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The buffering zone, which can control the stiffness of the backfill material, is applied at the integral abutment (IA) to reduce the horizontal earth pressure on the abutment and decrease the residual settlement at the transition zone. Numerical analyses are performed to evaluate the horizontal subgrade reaction modulus based on the stiffness change in the buffering zone. A 1 m section from the back of the abutment is set as the buffering zone, and materials such as sandy soil, gravel, and cement-mixed gravel are applied differently. By implementing the buffering zone, the passive and active coefficients of the horizontal subgrade reaction decrease by 28% and 31% at the height of 6.8 m. respectively. Hence, the possibility of adjusting the horizontal subgrade reaction of the IA by changing the stiffness of the buffering zone is confirmed.

The integral abutment (IA) with buffering zones is a technology that pre-constructs backfill before abutment construction. It can reduce the maintenance cost owing to the decrease in the residual settlement of the backfill after opening. Furthermore, it can reduce the construction cost owing to the decrease in the horizontal earth pressure on the abutment. In this study, to evaluate the modulus of horizontal subgrade reaction in the passive pressure for the design of IA, a half-scale testbed was designed and constructed. A horizontal load test with the maximum load of 1,500 kN was conducted. To verify the test result, the behavior of the IA under horizontal loads was analyzed using finite element analysis. The modulus of horizontal subgrade reaction of the IA using a half-scale test and numerical analysis was estimated to be 36,706 kN/m3 and 32,746 kN/m3, respectively.

Reinforced subgrade for railways (RSR) is a construction method in which reinforced subgrade is constructed first and a rigid facing wall later to minimize the residual settlement after the service of a roadbed. The RSR was designed and constructed at Osong railway test line in Korea. In this study, load sharing capacities from the reinforced subgrade to the rigid facing wall of it were evaluated through long-term measurement, extending 22 months from the start of roadbed construction to the completion of track construction. Under the condition of 0.4 m geogrid vertical spacing installation, the load sharing proportion of horizontal earth pressure of the rigid facing wall was 9%–22% in the lower part, and lesser in the upper part. The strain of geogrid during construction was 0.607%, which was relatively lower than the designed geogrid tensile strain of 5%. The change in geogrid strain after construction was closely correlated with temperature change in the soil.

An integral bridge, which is constructed without expansion joints and bearings, is an economical technology that permits slender abutment and footing design to decrease the associated maintenance and construction costs. In this study, a geosynthetic reinforced integral abutment (IA) for railways and a conventional reinforced concrete abutment (CA) are modeled, considering the two types of foundations, using the finite element method. The passive soil stiffness of the foundations was evaluated through the application of a uniform horizontal load in four separate models. The passive soil stiffness of the IA model is approximately 70% of that of the CA model. Additionally, we confirmed that the passive soil stiffness was affected by changes in the thickness of the abutment, size of the footing, number of installation piles, and elastic modulus of the ground.

We investigated the dynamic behavior of a railway ballast layer during tamping operation by 3D Discrete Element simulations. The ballast layer was prepared with ballast grains that had a realistic shape and was measured by a laser scanner and modeled by clumped spheres using the dynamic optimization technique. Three types of sleeper models that were embedded in the ballast layer were prepared, and a series of tamping operations (lifting of the sleeper, insertion of vibrating tines and packing, pulling out of tines, and settling of the sleeper) were simulated in a realistic manner. The compaction underneath the sleeper mainly occurred during the insertion of tines and the packing process, while the tine insertion zone was eventually loosened after the tines were pulled out. The final porosity differs with different sleeper models and packing process periods. On the other hand, the coordination number (the number of inter-granular contacts per grain) drastically decreased during the insertion of the vibrating tines and the packing process; then, it recovered to the original value after the tines were pulled out. This change is important to identify the extent of ballast grain agitation due to the processes. The contact force network is sensitive to the applied loading and the place where the tines are inserted, and the resulting force network localization at the final state can be understood by the Coulomb’s earth pressure theory. The degree of heterogeneity may be the key to the long-term stability of the ballast layer under repeated train wheel loading.

