Assessment of Interface Shear Behaviour of Sub-ballast with Geosynthetics by Large-scale Direct Shear Test

AbstractA series of large-scale direct shear test were conducted to study the interface shear strength of subballast reinforced with different types of geomembranes and geogrids. The impact of normal stress (σn), shearing rate (SR), relative density (DR) and open area (OA%) on the behaviour of granular material was investigated in unreinforced and reinforced condition. The results revealed that the performance of material was markedly influenced by σn and OA. The results also showed that geogrids provided a greater value of passive resistance owing to have transverse ribs, but the mobilised passive resistance became smaller with increase in OA. The triaxial grids offered more passive resistance than biaxial geogrid

Experimental and discrete element modelling of geocell-stabilized subballast subjected to cyclic loading

This paper presents a study of the load-deformation behaviour of geocell-stabilised sub-ballast subjected to cyclic loading using a novel track process simulation apparatus. The tests were conducted at frequencies varying from 10-30 Hz. This frequency range is generally representative of Australian Standard Gauge trains operating up to 160 km/h. The discrete element method (DEM) was also used to model geocell-reinforced sub-ballast under plane strain conditions. The geocell was modelled by connecting a group of small circular balls together to form the desired geometry and aperture using contact and parallel bonds. Tensile and bending tests were carried out to calibrate the model parameters adopted for simulating geocell. To model irregularly-shaped particles of sub-ballast, clusters of bonded circular balls were used. The simulated load-deformation curves of the geocell-reinforced sub-ballast assembly at varying cyclic load cycles were in good agreement with the experimental observations. The results indicated that geocell decreased the vertical and lateral deformation of sub-ballast assemblies at any given frequency. Furthermore, the DEM can also provide an insight into the distribution of contact force chains, and average contact normal and shear force distributions, which cannot be determined experimentally

The effects of NMDA receptor blockade on TMS-evoked EEG potentials from prefrontal and parietal cortex

Measuring the brain's response to transcranial magnetic stimulation (TMS) with electroencephalography (EEG) offers unique insights into the cortical circuits activated following stimulation, particularly in non-motor regions where less is known about TMS physiology. However, the mechanisms underlying TMS-evoked EEG potentials (TEPs) remain largely unknown. We assessed TEP sensitivity to changes in excitatory neurotransmission mediated by n-methyl-d-aspartate (NMDA) receptors following stimulation of non-motor regions. In fourteen male volunteers, resting EEG and TEPs from prefrontal (PFC) and parietal (PAR) cortex were measured before and after administration of either dextromethorphan (NMDA receptor antagonist) or placebo across two sessions in a double-blinded pseudo-randomised crossover design. At baseline, there were amplitude differences between PFC and PAR TEPs across a wide time range (15-250 ms), however the signals were correlated after ~80 ms, suggesting early peaks reflect site-specific activity, whereas late peaks reflect activity patterns less dependent on the stimulated sites. Early TEP peaks were not reliably altered following dextromethorphan compared to placebo, although findings were less clear for later peaks, and low frequency resting oscillations were reduced in power. Our findings suggest that early TEP peaks (<80 ms) from PFC and PAR reflect stimulation site specific activity that is largely insensitive to changes in NMDA receptor-mediated neurotransmission.Nigel C. Rogasch, Carl Zipser, Ghazaleh Darmani, Tuomas P. Mutanen, Mana Biabani, Christoph Zrenner, Debora Desideri, Paolo Belardinelli, Florian Müller-Dahlhaus, Ulf Zieman

Behaviour of geocell-reinforced subballast under cyclic loading in plane strain condition

