Recently, settlement in railway tracks is posing a serious challenge. In particular, ballasted tracks can experience settlement due to repeated dynamic loading and various geotechnical factors such as consolidated settlements of natural foundation soil and poor compaction, which lead to track irregularities. Among these factors, settlement in track foundation has been identified as the primary cause of track irregularities. Such settlement mainly results from permanent deformation, a form of progressive settlement found in the upper subgrade due to the repeated dynamic loading of trains. As such, it is necessary to conduct a behavioral analysis of upper subgrade soil, which is susceptible to permanent deformation. A large-scale finite element analysis was performed using an existing permanent deformation prediction model to analyze the effects of permanent deformation on settlement in underlying soil materials of ballasted tracks. The results were used to propose a prediction model for settlement in the upper subgrade of ballasted tracks. The proposed model allows more accurate predictions of settlement that may occur in the upper subgrade of ballasted tracks, and can also be employed in predicting track irregularities.

Gaps generated underneath railway track slabs may cause unstable conditions. Such gaps can form because of different reasons, including settlement of soft soil, unsuitable construction of a concrete slab on loosely compacted soil, and drastic stiffness change in a transition zone between the bridge deck and embankment. The gaps underneath railway track slabs are not easily detectable by common nondestructive test methods. A nondestructive test (NDT) based on a wavelet time–frequency concept is proposed for the practical purpose of detecting gaps under track slabs. The method uses a microphone sensor to catch leaked Rayleigh acoustic waves in the air and an accelerometer to measure surface Rayleigh waves on the slab. In order to investigate the possibility of developing the test system, a finite element analysis (FEA) was performed to simulate Rayleigh wave generation on the concrete surface and in the air. A test system module composed of a microphone and an accelerometer, data acquisition system (DAQ), and an analyzer program was also assembled for a small backyard pilot test. It was verified that the new NDT test system could be successfully adapted for detecting gaps underneath railway track slabs and track bed soil.

A rover is a planetary surface exploration device designed to move across the ground on a planet or a planetary-like body. Exploration rovers are increasingly becoming a vital part of the search for scientific evidence and discoveries on a planetary satellite of the Sun, such as the Moon or Mars. Reliable behavior and predictable locomotion of a rover is important. Understanding soil behavior and its interaction with rover wheels—the terramechanics—is of great importance in rover exploration performance. Up to now, many researchers have adopted Bekker’s semiempirical model to predict rover wheelsoil interaction, which is based on the assumption that soil is deformable when a pressure is applied to it. Despite this basic assumption of the model, the pressure-sinkage relation is not fully understood, and it continues to present challenges for rover designers. This article presents a new pressure-sinkage model based on dimensional analysis (DA) and results of bevameter tests. DA was applied to the test results in order to propose a new pressure-sinkage model by reducing physical quantitative parameters. As part of the work, a new bevameter was designed and built so that it could be successfully used to obtain a proper pressure-sinkage relation of Korean Lunar Soil Simulant (KLS-1). The new pressure-sinkage model was constructed by using three different sizes of flat plate diameters of the bevameter. The newly proposed model was compared successfully with other models for validation purposes.

Recycling of wasted soil becomes a hot issue due to the difficulty of disposal, whereas stiff soil is limited for construction. This paper investigates the properties of air-foam stabilized soil made from dredged soil recycled by air-foam stabilization method such as strength, resilient modulus, and evaluation of the pavement performance when using it as pavement sub-base material. Air-foam stabilized soil samples are prepared by mixing soil and water with various cement and air-foam contents. The unconfined compression test and the resonant column test are conducted; then, the relationship between the unconfined compressive strength and the resilient modulus of air-foam stabilized soil is evaluated. The resilient modulus values are applied in a layered elastic model to predict the allowable number of load repetitions based on fatigue cracking and rutting. According to the pavement performance, air-foam stabilized soil is sustainable and suitable in the role of pavement sub-base material.

This study introduces a Multi-Depth Deflectometer (MDD) combined with a Global Navigation Satellite System (GNSS) which was developed for measuring the deformation of railway slab track layers. We newly designed the MDD with the addition of laser sensor modules for increasing precision in which the MDD head is fixed at the top of the track slab. The MDD/GNSS system can measure the relative deflection between each track layer as well as the total deflection at the top of the track slab, which makes it possible to evade the fixed condition problem of classical MDD. The new MDD/GNSS system was installed at the transition zone between a tunnel entrance and its embankment, which experienced high settlement levels prior to repair. The system was used to monitor whether the repaired concrete track foundation with pressurized cement grouting was stabilized effectively and what track layer position was most unstable so that it had the most influence. The GNSS system was designed and built for computing net settlement at each track layer even when the MDD could not be fixed firmly at the end point, which is a major drawback of classical MDD. The results obtained from MDD and GNSS measurements indicated significant potential in aiding railway track settlement measurements.

The equivalent radius $$\:{R}_{eq}$$ has been used for calculation of strain in Resonant Column (RC) testing. Present calculation methods for $$\:{R}_{eq}$$ are not adequate since they are not precise over a wide range of strain. In this study, a new equation of $$\:{R}_{eq}$$ that can be used over a wide range of strain is proposed by developing a new method of determining $$\:{R}_{eq}$$ based on a numerical integration technique using a theoretical modified hyperbolic model. The new method for obtaining optimum $$\:{R}_{eq}$$ can be used for evaluating shear modulus more precisely in an RC test at any strain level. The prediction equation of $$\:{R}_{eq}$$ was successfully applied to typical unbound granular materials such as the simulated lunar granular soils to get the shear modulus reduction curves. The R _eq values computed using the developed equation slope down sharply when the strain value varies from 0.1 to 0.001. The conventional equivalent radius approach could be inadequate at small strains less than 0.01. This means that for obtaining the best results from the RC testing, different values of R _eq must be used considering the range of shear strain.