Conventional Embankment Research Articles

Cooling Performance of a Novel Ventilated Slope on Railbed in Permafrost Regions

ABSTRACTThe heat absorption of the railbed mainly originates from the embankment slope in permafrost regions. A novel ventilated slope (NVS) with a double‐layer convection channel is proposed and verified. By applying this method to the Qinghai–Tibet Railway (QTR), the annual average temperature at the 10 cm depth below the embankment slope surface under NVS was reduced by 4.95°C. The freezing index at the 10 cm depth of NVS was 1.78 times higher than that of the slope without any cooling approaches. The numerical simulation results showed that heat was accumulated for the conventional embankment, while heat was released from the railbed after the application of NVS. With the cooling effect of NVS, the 0°C isotherm would rise above the original natural ground surface in the 2nd year after the embankment construction. A low‐temperature region of −2°C would be observed in the underlying permafrost by the 10th year. The underlying permafrost would remain frozen in the 50th year. This study provides a novel method for protecting the underlying permafrost in permafrost regions.

Long-Term Performance Assessment of a Geosynthetic-Reinforced Railway Substructure

Significant savings in carbon emissions, cost, and time could be achieved via the reduction in maintenance frequency, capital costs of track construction, and land used. Geosynthetic-reinforced soils offer such sustainable solutions. The experimental work presented in this paper investigates the long-term performance of a Geosynthetic-Reinforced Soil Retaining Wall (GRS-RW) system as an alternative to the conventional railway embankment. Full-scale testing was carried out on three sleeper sections of ballasted and slab tracks by simulating train loads cyclically, phased to 360 km/h. The tracks were supported by either a low-level fully confined conventional embankment or a GRS-RW substructure. The substructures were formed of a 1.2 m deep subgrade and frost protection layer, in accordance with high-speed railway design standards. The overall aim was to assess the performance of the tracks, in terms of transient displacements and total settlements. It was observed that once the GRS-RW system reached its active state, it deformed in a very similar way to a conventional embankment despite the fact that the GRS-RW system is less confined than the conventional embankment. The results indicate that the cumulative settlement of the slab track, which is due to the plastic deformation of the soil, is significantly less than that of the ballasted track, which is primarily caused by the movement of the ballast particles.

Improvement in geotechnical properties of soft filter cake stabilized with autoclaved aerated concrete powder: Experimental evidence and micro-mechanism

Filter cake is a type of engineering waste soil composed of fine-grained particles, typically characterized by its high initial saturation and poor engineering performance. In this study, autoclaved aerated concrete powder (AACP) was used as an admixture to improve the mechanical properties of filter cake. The effects of AACP content and curing time on the unconfined compressive strength (UCS) and volume change behavior of compacted specimens were investigated. The test results showed that the UCS of compacted AACP/filter cake mixtures initially increased with increasing AACP content, reaching a peak value at 40 % AACP content, and subsequently decreased. The sample containing 40 % AACP (cured for 28 days) exhibited a constrained modulus comparable to that of conventional embankment filling materials, but with the added advantage of a lower dry density. Expansion of the parent soil, when exposed to water, occurred through interparticle expansion. The addition of AACP resulted in a reduction in the thickness of the diffuse double layer (DDL) of clay particles, as well as a decrease in the interparticle repulsive force. This allowed soil particles to approach each other more closely and facilitated the formation of aggregated soil particles. AACP incorporation further altered the particle size distribution and soil structure, thereby contributing to the improvement in mechanical properties of the filter cake. The physicochemical and microstructural observations, such as SEM, XRD, and MIP analyses, and zeta potential tests, were in good agreement with the changes in the geotechnical properties of the samples. These experimental results provide technical references for the utilization of AACP and filter cake in embankment engineering.