Ballasted rail tracks have gained a competitive edge over other modes of transportation systems in terms of long term performance, better ride quality, higher safety, lower cost of construction and relatively acceptable speed and efficiency of services. In order to keep rail infrastructure costs minimal, the railway industry needs to use locally available materials during track construction, some of which do not have sufficient shear strength. At times owing to use of poor quality material, ballast and subballast cause excessive lateral spreading that leads to differential track settlement, cases of derailment and regular costly maintenance. In addition, presence of soft estuarine clay deposits along the coastal belt of Australia pose serious concerns on track stability. On other hand, considering significant demand for urban transportation, substantial urban growth, the construction of new tracks as well as the maintenance and modernisation of existing tracks have been more challenging. As result, other engineering solutions should be pursued to improve ballasted rail track substructure, which can help to maintain railways as the most economical and safest mode of transportation in Australia. In the view of above, reinforcing the subballast is an economical alternative for stabilizing the track substructure. Unlike conventional rigid reinforcement such as steel and timber, flexible geosynthetics have shown a promising approach for improving the performance of granular media (ballast and subballast) placed over weak and soft subgrade. In the recent past, different varieties of geosynthetics, including planar (two dimensional) and cellular (three dimensional) geosynthetics, have been successfully employed. Geosynthetics have been proven to be effective in terms of reducing the settlements and enhancing track stability. Nevertheless, among different types of reinforcement, a geocell mattress due to its unique honeycomb shape, provides an effective cellular confinement, to reduce lateral displacement. Additional confinement induced by the geocell, mobilized by the tensile stresses of the membrane (i.e. hoop stress), arrests almost all lateral spreading of the infill material and increases the overall material stiffness. It is important to note that the potential use of geocells to stabilise the ballast layer has often been regarded with some scepticism from a track maintenance point of view. In other words, cleaning and replacement of spent material is not convenient if a geocell mattress interferes with the tamper ‘tines’. In this context, Australian rail organisations have now made attempts to use geocells and other methods of stabilisation to improve the subballast that rarely requires maintenance, rather than the overlying ballast. This study was the result of applied research undertaken within the Cooperative Research Centre for Rail Innovation in collaboration with the rail organisations, namely ARTC and Sydney Trains. In this study, triaxial tests were conducted to characterize the behaviour of reinforced and unreinforced subballast under cyclic loading using large-scale process simulation prismoidal triaxial apparatus (PSPTA) designed and built at the University of Wollongong, Australia. The laboratory tests were conducted in plane strain condition and stress controlled mode. Cyclic loading with different frequencies under very low confining pressure was applied to study the performance of subballast. Granular material with an average particle size of 3.3 mm and a geocell system with a depth of 150 mm and a nominal area of 46 x 103 mm2, made from high density polyethylene (HDPE) material, were used in this study. The laboratory results revealed that subballast stabilisation was influenced by the number of cycles, the confining pressure and the frequency. The results proved that the geocell reinforcement is an ideal technique to improve subballast performance under very low confining pressure. The outcome of this investigation confirmed that the geocell could effectively arrest lateral spreading and reduce excessive settlement of the subballast under cyclic loading, hence increase track longevity. The results also showed that the geocell performs effectively, especially under low confining pressure (5 ≤ σˊ3 ≤ 30 kPa) and higher frequencies (10 ≤ f ≤ 30 Hz). Moreover, the geocell increased the resilient modulus of the composite layer, providing enhanced track stability of increased train speed. An optimum confining pressure required to reduce excessive volumetric dilation of the subballast was also identified in this study. The interface shear resistance developed between the subballast and geocell has important consequences on the shear behaviour of the geocell reinforced soil. In this regard, the interface shear resistance of unreinforced and reinforced subballast with different types of geosynthetics was also investigated using a large-scale direct shear box apparatus (DSBA). The results showed that the loading mechanism had a significant impact on the interface shear strength of the subballast. A new analytical model was developed to calculate the additional confining pressure induced by the geocell mattress. The proposed model investigate the influence of several factors i. e. (a) frequency (b) confining pressure (c) number of cycles (d) the tensile strength on the behaviour of geocell reinforced subballast. Practical design guidelines in terms of allowable train speeds for different levels of confining pressure are provided for unreinforced and geocell reinforced subballast. Finally, a three-dimensional numerical analysis was developed for unreinforced and geocell-reinforced subballast to simulate practical or real-life railroad conditions to support experimental observations. The numerical predictions indicated that the loaddistribution mechanism of subballast could be improved by the geocells. The finite element predictions were found to be in good agreement with the laboratory data. This numerical analysis can be used as a primary tool in the design of geocellreinforced granular material with known shear strength, subjected to cyclic loading in typical railway environments