본 논문에서는 추가 용지 없이 철도노선의 선로 용량을 증대시킬 수 있는 RSR(철도보강노반)의 장기성능을 평가하고 자 한다. 철도보강노반은 짧은 보강재를 강성벽체와 일체화하는 특징을 갖고 있어 협소한 공간에서의 적용이 가능하다. RSR의 장기성능을 평가하기 위한 시험시공은 높이 7m, 연장 40m의 규모로 장항선 주...

The minimum crack size for growth a min , which is defined as the smallest sized crack that grows fast enough to stay ahead of removal by wear and periodic grinding, was studied by employing Archard׳s wear model and Fletcher and Kapoor׳s “2.5D” fatigue crack growth model. For this purpose, a numerical analysis process was proposed by modeling the real railway operation conditions: typical crack driving forces, including bending, contact, thermal and residual stresses, and crack truncation, including contact wear and periodic grinding. A series of parametric studies was then conducted to predict a min by varying the dominant crack growth contributors, such as the tractive coefficient ( t c =0.1, 0.2, 0.3 and 0.4), creepage coefficient ( γ =0.1%, 0.2%, 0.3%, 0.4% and 0.5%) and temperature difference (Δ T =−20, 0 and 20 °C). From the analysis results, we found that the tractive coefficient is the most influencing parameter in the determination of a min , while the creepage coefficient has a large effect on a min under a low tractive coefficient, but the effect is diminished as the tractive coefficient is increased. The sizes of a min vary from 0.106 ( t c =0.4, γ =0.1%) to 5.730 mm ( t c =0.1, γ =0.5%) without the application of a periodic grinding condition, but they are increased by approximately 24% on average with the application of periodic grinding. This means that even though a larger crack can be worn out with the implementation of grinding, once a crack grows over a certain size, the periodic grinding does not stop its growth.

This paper introduced the RAR(Reinforced Abutment for Railroads) to reduce settlement of transitional zone and horizontal displacement of abutment by constructing backfill before abutment. We expect that it has more economical and better performance which was validated by numerical analyses. First, transitional zone settlements and horizontal displacements of existing abutment were evaluated for various heights and ground conditions by using finite element analysis program. Then, numerical analyses of it under the same conditions were performed and its results were compared with existing abutment's ones. From the numerical analysis, we found that the responses(settlement and horizontal displacement) of transitional zone of the RAR is about 20% and 34% of one of existing abutment due to the effect of backfill stabilizing. We expected that the RAR having small foundations could be economic way to construct abutment with the control of responses such as, settlement, horizontal displacement, and earth pressure.

The Reinforced subgrade for railroad (RSR) was constructed for one way railway line with the dimension of 5 m high, 6 m wide and 20 m long to evaluate its performance under train design load. The RSR has characteristics of short length (0.3-0.4 H) of reinforcement and rigid wall, 30 and 40 cm vertical spacing of reinforcement installation. To enhance economics and constructability, three kinds of connections (welding, hinge & bolt, bold wire) were also designed to realize the integration between rigid wall and reinforced subgrade. Two times of static loading tests were done on the full size railroad subgrade. The maximum applied pressure was 0.98 MPa (the maximum test load 5.88 MN), which corresponds to 19.6 times of the design load for railroad subgrade, 50 kPa. The performance on the RSR was evaluated with the safety on the failure, subgrade bearing capacity and settlement, horizontal displacement of wall, and reinforcement strain. Based on the full scale test, we confirmed that the RSR with the conditions of 0.35 H (35% of height) short reinforcement length, hinge & bolt type connection for integration between rigid wall and reinforced subgrade, and 40cm vertical spacing of reinforcement installment shows good performance under train design load.

