• Structural Engineering and Mechanics
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• 제80권5호
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• pp.491-501
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• 2021

A difference in subgrade settlement between two rails of a track manifests as lateral differential subgrade settlement. This settlement causes unsteadiness in the motion of trains passing through the corresponding area. To illustrate the effect of lateral differential subgrade settlement on the dynamic response of a vehicle-track coupling system, a three-dimensional vehicle-track-subgrade coupling model was formulated by combining the vehicle-track dynamics theory and the finite element method. The wheel/rail force, car body acceleration, and derailment factor are chosen as evaluation indices of the system dynamic response. The effects of the amplitude and wavelength of lateral differential subgrade settlement as well as the driving speed of the vehicle are analyzed. The study reveals the following: The dynamic responses of the vehicle-track system generally increase linearly with the driving speed when the train passes through a lateral subgrade settlement area. The wheel/rail force acting on a rail with a large settlement exceeds that on a rail with a small settlement. The dynamic responses of the vehicle-track system increase with the amplitude of the lateral differential subgrade settlement. For a 250-km/h train speed, the proposed maximum amplitude for a lateral differential settlement with a wavelength of 20 m is 10 mm. The dynamic responses of the vehicle-track system decrease with an increase in the wavelength of the lateral differential subgrade settlement. To achieve a good operation quality of a train at a 250-km/h driving speed, the wavelength of a lateral differential subgrade settlement with an amplitude of 20 mm should not be less than 15 m. Monitoring lateral differential settlements should be given more emphasis in routine high-speed railway maintenance and repairs.

• Structural Engineering and Mechanics
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• 제66권1호
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• pp.15-25
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• 2018

Post-construction subgrade settlement especially differential settlement, has become a key issue in construction and operation of non-ballasted track on high-speed railway soil subgrade, which may also affect the dynamic performance of passing trains. To estimate the effect of differential subgrade settlement on the mechanical behaviors of the vehicle-slab track system, a detailed model considering nonlinear subgrade support and initial track state due to track self-weight is developed. Accordingly, analysis aiming at a typical high-speed vehicle coupled with a deteriorated slab track owing to differential subgrade settlement is carried out, in terms of two aspects: (i) determination of an initial mapping relationship between subgrade settlement and track deflections as well as contact state between track and subgrade based on a semi-analytical method; (ii) simulation of dynamic performance of the coupled system by employing a time integration approach. The investigation indicates that subgrade settlement results in additional track irregularity, and locally, the contact between the concrete track and the soil subgrade is prone to failure. Moreover, wheel-rail interaction is significantly exacerbated by the track degradation and abnormal responses occur as a result of the unsupported areas. Distributions of interlaminar contact forces in track system vary dramatically due to the combined effect of track deterioration and dynamic load. These may not only intensify the dynamic responses of the coupled system, but also have impacts on the long-term behavior of the track components.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2009년도 춘계학술대회 논문집
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• pp.1542-1549
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• 2009

The function of subgrade in the railway is to support track load on the subgrade as well as train load. Unlike the traditional railway, the uppermost subgrade layer in the Gyeongbu high speed railway was constructed as the reinforced road bed. The reinforced road bed comprises sub-ballast in the upper part and grade ballast in the lower part. The filling material such as soil and rocks in the subgrade can be settled by consolidation of original ground, compression due to self weight, plastic displacement due to train operation, and unequal settlement due to embankment material or improper compaction, therefore many efforts have been given for sufficient compaction and use of proper filling materials in the construction stage. The purpose of this study is to investigate the deformation state of subgrade in the Gyeongbu high speed railway. The investigation on the subgrade settlement was performed by choosing representative sections suspected to be settled based on the previous GPR test results and track maintenance history, measuring the settlement for some time period after installing settlement measuring instruments on and under the reinforced road bed. and analyzing the long-term subgrade settlement data from monitoring system which was installed at the construction stage of the high speed railway.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2010년도 춘계학술대회 논문집
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• pp.1506-1512
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• 2010

산악지형이 많은 지역에서의 고속철도 건설에는 노선의 선형상의 이유로 터널구간이 많이 존재하며, 터널 건설로 발생하는 암버럭을 유용하기 위하여 노반 건설은 주로 암과 흙의 혼합성토로 이루어지고 있다. 본 연구에서는 이암을 주암으로 하는 혼합토로 이루어진 고속철도 노반의 열차반복하중에 의한 침하특성을 분석하기 위하여 모형토조 실험을 수행하였다. 특히 강우 또는 지하수위 상승에 의한 노반의 포화도 증가가 열차 반복하중 작용 시 노반의 침하특성에 미치는 영향을 분석하기 위하여 초기 포화도 조건을 변화시키면서 실험을 수행하였다. 실험결과, 낮은 포화도 조건에서는 열차반복횟수가 증가할수록 침하가 어느 일정 값에 수렴하는 결과를 나타냈으나, 일정 수준 이상의 포화도 조건에서는 침하가 급격히 증가하는 것을 알 수 있었다. 따라서 노반의 포화도를 일정수준 이하로 관리하는 것이 침하 예방에 중요한 요소임을 확인 할 수 있었다.

• Wind and Structures
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• 제37권4호
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• pp.275-287
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• 2023

Subgrade differential settlement of high-speed railways was a pivotal issue that could increase the risk of trains operation. The risk will be further increased when trains in the subsidence zone are affected by crosswinds. In this paper, the computational fluid dynamics (CFD) model and finite element (FE) model were established, and the data transmission interface of the two models was established by fluid-solid interaction (FSI) method to form a systematic crosswind-train-track-subgrade dynamic model. The risk of high-speed train encountering crosswind in settlement area was analyzed. The results showed that the aerodynamic force of the trains increased significantly with the increase in crosswind speed. The aerodynamic force of the trains could reach 125.14 kN, significantly increasing the risk of derailment and overturning. Considering the influence of crosswind, the risk of train operation could be greatly increased. The safety indices and the wheel-rail force both increased with the increase of the wind speed. For the high-speed train running at 350 km/h, the warning value of wind speed was 10.2 m /s under the condition of subgrade settlement with wavelength of 20 m and amplitude of 15 mm.

