Embankment Structure Research Articles

Evaluation on the stability of expressway embankment combined with L-shaped thermosyphons and insulation boards in warm and ice-rich permafrost regions

The embankment construction in permafrost regions changes the energy balance on the surface, resulting in the degradation of the underlying permafrost and instability in the embankment structure. Considering the strict evenness requirement for an expressway, large deformation and instability in expressway embankment cannot be allowed. Accordingly, in this study, a composite measure combined with two-phase closed thermosyphons (TPCTs) and insulation boards is proposed for stabilizing embankments. Moreover, a full-scale experimental expressway embankment is constructed in the Qinghai–Tibet Plateau (QTP) to analyze and investigate the stability of the composite embankment. The experimental results show that the composite measure significantly cools the permafrost under the embankment center and shady slope, and reliably alleviates the embankment deformation and deformation difference. However, the special ground temperature distribution around the TPCTs causes the asymmetric thermal regime and longitudinal cracks in the composite embankment. Additional reinforcement measures should be developed to alleviate the asymmetric thermal regime and prevent such longitudinal cracks. Moreover, timely repair of existing cracks and taking waterproofing measures in advance are favorable for embankment stability.

Site effects of the Denis-Perron dam (SM-3): A case study in Eastern North America

Eastern North America (ENA) is part of a region with low-to-moderate seismicity; nonetheless, some significant seismic events have occurred in the last few decades. Recent events have reemphasized the need to review ENA seismicity and ground motion models, along with continually reevaluating and updating procedures related to the seismic safety assessment of hydroelectric infrastructures, particularly large dams in Québec. Furthermore, recent researchers have shown that site-specific characteristics, topography, and valley shapes may significantly aggravate the severity of ground motions. To the best of our knowledge, very few instrumental data from actual earthquakes have been published for examining the site effects of hydroelectric dam structures located in eastern Canada. This article presents an analysis of three small earthquakes that occurred in 1999 and 2002 at the Denis-Perron (SM-3) dam. This dam, the highest in Québec, is a rockfill embankment structure with a height of 171 m and a length of 378 m; it is located in a narrow valley. The ground motion datasets of these earthquakes include the bedrock and dam crest three-component accelerometer recordings. Ground motions are analyzed both in the time and frequency domains. The spectral ratios and transfer functions obtained from these small earthquakes provide new insights into the directionality of resonant frequencies, vibration modes, and site effects for the Denis-Perron dam. The crest amplifications observed for this dam are also compared with previously published data for large dams. New statistical relationships are proposed to establish dam crest amplification on the basis of the peak ground acceleration (PGA) at the foundation.

Analysis of the effect of sand replacement as a counterweight towards stability of embankment in Belawan Port reclamation

Soil improvement with preloading and PVD on large area has a side effect, where the load received by soft soil does not quickly release soil pore water. Due to the nature of soft soil which has low permeability and low internal friction angle, the soil will experience lateral deformation, this causes the soil around the preloading embankment to be lifted. In this project, sand replacement is carried out at a location adjacent to other constructions as a counterweight so that the subgrade is not lifted. This analysis aims to determine the effect of installing a sand replacement in the sand key area on the stability of the preloading embankment structure in the reclamation area. The method used in this research is the analytical method as well as numerical method using finite element method program. It was found that using a sand replacement as a counterweight was able to prevent the lifting of the soil, to maintain the stability of the embankment structure and to prevent the subgrade lift in the shipping channel. Sand replacement is able to balance the lateral ground pressure so that it does not increase the surface of the shipping channel. Preloading construction without using a counterweight on soft soil will collapse due to lateral deformation of the preloading pile load.

