• Smart Structures and Systems
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• v.2 no.3
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• pp.237-251
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• 2006

Piezoelectric sensors have many applications in geotechnical engineering, especially in characterizing soils through measurement of wave velocities. Since mechanical properties of a material are closely associated with wave velocities, piezoelectric sensors provide a reliable and non-destructive method for the determination of soil properties. This paper presents results of recent research on measuring stiffness of a wide range of soils such as clay, sand, and gravel, characterizing anisotropic properties of soil induced by external loading, measuring stiffness of base and subgrade materials in the pavement, determining soil properties in a centrifuge model during the flight of a centrifuge, and understanding wave propagation in granular materials under micro-gravity environment using this technique.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.10
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• pp.23-29
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• 2020

The soil structures settle down continuously under cyclic dynamic loading after opening railway lines. This study examined the characteristics of the settlement and stiffness of cement-treated soils with the change in the content of fines under cyclic dynamic loading. Eighteen cases of the test were carried out with the changes in the fines content of soils, cement content, and curing days. Based on the test results, cement-treated soils containing more than 3% of cement could decrease settlement sufficiently even with a high portion of fines under cyclic dynamic loading. In addition, the elastic and plastic settlements could be reduced using 3 to 4% cement to the level of 1/4 and 1/6, respectively. In the viewpoint of stiffness, the resilient modulus of cement-treated soils increases with increasing cement content. Using more than 3% of cement, the 80MPa compaction stiffness standard for the upper subgrade of railways was satisfied, even with 40% of fines content of soils.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.03b
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• pp.435-440
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• 2000

It is important to pay careful attention to construction backfill for the structural integrity of concrete box culvert. The stability of the surrounding soil is important to the structural performance of most culverts. Good compaction by the dynamic compaction roller with big capacity is as effective as good backfill materials to increase the structural integrity of culvert. However structural distress of the culvert could be occur due to the excessive earth pressure by dynamic compaction load. In this study, 16 box culverts were constructed with various compaction materials and construction methods. Three types of on-site soils such as subbase, subgrade and roadbed materials were used as backfill materials in the test program. Compaction methods were adapted based on the site conditions. In most cases, dynamic compaction rollers with 10 to 16 ton weights were used and vibration speed were applied from 2400 to 2500 rpm for the great compaction energy. Some backfill compactions with good quality soils were carried out to examine the effect of EPS(Expanded Polystyrene) panels with changes of compaction thickness. This paper presents the main results of the research conducted to access the engineering performance of the backfill materials. The characteristics of earth pressures are discussed. It is observed that subgrade and roadbed materials are needed more careful compaction than subbase materials. It is shown that EPS panels are effective to mitigate dynamic lateral earth pressure on the culverts. It is also obtained that the dynamic pressure depends on the soil properties. In addition, the coefficient of dynamic earth pressure (K$\sub$dyn/=ΔP$\sub$H/ ΔP$\sub$V/) during compaction is discussed.

• International Journal of Highway Engineering
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• v.6 no.3 s.21
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• pp.55-64
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• 2004

Maximum dry unit weight, ${\gamma}_{dmax}$, is the most important engineering properties for subgrade soil. Existing models to predict ${\gamma}_{dmax}$ containing many parameters, seem to be rather complex. This paper presents new simple models to predict ${\gamma}_{dmax}$. for sandy soils, A number of sieve analysis and compaction tests for 36 types of sands were conducted to develop the regression-based models. Parameters used to estimate ${\gamma}_{dmax}$ are both the geometric mean and geometric standard deviation of the soils, or the particle-size distribution curve parameters. Maximum dry unit weights predicted by the models are in good agreement with the laboratory measurements for the soil samples obtained at 16 locations within the Korea.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.406-411
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• 2011

An active application of tram is being expected in Korea in the near future. For the tram operation in urban area, the embedded rail tracks where rails are completely embedded with pavements is required. When the embedded rail track is constructed on fine-grained subgrade soil, excessive cumulative plastic settlements due to repetitive tram road may occur. In this study, repetitive load tests were carried out to evaluate the accumulative plastic settlements of subgrade soils underneath embedded rail tracks. Two real-scale track specimens of 5 m lengths were constructed considering the maximum cant of a curved line. Repetitive tram loads of three million times were applied to the tracks in 5 Hz frequency. The accumulating patterns of plastic settlements were analyzed. Tram load distributing effects of the concrete slabs were also evaluated using the measured data of earth pressures cells that were installed underneath track. Also the measured settlements were compared with the estimated settlements calculated from an existing experimental equations, and its validity is discussed.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.1164-1171
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• 2010