• 한국철도학회논문집
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• 제18권4호
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• pp.354-362
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• 2015

콘크리트궤도의 경우, 허용침하기준이 30mm 이하로 매우 엄격하게 관리되기 때문에, 궤도 하부의 토공노반(강화노반, 상부노반, 하부노반)의 침하에 대한 관리가 필수적으로 요구되고 있다. 이를 위해서는 먼저 이들 노반 재료의 침하특성에 대해 보다 정확한 이해와 자료의 축적이 우선되어야 할 것이다. 이에 본 연구에서는 노반 재료를 대상으로 대형 오이도미터시험과 삼축압축시험을 통해 여러 입도조건, 함수비 변화조건, 반복하중 조건 등에 의한 장기침하특성을 평가하였다. 강화노반 재료가 설계기준에 적합하게 조성될 경우, 열차하중 하에서 발생되는 침하는 매우 적었다. 한편, 노반재료의 경우 일정 하중 하에서 함수비가 증가할 때, 입도조건에 따라 침하 발생량이 매우 크게 발생할 수 있는 것을 확인할 수 있었다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2001년도 봄 학술발표회 논문집
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• pp.525-532
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• 2001

In this study, performance of reinforced railroad roadbeds with the crushed stones was investigated through the real scale railroad roadbed tests. Several real scale reinforced railroad roadbeds were constructed in the laboratory with different subgrade conditions and were tested with the estimated actual train loads including the impact loading of train. The affecting factors such as settlement, earth pressure and stress change at the surface of reinforced roadbed, subgrade layers as well as surface of rails were measured. It was found through the actual testing that for the roadbed with the same thickness, the settlement and vibration level (velocity) of reinforced roadbed decreases with the increase of reaction modulus of subgrade. The settlement of reinforced roadbed with the same reaction modulus of subgrade also decreases with the increase of thickness of the reinforced roadbed.

• 한국철도학회논문집
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• 제12권2호
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• pp.183-189
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• 2009

경부고속철도 2단계 구간은 콘크리트궤도 형식으로 건설되고 있다. 콘크리트궤도는 궤도의 강성 구조적 특징으로 인하여 잔류침하 규정이 엄격하게 적용되고 있다. 궤도의 잔류침하는 궤도를 지지하는 하부구조인 노반과 원지반으로부터 기인된다. 암버럭과 흙 재료로 건설되고 있는 노반의 잔류침하는 현장다짐품질에 따라 원지반을 포함한 총 잔류침하의 중요한 부분이 될 수 있다. 따라서 암버럭 토사 혼합성토재로 이루어진 노반에서의 잔류침하를 최소화하는 것은 콘크리트궤도의 성공적인 건설을 위하여 중요한 요소 중 하나이다. 본 논문에서는 암버럭-토사 혼합성토재의 거동을 이해하기 위하여 총 31회의 대형다짐시험을 수행하였다. 다짐시료는 건설 중인 2개 현장으로부터 혈암과 이암을 주성분으로 하는 노반 재료를 채취하여 조성하였고, 다짐시험은 암 종류, 4번체 통과율, 최대입경, 함수비를 변화시키면서 수행하였다. 시험결과로부터 혼합성토재의 최대건조단위중량에 영향을 미칠 수 있는 인자들에 대한 평가를 수행하였다.

• 한국지반공학회논문집
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• 제39권11호
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• pp.23-31
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• 2023

콘크리트 궤도의 침하는 고속열차의 안전한 운행을 크게 저해할 수 있으며 복구에 상당한 비용이 소요되므로 최근 큰 문제로 대두되고 있다. 침하의 가장 큰 원인 중 하나는 터널공사의 부산물로 발생하는 암석재료를 적정한 입도분를 가진 토사 혼합 없이 하부노반 성토에 사용하기 때문으로 보고되고 있다. 본 논문에서는 암석재료로 성토된 하부노반의 부분 보강으로 인한 침하억제 효과를 수치해석으로 평가하였다. 하부노반에 일정하게 배치된 기둥 형태의 보강 영역은 상부노반에 지반아칭을 유발하게 되며 성토하중이 보강된 영역에 집중하게 되어 침하가 억제되는 효과가 있다. 유한요소해석을 통하여 보강된 영역의 크기, 강성, 간격이 하부노반의 침하억제에 미치는 효과를 평가하였으며, 해석 결과를 토대로 침하를 허용치 이내로 억제하기 위한 최소 보강 간격을 결정하는 설계 방법을 제안하였다.

• Geomechanics and Engineering
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• 제29권5호
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• pp.583-598
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• 2022

The Compaction effect is important for evaluating the subgrade construction. However, there is little research exploring the compaction quality of deep soil using hydraulic compaction. According to reinforcement effect analysis, dimensional analysis is adopted in this work to analyze subgrade compactness within the effective reinforcement depth, and a prediction model is obtained. A hydraulic compactor is then employed to carry out an in-situ reinforcement test on gravel soil subgrade, and the subgrade parameters before and after reinforcement are analyzed. Results show that a reinforcement difference exists inside the subgrade, and the effective reinforcement depth is defined as increasing compactness to 90% in the depth direction. Layered compactness within the effective reinforcement depth is expressed by parameters including the drop distance of the rammer, peak acceleration, tamping times, subgrade settlement, and properties of rammer and filler. Finally, a field test is conducted to verify the results.