Hydraulic Modelling of Riverbed Embankment Under the Hričov Weir

The weir of the Hričov water structure has an untypical shortened stilling basin, which affects significant scour development in the downstream riverbed. A rockfill embankment structure adjacent to the stilling basin was constructed to prevent the formation of scours in the riverbed. However, increased flows at the weir erode this fortification and it is necessary to replenish the material back to the embankment after the flow situations. A 2D hydraulic model constructed in a flume of the Hydraulic laboratory was used for the research of new downstream fortification, which would be better resist the scouring effects. The model was created according to Froude’s modelling similarity as a 2D model of the weir structure with control gates and part the downstream riverbed consisting of gravel. Different designs of the embankment were not allowed to interfere with the existing construction of the water structure. The construction of the embankment was designed as a concrete “secondary” stilling basin adjacent to the existing one. Tested variants of the embankment were of different length and depth of the stilling basin. The length varied from 11 to 24 m and the depths varied from 0 to 1,8 m. Overall 11 different design of the embankment were investigated. Each design was tested for three different flow rates on the model simulating common and extreme flow situations at the weir. The flows were selected to simulate also different hydraulic phenomena at the weir – overflow, outflow, and free overflow. After each flow simulation the scour in the riverbed was measured. The measured scour parameters were depth of the scour, the distance of the deepest point from the existing water structure and the amount of the material carried away. The resulting parameters were assessed with respect to each other for the corresponding flow rates. The best results in scour reduction were achieved for horizontal embankment with the depth of 0 m. The designs with increased depth were causing secondary hydraulic jump in the riverbed which increased the scours. The tested designs of the embankments were able to reduce scour size by up to 45% for the outflow, by less than 20% for free overflow and by more than 80% at the overflow.

Prediction Model of Thermal Thawing Sensibility and Thaw Depth for Permafrost Embankment along the Qinghai-Tibet Engineering Corridor Using MODIS Data

The aim of this paper was to reveal the distribution law of permafrost thermal thawing sensibility and thaw depth caused by road construction in Qinghai-Tibet engineering corridor (QTEC). The prediction models of permafrost thermal thawing sensibility and thaw depth have been developed by incorporating the MODIS and in situ soil temperature observation data. The comprehensive earth-atmosphere-coupled numerical models of different embankment structures have been utilized to calculate the thaw depth of the underlying permafrost foundation. Finally, using the given data and above developed prediction models, the distribution maps of permafrost thermal thawing sensibility and thaw depth in QTEC are obtained by grid calculation. The results show the following: (1) Insensitive permafrost of QTEC mainly distributes in the large-scale mountain and high latitude area, and highly sensitive permafrost is located in the perennial river bed, flood plain, and terrace regions. (2) Road construction has a strong thermal disturbance to underlying permafrost, and the proportion of large thaw depth area of separate embankment is obviously smaller than that of 26 m full-width embankment. (3) Increase of subgrade interval reduces the proportion of large thaw depth areas, and the application of separate embankment structure is an effective engineering means for the Qinghai-Tibet expressway.

Study on thermal performance of novel asymmetric crushed-rock-based embankment on the Qinghai-Tibet Railway in permafrost region

Railway embankments in permafrost regions are often affected by serious thaw settlement diseases resulting from permafrost degradation. For this reason, a novel, asymmetric crushed-rock-based embankment (ACBE) structure was employed in the construction of the Qinghai-Tibet Railway in Beiluhe, China, in order to increase cooling capacity and protect the transverse thermal stability of the tracks. This study developed a heat transfer model which accounts for heat conduction occurring in the soil layers and the air convection occurring in its crushed-rock layers. The model helped to reveal the forced convection mechanism of air within the crushed-rock layer. The thermal characteristics of the ACBE for different soil layers were analyzed using ten years of measured data, and its long-term thermal regime was predicted by numerical model. Results indicate that novel ACBE plays a positive role in lifting the permafrost table (PT), lowering the ground temperature surrounding the PT, and maintaining the embankment's temperature distribution symmetry. Novel ACBE is thus an effective, active cooling measure which can mitigate permafrost degradation and transverse non-uniform deformation. These findings provide important guidance for future embankment construction in permafrost regions.

The influence of pavement type on the thermal stability of block-stone embankments in the warm permafrost region

