio and damping ratio, with fitting degree values greater than 0.1263 for both. However, other physical indices such as the void ratio, natural density, water content and specific gravity have only a small effect on the dynamic shear modulus ratio and the damping ratio, with fitting degree values of less than 0.1 for all of them. This indicates that it is important to consider the influence of effective confining pressure and plasticity index when studying the nonlinear dynamic properties of clays in this area. Based on the above, prediction models for the dynamic shear modulus ratio and damping ratio in this area were constructed separately. The results showed that the model that considered the combined effect of effective confining pressure and plasticity index performed best. The predicted dynamic shear modulus ratio and damping ratio closely matched the actual curves, with approximately 88% of the data falling within ±1.3 times the measured dynamic shear modulus ratio and approximately 85.1% of the data falling within ±1.3 times the measured damping ratio. In contrast, the prediction models that considered only a single influence deviated from the actual values, particularly the model that considered only the plasticity index, which predicted the dynamic shear modulus ratio and the damping ratio within a small distribution range close to the average of the test values. When compared with existing prediction models, it was found that the predicted dynamic shear modulus ratio in this paper was slightly higher, which was due to the overall hardness of the clay in this area, leading to a slightly higher determination of the dynamic shear modulus ratio by the prediction model. Finally, for the dynamic shear modulus ratio and damping ratio of the engineering site in the starting area of Xiong'an New Area, we confirm that the prediction formulas established in this paper have high reliability and provide the applicable range of the prediction model.

• Journal of the Korea Concrete Institute
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• v.15 no.1
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• pp.102-109
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• 2003

The grouted splice steeve has been applied widely due to its superior construction efficiency, such as the unnecessity of post concrete and the large allowable limit to the arrangement of reinforcing bars. However, studies on grout-filled splice steeve still have not been sufficiently peformed. The purpose of this study is to investigate the confining effect of mortar grouted splice sleeve on reinforcing bar, known to strengthen the bond capacity between grout mortar and reinforcing bar. To accomplish this objective, totally 6 full-sized specimens were made and tested under monotonic loading. Each specimens were equipped with strain gauges at the 12 location of sleeve and reinforcing bar. The experimental variables adopted in this study are embedment length and size of reinforcing bars. Following conclusions are obtained; 1) Under ultimate strength condition, the confining pressure of grouted splice sleeve calculated from measured tangential and axial strain of the sleeve is over $200{\sim}300kgf/{cm}^2$ at any location of sleeve and improved with reduction in embedment length of reinforcing bar. 2) Untrauer and Henry's equation which describe bond strength of mortar as a function of its compressive strength and confining pressure, predicted the measured bond capacity of this test within the 5% limits.

• Land and Housing Review
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• v.2 no.4
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• pp.387-395
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• 2011

According to the seismic design criteria for structural buildings in Korea, the ground is classified into 5 types based on the average shear wave velocity measured from elastic wave tests on site and seismic load applied to the structure is estimated. However, elastic wave tests in site, however, on the engineering fill, cannot be performed during the construction period. Therefore, to evaluate shear wave velocity considering field conditions, resonant column (RC) and torsional shear (TS) tests are performed and compared with various elastic wave test results. As a result, if confining pressure for the tests using engineering fill are considered properly, we can obtain similar results comparing with those of elastic wave tests. In addition, by considering the effect of maximum shear modulus and confining pressure by RC/TS tests, n values shows typical values ranging from 0.434 to 0.561 so that utilization of RC/TS tests can be useful to infer shear modulus in field.

• Earthquakes and Structures
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• v.3 no.6
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• pp.889-910
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• 2012

Because of the heavy demand of confining steel to restore the column ductility in seismic regions, it is more efficient to confine these columns by hollow steel tube to form concrete-filled-steel-tube (CFST) column. Compared with transverse reinforcing steel, steel tube provides a stronger and more uniform confining pressure to the concrete core, and reduces the steel congestion problem for better concrete placing quality. However, a major shortcoming of CFST columns is the imperfect steel-concrete interface bonding occurred at the elastic stage as steel dilates more than concrete in compression. This adversely affects the confining effect and decrease the elastic modulus. To resolve the problem, it is proposed in this study to use external steel confinement in the forms of rings and ties to restrict the dilation of steel tube. For verification, a series of uni-axial compression test was performed on some CFST columns with external steel rings and ties. From the results, it was found that: (1) Both rings and ties improved the stiffness of the CFST columns and (2) the rings improve significantly the axial strength of the CFST columns while the ties did not improve the axial strength. Lastly, a theoretical model for predicting the axial strength of confined CFST columns will be developed.