Numerical Modelling of Soft Soil Improvement Using Expanded Polystyrene Geofoam for Road Embankment

Soft soil brings abundant engineering issues due to low bearing capacity and shear strength. A comprehensive study of soft ground needs to be reviewed and identified before construction can start. Various techniques can be used to improve the soil. However, this study focuses on using material namely expanded polystyrene. The geotextile is embedded with expanded polystyrene to strengthen the soil condition. This study adopted the soil parameters from East Coast Expressway. There are two models in this study, which are earth embankment and EPS embankment. The settlement of the earth embankment is compared with the EPS embankment after construction. The Mohr-Coulomb parameters are used to model the soft soil and embankments, while the linear elastic parameters were adopted to model the EPS and geotextile. This study produced two embankment models, the conventional embankment models with and without surcharge. The second model is an EPS embankment with various densities (22 kg/m3, 29 kg/m3, and 39 kg/m3). The settlement is recorded for ten years after the embankment construction was completed. The difference settlement value for the conventionalmodel is 28mm. The settlement value for EPS 22 is 3.18mm, EPS 29 is 2.06mm, and EPS 39 is 1.51mm. For the geotextile embedded in EPS, the settlement for EPS 22 is 3.17mm, EPS 29 is 2.04mm, and EPS 39 is 1.49mmrespectively. Since EPS uses three different densities, from the prediction of PLAXIS 2D, the higher density gives the lower value of the settlement. However, when the geotextile is embedded with EPS, there is no significant difference in settlement behaviour. In conclusion, the model with a surcharge gives a lower settlement than themodel without a surcharge. But the expanded polystyrene block is the best model to reduce the settlement compared with the conventional model with a surcharge. Different densities of EPS resulted in different settlement value, and EPS 39 gives the lowest settlement value. In terms of the geotextile embedded with EPS, it does not give a significant change in settlement.

Geo technical Laboratory Evaluation of Construction Demolition Recycled Material for Road Embankments

The recycling of construction demolition waste material has already become a prime focus under sustainable technologies and innovations across the globe. A report announced by the Centre for Science and Environment (CSE), Delhi, in August 2020 stated, India generates approximately 150 million tons of construction demolition waste every year and recycles only 1%. The rest remains strewn across, in landfills causing air contamination and water tainting. Whereas “The United States Environment Protection Agency (USEPA)” approximated that 600 million tons of construction waste had been generated in 2016 in the USA, around 75% of the waste was recycled and also used effectively. The present paper focuses on predicting the suitability of recycled construction demolition waste material for road embankment and comparing its characteristics with conventional embankment materials. The Guidelines given by IRC and BIS were following to predict the feasibility of recycled construction demolition waste as fill material for road embankment. Laboratory results indicated the suitability of recycled construction demolition waste material for road embankments. This study probed a single source of construction demolition waste with one particular gradation as it can significantly alter the properties and suitability requirements.

Stress distribution in reinforced railway structures

This paper evaluates the performance of a geosynthetic reinforced soil retaining wall (GRS-RW) system as an alternative to a conventional railway embankment. The aim is to investigate the behaviour of the GRS-RW system in terms of displacements and stress levels at different locations in the track and substructure. Full-scale laboratory experimental testing is carried out on a GRS-RW structure, supporting sections of ballasted and slab track, under moving loads at 360 km/h. The tracks are supported by a low-level fully confined conventional embankment and a GRS-RW system, which are constructed to high-speed standards. Displacement transducers and earth pressure cells are placed at different locations to record the displacements of the track and the stress levels in the substructure. The test results show that the pressure levels on the GRS-RW wall are negligibly small for the particular test setup, proving the GRS structure under the action of compaction reached its active state. This means that the reinforced soil was self-supporting under its self-weight and train loads, meaning there was minimal pressure on the walls. Therefore, GRS-RW systems are better alternatives to traditional earth embankments due to enhanced soil stabilisation and less land take.

