• Title, Summary, Keyword: 노반응력

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Resilient Moduli of Sub-ballast and Subgrade Materials (강화노반 및 궤도하부노반 재료의 회복탄성계수)

  • Park, Chul-Soo;Choi, Chan-Yong;Choi, Choong-Lak;Mok, Young-Jin
    • Journal of the Korean Society for Railway
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    • v.11 no.1
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    • pp.54-60
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    • 2008
  • In the trackbed design using elastic multilayer model, the stress-dependent resilient modulus $(E_R)$ is an important input parameter, that is, reflects substructure performance under repeated traffic loading. However, the evaluation method for resilient modulus using repeated loading triaxial test is not fully developed for practical purpose, because of costly equipment and the significantly fluctuated values depending on the testing equipment and laboratory personnel. The this study, the paper will present an indirect method to estimate the resilient modulus using dynamic properties. The resilient modulus of crushed stone, which is the typical material of sub-ballast, was calculated with the measured dynamic properties and the range of stress level of the sub-ballast, and approximated with the power model combined with bulk and deviatoric stresses. The resilient modulus of coarse grained material decreases with increasing deviatoric stress at a confining pressure, and increases with increasing bulk stress. Sandy soil (SM classified from Unified Soil Classification System) of subgrade was also evaluated and best fitted with the power model of deviatoric stress only.

Development of Finite Element Analysis Program for the Concrete Pavement (유한 요소법에 의한 콘크리트 포장도로의 구조해석 프로그램개발)

  • 조병완
    • Computational Structural Engineering
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    • v.3 no.2
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    • pp.89-95
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    • 1990
  • As modern industry go further, a rigid concrete pavement has been widely constructed. The load carrying capacity of the flexible asphalt pavements is brought about by a layered system, distributing the load over the subgrade, rather than by the bending action of the slab. On the other hand, the rigid pavement, because of its rigidity and high modulus of elasticity, tends to distribute the traffic load over wide subbases, and its capacity of the strength is supplied by the slab itself. Thus, it is necessary to study the structural behavior of concrete slab under the variations of temperature changes and applied traffic loads. It reguires the development of finite element analysis program for the concrete highway pavement, which provides better understanding of concrete pavement behavior and effective design data to highway engineers.

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Development of Permanent Deformation Prediction Model for Trackbed Foundation Materials based on Shear Strength Parameters (강화노반 쇄석재료의 전단강도특성을 고려한 영구변형예측모델 개발)

  • Lim, Yujin;Hwang, Jungkyu;Cho, Hojin
    • Journal of the Korean Society for Railway
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    • v.15 no.6
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    • pp.623-630
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    • 2012
  • Formation used as trackbed foundation for providing vertical bearing capacity onto rail foundation are composed of crushed stones usually with certain type of grain size distribution. Permanent deformation in trackbed foundation can be generated by increasing number of load repetition due to train traffic increases, causing track irregularity. In this study, a specially prepared trackbed foundation materials (M-40) used in Korea has been tested using a large repetitive triaxial compression apparatus in order to understand resilient and permanent deformation characteristics of the material. From these test results, resilient and permanent deformation characteristic are analyzed so that a permanent deformation model is developed which can consider number of load repetition N, confining stress (${\sigma}_3$), shear stress ratio(${\tau}/{\tau}_f$) and stiffness of the material.

Dynamic Change of Stresses in Subsoil under Concrete Slab Track Subjected to Increasing Train Speeds (열차 증속에 따른 콘크리트 궤도 노반의 동적 응력 변화)

  • Lee, Tae-Hee;Choi, Chan-Yong;Nsabimana, Ernest;Jung, Young-Hoon
    • Journal of the Korean Geotechnical Society
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    • v.29 no.10
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    • pp.57-66
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    • 2013
  • Societal interest on a faster transportation demands an increase of the train speed exceeding current operation speed of 350 km/h. To trace the pattern of variations in displacements and subsoil stresses in the concrete slab track system, finite element simulations were conducted. For a simple track-vehicle modeling, a mass-point system representing the moving train load was developed. Dynamic responses with various train speeds from 100 to 700 km/h were investigated. As train speeds increase the displacement at rail and subsoil increases nonlinearly, whereas significant dynamic amplification at the critical velocity has not been found. At low train speed, the velocity of elastic wave carrying elastic energy is faster than the train speed. At high train speed exceeding 400 km/h, however, the train speed is approximately identical to the elastic wave velocity. Nonlinearity in the stress history in subsoil is amplified with increasing train speeds, which may cause significant plastic strains in path-dependent subsoil materials.