Abstract Based on long-term, continuously monitored data of an expressway, this paper analyzes the influence of pavement types on thermal stability of block-stone embankments with variations of temperature, heat flux, heat budget change, freeze-thaw cycles, permafrost table, and thawing plate area. Results show that closer to the ground, the annual average temperature of the block-stone embankment with asphalt concrete is 0.04–1.99 °C higher than that of cement concrete pavement. Due to the distinct endothermic characteristics of the pavement materials, a block-stone layer with asphalt concrete pavement exhibits a higher temperature and heat budget than cement concrete pavement, causing varied rates of permafrost table’s downward movement, in other words, different growth rates of active layer thickness or thawing plate area. Moreover, the freezing and melting processes of block-stone embankment with different pavements have inconsistent onset times, durations, and offset times. Compared with ordinary embankment, the existence of block-stone layer can greatly raise or slow down the declining of permafrost table, and light-colored cement concrete pavement is more conducive to the thermal stability of embankment. The central active layer and asymmetric thawing plate of the block-stone embankment with cement concrete pavement grows more slowly than that of the asphalt concrete pavement, but this growth has not been eliminated. Rather, it continues at 17.75 cm/a and 8.55 m2/a, compared to 26.75 cm/a and 12.41 m2/a for asphalt concrete pavement. Thus, the block-stone embankments, whether constructed with asphalt concrete pavement or cement concrete pavement, did not entirely ensure the thermal stability. Some reinforcement measures or a composite embankment structure should be adopted to improve the thermal stability of expressway embankments in the warm permafrost region.

STRESS ANALYSIS OF EMBANKMENT DUE TO DIFFERENT IN CONSTRUCTION CONDITIONS

: In recent years, many examples of soil structure collapse due to heavy rainfall have occurred. Because of this, it is urgent to establish a method to evaluate and examine long-term embankment structure quality. Japan's conventional design method insufficiently evaluates embankments. Although this method is shifting to a performance-based design to cope with recent abnormal weather, an effective design method has not yet been established. Therefore, this research performs an initial stress analysis of embankment, accounting for differences in construction conditions. Notable in this study, is the comparative analysis of results, considering the initial water content ratio, one layer of discharge thickness, rolling compaction, and other given structural conditions that differed from conventional design standards. To do this, first the initial moisture content ratio was determined by reproducing the compaction by analysis. Second, based on the dynamics of unsaturated soil, the rainfall intensity was analyzed in order to confirm the variation of the initial stress due to rainfall. Lastly, and most critically, the dynamic change in embankment performance was analytically expressed, and the optimal structural conditions of embankment, grouped by rainfall history, was examined

Numerical Analysis for Liquefaction Deformation of Low Embankment on Soft Foundation Based on Water Level Changes in Coastal Highway

Zhang, X.-G.; Zhu, J.-X.; Zeng, Y.; Jiang, P.; Yi, N.-P.; Yan, L.-E., and Li, Y.-J., 2019. Numerical analysis for liquefaction deformation of low embankment on soft foundation based on water level changes in coastal highway. In: Gong, D.; Zhu, H., and Liu, R. (eds.), Selected Topics in Coastal Research: Engineering, Industry, Economy, and Sustainable Development. Journal of Coastal Research, Special Issue No. 94, pp. 321–326. Coconut Creek (Florida), ISSN 0749-0208.This paper mainly studies the water level change of coastal soft foundation by taking the soft foundation in the liquefaction zone of the Xiniujiao-Dafengjiang section of the coastal first-class highway in Guangxi, China as the research object. To this end, by arranging the saturated silt soft foundation of 6 1.5m inverted trapezoidal gravel wall low embankment structure in the vertical direction, the numerical simulation method was adopted to simulate its liquefaction deformation of the soft foundation problem under the traffic load in the working condition I (constant annual water level) and working condition II (temporary water level rise), and also judge its liquefaction potential, the development and dissipation of the pore water pressure, and the excess pore pressure ratio. Finally, the results show that under different water levels, the gravel-paving on embankment can effectively improve the liquefaction-resistant ability of the soft foundation and improve the uneven settlement of the original compacted fill embankment.

Testing of Subsoil Support in Physical Model of Piled Embankment

Abstract Piled embankment is a type of soil structure that offers convenient technical and cost effective solution for the construction of transport lines in situations when soft soils are present, groundwater is near to surface, or there is an organic unbearable soil profile of significant depth. Other reasons for using pile support for embankment is that total replacement of soft soil is not a cost effective solution or that any other ground improvement techniques are not efficient enough. The article describes continuation of research on pile embankment structure design and its verification by a physical model. Partial support of subsoil and load transfer can be considered in piled embankment structure at some cases of subsoil type. Partial support means that the calculated tensile forces induced in reinforcement on pile heads are lower compared to the case of a very soft subsoil (without subsoil support). After a series of tests of physical models of piled embankments without subsoil support, new models with subsoil support have been prepared. There are many possibilities of simulating soft subsoil, our team decided to use mattress foam which has a non-linear stiffness and this material is convenient for the installation. A foam type was selected to simulate partial soil support for which basic parameters were determined for further research.

