• Title/Summary/Keyword: Subgrade layer

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Evaluation of Freeze-Thaw Effect on the Modulus of Subgrade Soils from Impact Resonance Test (충격공진시험을 이용한 동결.융해에 따른 노상토의 탄성계수 평가)

  • Lee, Jae-Hoan;Kweon, Gi-Chul
    • International Journal of Highway Engineering
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    • v.12 no.3
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    • pp.71-77
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    • 2010
  • Anti-freezing layer does not used in case of non frost heaving in subgrade soils. In this case, the modulus of subgrade soils were varied with freezing and thaw cycles under non frost heaving. That effect should be properly considered in pavement design. Impact resonance test that is nondestructive testing method was used for continuously determining the modulus of subgrade soils during freezing and thaw cycle. The modulus of subgrade soils was identical with freezing and thaw cycles under closed freezing and thaw system which is no water supplement into specimen during testing. There was also no difference in the modulus of subgrade soil between before and after freezing-thaw cycles for all specimens with different water content and density. That is thaw-weakening of subgrade soils do not occur under closed freezing and thaw system. The moduli at freezing conditions are varied with water content and density, but it can be ignored in practical design sense.

Analisys on Freezing Characteristics of Pavement Layer Using the Feild Pavement Model test (현장 모형 도로 축소 실험을 이용한 포장구성층의 동결 특성 분석)

  • Shin, Eun-Chul;Ryu, Byung-Hyun;Moon, Yong-Soo;Park, Jeong-Jun
    • 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.

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Vehicle/track dynamic interaction considering developed railway substructure models

  • Mosayebi, Seyed-Ali;Zakeri, Jabbar-Ali;Esmaeili, Morteza
    • Structural Engineering and Mechanics
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    • v.61 no.6
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    • pp.775-784
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    • 2017
  • This study is devoted to developing many new substructure models for ballasted railway track by using the pyramid model philosophy. As the effect of railway embankment has been less considered in the previous studies in the field of vehicle/track interaction, so the present study develops the pyramid models in the presence of railway embankment and implements them in vehicle/track interaction dynamic analyses. Considering a moving car body as multi bodies with 10 degrees of freedom and the ballasted track including rail, sleeper, ballast, subgrade and embankment, two categories of numerical analyses are performed by considering the new substructure systems including type A (initiation of stress overlap areas in adjacent sleepers from the ballast layer) or type B (initiation of stress overlap areas in adjacent sleepers from the subgrade layer). A comprehensive sensitivity analyses are performed on effective parameters such as ballast height, sleepers spacing and sleeper width. The results indicate that the stiffness of subgrade, embankment and foundation increased by increasing the ballast height. Also, by increasing the ballast height, rail and ballast vertical displacement decreased.

Migration of fine granular materials into overlying layers using a modified large-scale triaxial system

  • Tan Manh Do;Jan Laue;Hans Mattsson;Qi Jia
    • Geomechanics and Engineering
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    • v.37 no.4
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    • pp.359-370
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    • 2024
  • The primary goal of this study is to evaluate the migration of fine granular materials into overlying layers under cyclic loading using a modified large-scale triaxial system as a physical model test. Samples prepared for the modified large-scale triaxial system comprised a 60 mm thick gravel layer overlying a 120 mm thick subgrade layer, which could be either tailings or railway sand. A quantitative analysis of the migration of fine granular materials was based on the mass percentage and grain size of migrated materials collected in the gravel. In addition, the cyclic characteristics, i.e., accumulated axial strain and excess pore water pressure, were evaluated. As a result, the total migration rate of the railway sand sample was found to be small. However, the total migration rate of the sample containing tailings in the subgrade layer was much higher than that of the railway sand sample. In addition, the migration analysis revealed that finer tailings particles tended to be migrated into the upper gravel layer easier than coarser tailings particles under cyclic loading. This could be involved in significant increases in excess pore water pressure at the last cycles of the physical model test.

Laboratory Test for Permanent Settlement Behavior of Geo-materials used in Railway Considering Grain size distribution and Water content (입도 및 함수비 조건에 따른 철도 노반 재료의 영구침하거동 요소시험평가)

  • Lee, Sung Jin;Lee, Il Wha;Lee, Su Hyung;Eum, Ki Young
    • Journal of the Korean Society for Railway
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    • v.18 no.4
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    • pp.354-362
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    • 2015
  • Since allowable settlement of concrete slab track is about 30mm, a lot of attention must be paid to the settlement of the earthwork (reinforced trackbed, upper subgrade, under subgrade) under the concrete track. To this end, more experimental data should be accumulated through tests for these materials. In this study, we evaluate the long-term settlement of reinforced trackbed and subgrade materials using factors such as repeated loading conditions, water content, and grain size distributions in a large triaxial test and a large oedometer test. In cases in which the performance of the reinforced trackbed layer meets the design criteria, the settlement caused by train load was considerably small. But, when the water content increases in the subgrade, unexpectedly large settlement might occur for certain grain size distributions of the subgrade materials.