Characteristic Analysis of Permanent Deformation in Railway Track Soil Subgrade Using Cyclic Triaxial Compression Tests (국내 철도 노반 흙재료의 반복재하에 따른 영구변형 발생 특성 및 상관성 분석)

  • Park, Jae Beom;Choi, Chan Yong;Kim, Dae Sung;Cho, Ho Jin;Lim, Yu Jin
    • Journal of the Korean Society for Railway
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    • v.20 no.1
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    • pp.64-75
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    • 2017
  • The role of a track subgrade is to provide bearing capacity and distribute load transferred to lower foundation soils. Track subgrade soils are usually compacted by heavy mechanical machines in the field, such that sometimes they are attributed to progressive residual settlement during the service after construction completion of the railway track. The progressive residual settlement generated in the upper part of a track subgrade is mostly non-recoverable plastic deformation, which causes unstable conditions such as track irregularity. Nonetheless, up to now no design code for allowable residual settlement of subgrade in a railway trackbed has been proposed based on mechanical testing, such as repetitive triaxial testing. At this time, to check the DOC or stiffness of the soil, field test criteria for compacted track subgrade are composed of data from RPBT and field compaction testing. However, the field test criteria do not provide critical design values obtained from mechanical test results that can offer correct information about allowable permanent deformation. In this study, a test procedure is proposed for permanent deformation of compacted subgrade soil that is used usually in railway trackbed in the laboratory using repetitive triaxial testing. To develop the test procedure, an FEA was performed to obtain the shear stress ratio (${\tau}/{\tau}_f$) and the confining stress (${\sigma}_3$) on the top of the subgrade. Comprehensive repetitive triaxial tests were performed using the proposed test procedure on several field subgrade soils obtained in construction sites of railway trackbeds. A permanent deformation model was proposed using the test results for the railway track.

Roadbed Behavior in Managanese Crossing of Turnout System (분기기 망간 크로싱부 노반거동)

  • Jeon, Sang-Soo;Eum, Ki-Young;Kim, Jae-Min
    • Journal of the Korean Geotechnical Society
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    • v.24 no.2
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    • pp.45-57
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    • 2008
  • The improved turnout system is developed to speed-up the pre-existing railroad. The research has been actively carried out far the improved turnout system and the impact factor is estimated using the data sets achieved from the dynamic wheel-load field tests in both the conventional and the improved turnout system. In this study, the track performance and roadbed behavior are examined for the conventional and improved turnout system using the estimated impact factor. Dynamic wheel load and rail pressure are evaluated to assess the track performance. Roadbed stress and settlements are estimated using numerical analysis. Additionally, the stability of roadbed is estimated in soft roadbed condition influenced by the weather effects and cyclic train loading. The results show that dynamic wheel load, rail pressure, roadbed stress, and roadbed settlements in the improved turnout system substantially decrease compared with those in the conventional turnout system.

Roadbed Bearing Capacity Associated with Estimated Impact Factor in Conventional and Improved Turnout System (기존 및 개량 분기기 충격계수 산정에 따른 노반 지지력)

  • Jeon, Sang-Soo;Eum, Ki-Young;Kim, Jae-Min
    • Journal of the Korean Society for Railway
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    • v.10 no.5
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    • pp.582-588
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    • 2007
  • Since the turnout system in railroad restricts the train speed, the KNR (Korean National Railroad) provides the specification for the speed (130km/h) of the train when the train passes the turnout system. Therefore, the turnout system in pre-existing railroad is necessary to be improved to speed-up for the train. In this study, the dynamic wheel-load field tests have been performed to evaluate the track performance and the roadbed bearing capacity has been examined using numerical analysis at the turnout crossing in the conventional and improved turnout system. The impact factor is estimated using the data sets achieved from the dynamic wheel-load field tests in the conventional and improved turnout system. The stress acting on the roadbed for the improved turnout system is substantially decreased compare to that for the conventional turnout system.

