• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.1415-1424
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• 2009

Measuring dynamic properties of gravel-sized materials demands large specimens. Due to the difficulties in experiment as well as equipment, the dynamic properties of gravel-sized material has rarely been investigated. To realize free-free end condition more properly and stabilize specimen during testing with new specimen support system, a free-free resonant column testing device, which is capable of testing gravel-sized materials and constraining a specimen in free-free boundaries, is developed. We report the calibration of the equipment and preliminary testing results on Jumunjin sand. The testing data are compared with the previous data obtained from the existing fixed-free resonant column test.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.626-633
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• 2009

A large scale resonant column testing equipment is under development. The would-be equipment is aiming to test 150mm-diameter specimens, which can contain as large a grain size as 25mm. Such a large specimen is hardly excitated with the existing fixed-free end condition because the torsional force cannot be effectively coupled to the specimen. The specimen will be rather resonated with free-free condition and the scheme is implemented with a rotational bearing installed between coil-magnet exciter and base pedestal. Presently the equipment was assembled and is under calibration with a cylindrical brass specimen.

• International Journal of Highway Engineering
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• v.2 no.2
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• pp.149-161
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• 2000

The stiffness of the subbase materials is represented by the resilient modulus, $M_R$, which are very important properties in the mechanistic design of flexible pavement system. However, the cyclic $M_R$ testing method is too complex, expensive, and time consuming to be applicable on a production basis. In this study, the alternative $M_R$ testing technique for subbase materials was developed using a free-free resonant column (FF-RC) test considering deformational characteristics of subbase materials. To estimate the deformational characteristics of subbase materials, effects of strain amplitude and mean effective stress on modulus of subbase materials were investigated. The $M_R$ values determined by alternative testing procedures matched well with those determined by standard $M_R$ test, showing the capability of the proposed methods being used in determining $M_R$ values.

• Tunnel and Underground Space
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• v.21 no.6
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• pp.480-493
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• 2011

Dynamic rock property is one of most important parameters in design of earthquake-resistant structures. In this study, free-free resonant column test has been conducted to obtain dynamic Young's modulus, dynamic shear modulus, and damping ratio among dynamic properties with granite specimen of Chungnam Yeongi area. The dynamic properties obtained from this test were compared with the physical properties from static rock tests, and their relationship has been analyzed. From our study, it has been concluded that the dynamic Young's modulus and the dynamic shear modulus are linearly proportional to the elastic wave velocity. And also the damping ratio has been identified to be in non-linear inverse proportion to the elastic wave velocity.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.1190-1200
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• 2010

A method was developed to determine resilient modulus for crushed rock-soil mixtures whose usage has been increased recently without engineering specifications. The method is based on the subtle different modulus called nonlinear dynamic modulus and was lately implemented in residual soils and engineered crushed-stones. Hereby. the same method was expanded to crushed rock-soil mixtures containing as large grain diameter as 300mm. The method utilize field direct-arival tests for the determination of maximum Young's modulus, and a large scale free-free resonant column test, which is recently developed to is capable to test as large grain diameter as 25mm, for modulus reduction curves. The prediction model of resilient modulus was evaluated for crushed rock-soil mixtures of a highway construction site at Gimcheon, Korea.

• International Journal of Highway Engineering
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• v.12 no.4
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• pp.147-155
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• 2010

A prediction model of resilient modulus($E_R$) was developed for recycled crushed-rock-soil mixtures. The evaluation of $E_R$, using the "orthodox" repeated loading tri-axial test, is not feasible for such a large-size gravelly material. An alternative method was proposed hereby using the subtle different modulus called nonlinear dynamic modulus. The prediction model was developed by utilizing in-situ measured shear modulus($G_{max}$) and its reduction curves of modeled materials using the large free-free resonant column test. A pilot evaluation of the model parameters was carried out for recycled crushed-rock-soil-mixture at a highway construction site near Gimcheon, Korea. The values of the model parameters($A_E,\;n_E,\;{\varepsilon}_r\;and\;{\alpha}$) were proposed as 9618, 0.47, 0.0135, and 0.8, respectively.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.345-352
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• 2000