Thermal performance of a novel crushed-rock embankment structure for expressway in permafrost regions

The current crushed-rock interlayer structure, which was successfully adopted in construction of the Qinghai-Tibet Railway, cannot maintain the foundation stability of expressways in permafrost regions because of the strong heat absorption of the wide and dark-colored asphalt pavement surface. To satisfy the higher cooling requirement of expressways, a novel crushed-rock interlayer structure, which especially focuses on enhancing the cooling performance on the embankment core, is presented. A heat transfer model, which includes air convection in the crushed-rock interlayer and the heat conduction with a phase change in the soil layers, was developed to simulate the temperature evolution of a full-scale testing expressway embankment section built in Huashixia, the Qinghai-Tibet Plateau. The numerical results indicated that the new structure has a significant cooling performance and especially plays an effective role in lowering the permafrost temperature beneath the centerline of the expressway. Moreover, the new structure has the benefit of maintaining symmetry of the embankment temperature distribution. Therefore, it can be concluded that the new structure is an effective method to prevent permafrost degradation under expressways and can ensure the long-term thermal stability of embankments under the climate warming. The study provides reference and guidance for expressway design and construction in permafrost regions, such as the planned Qinghai-Tibet Expressway.

Use of Constant Energy Source in SASW Test and Its Influence on Seismic Response Analysis

Abstract The quality and acceptability of the results of the spectral analysis of surface waves (SASW) field test are dependent upon the coherence function, in conjunction with the transfer function. The coherence value is a measure of the quality of the test, and the transfer function denotes the phase lag between signals that are received by the geophones. This article presents a methodology for obtaining high-quality field test data, using a source capable of producing constant impact energy for several repeated impact strikes in an SASW test. Both laboratory and field investigations were performed to assess the effectiveness of the constant impact energy source at improving the coherence value. Tests were conducted on the surface of the soil compacted in a metal box and on the crest of an earthen dam using (a) handheld hammers, resulting in variable impact energy and (b) a drop hammer, dropped from a predetermined fixed height, resulting in constant impact energy. The variation in the shear wave velocity (Vs) profile obtained using the two testing methodologies and its impact on the seismic response analysis of an earthen embankment structure were studied. The SASW tests performed in the laboratory using constant impact energy were more efficient and repeatable than those performed using varying impact energy, and the results showed increased coherence values over a wide range of frequencies. A similar improvement in coherence data was observed in the field studies, and the Vs profiles were found to be significantly different for tests conducted using both methodologies. It was observed that the peak and spectral accelerations at the crest of embankments are significantly different when embankments with different Vs profiles are subjected to seismic excitation. This study emphasizes the importance of performing the SASW test, using a constant impact energy source to obtain a reliable estimate of Vs profiles of subsurface layers.

Model test study on the anti-saline effect of the crushed-rock embankment with impermeable geotextile in frozen saline soil regions

In the road construction in frozen saline soil regions, treatments on both permafrost and saline soils are the main challenges to keep the stability of embankments. The crushed-rock embankment was proved to be an effective cooling measure to protect underlying permafrost layers from thawing. In this paper, as a countermeasure to salt migration and salt expansion, impermeable geotextile was added in the crushed-rock embankment. However, little research work has been done on the cooling and anti-saline effects. Thus, the tests of two embankment models, the crushed-rock embankment with impermeable geotextile and the ordinary filling embankment, were carried out to compare this novel embankment structure with ordinary one. The variation characteristics of temperature, moisture, salt and deformation were investigated, and it was found that their variations were a coupled process. The novel embankment structure showed an efficient cooling effect. Meantime, it can efficiently prevent water and salt from migrating to the upper soil layer. More importantly, it can efficiently alleviate frost heaving and salt expansion, and consequently avoid the appearance of longitudinal cracks. The results will provide a good reference to the widespread application of this novel embankment structure in frozen saline soil regions.

