Quantifying the influence of sleeper spacing on lateral resistance using a novel experimental method

A new approach for evaluating lateral resistance of railway ballast associated with extended sleeper spacing

Failures of mainline railway sleepers and suggested remedies – Review of current practice

Lateral displacement of different types of steel sleepers on ballasted track

To enhance the stability of continuous welded rail (CWR) tracks, frictional sleepers have been developed. The frictional sleepers are new types of sleepers with grooves on the bottom, and different bottom grooves improve lateral resistances at different magnitudes. In this study, single sleeper push test (SSPT) and its model with discrete element method (DEM) were carried out to confirm how much arrowhead groove frictional (AGF) sleeper increases the lateral resistance of ballasted track. The SSPTs were performed to confirm the lateral resistance results, and also to validate and calibrate the DEM models. With the validated models, the groove factors influencing the lateral resistances were studied, including groove sizes (depth, width), arrowhead groove direction and groove numbers. The reason of lateral resistance improvement was studied at mesoscopic level, including the ballast-sleeper contact numbers and contact force chains. Results show that applying the AGF sleeper is able to improve lateral resistance by 7–24%, and it can provide enough lateral resistance after reducing ballast shoulder width from 500 mm to 300 mm. The AGF sleeper can improve the sleeper-ballast interaction by increasing sleeper-ballast contact number. The study is helpful for frictional sleeper design, further improving track stability.

The continuously welded rail tracks are very popular and wide because of their advantages. Although the continuously welded rail tracks have special mechanical properties and requirements and they need special construction and maintenance. One of the most important requirements of the continuously welded rail tracks is the big lateral resistance. The lateral resistance can be increased by several solutions, which are highlighted in the following three methods: ballast bonding technology and safety caps and Y steel sleepers. The main goal of this publication is to demonstrate the tests and measurements made in three different track sections, to compare and analyze the results of the measurements and to summarize the conclusions.

The mechanical behavior of railroad trackbeds, especially their lateral resistance under dynamic train loads, is significantly influenced by ballast angularity. Using simulations using the Discrete Element Method and realistic particle geometries acquired through 3D scanning, this study examines the function of ballast particle angularity. An Artec Space Spider was used to scan and import five ballast samples into PFC3D, each of which had a unique size distribution and angularity index. To simulate a Single Tie Push Test, a B70 concrete sleeper, which is frequently found in European tracks, was modelled and put through lateral loading. Results for the standard No. 24 ballast gradation were compared with experimental data to validate the simulation framework, and the results indicated a high degree of agreement in the lateral force-displacement behavior. By examining changes in the particle size distribution, ballast degradation was measured, and the resulting Ballast Breakage Index and Breakage Ratio were calculated. Using accepted techniques, lateral resistance was calculated as the area under the displacement curve at 3.5mm. According to the results, samples with more angular particles had lower degradation and higher lateral resistance. The importance of angularity in stabilising ballast layers under lateral loads was validated by regression analysis. These results offer guidance for better ballast selection and maintenance practices in the field of railway engineering.

Vision-based measurement of crack generation and evolution during static testing of concrete sleepers

Most of the engineering failures especially in mechanical and aerospace industry are due to the fatigue. Fatigue cracks and their propagation can be monitored by observing changes in the structural stiffness resulting from strength reduction as a function of the number of loading cycles. This monitoring can be observed using piezoceramic (PZT) transducer based electromechanical impedance (EMI) technique, and digital image correlation (DIC) system which uses variations on structural surface. The fatigue load usually aggravates the fracture if any defects pre-exist in the structure. The present work monitors multiple-crack emanating from electrode sparked multiple plane defects which are induced in to the specimens prior to the fatigue test, using EMI technique and DIC system. The fracture occurs much below the ultimate stress for the structures which already have defects as in the present case. EMI technique uses signature comparison of healthy and cracked state of the structure to depict crack growth. Initial detection of surface hair-line cracks from the corners of induced defects and their propagation till merging and subsequent failure were explained by signature variations and DIC techniques. Thus, a signal processing technique EMI, and image processing technology DIC were found to complement each other in prediction of early crack and their appearance on surface of the specimens.