Temperature Sensitivity Analysis of TDR Moisture Content Sensor for Road Pavement (도로하부 함수비 계측을 위한 TDR 방식 함수비 센서 온도 민감도 분석)

  • Cho, Myunghwan;Lee, Yoonhan;Kim, Nakseok;Jee, Keehwan
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.33 no.1
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    • pp.329-336
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    • 2013
  • The infrastructure of flexible pavement is composed of aggregate subbase, anti-frost layer, and subgrade. In particular, the subgrade performance is affected by climates such as frost action and precipitation. The method of TDR(Time Domain Reflectometry) sensors to measure moisture contents in subgrade layer has been used in the research. Due to the TDR method using dielectric permitivity of soil and water, the sensors can be affected by the low subgrade temperatures. The air temperatures frequently drops below $-20^{\circ}C$ in the winter in Korea. As a result, it is necessary to estimate the accuracy of the TDR moisture sensors in the range of below zero temperatures. In this study, the subgrade temperatures of lower than $-2^{\circ}C$ were extended to evaluate temperature sensitivity of the TDR moisture sensors. The test results revealed that the moisture contents around the sensors were reduced while those of the upper part of specimen showed a tendency to increase as the specimen surface temperature drops below zero under the volumetric moisture contents(VMC) of 20% and 30%. However, the impact of temperature on the function of the sensor at lower water contents was found to be negligible if any.

Railbed Evaluation by using In-situ Penetration Test (원위치 관입실험기를 활용한 철도 노반 평가)

  • Kim, Ju-Han;Park, Jung-Hee;Yoon, Hyung-Koo;Koh, Tae-Hoon;Lee, Jong-Sub
    • Proceedings of the KSR Conference
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    • 2011.10a
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    • pp.261-267
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    • 2011
  • The test fit has commonly used for the evaluation of the railbed condition, and indirect methods by using the compressional wave are also studied. the direct evaluation method by penetration test has not been studied. For the measurement of in-situ cone tip resistance of the railbed with minimizing the disturbance of the upper railbed. the cone penetrometer with the helical type outer rod(CPH) was developed. The outer rod, which has helical screw, is penetrated through the gravel layer and provides the reaction force for cone penetration testing. the cone tip resistances are measured by the mini cone penetrometer, where diameter is 15mm. For the developing the mini cone, strain gauge installation, circuit configuration, penetration rates and calibration process are considered. For the easy penetration of the screw rod in the field, the reaction force stepping plate and guide column are arranged. The screw rod are penetrated through the gravel layer. And the mini cone was pushed into the subgrade railbed at the penetration rate of 1mm/sec. The penetration test shows that the cone tip resistance increases along the depth. In addition, the subgrade condition is evaluated. This study demonstrates that the CPH may be effectively used for the evaluation of subgrade method any damage of the gravel layer.

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Analysis of the lateral displacement to the Large Diameter Bored Pile based on the application of the Lateral coefficient of subgrade reaction (수평지반반력계수에 따른 대구경 현장타설말뚝의 수평변위 분석)

  • Chae, Young-Su;Kim, Nam-Ho;Bang, Ei-Souk;Lee, Kyoung-Jea
    • Proceedings of the Korean Geotechical Society Conference
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    • 2005.10a
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    • pp.528-535
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    • 2005
  • Using the case of design to the Large diameter Bored Pile, We showed the various method to estimate the Lateral coefficient of subgrade reaction and analyzed the lateral displacement behavior according to the characteristics of sub layer distribution. According to the study, Mutual relation to the N value and the soil modulus of deformation showed 400N to 800N to the fine grained soil and weathered soil. It showed simular tendancy with the proposed expression of Schmertmann. But Weathered rock was over estimated as 4,200N. $k_h$ to the sedimentory soil and weathered rock each showed these orded of Schmertmann-PMT-2,800N and Schmertmann-2,800N-PMT. As the factor($\alpha$) 4 was applied to the estimation in weathered rock, $k_h$ to the PMT was calculate as a big value. If the pile is long and the pile is surpported to the soil, Lateral displacement was in inverse proportion ratio to the value of $k_h$. But the case of shallow soil layer(early bedrock) and the short pile, Lateral displacement was affected by the behavior of socheted pile to the bedrock not by the upper soil layer.

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The Freezing Characteristics of Pavement Layer Using the Field Road Model Test (현장도로 모형실험을 이용한 포장구성층의 동결 특성 분석)

  • Shin, Eun-Chul;Ryu, Byung-Hyun;Park, Jeong-Jun
    • Journal of the Korean Geotechnical Society
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    • v.26 no.7
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    • pp.71-80
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    • 2010
  • Korea is considered to be a seasonal frozen soil area that thaws in the spring, and freezes in winter. In the current design codes for anti-freezing layer, the thickness of anti-freezing layer is calculated by the depth frozen due to the temperature condition. Therefore, there is a tendency of over-design and applying uniform thickness without the consideration of thermal stability, bearing capacity and frost susceptibility of materials. So, it is essential to study the structural appropriateness of pavement layer and bearing capacity besides the seasonal and mechanical properties of pavement materials to take an appropriate and reasonable design of the road structure. In this paper, the evaluation of frost susceptibility on subgrade, ant-freezing layer, subbase was conducted by means of the mechanical characteristics and model experiment. The temperature, heaving amount, unfrozen water contents and freezing depth of soil samples, the subgrade, anti-freezing layer, subbase soils of road construction site were measured to determine the frost susceptibility.