Experimental investigation on the enhanced cooling performance of a new crushed-rock revetment embankment in warm permafrost regions

It has been proved that the crushed-rock revetment (CRR), used as technique for improving foundation stability in the Qinghai-Tibet Railway (QTR), produces an insufficient cooling effect on warm permafrost; this may affect the stability of the roadbed and pose a threat to its long-term safe operation, particularly in a warming climate. To solve this problem, a new embankment structure that combines the CRR and a slope thermal protection measure was designed, and a field experiment was carried out in a section of the QTR at Tuotuohe to examine its convection and thermal characteristics and to assess its cooling performance. The experimental results indicate that, compared with the traditional CRR, the new structure has a significantly increased cooling effect on the embankment slope. This is due to an effective prevention of side-slope warming in hot seasons and an enhanced forced convection cooling effect in cold seasons. In addition, this structure prevents sand-filling, which is beneficial in protecting the long-term cooling effect of the CRR on side slopes. This study provides valuable guidelines for the design and maintenance of roadbeds in warm permafrost regions.

The Impact of Engineering-geologic Conditions on the Development of Railway Subgrade Design Solutions

An analysis of hydro-meteorological and engineering-geological conditions of the Russia's Eastern Siberia and the Far East is provided in the article.To assess the disruptive effect of earthquakes on the railway track elements a unified parameter is selected – the magnitude of admissible stress σr. A multi-factor research is conducted for the fixed seismicity value of 8 points. The analysis of stability is based on the formula by G.M. Shakhunyants accounting for seismicity.Basing on the analysis performed the optimal design solutions for embankments with account of soil conditions and earthquake effects are proposed. Recommendations for the embankment structure's optimization are given.

Time-lapse monitoring of fluid-induced geophysical property variations within an unstable earthwork using P-wave refraction

A significant portion of the UK’s transportation system relies on a network of geotechnical earthworks (cuttings and embankments) that were constructed more than 100 years ago, whose stability is affected by the change in precipitation patterns experienced over the past few decades. The vulnerability of these structures requires a reliable, cost- and time-effective monitoring of their geomechanical condition. We have assessed the potential application of P-wave refraction for tracking the seasonal variations of seismic properties within an aged clay-filled railway embankment, located in southwest England. Seismic data were acquired repeatedly along the crest of the earthwork at regular time intervals, for a total period of 16 months. P-wave first-break times were picked from all available recorded traces, to obtain a set of hodocrones referenced to the same spatial locations, for various dates along the surveyed period of time. Traveltimes extracted from each acquisition were then compared to track the pattern of their temporal variability. The relevance of such variations over time was compared with the data experimental uncertainty. The multiple set of hodocrones was subsequently inverted using a tomographic approach, to retrieve a time-lapse model of [Formula: see text] for the embankment structure. To directly compare the reconstructed [Formula: see text] sections, identical initial models and spatial regularization were used for the inversion of all available data sets. A consistent temporal trend for P-wave traveltimes, and consequently for the reconstructed [Formula: see text] models, was identified. This pattern could be related to the seasonal distribution of precipitation and soil-water content measured on site.

Time-lapse monitoring of climate effects on earthworks using surface waves

The UK’s transportation network is supported by critical geotechnical assets (cuttings/embankments/dams) that require sustainable, cost-effective management, while maintaining an appropriate service level to meet social, economic, and environmental needs. Recent effects of extreme weather on these geotechnical assets have highlighted their vulnerability to climate variations. We have assessed the potential of surface wave data to portray the climate-related variations in mechanical properties of a clay-filled railway embankment. Seismic data were acquired bimonthly from July 2013 to November 2014 along the crest of a heritage railway embankment in southwest England. For each acquisition, the collected data were first processed to obtain a set of Rayleigh-wave dispersion and attenuation curves, referenced to the same spatial locations. These data were then analyzed to identify a coherent trend in their spatial and temporal variability. The relevance of the observed temporal variations was also verified with respect to the experimental data uncertainties. Finally, the surface wave dispersion data sets were inverted to reconstruct a time-lapse model of S-wave velocity for the embankment structure, using a least-squares laterally constrained inversion scheme. A key point of the inversion process was constituted by the estimation of a suitable initial model and the selection of adequate levels of spatial regularization. The initial model and the strength of spatial smoothing were then kept constant throughout the processing of all available data sets to ensure homogeneity of the procedure and comparability among the obtained [Formula: see text] sections. A continuous and coherent temporal pattern of surface wave data, and consequently of the reconstructed [Formula: see text] models, was identified. This pattern is related to the seasonal distribution of precipitation and soil water content measured on site.

