Embankment Structure Research Articles

Thermal stability analysis of crushed-rock embankments on a slope in permafrost regions

Highways/railways often pass across slope areas and their embankments are often built on the slopes in permafrost regions. It is difficult to ensure the thermal stability of the embankments at the slopes due to the effect of slopes. To protect the underlying permafrost, the crushed-rock embankments are often used in the slope areas. Therefore, it is very necessary to explore the thermal state of crushed-rock embankments located on the slopes. In this study, we studied numerically the temperature characteristics of three kinds of crushed-rock embankments located on a slope under global warming, i.e. crushed-rock interlay embankment, crushed-rock interlayer-revetment embankment and crushed-rock base embankment. Numerical results indicate that the crushed-rock interlayer embankment and the crushed-rock interlayer-revetment embankment, located on a slope with a ratio of 1:3.73 (about 15° from the horizontal), cannot effectively eliminate the negative effect of climate warming and construction-induced warming, and the effect of slope is still obvious on the thermal stability of permafrost under the crushed-rock interlayer embankment. However, the crushed-rock base embankment can significantly reduce the temperature of underlying permafrost and keep the underlying permafrost table stable for a long term; furthermore, the ground temperatures under the long side slope are far lower than those under the short side slope, and this will be more advantageous to control the slide of the embankment located on a slope and increase its stability. We also find that the three kinds of embankments cannot all remove the thermal effects of construction from themselves in a short term. Generally speaking, the crushed-rock base embankment structure can be very advantageous to the thermal stability of the embankment on a slope.

Experimental investigation on porosity reduction of a coarsely crushed rock layer subject to vertically cyclic loading

The long-term cyclic loadings from traffic and maintenance may weaken the occurrence of buoyancy-driven natural convection of the pore air in the coarsely crushed rock layer during winter months and the effectiveness of cooling down the embankment and underlying foundation soils, thus resulting in instability and failure of the highway/railway embankment structure. Obviously, successful application of the coarsely crushed rock embankments in cold regions has to study both theoretically and experimentally the impact of cyclic loadings on the particle shape, grain size distribution and rearrangement of the crushed rock aggregates and the porosity variation of coarsely crushed rock layer. Therefore, some experiments on the crushed rock samples with dimensions of 75×75×87cm under vertically cyclic loadings have been carried out. Three coarsely crushed rock samples with initial grain sizes of 16–40, 25–50 and 50–80mm were used to measure the related parameters to study their variations in cooling capability after the vertically cyclic loadings, respectively. The experimental approach on examining the particle shape and grain size distribution variations and the rearrangement of the crushed rock aggregates and the porosity reduction of the crushed rock layer under vertically cyclic loadings is developed. The porosities of three crushed rock samples with vibrating loading cycles have been measured using the water flooding approach.The results show that the cyclic vibrating loadings can cause the breakage and abrasion of the particles and their edges in the coarsely crushed rock layer and the particles also tend to be rounding and non-angular. These result in rearranging of particles and decreasing of particle size and increasing of fines content in the coarsely crushed rock layer, thus reducing the porosity of the crushed rock layer. Compared with the initial average porosities before cyclic loading, the reduction rates of final average porosity in three crushed rock samples after cyclic loading with 18,000cycles reach to 6.53, 7.45 and 8.08% corresponding to initial grain sizes of 16–40, 25–50 and 50–80mm, respectively. These reduction rates of the final average porosities in the vibrated crushed rock samples after cyclic loading increase relatively with increasing of an initial grain size. Under such conditions, the long-term cyclic loadings from traffic and maintenance can weaken the effectiveness of cooling down the embankment and underlying foundation soils due to natural convection in the coarsely crushed rock layer during winter months.

Finite Element Analysis of Pier Top Horizontal Displacement Caused by Newly-Built Road under High-Speed Railway Bridge

In order to meet the requirements of high-speed train's safe operation, the horizontal displacement of high-speed railway bridge pier top must be strictly controlled. This paper relies on one road construction engineering beneath an existing high-speed railway bridge. We use 2D finite element software to analyze the magnitude and direction of pier top horizontal displacement caused by road load. We take it into account that the effect of the soil nature on pier top horizontal displacement. The analysis showed that the nature of soil around piles of high-speed railway bridge is closely related to the magnitude and direction of the pier top horizontal displacement. Authors believe that the horizontal displacement of pier top consists of two parts. One is pier top pure horizontal displacement dragged by horizontal displacement of the top of piles, the other is pier top rotation horizontal displacement driven by the rotation of pile cap. The analysis result can be used for the design of road with embankment structure beneath high-speed railway bridge.