By changing from ballasted track to concrete slab track, new type railroad subgrade is strongly required to satisfy strict regulations for displacement limitations of concrete slab track. In this study, sensitivity analysis was performed to assess the design characteristics of new type reinforced railroad subgrade, which could minimize residual settlement after track construction and maintain its function as a permanent railway roadbed under large cyclic load. With developed design program, the safety analysis (circular slip failure, overturning, and sliding) and the evaluation of internal forces developed in structural members (wall and reinforcement) were performed according to vertical installation spacing and stiffness of short and long geotextile reinforcement. Based on this study, we could evaluate the applicabilities of 0.4 H short geogrid length with 0.4 m vertical installation spacing of geotextile as reinforcement and what the ground conditions are for the reinforced railroad subgrade. And also, we could grasp design characteristics of the reinforced railroad subgrade, such as the importance of connecting structure between wall and reinforcement, boundary conditions allowing displacement at wall ends to minimize maximum bending moment of wall.

The high-speed rail (HSR) line in South Korea has been in service since 2004 with a maximum design speed and operating speed of 350 km/h and 300 km/h, respectively. Recently, South Korea developed a high-speed electric multiple unit (HEMU-430X, 430-km/h eXperiment) with a maximum design speed and operating speed of 430 km/h and 400 km/h, respectively; the government was waiting for a trial run on a conventional HSR line. This study tried to predict wheel load fluctuation (WLF), one of the key factors affecting acceleration to speeds over 400 km/h. For WLFs to be understood accurately in the high-speed range greater than 400 km/h, field running tests were performed twice with the KTX-Sancheon trains on the Gyeongbu high-speed line. The trains traveled between Gwangmyeong and Daejeon at maximum running speeds of 302 and 335 km/h, respectively, and WLFs were measured with a telemetry system (radio data transmitter and receiver system) at varying speeds. On the basis of probabilistic data analysis with a Gaussian function, the WLF (σ/Pst) normalized nondimensional parameter at speeds of 400 km/h and 500 km/h was modeled into quadratic functions. The WLFs at speeds of 400 km/h and 500 km/h were predicted to be 0.356 and 0.512, respectively. In addition, impacts from structures that greatly affected WLFs, such as turnouts, transition zones, and loose sleepers, were evaluated quantitatively. Of those, turnouts had the greatest impacts on the WLFs.

Facings of mechanically stabilized earth retaining walls have function to fix the reinforcement and prevent backfill loss, but the walls are lack of structural rigidity capable of resisting applied loads. The reinforced subgrade with rigid wall was developed to have the structural functions under train loading. Though it has lots of advantages such as small deformation after construction, its negative side effects of economics and difficult construction were mainly mentioned and not practically used. To apply it for railroad subgrade, this study focus on the construction cost down and the enhancement of constructability without functional loss. To do so, the behaviors of reinforced subgrade with rigid wall were evaluated with the change of the vertical spacing and length of reinforcement. Small scale model tests (1/10 scale) and 3 m full scale tests were performed to evaluate deformation characteristics of reinforced subgrade under simulated train loading. Even though it uses short reinforcement, it showed small horizontal displacement of wall and plastic settlement of subgrade. Also, it was verified that not only 30 cm but also 40 cm of vertical spacing of reinforcement had good performance in serviceability aspects.

The current paper presents the results of parametric analyses on the stress intensity factor (SIF) of railways with inclined cracks under rolling contact fatigue (RCF). A 3D finite element (FE) model was proposed to demonstrate the shear mechanism in RCF. The feasibility of the suggested numerical model was verified through the SIF (K) obtained from advanced 3D FE analysis compared with existing 2D FE results. Based on the series of FE analyses, the sensitivity analysis on the cracked depth, surface/crack friction coefficients, and in- clined angle, which mainly affected SIF history at the cracked tip, was examined. SIF distributions for various locations of the wheel along the cracked tip were also presented.

A fiber-optic distributed sensor system is configured to measure the longitudinal strain distribution of a rail in real time. The system is based on the Brillouin correlation domain analysis (BOCDA), in which the variation of local Brillouin frequency (νB) is measured that linearly depends on the strain applied to the optical fiber. In the test measurement, the longitudinal strain distribution along a 2.8 m rail is measured under different loading conditions with a spatial resolution of 3.8 cm and an accuracy of ±15 μe.