The development of measurement methods, and in particular digital image correlation (DIC) systems, which are designed to measure of entire displacements and deformations fields, opens up new areas of research. In general, the materials constitutive relations are formulated in such a way that material parameters could be determined with relatively simple experimental tests carried out on samples with uniform (approximately) stress and strain fields. Then it is possible to apply them to complex boundary value problems formulated e.g. in the small or large deformation theories. The application of DIC allows to verify the accuracy of their predictions by comparing the results of the experiment with solutions to boundary value problems obtained using the finite element method (FEM).

Analysis of the aspects of residual stresses quantification performed by 3D DIC combined with standardized hole-drilling method

The continued upscaling of offshore wind turbines (OWTs) necessitates the development of foundation systems capable of sustaining increased lateral loads. As monopiles remain the most widely used foundation type for OWTs, a detailed investigation into their lateral behavior and soil flow under operational loading is warranted. This study utilized a nonlinear three-dimensional finite element model (FEM) to assess the lateral performance of monopiles supporting a 5 MW turbine in clayey soils. The results revealed that the lateral capacity and deformation behavior are governed primarily by soil shear strength and the monopile’s length-to-diameter ratio (L/D). In softer soils, increasing the L/D ratio led to notable enhancements in lateral resistance, up to fivefold, as well as significant reductions in pile head displacement and rotation. In contrasts, monopiles in stiff clay exhibited distinct failure patterns and less sensitivity to L/D variations. Soil deformation patterns at the ultimate state varied depending on stiffness, indicating distinct failure mechanisms in soft and stiff clays. These findings highlight the importance of incorporating realistic soil behavior and geometric influences in monopile foundation design for large OWTs.

Determination and prediction of crack patterns in hot mix asphalt (HMA) mixtures

Trees are subjected to mechanical stressors, induced via dynamic (wind) and static (gravitational) forces, and must properly acclimate during their lifespan or face premature mortality. Resource allocation as a stress response is vital for tree survival, and can include the shedding of woody parts, adaptive growth, hormonal signaling cascades, and the initiation of energy transfer mechanisms. The strain resulting from stress intercepted by the canopy and transferred throughout the tree is of significant importance, not only for tree survival, but for the safety and well-being of the human population found in close proximity. As trees age and adapt to stressors and an ever changing environment, material properties also change that can influence tree stability, of which arborist and tree managers should account for. To test the function of tree orientation to an applied load, static load tests were conducted on 15 mature pin oak trees (Quercus palustris Muenchh.). Static load tests were applied to tilt the trees 0.1o from natural position to concentrate strain at the root-stem transition zone (RSTZ) and nondestructively mapped resulting strain patterns with an ARAMIS digital image correlation (DIC) system. Using bark as a surrogate for strain on the xylem, strain resulting from static loading was mapped with the DIC system from the main stem into the structural root system. Strain patterns were analyzed across the RSTZ in the leeward, tangential, and windward directions. Results indicate that mean maximum strain magnitudes are similar at the RSTZ on the leeward (0.088) and windward sides (0.090) and lower on the tangential direction (0.058). The leeward strain was comprised of 4% tensile strain and 96% compressive strain and windward strain was comprised of 95% tensile strain and 5% compressive strain. Mean maximum strain for the tangential orientation constituted 65% tensile strain and 35% compressive strain. The changes of proportional strains found on the tangential RTSZ orientation is poorly understood and often disregarded in tree biomechanical studies. This information could prove to be beneficial to the arboricultural and plant science communities to better understand how trees manage loading events and to further enhance tree risk assessment and root zone management protocols.

Despite the great development in the manufacture of the helical pile and the development of their use, especially in transmission towers and wind turbines, there is little research on their lateral behavior. In this laboratory study investigate the behavior of screw piles group (2×1) and (1×2) with the spacing to the diameter of helix ratio (S/Dh =1.5, 3, and 4.5) having a diameter (10 mm) and embedded length to diameter ratio (L/D = 40) by using single and double helix embedded in soft clay and extend to stiff clay under a cyclic lateral load of frequency (0.2 Hz). The results showed that increasing the distance between the piles had a great effect on increasing the lateral resistance. the increase of pile spacing in the groups from (1.5 Dh) to (3 and 4.5 Dh) increases the lateral resistance about 34-38% and 50% respectively. Also, from result showed that the group (2×1) gave a lateral resistance more than the group (1×2) about 11% for single helix and about 6% for a double helix, and for the same spacing and configuration the screw pile with double helix gives an increase in lateral resistance about 5-10 % from the single helix.

A new soil reaction model for large-diameter monopiles in clay