Study on Young's Modulus of Geomaterials used in Korean Railway Infrastructures

In this study, cyclic triaxial tests were carried out with the coarse granular materials used in Korean railway infrastructure (reinforced trackbed, gravel of transition zone, upper subgrade of railway) and Young's modulus for the target materials in small strain level were suggested. And the result of elastic modulus suggested in this study is expected to be effectively applied to dynamic analysis of the railway embankment structure using similar material, since the grain size distributions and unit weight of the material tested in this study are specified in Korean Railway Design Criteria.

Geometric and frequency EMI sounding of estuarine earthen flood defence embankments in Ireland using 1D inversion models

Abstract Earthen flood defence embankments are linear structures, raised above the flood plain, that are commonly used as flood defences in rural settings; these are often relatively old structures constructed using locally garnered material and of which little is known in terms of design and construction. Alarmingly, it is generally reported that a number of urban developments have expanded to previously rural areas; hence, acquiring knowledge about the flood defences protecting these areas has risen significantly in the agendas of basin and asset managers. This paper focusses, by reporting two case studies, on electromagnetic induction (EMI) methods that would efficiently complement routine visual inspections and would represent a first step to more detailed investigations. Evaluation of the results is presented by comparison with ERT profiles and intrusive investigation data. The EM data, acquired using a GEM-2 apparatus for frequency sounding and an EM-31 apparatus for geometrical sounding, has been handled using the prototype eGMS software tool, being developed by the eGMS international research consortium; the depth sounding data interpretation was assisted by 1D inversions obtained with the EM1DFM software developed by the University of British Columbia. Although both sounding methods showed some limitations, the models obtained were consistent with ERT models and the techniques were useful screening methods for the identification of areas of interest, such as material interfaces or potential seepage areas, within the embankment structure: 1D modelling improved the rapid assessment of earthen flood defence embankments in an estuarine environment; evidence that EMI sounding could play an important role as a monitoring tool or as a first step towards more detailed investigations.

Forensic analysis of the failure of the foundations of a tunnel built to channel the course of a river

This paper presents the results of a forensic analysis of a tunnel above which an embankment was built that served as a roadbed. The joint tunnel–embankment structure is located on the outskirts of the town of Piedrafita in northwestern Spain. The tunnel channels the course of the River Vilela in its crossing of the aforementioned road.This article presents a detailed report of the problem, including the damage caused to the structure of the tunnel and the embankment, and it presents the measurements taken and the determination of the origin of the problem. For this determination, a numerical simulation of the joint tunnel–embankment–ground structure was conducted on the basis of the data obtained from tests carried out both in situ and in the laboratory. The study was complemented by an analysis performed using classical methods that confirmed that the movements detected in the overall structure were caused by the collapse of the foundations.The uniqueness of the study presented in this paper lies in the combination of very simple analytical calculations to evaluate the stresses transmitted by the foundations to the ground with a numerical model that enables us to evaluate the stress and deformational state of the study area in a highly detailed way.

海岸堤防の構造に依存した津波被害と数値モデルによる検証

海岸堤防の構造に依存した津波被害と数値モデルによる検証

Nonlinear numerical simulation of rainwater infiltration through road embankments by FEM

This paper presents the results of nonlinear numerical simulations carried out to analyze rainwater infiltration through a road embankment structure using the finite element method (FEM) technique. The analysis of this paper includes a simplification of a cross-sectional road embankment located in Santander (Northern Spain) and considers different realistic hydraulic material parameters, according to the relevant literature, in order to study their effect on water movement throughout the section over time. The model solved the nonlinear Richards’ equation using the constitutive relationships of van Genuchten–Mualem. Finally, the analysis of the numerical results reveals four main conclusions: (1) models based on FEM are suitable for analyzing rainwater infiltration in road structures, (2) the hard-shoulder area of the highway represents an important infiltration point for rainwater in road structures, (3) the embankment material can greatly affect the soil’s water content in this part of the road, and (4) the analysis of the soil water retention curve of the embankment material provides relevant information about its hydraulic behavior under unsaturated conditions.