Long-term thermal stability and settlement of heat pipe-protected highway embankment in warm permafrost regions

Warm permafrost is a challenging geological material for infrastructure engineering. This study presents the observed damage, ground temperature, and settlement at varying depths from three-year continuous monitoring of two selected highway embankment segments along the Qinghai-Tibet Highway in warm permafrost areas, including one conventional embankment and the other with heat pipes on the sunny slope side. Field monitoring data reveal that the embankment settlement mainly results from thaw consolidation of warm permafrost, and the permafrost table beneath a conventional embankment is concave-shaped due to the polythermal effects of asphalt pavement. In contrast, the permafrost table underneath the embankment equipped with heat pipes on the sunny side is convex-shaped due to heat pipes' cooling effects. The different causes of longitudinal cracks on the two embankment surfaces were uncovered based on field observed data. Results of coupled hydro-thermal-mechanical model simulation considering climate warming show that while the configurations of heat pipes on both sides of the embankment can generally ensure the long-term thermal stability and limit the differential settlement across the road surface, the one with slanted heat pipes delivers the best performance and is recommended for future applications. Results from this study, including field monitoring data and recommended heat pipe configuration, will be of value for the construction and maintenance of transportation infrastructure in warm permafrost regions.

Correlation of UCS and CBR on Lightweight Geocomposite of Soil-EPS Stabilized by Waste of Buton Asphalt

The conventional embankment has disadvantages in terms of its weight; it has an implication for the level of deformation that will occur on the subgrade layer. This study was conducted dealing with the design of geocomposite material compositions based on their mechanic characteristics. The lightweight geocomposit material (LWGM) was constructed by composing soil with expanded polystyrene (EPS) with by-product of buton asphalt as the binder agent (WBA). Unconfined Compression Test (UCT) and California Bearing Ratio (CBR) were examined to figure out the mechanical behavior of LWGM. The percentages of WBA used on specimens were 3%, 5%, 7% and 9%, while those of EPS were 0.15% and 0.30%, based on weight of soils dry density. Furthermore, to understand the curing period effect, all the specimens were cured and tested within 7 days and 28 days. The results showed that the LWGM could reduce the embankment densities from 20% to 35%, compared to conventional embankment. The compressive strength and CBR values presented the same tendency, so that, based on correlation of UCS and CBR value, the LWGM compositions that are appropriate for road foundation criteria as subbase courses are 3.2% to 7% for the WBA and 0,15% - 0,30% for the EPS.

Direct Shear Strength Properties of Limestone-Blended Embankment Materials

The vast distribution of limestone in the Philippines makes limestone quarrying prevalent resulting to the accumulation of waste limestone. This opened the idea of utilizing the wastes as embankment materials which would result to a more economical construction. In order to test the ability of limestone to be an embankment material, its strength and consolidation parameters are evaluated in different mixed proportions, at 0%, 20%, 40%, 60% and 100%, with the conventional embankment material using the direct shear test. Index properties (i.e. specific gravity, Atterberg limits, and maximum and minimum index densities) were obtained for all the blends in order to produce empirical relationships with the different percentage of limestone. It was found out that the cohesion increased with the addition of limestone, although there was a decrease in the internal angle of friction.

Back-analyses of flow parameters of PVD improved soft Bangkok clay with and without vacuum preloading from settlement data and numerical simulations

Prefabricated vertical drains (PVDs) with embankment preloading (conventional PVDs) and with embankment combined with vacuum preloading (Vacuum-PVDs) are examined using the field data obtained from the site of the Suvarnabhumi Airport, Thailand. The flow parameters were back-analyzed by comparison of measured and predicted or simulated data. The flow parameters were illustrated in terms of the horizontal coefficient of consolidation (Ch) and the ratio between the horizontal hydraulic conductivity in undisturbed zone (kh) and the horizontal hydraulic conductivity in smear zone (ks) or (kh/ks). Numerical simulations using one-dimensional FEM PVDCON software with equivalent vertical permeability, kev, to determine the appropriate Ch and kh/ks of PVDs with conventional embankment preloading and with embankment combined with vacuum preloading schemes were made. Furthermore, numerical simulations using axisymmetric FEM by ABAQUS software, incorporating horizontal (kh) and vertical (kv) permeabilities, to determine the appropriate kh/ks based on back-calculated Ch of conventional PVD and Vacuum-PVD schemes were also done. The Vacuum-PVD scheme indicated faster rate of settlement than conventional PVD scheme by about 1.7–1.8 times with slight reduction of the kh/ks ratios. For conventional PVD, it was demonstrated that the increase in kh/ks ratios reduced the simulated rate of settlement.