• Geomechanics and Engineering
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• v.11 no.5
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• pp.639-655
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• 2016

The effect of particle breakage and intermediate principal stress ratio on the behaviour of crushable granular assemblies under true triaxial stress conditions is studied using the discrete element method. Numerical results show that the increase of intermediate principal stress ratio $b(b=({\sigma}_2-{\sigma}_3)/({\sigma}_1-{\sigma}_3))$ results in the increase of dilatancy at low confining pressures but the decrease of dilatancy at high confining pressures, which stems from the distinct increasing compaction caused by breakage with b. The influence of b on the evolution of the peak apparent friction angle is also weakened by particle breakage. For low relative breakage, the relationship between the peak apparent friction angle and b is close to the Lade-Duncan failure model, whereas it conforms to the Matsuoka-Nakai failure model for high relative breakage. In addition, the increasing tendency of relative breakage, calculated based on a fractal particle size distribution with the fractal dimension being 2.5, declines with the increasing confining pressure and axial strain, which implies the existence of an ultimate graduation. Finally, the relationship between particle breakage and plastic work is found to conform to a unique hyperbolic correlation regardless of the test conditions.

• Steel and Composite Structures
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• v.10 no.5
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• pp.415-428
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• 2010

Proper material constitutive models for concrete-filled tube (CFT) columns of circular cross section and subjected to pure bending moment are proposed. These material models are implemented into the Abaqus finite element program and verified against experimental data. It has been shown that the steel tube does not provide good confining effect to the concrete core when the CFT columns is subjected to pure bending moment. When the diameter-to-thickness ratio of the CFT columns is small, the behavior of the CFT column is the same as the steel tube without a concrete core.

• Geomechanics and Engineering
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• v.10 no.1
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• pp.77-94
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• 2016

Cyclic triaxial and resonant column tests were conducted to understand the beneficial effects of various grouted sands on liquefaction resistance and dynamic properties. The test procedures were performed on a variety of grouted sands, such as silicate-grouted sand, silicate-cement grouted sand and cement-grouted sand. For each type of grout, sand specimen was mixed with a 3.5% and 5% grout by volume. The specimens were tested at a curing age of 3, 7, 28 and 91 days, and the results of the cyclic stress ratio, the maximum shear modulus and the damping ratio were obtained during the testing program. The influence of important parameters, including the type of grout, grout content, shear strain, confining pressure, and curing age, were investigated. Results indicated that sodium silicate grout does not improve the liquefaction resistance and shear modulus; however, silicate-cement and cement grout remarkably increased the liquefaction resistance and shear modulus. Shear modulus decreased and damping ratio increased with an increase in the amplitude of shear strain. The effect of confining pressure on clean sand and sodium silicate grouted sand was found to be insignificant. Furthermore, a nonlinear regression analysis was used to prove the agreement of the shear modulus-shear strain relation presented by the hyperbolic law for different grouted sands, and the coefficients of determination, $R^2$, were nearly greater than 0.984.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.888-895
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• 2006

In this study, anisotropically consolidated undrained shear(CAU) test was performed to examine the variation of the shear strength according to the stress history. The specimen having 30% relative density was homogeniously prepared, and 200KPa of back pressure was applied to increase the B value more than 0.95. To make NC specimens, the vertical stress was applied on the specimen by 100KPa, 200KPa and 400KPa, and to make OC specimens, the vertical stress was applied upto 400KPa and was reduced to 200KPa and 100KPa resulting in OCR 2 and 4 respectively. The test result indicates the shear strength for the OC specimens are slightly higher then that of the NC specimens at the same confining pressure. The elastic modulus varies according to the confining stress and considerably affected by preconsolidation stress.

• Journal of the Korean Geotechnical Society
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• v.18 no.3
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• pp.126-126
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• 2002

In dynamic analyses such as seismic ground response and soil-structure interaction problems, it is very crucial to obtain accurate dynamic shear modulus of soil deposit. In this study, an extensive data base of available experimental data is compiled and reanalyzed to establish a simple empirical formula for the dynamic shear modulus reduction curve to cover wide range of strain for sandy soils. The proposed empirical equation is to represent the dynamic shear modulus degradation with strain in terms of low-amplitude dynamic shear modulus and effective mean confining Pressure, since those factors have the most significant effect on the Position and shape of the shear modulus reduction curve for nonelastic soils. If low-amplitude shear modulus is measured, degraded modulus at any shear strain amplitude can be calculated using the proposed equation.