Risk assessment and economic appraisal of protection methods for the Tarascon-Arles railway embankment

The coordination of flood management practices and the reduction of flood risk as proposed under the Plan Rhone project has led to a vast program of flood defence modernization and construction in the lower Rhone valley. One key element of the project involves the construction of a new 9km levee structure parallel to an existing railway line between the towns of Tarascon and Arles (Bouches-du-Rhone, France ) on the left bank of the Rhone, which has historically been an obstacle to the propagation of flood flows. The new levee is designed to protect the towns of Arles and Tarascon up to the 10−2 annual probability flood event, after which floodwater will flow over a 5km spillway which will be integrated into the structure. In case of overtopping of the spillway via a spillway structure, floodwater is collected in the space between the two embankments and will subsequently flow towards one of ten newly constructed flood discharge structures, spaced at regular intervals in the railway embankment. The levee will form part of a global system of defence which is designed against flooding on the Rhone with an annual probability of occurrence of 10−3 . In the event of overtopping of the levee, the railway embankment will be subjected to hydraulic loading and is at risk of damage from flood flows. During the detailed design phase of the project, options were explored for optimizing the permanent protection for the railway embankment. Using results from 2D and 3D hydraulic numerical modelling, a detailed risk assessment of the railway embankment was undertaken to evaluate its vulnerability under different hydraulic loading conditions and for different failure mechanisms using various parameters including water depth, hydraulic load, the duration of flood exposure and flow velocity. A comprehensive understanding of the main mechanisms of embankment damage under hydraulic loading (internal/ external erosion, overtopping, rotational failure etc.), existing geotechnical conditions and the railway embankment structure were required to undertake the risk assessment. For each hydraulic loading scenario, a detailed economic appraisal was undertaken for each method of protection involving the evaluation of damages associated with disruption to train services and the associated costs to repair the structure. The final stage of the project involved integrating the economic assessment into a wider reaching multi-criteria analysis including indicators for train security, maintainability and environmental impact aspects. The multi-criteria approach was tested under two management strategies to evaluate the effectiveness of each embankment protection system. This paper outlines how the risk assessment, economic appraisal and management-strategy based multi-criteria approach resulted in a highly optimized system of embankment protection with significant gains in terms of both reduced cost of implementation and environmental enhancement whilst maintaining the high levels of railway security required by SNCF-RESEAU.

Assessment of Vertical Deformation of the Atatürk Dam Using Geodetic Observations

AbstractThe Ataturk Dam in Turkey, constructed on the Firat River, is one of the world’s largest rockfill embankment dams. It was built to harvest and conserve water and to serve crucial agricultural, social-economic, recreational, and other activities in the Harran region. In this study, geodetic techniques were exploited to assess possible deformations of the embankment structure and add insight on critical dam safety. The geodetic approach included differential, trigonometric, and global positioning system (GPS) leveling observation campaigns over a period of 6.5 years from May 2006 through November 2012. The geodetic control network included 32 reference points and approximately 200 object points located on the surface of the embankment structure. The primary object points were stable concrete platforms embedded on the compacted rock surface, whereas the secondary object points were mounted directly to the compacted rock. All object points were equipped with forced centering mechanisms to support eith...

The Dynamic Analysis of Soft Soil Subgrade in High-Speed Railway Strengthened by PHC Pile

The combination of PHC pile (prestressed concrete pile) with geogrid to reinforce the foundation has been widely used in high-speed railway, and the response of dynamic stress under the high-speed train is worth studying. By using Midas/GTS NX software to establish a 3-D model of pile-net composite foundation in one section of Hangzhou - Shenzhen line, the influence of pile-net composite foundation generated by high-speed train is studied. Moreover, this paper also studies the distribution and propagation of dynamic stress generated by train load in soft soil area. The results show that the dynamic stress reducing quickly in the embankment structure and the time –history curve of the dynamic stress behaves differently along the depth. With the depth increasing, there is phenomenon of peak superposition in the time-history curve of the vertical dynamic stress. In the meanwhile, the PHC pile is the main structure to propagate and sustain the dynamic stress in soft soil area, and with the tendency of ‘large in the middle, small on both ends’.