Modelling of geocell-reinforced subballast subjected to cyclic loading

This paper presents the experimental and numerical studies of geocell-reinforced subballast subjected to cyclic loading. A series of laboratory experiments were conducted using a large-scale prismoidal triaxial apparatus that was subjected to relatively low confining pressures of σ\u273 = 10-30 kPa and a frequency of f = 10 Hz. Numerical simulations were performed using the commercial finite element package ABAQUS in three dimensions to realistically model cellular confinement, and to study the effectiveness of geocell reinforcement on subballast. A cyclic loading with a periodic and positive full-sine waveform was adopted to model the geocell-reinforced subballast, which is similar to the load carried out in the laboratory. The results of numerical modelling agreed well with the experimental data, and showed that geocell could effectively decrease the lateral and axial deformations of the reinforced subballast. The numerical model was also validated by the field data, and the results were found to be in good agreement, indicating that the proposed model was able to capture the load-deformation behaviour of geocell-reinforced subballast under cyclic loading. A parametric study was also carried out to evaluate the effect of the subballast strength and geocell stiffness on the mobilized tensile strength in the geocell mattress. It was found that the maximum mobilized tensile stress occurs on the subballast with the lowest degree of stiffness. Also the results revealed that lateral displacement decreased further by increasing geocell stiffness, and geocell with a relatively low stiffness performs very well compared to the geocell with a higher stiffness

An evaluation of the interface behaviour of rail subballast stabilised with geogrids and geomembranes

In a rail track, the compacted granular medium (subballast) placed underneath the ballast influences track resiliency, and controls the load propagation to the softer subgrade (e.g. clay). A series of large-scale direct shear tests were carried out to investigate the interface shear strength of subballast stabilised with geogrids and geomembranes, respectively. In this study, the beneficial effects of these two different types of geosynthetics on the stress-strain behaviour of unreinforced and reinforced subballast were examined. The influences of normal stress (σn), relative density (DR), and the shearing displacement rate (SR) were studied. The results showed that the shear strength of the subballast-geogrid interface was significantly higher than that of the subballast-geomembrane interface. These results also showed that the reinforced subballast with a higher density provided enhanced performance over a wide range of relative densities. The results also indicated that the shear strength was significantly affected by the shearing rate

Agronomic performance of two intercropped soybean cultivars.

Abstract Broader environmental tolerance associated with mixed population of soybean (Glycine max Merr.) cultivars may increase soybean yield potential and play a significant role in yield stability. A field study was carried out to assess whether intercropping of two commonly used cultivars of soybean with different morphological characteristics may increase seed yield in Iran. A split-plot design was used with three replications. The main plots were 3 densities; 23.8, 33.3, and 55.5 plants m -2 . Sub-plots consisted of intercropping ratios row by row of 100:0 (pure stand of Harcor), 75:25, 50:50, 25:75, and 0:100 (pure stand of Bonus) of Harcor and Bonus cultivars, respectively. The results indicated that the highest seed yield was obtained from 50:50 ratios of the cultivars which had land equivalent ratio (LER) above 1.11. Calculation of LER revealed that seed yield in treatment HBHB was 11% higher than the pure stand. The superiority of intercropping over pure stands occurred only in the highest plant density. Intercropping ratio showed no significant effect on any of yield components. However, pod number per plant was decreased with increasing plant density

Closure to Behaviour of geocell reinforced subballast subjected to cyclic loading in plane strain condition

The writers wish to thank the discusser for his valuable comments. While the writers are in general agreement with the discusser, some of his points warrant further clarification. Firstly, the aim of the paper was to investigate the effectiveness of the geocell mattress used as reinforcement in subballast under cyclic loading. The authors agree that the vertical strains reported for the geocell and subballast were different in magnitude from those reported for the geocell mattress. This is because strains in the geocell mattress were measured using strain gauges attached to the geocell strips. Strain gauges inclined in both vertical and horizontal directions were used to measure axial and radial strains, respectively. As clearly stated in the original paper, linear variable differential transformers (LVDTs) were used for recording the vertical and lateral strains of unreinforced as well as reinforced subballast specimens