Korea is considered to be a seasonal frozen soil area that is thawed in the spring, and most of the area is frozen in winter as to the characteristic of geography. In the current design codes for anti-freezing layer, the thickness of anti freezing layer is calculated by freezing depth against the temperature condition. Therefore, they have a tendency of over-design and uniform thickness without the considerations of thermal stability, bearing capacity and frost susceptibility of materials. So, it is essential for studying the appropriateness and bearing capacity besides the seasonal and mechanical properties of pavement materials to take a appropriate and reasonable design of the road structure. In this research, the evaluation of frost susceptibility on subgrade, ant-freezing layer, sub base was conducted by means of the mechanical property test and laboratory field road model downed scale experiment. The temperature, heaving amount, heaving pressure and unfrozen water contents of soil samples, the subgrade, anti-freezing layer, sub base soils of highway construction site, were measured to determine the frost susceptibility.

• The Journal of Engineering Geology
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• v.21 no.3
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• pp.239-246
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• 2011

Upon encountering weathering soil at a construction site, it may be necessary to change the design and construction plans for geotechnical structures. When weathering soil is exposed to air, the weathering process proceeds rapidly, resulting in significant damage to geotechnical structures, particle defects, and an increase in moisture sensitivity. The management of weathering-soil compaction is challenging. Because the engineering properties of weathering-soils vary regionally, it is important to report the result of research into the regional characteristics of such soils. At two locations of granite gneiss in the Gansung area of Gangwon-do, geological studies were performed at 22 and 8 sites, respectively. At each site, test samples were collected for analysis by XRD and to measure particle size, consistency, and compaction. To evaluate the suitability of the material for road subgrade, we examined the interrelationship between CBR value and the uniformity coefficient, the 200 sieve passing ratio and the aggregate ${\geq}$ 2 mm) content. We found that for the weathered granite soil, aggregate sized > 2 mm has a significant effect on the CBR value. In addition, the mixing of aggregate sized > 2 mm with sub-quality soil improves the soil condition.

• Journal of the Korean Geosynthetics Society
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• v.12 no.2
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• pp.13-23
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• 2013

The Korean Peninsula is considered as a seasonal frozen area that is thawed in the spring and frozen in the winter. The influence of fines of the frost susceptibility of subgrade soils were established by laboratory freezing tests simulating closely the thermal conditions in the field. During the winter season, the climate is heavily influenced by the cold and dry continental high pressure. Because of siberian air mass, the temperature of January is $-6{\sim}-7^{\circ}C$ on average. This chilly weather generate the frost heaving by freezing the moisture of soil and damage potential of the geotechnical structure. In the freezing soil, the ice lenses increase the freeze portion of soil by absorbing the ground water with capillary action. However, the capillary characteristics differ from the sort of soil on the state of freezing condition. In this study, ten soil samples are prepared. The basic physical property tests were performed by following the Korean Industrial Standard and the soil specimens were classified by the Unified Soil Classification System (USCS). These classified soils are used to perform the laboratory opened systems freezing test in order to determine the frost heaving characteristics of soils such as unfrozen water content, heaving amount, and freezing depth.

• Journal of the Korean Society for Railway
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• v.18 no.2
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• pp.127-138
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• 2015

It is important to evaluate the stiffness characteristics of compacted subgrade soil under track that is loaded dynamically. Using a mid-size Resonant Column test apparatus, normalized shear modulus and shear modulus variation with changing of confining pressure were investigated with change of degree of saturation (DOS). From an analysis of the test results, it was verified that the maximum shear modulus decreased with increases of DOS. However, normalized shear modulus increased with increases of DOS. Using the test results, a relation of G~${\gamma}$~DOS can be constructed and characterized. In the future, by performing tests with soils used as trackbed broadly in the field, a prediction model for DOS~G~${\gamma}$ can be proposed.

• Journal of the Korean Geotechnical Society
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• v.18 no.5
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• pp.109-122
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• 2002

The water content of soil near the ground subgrade varies seasonally, and dynamic deformational characteristics of soil are affected by the variation of water content. Contrary to previous studies which used various specimens of different compaction moisture contents, the influences of water content and capillary Pressure on dynamic deformational characteristics of soil were investigated using the given specimen controlling the matric suction. RC/TS(resonant column and torsional shear) testing equipment was modified so that it can control water content with changing capillary pressure(matric suction). RC/TS tests were performed on subgrade soil collected in the KHC(Korea Highway Corporation) test road. In the field, the cross-hole tests were performed and the water contents were measured at the same site to verify the feasibility and applicability of RC/TS test results. As water content decreased, the tendency of increasing shear moduli in field was well matched with laboratory test results.