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This study evaluates the air permeability of epoxy-coated normal concrete and ultra-high performance concrete (UHPC) for use in Hyperloop tube structures, where maintaining ultra-low air permeability is crucial to preserving the vacuum environment. While UHPC is recognized for its exceptionally low permeability due to its dense microstructure, this research explores epoxy-coated conventional concrete as a cost-effective alternative. Using a vacuum-based permeability test simulating Hyperloop's near-vacuum conditions, the study found that epoxy-coated concrete significantly reduced air permeability compared to uncoated concrete, with specimens coated on both sides approaching near-zero permeability. Although UHPC exhibited superior performance, the epoxy-coated concrete demonstrated air-tightness and was suitable for Hyperloop applications, offering a viable and economical alternative. These findings provide important insights for material selection, suggesting that epoxy-coated conventional concrete can effectively meet the stringent requirements for Hyperloop tube construction while balancing performance with cost-efficiency.

In the transition zone of railway tracks, track irregularities occur frequently due to differential settlement, which arises from the difference between the vertical supporting stiffness of the abutment and the backfill. This is disadvantageous because it increases the maintenance requirements and deteriorates the ride quality. To address this challenge, this study proposes a strategy involving the application of cement-treated gravel reinforced with geogrids and rigid facing walls. The reinforced subgrade for railways (RSR), which can reduce residual settlement through the initial construction of the backfill reinforced with geogrids and the subsequent development of the rigid facing wall, was constructed at the transition zone with cement-treated gravel as the backfill material. The long-term behaviors during and after construction on the RSR for a period of 16 months were evaluated by analyzing the surface and ground settlements, horizontal earth pressure, and geogrid strain. The minor net settlement of the reinforced backfill converges at the early stage of subgrade construction, and the horizontal earth pressure was approximately reduced to the level of 54–63% of the Rankine active earth pressure.

In areas where it is difficult to secure additional land for railways, a plan to increase rail transport capacity by widening existing embankments is required. When widening the embankment, additional stress is generated at the bottom of the existing embankment, resulting in an additional settlement (interlocking settlement) of the existing embankment. Reinforced subgrade for railways (RSR) is an efficient method for widening embankments without additional sites. In this study, an existing railway embankment in operation was widened using the RSR, with the interlocking settlement evaluated and analyzed during and after construction. Results show that a widened embankment using RSR can secure train operation stability on existing tracks, even in ground conditions including shallow soft layers. The interlocking settlement was mainly affected by the backfill load and hardly affected by the wall load of the RSR. In addition, it was confirmed that the interlocking settlement mainly occurred in the backfill construction and stabilization period of RSR construction and converged early.

A full-scale reinforced subgrade for railways (RSR) was constructed, and repetitive and static load tests were performed to analyze the deformation characteristics of reinforced rigid walls with short reinforcements for railway subgrades that require strict displacement restrictions. Load test results were obtained for four sections, in which the reinforcement arrangement (vertical spacing and length) and wall-reinforcement connection method were applied differently, and the behavior of the reinforced rigid wall was observed according to each parameter. A repetitive load of 500 kPa and a static load of 1000 kPa were applied to the outside of the reinforcement area to evaluate the behavior of the subgrade when utilizing short reinforcement. The test results confirmed the reduction of the settlement and horizontal displacement of the wall, owing to the restraining effect of the short reinforcement and rigid wall. In addition, it was observed that the greater the applied load, the greater the influence of the reinforcement on the behavior of the subgrade; this pattern was more marked in loads above the yield of soil.

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]