Embodied energy evaluation for sections of the UK Channel Tunnel rail link

Using embodied energy as a quantitative measure of environmental impact, this study evaluated the embodied energy of two built sections of the UK Channel Tunnel rail link, now known as High Speed 1, and an alternative design. Results show that contract 220's 7·15 m diameter twin bored tunnel section of 7·5 km has an embodied energy of 949 TJ, whereas 7·3 km of contract 310's, consisting mainly of a pile-slab structure, consumed 678 TJ. The alternative design for contract 310, based on a conventional embankment design, would have consumed 640 TJ. By examining the embodied energy content, these geotechnical structures can be categorised into the following two types: (a) structures of which the materials are totally dominant at 90% of the total energy, such as pile-slab; and (b) more direct energy-intensive constructions, where the transportation and installation can collectively account for as much as 40% of the total, such as the tunnel and the embankment. In both types materials are generally the dominating energy consumer: therefore engineers should optimise designs using fewer embodied energy-intensive materials. When compared with the annual UK household energy consumption, the embodied energy values of these structures are equivalent to over 10 000 annual households' consumption. This comparison reveals the large scale of energy involved in geotechnical infrastructure construction, compared to activities in everyday life. This calls for more attention to evaluate the embodied energy of geotechnical constructions as part of design evaluations.

Lightweight recycled geomaterials reinforced with geogrids

Scrap tyres are unwanted urban waste, the volume of which is increasing every year. One possible recycling method is for the shredded tyres, either alone or mixed with soil, to be used as a lightweight geomaterial. The present study aimed to examine (a) the interactions between geogrids and a tyre chips–sand mixture, (b) the performance of a full-scale geogrid-reinforced test embankment and (c) a numerical simulation of this full-scale test embankment. Numerous experiments were performed in the laboratory to investigate the interactions between the geogrid and the tyre chips–sand mixture. A full-scale, geogrid-reinforced embankment with lightweight tyre chips–sand fill was then constructed on soft Bangkok clay and extensively instrumented to evaluate its performance. The unit weight of rubber tyre chip–sand mixtures with ratio 30:70 per cent by weight was 13·6 kN/m3 compared with 18·0 kN/m3 for conventional sand backfill. The total settlement magnitude of 122 mm of the lightweight embankment was 67·5% less when compared with the corresponding value of 400 mm for conventional embankment. Numerical analysis using two-dimensional plane strain conditions provided satisfactory predictions for the full-scale field test.

Field experiment study on effects of duct-ventilated railway embankment on protecting the underlying permafrost

Abstract Cooling principle is adopted in roadbed constructions in permafrost regions on the Qinghai–Tibet Plateau for protecting the underlying permafrost. One way is to use duct-ventilated embankment. Ground temperature data were collected along experimental embankments in Beiluhe section of the Qinghai–Tibet railway. Analyses of ground temperature changes and heat influx indicate that ventilation ducts effectively cool the soils surrounding the ducts in the embankment. Permafrost behavior beneath conventional embankment and test embankments with ducts installed at high and low positions was studied over 3 years. The permafrost under the conventional embankment and the duct at a high position in the embankment decreasingly absorbs heat during the period. The ground temperature of the permafrost under the conventional embankment rises and that under the duct at a high position embankment decreases slightly. The temperature of the permafrost under the duct at a low position decreased remarkably. These findings demonstrate that a ventilated embankment with a low position duct produces beneficial effects that actively cool the subgrade soils and keep the roadbed thermally stable. Accordingly, they were strongly recommended for use in the construction of embankments in the permafrost regions on the plateau.