It is very important to evaluate the reliable nonlinear modulus characteristics of soils not only in the analysis of geotechnical structures under working stress conditions but also for the soil dynamic problems. For the evaluation of modulus characteristics of soils, various tests have been mostly employed in laboratory. However, different testing techniques are likely to have different ranges of reliable strain measurements, different applied stress level, and different loading frequencies, and the modulus of soils can be affected by these variables. For reliable evaluation, therefore, those effects on the modulus need to be considered, and measured values should be effectively adjusted to actual conditions where the soil is working. In this paper, to evaluate the modulus characteristics of soils, laboratory testing such as free-free resonant column (FF-RC), resonant column (RC), torsional shear (TS), static TX, and cyclic M/sub R/ tests were performed. The effects of strain amplitude, loading frequency, loading cycles, confining pressure, density, and water content on modulus were investigated. It is shown that the FF-RC test, which is simple and inexpensive testing technique, can provide a reliable estimation of small strain Young's modulus (E/sub max/), and the modulus evaluated by various laboratory tests are comparable to each other fairly well when the effects of these factors are properly taken into account.

• Journal of the Korean Geotechnical Society
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• v.35 no.7
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• pp.41-50
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• 2019

Gyeongju bentonite is a buffer material primarily considered in Korea and it is highly compacted as a part of an engineered barrier system (EBS) of high-level radioactive waste repository. The compacted bentonite undergoes swelling stress by groundwater penetration and thermal stress by decay heat from a canister. Therefore, the mechanical properties of the compacted bentonite buffer material is crucial for the performance assessment of EBS. This paper aims to evaluate deformation properties of Gyeongju compacted bentonite using seismic methods. Two sets of compacted bentonite specimens were prepared having dry densities of $1.59g/cm^3$ and $1.75g/cm^3$ with water contents of 10.6% and 8.7%. Free-free resonant column tests were performed to measure constrained and unconstrained compression wave velocities. With the measured wave velocities, Young's modulus ($E_{max}$) and constrained modulus ($M_{max}$), material damping ratio ($D_{min}$), and Poisson's ratio at small strain were determined. As results, this paper evaluates the deformation properties of Gyeongju compacted bentonite and compares them with the results of previous researches.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6C
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• pp.295-304
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• 2012

In this study, a resonant column testing system which is the largest in Korea has been developed to evaluate the dynamic deformation characteristics of coarse granular geomaterials, and the performance and the applicability of the testing system have been verified. The system has been developed as a typical Stokoe type device whose boundary conditions are fixed bottom and free top with additional mass, and can adopt a large specimen with 200 mm in diameter and 400 mm in height. The driving and measurement instruments are configured as high performance and precision systems, hence the automated testing system is appropriate to drive enough stress and to measure the behavior precisely for the test in practical manner. The dynamic response of the mechanical components and the applicability of the system have been evaluated using metal specimens as well as polyurethane specimens, and its precision was verified by comparing its results with those from other equipment and/or methods. To confirm the applicability of the large system for coarse geomaterials, the resonant column test results from both large and normal scale apparatus for the same material were compared and it was found that the result can be partially affected by scale. Finally, the dynamic deformation characteristics of coarse geomaterial which is used for construction of large dam was evaluated using the large system and its practicality could be confirmed.

• Journal of the Korean Society for Railway
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• v.15 no.5
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• pp.476-484
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• 2012

In this study, a mid-size RC test apparatus equipped with analyzing program is developed that can test samples up to D=10cm diameter and H=20cm height which is larger than usual samples of D=5cm and H=10cm used mostly in practice. Thus, crushed stones with larger grains up to 38mm in diameter used mostly in Korea as reinforced trackbed materials in track construction could be considered effectively than conventionally used RC apparatus for evaluation of the dynamic properties of the materials by using the newly developed RC apparatus. The RC test apparatus was designed and assembled based on the concept of fixed-free fixity conditions and driving mechanism proposed by Stokoe. Using the developed RC test apparatus, three types of representative crushed reinforced trackbed materials were tested in order to get the dynamic properties of the materials such as $G/G_{max}$ reduction curves and damping ratio D. For comparison purpose, a small RC test apparatus has been used to test the same materials.