Stability Evaluation of Reinforced Subgrade with Short Geogrid for Railroad During Construction (짧은 보강재를 사용한 철도보강노반의 시공 중 안정성 평가)

  • Kim, Dae Sang
    • Journal of the Korean Geosynthetics Society
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    • v.13 no.4
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    • pp.11-20
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    • 2014
  • The behaviors and stability of reinforced subgrade with short geogrid were examined and evaluated during construction. First of all, analytical approach for the minimum length of geogrid was performed to guarantee stability during construction loading state. Secondly, the economic aspects for reinforced subgrade were compared with between domestic standards applying with 0.7 H reinforcement length and new way to mix short and long reinforcement. Full scale railroad subgrade was constructed with the size of 5 m high, 6m wide, and 20m long to verify the stability of the subgrade with the length of 0.3 H, 0.35 H, 0.4 H reinforcement. Total 51 sensors were installed to measure settlement, bulging, and the change of stress of the subgrade. It is concluded that the reinforced subgrade with short(0.35H, 35% of height) geogrid had stability within allowable level of deformation and stress increment during construction.

Tilting Train-induced Roadbed Response on the Conventional Line (틸팅열차 주행시 기존선 흙 노반의 응답특성)

  • Koh, Tae-Hoon;Kwak, Yeon-Suk;Hwang, Seon-Keun;SaGong, Myung
    • Journal of the Korean Society for Railway
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    • v.14 no.5
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    • pp.433-441
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    • 2011
  • It is a fact that the straightening of track alignment is one of the undoubted ways to improve the train speed on conventional lines, while that requires huge investment resources. Therefore, the operation of a tilting train as well as the minimum improvement of track is suggested as an effective and economical alternative way for the speed-up of conventional lines. Since a driving mechanism of tilting train is different from those of existing trains, in order to make sure its operation safety and stability on conventional line, the performance of track and roadbed must be preferentially evaluated on the conventional line. Furthermore, it is necessary to estimate the tilting-train-induced roadbed response in detail since the roadbed settlement can lead to the track deformation and even derailment. In this research, the patterns of wheel load and lateral force were monitored and analyzed through the field tests, and the derailment coefficient and degree of wheel off-loading were calculated in order to evaluate the tilting train running safety depending on the running speeds (120km~180km) on the conventional line. Moreover, roadbed pressure, settlement and acceleration were also observed as tilting-train-induced roadbed responses in order to estimate the roadbed stability depending on the running speeds. Consequently, the measured derailment coefficient and degree of wheel off-loading were satisfied with their own required limits, and all of the roadbed responses were less than those of existing high-speed train (KTX) over an entire running speed range considered in this study. As a result of this study, the tilting train which will be operated in combination with existing trains is expected to give no adverse impact on the conventional line even with its improved running speed.

Estimation of the Roadbed Settlement and Bearing Capacity According to Radius of Curve and Cant in Railroad (철도의 곡선반경 및 캔트에 따른 노반의 침하 및 지지력 산정)

  • Jeon, Sang-Soo;Eum, Gi-Young;Kim, Jae-Min
    • Journal of Korean Society of Hazard Mitigation
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    • v.7 no.1
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    • pp.29-38
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    • 2007
  • The research on the track performance and stability of the tilting-train was performed and the settlement of the roadbed was estimated as the tilting train was being operated on the rail joint under the allowable velocity subjected to the track performance and the stability of the tilting-train. Since the impact on the continuous welded rail (CWR) induced by the tilting-train loading is different from the impact on the rail joint, it needs to investigate the settlement of the roadbed beneath the CWR. In this study, when the tilting-train is being operated on the CWR under the allowable velocity subjected to the track performance and the stability of the tilting-train, the settlement and bearing capacity of the roadbed beneath the CWR have been evaluated using numerical analysis and compared with those beneath the rail joint. The numerical results show that the settlements of the roadbed beneath CWR and rail joint are amount to 71.2% and 88.8% of the allowable settlement, respectively. And the stresses are amount to 10.4% and 12.1% of the allowable bearing capacity, respectively.