Influence of Soil Parameters to Numerical Simulation Results of Double-Sided Upright Embankment Structure

Influence of Soil Parameters to Numerical Simulation Results of Double-Sided Upright Embankment Structure

Influence of Soil Parameters to Numerical Simulation Results of Double-Sided Upright Embankment Structure

Influence of Soil Parameters to Numerical Simulation Results of Double-Sided Upright Embankment Structure

Similitude Conditions Modeling Geosynthetic-Reinforced Piled Embankments Using FEM and FDM Techniques

The numerical modelling of geosynthetic-reinforced piled embankments using both the finite element method (FEM) and finite difference method (FDM) are compared. Plaxis 2D (FEM) was utilized to replicate FLAC (FDM) analysis originally presented by Han and Gabr on a unit cell axisymmetric model within a geosynthetic reinforced piled embankment (GRPE). The FEM and FED techniques were found to be in reasonable agreement, in both characteristic trend and absolute value. FEM consistently replicated the FDM outputs for deformational, loading, and load transfer mechanism (soil arching) response within the reinforced piled embankment structure with a reasonable degree of accuracy. However the FDM approach was found to give a slightly higher reinforcement tension and stress concentration but lower reinforcement strain at the pile cap than FEM, which was attributed to the greater discretize of the model geometry in the FDM than in FEM.

Dynamic Analysis of the Piled Embankment under Seismic Excitations

Aiming at discussing the behavior of piled embankment under seismic excitations, the numerical analysis model is built by employing ADINA. The interaction of embankment backfill with piles and subsoil is considered. And Coulomb contact pairs based on penalty algorithm is adopted to simulate the contact behavior between pile and soil. Through the varieties of relative displacement and acceleration of embankment structure acted by earthquake loads are analyzed, the weakness of structure is marked and corresponding design suggestion is proposed. It reveals that the displacement and acceleration response of embankment vary non-monotonically, and the peak value of acceleration response of pile firstly increases and then decreases with height of pile, and one of displacement response relative to pile bottom firstly increases and then decreases as well.

A new structure to control frost boiling and frost heave of embankments in cold regions

Frost boiling and frost heave are the main factors that cause road damage in cold regions. A new kind of embankment structure, which consists of geotextile, crushed-rock layer and geomembrane, was designed and investigated both in the laboratory and at the field of Budongquan located at Qinghai–Tibet Plateau. Comparison tests were conducted at the same time. The key of the new structure is the porous crushed-rock layer which has smaller thermal conductivity with function of drainage and blocking of moisture migration induced by freezing. Both the laboratory and field research results show that the frost penetration and thawing depths of the new structural embankment are much smaller than those of the coarse-grained soil embankment. Also, the new embankment structure has lower water content in the upper layer and smaller frost heave and thawing settlement than the latter does. In addition, it has good drainage effect. Water coming from the road surface can be drained away from the embankment through the porous crushed-rock layer. All these states that the new structure consisting of the porous crushed-rock layer is superior in frost damage mitigation to the normal structure used in cold regions.

Cooling processes and effects of crushed rock embankment along the Qinghai–Tibet Railway in permafrost regions

Crushed rock embankment (CRE) was most prevalent embankment structure with cooling measures along the Qinghai–Tibet Railway in permafrost regions. Ground temperature dataset from embankment construction (in 2002) to 2010 at nine monitoring sites along the railway were compiled to study long term cooling processes and cooling effects of CRE. Monitoring results indicated that the heat stored in filling materials could dissipate out in two cold seasons after embankment construction. Under cooling effect of CRE, permafrost tables beneath CRE moved upwards significantly during the first three years after embankment construction and then maintain almost constant. But underlying permafrost experienced different thermal process in relative warm and cold permafrost regions. In cold regions, underlying permafrost up to 14 m in depth experienced considerable cooling trends during the first five to sixth years after embankment construction. While in warm regions, the uppermost permafrost layer warmed after upwards movement of permafrost table, and underlying deep permafrost had no obvious cooling trends with time. Finally, differences in freezing and thawing seasons of, and differences in ground thermal regimes of cold and warm permafrost regions were investigated based on ground temperature from natural borehole. Then, the different cooling effects of CRE in two regions were interpreted based on these differences.

Design of embankment–structure transitions for railway infrastructure

The introduction of a structure (bridge, viaduct) along a railway represents a transition point with an abrupt change in the vertical stiffness from one transverse section to another. This condition is even more important in high-speed railway, since the layout criteria are stricter than for conventional train lines. However, in many cases, it is nevertheless necessary to construct a structure (viaduct, bridge). This paper presents the key ideas that explain the atypical behaviour exhibited by embankment–structure transitions and demonstrates the influence that longitudinal variations in vertical stiffness have on track deterioration. The deterioration problem remains unsolved and, at present, there are no common design solutions employed by the different European railway administrations. In the present study, three-dimensional numerical simulations of designs, which are currently employed in embankment–structure transitions, are generated using the finite-element method. Analysis of the results leads to design recommendations that can be used by railway infrastructure designers when designing embankment–structure transitions.