Crack propagation due to rolling contact fatigue (RCF) could be a significant potential challenge to the integrity of railway rails because it may lead to a serious disaster. Fatigue cracks subjected to cyclic rolling contact force experience a complex non-proportional mixed loading and complicated boundary condition. In the present research, complex crack opening/closure/sliding/locked behaviors as the cyclic contact loading movement is analyzed considering liquid lubrication action on rail surfaces as well as crack faces. Based on a series of FE analyses, the calculations of the effective SIF ranges for RCF cracks under certain contact loading and boundary conditions are proposed in the form of polynomial functions which will be appropriately used to predict RCF crack growth rate.

The scope of the electrical resistivity survey has recently been extended to various fields beyond groundwater and underground resource exploration. Electrical resistivity techniques were evaluated in two case studies to substantiate their applicability to geotechnical and environmental problems. First, electrical resistivity imaging (ERI) was used to map the fractured zone ahead of the tunnel face during construction using the new Australian tunneling method (NATM). The ERI technique could adequately modify tunnel support patterns in quasi-real time, on the basis of the field test results, and could subsequently improve the stability of tunnel excavation. Second, electrical resistivity tomography (ERT) was used between two test boreholes in a research tunnel site to monitor the movement of brine after it was injected in one of the two boreholes. A pair of low-conductivity zones that were regarded as the pathway of groundwater flow between the two boreholes was clearly imaged because of enhancement of conductivity caused by diffusion of the brine. The applicability of electrical resistivity techniques to geotechnical and environmental problems was successfully substantiated.

n the event of an earthquake, additional stresses can occur in the continuous welded rails (CWR) of High-speed railway (HSR) bridges due to relative displacements at expansion joints, and this stress can cause derailment. The amplification of ground motion occurs as a result of site effects, and this is pronounced at the site of a soft surface soil layer and of a rigid surface soil layer over a soft one. As a result, the amplified ground motion leads to an amplified seismic response in HSR bridges. A change in bridge pier height affects the seismic behavior of the bridge. A HSR bridge with gravel ballast tracks will show different dynamic behavior during an earthquake than one with concrete ballast tracks. The seismic responses of HSR bridges and their CWR are analyzed considering the derailment-inducing factors.

Earthquake observations at different sites within alluvial soil deposits have demonstrated that the motion of buried underground structures closely follows that of the surrounding soil. Therefore, it is usual in a seismic design process to apply free-field ground displacements through Winkler-type soil springs to an underground structure to evaluate stress patterns induced within its structural members. Using a simplified approach, this paper provides a clear understanding of resonant horizontal ground displacement of and strain in a surface soil deposit with a radical change of depth and of where they occur.Key words: simple approach, seismic design, earthquake, resonance, underground structures.

Long-term earthquake observations at different tunnel sites within a variety of alluvial soil deposits have clearly demonstrated that a tunnel, which exhibits rather flexible nature within its surrounding soil, follows closely the motion of the soil mass during an earthquake. Therefore, coating a tunnel with a soft material will be a possible measure for minimizing damage to tunnels. This paper provides a clear perspective on the feasibility of this measure by using simple solutions to idealized problems.

A method to cover a tunnel lining with a soft and thin coating is discussed herein as a possible measure for mitigating seismic damage to tunnels. Long-term earthquake observations at different tunnel sites within a variety of alluvial soil deposits have demonstrated that a circular tunnel is liable to deform in such a way that its two diagonal diameters crossing each other expand and contract alternately. Narrowing down vibration modes, in order to discuss this particular and the most important mode, any of the essential items of the soil–tunnel system, namely the soil, the coating and the tunnel lining, has only one degree of freedom, allowing the coating effect to be simply evaluated in terms of a limited number of key parameters. Copyright © 2001 John Wiley & Sons, Ltd.