Effect of Vibrating Load on Grain Size Distribution of Crushed Rock Layer

For the construction of the proposed Qinghai-Tibet Express Highway in warm and ice-rich permafrost regions, it will be necessary to utilize the new technique of cooling the ground temperature by the coarsely crushed rock layer with a low fines content, instead of the traditional measures taken to increase simply thermal resistances, so as to protect from damage to highway embankment due to thaw settlement. The vibrating loads such as wheel load and tamping load may cause the breakage and abrasion of the matrix grains in the coarsely crushed rock layer. This results in decreasing of grain size and increasing of fines content in the crushed rock layer, thus decreasing the porosity of crushed rock layer. The smaller porosity of crushed rock layer may weaken the cooling effect of buoyancy-driven natural convection of the pore air in the crushed rock layer of the highway embankment, thus resulting in instability and failure of the embankment structure in permafrost regions. Under these conditions, the influence of vibrating load on the grain size distribution of the coarsely crushed rock layer has to be investigated experimentally. In the present study, laboratory experiments on the grain size variation of the coarsely crushed rock layer under vertically vibrating loads were carried out. The test results show that the vibrating load can cause the breakage and abrasion of the matrix grains in the coarsely crushed rock layer and the shapes of coarely crushed rock grain tend to be non-angular.

Laboratory Experiment on Porosity Variation of Crushed Rock Layer under Vibrating Load

Under the background of the express-reconstruction of the Qinghai-Tibet Highway being proposed, it will be necessary to employ the special technique of cooling the ground temperature by the crushed rock embankment in order to protect from damage to highway embankment due to thaw settlement. Under vibrating load, the porosity variation of crushed rock layer may weaken the cooling effect of buoyancy-driven natural convection of the pore air in the crushed rock layer of the highway embankment, thus resulting in instability and failure of the road embankment structure. Under these conditions, the effect of vibrating load on the porosity of the crushed rock layer must be studied both theorectically and experimentally. In this work, laboratory experiment on the porosity variation of the crushed rock layer under vertically vibrating loads is developed based on the water flooding approach and the experimental method is introduced. The test results indicate that due to the vibrating load the crushed rock layer causes the compacting effect and the shapes of crushed rock grain tend to be non- angular.

Discussion of “Hydraulics of Broad-Crested Weirs with Varying Side Slopes” by J. E. Sargison and A. Percy

The hydraulics of broad-crested weirs is influenced by the weir inflow design. It is highlighted herein that the inflow geometry including the rounding of the weir upstream edge has a marked effect on the flow pattern and discharge coefficient. In the case of an upstream vertical wall, the optimum design includes a rounded upstream corner (Harrison 1967, Bos 1976, Montes 1998). An upstream side slope may provide an alternative design for embankment structure although with a lower discharge coefficient (Sargison and Percy 2009).

Embankment structure “Hantiku” in castle masonry stone wall and their seismic stability

Embankment structure “Hantiku” in castle masonry stone wall and their seismic stability

Numerical study on temperature characteristics of expressway embankment with crushed-rock revetment and ventilated ducts in warm permafrost regions

The crushed-rock revetment embankment and duct-ventilated embankment, as effective cooling measures, have been used to protect the underlying permafrost from thawing in Qinghai–Tibet Railway construction of China. However, the two cooling measures cannot be directly applied to the expressways with a wide and high-temperature pavement surface in warm permafrost regions. Therefore, considering the heat transfer characteristics of crushed-rock revetment embankment and duct-ventilated embankment, we designed a new-type embankment with crushed-rock revetment and ventilated ducts. For cold regions engineering, the temperature is the most important factor that determines the stability of construction. To research the thermal stability of the new-type embankment, according to the related theories of heat and mass transfer, a three-dimensional theoretical and numerical model for the embankment, which is composed of the coupled heat transfer problem between airflow and duct wall, the air convective heat transfer problem within crushed-rock layer, and the heat conduction problem with phase change in soil layers, was presented to analyze the temperature characteristics of the new-type embankment. Three points can be concluded from the numerical results based on the assumption that the air temperature will be warmed up by 2.6 °C in the next 50 years. First, the crushed-rock revetment embankment would be unstable because the crushed-rock revetment can reduce only the ground temperature at the side-slope foots of embankment, but the permafrost table descends severely in the middle. Second, the ventilated-duct embankment can effectively cool the soil at the middle of the embankment but not at the side-slope foots, so that the uneven temperature distributions would be deleterious to the stability of expressway. Third, the new-type embankment structure is effective to decrease the underlying ground temperature and to ensure the stability of expressway with a wide (multi-lane) and high-temperature upper surface in warm permafrost regions.