Embankment Surface Research Articles

Diffused arching in embankments supported by non-compliant columns with capping beams

A column-supporting system for embankments on soft soils is analyzed using the Finite Element Method. The numerical problem has boundary conditions similar to that of a trap-door, but, contrary to the classical trap-door studies, the focus in this paper is on the load transfer to the supporting columns measured by the system efficacy, and on the critical embankment height that prevents differential settlements on the embankment surface. The stress state simulated in the embankment rapidly evolves in the first stages of the soft soil settlement, measured by millimeters, but the changes to the elastic–plastic stress field developed are marginal in the subsequent stages of settlement simulated up to 10 cm. The displacement field in low embankments with a height comparable to the column spacing is dominated by the failure mechanism with shear bands reaching the embankment crown, causing differential settlements on the embankment surface. In higher embankments, the failure mechanism is confined to the lower portion of the fill, and no differential settlements were detected on the embankment surface. It was suggested that a hypothetical diffused soil arch formed above the failure mechanism, with a shape approximately following the principal stress trajectories. This conjecture was made based on the presence of elevated stress along the symmetry plane of the embankment-column periodic cell. Numbers related to system efficacy and critical height are reported for a limited set of model parameters, but the qualitative outcome of the study is likely applicable to a wider variety of embankments.

LARGE-SCALE OPEN-CHANNEL EXPERIMENTS ON THE COLLAPSE OF ABUTMENT BACKFILL OWING TO FLOODS AND PROPOSED COUNTERMEASURE

In Japan, great damage to abutment backfills caused by large-scale floods occurs every year. It is necessary to examine the fundamental collapse mechanism on as close to full scale as possible, in order to achieve a sufficient effect of the similarity laws in geotechnical engineering, river engineering, and bridge engineering. In this study, geotechnical evaluations were carried out, such as observation of pore water pressure behavior in an embankment, settlement of an embankment crest, and applicability of a reinforced soil wall as a countermeasure construction, under conditions affected by flowing water. The results show that the collapse behavior of an embankment surface differs depending on the soil properties of the embankment material. The erosion of the river bed progressed even in the footing lower surface of the abutment foundation and in the upstream side of the abutment, where the flow velocity was locally large and changes in the flow direction were confirmed. In addition, when a gabion-reinforced earth wall with water permeability was used for the wall surface construction as a countermeasure, washout of the embankment in the abutment to the extent that a pavement surface above would collapse did not occur, thereby confirming the gabion’s usefulness as a countermeasure.

Roller compaction of rock-fill with automatic frequency control

A new intelligent compaction method for vibratory soil compaction rollers that automatically and continuously adjusts the vibration frequency to obtain resonance in the coupled roller–soil system was evaluated in full-scale field tests on a 1 m high rock-fill embankment. This method has been called automatic frequency control (AFC). Compacting at the resonant frequency results in maximised deformations in the soil by optimising the dynamic behaviour of the system and improving the interaction between the drum and the soil. The embankment was also compacted conventionally at a fixed standard frequency in order to quantify the difference between the two methods. Applying AFC resulted in a higher degree of compaction of the embankment layer. The effect was most significant at the top of the embankment, where considerable compression was obtained – in contrast to the very loose material resulting from conventional compaction – thus eliminating the need for subsequent static passes. Spot tests showed a considerably stiffer embankment surface after a high number of passes using AFC. Other observed benefits of AFC include a more homogeneously compacted embankment, which benefits long-term behaviour, up to 15% reduced fuel consumption, reduced environmental impact and less machine wear.

Geosynthetic-reinforced pile-embankments: numerical, analytical and centrifuge modelling

This paper presents numerical and analytical models to complement experimental data obtained from 40 centrifuge tests of geosynthetic-reinforced piled embankments, 12 of which had a surcharge applied at the embankment surface. The main parameters of study were pile diameter, pile spacing, embankment height and geosynthetic stiffness. The tests measured the force transferred to the piles, the embankment surface settlements and the maximum geosynthetic reinforcement deflections below the embankment under conditions without any support from the underlying soil. Maximum geosynthetic deflections measured longitudinally between piles were then compared with values predicted by European design guidelines. A 3D numerical model, initially validated by centrifuge tests, was then used to compute those geosynthetic tensile forces not measured in the reduced-scale physical models. Numerical values of geosynthetic tensile forces were also compared with corresponding values predicted by European guidelines.

Experimental and numerical analyses of lightweight foamed concrete as filler for widening embankment

In order to control the differential settlement between the existing and widened embankments, lightweight foamed concrete (LWFC) was proposed as a filler of the widened embankment to decrease its self-weight. A series of compressive strength tests, dynamic triaxial tests, dry–wet cycle tests, and water immersion tests were performed to analyze the variation of the LWFC strength with design dry density and the influence of water and adding glass fiber (GF) on the properties of the LWFC. Then two centrifugal models of the widened embankment, which was filled with the LWFC and traditional soil respectively, and their numerical models were established in this study. The results show that water adversely affects the LWFC strength. A lower density for LWFC is corresponded by greater compressive strength loss after the LWFC underwent 15 dry–wet cycles. When the LWFC with a design dry density of 300–800 kg/m3 was immersed in dead water, the compressive strength and dynamic stress threshold ratios of the LWFC decrease quickly at first and then increases slightly with increasing soaking days. While the LWFC was immersed in live water, these parameters gradually stabilize for a design dry density of no less than 600 kg/m3 and decrease for a design dry density of less than 500 kg/m3 with increasing soaking days. Mixing GF into the LWFC can significantly improve the compressive strength and dynamic stress threshold and reduce the influence of water. Furthermore, the use of the LWFC as a filler of the widened embankment can significantly decrease the settlement of the embankment surface, soil pressure on the foundation surface, and horizontal deformation of the foundation compared to the traditional soil used as filler for widening embankment.

Structure Functions of Pseudo Null Curves in Minkowski 3-Space

In this work, the embankment surfaces with pseudo null base curves are investigated in Minkowski 3-space. The representation formula of pseudo null curves is obtained via the defined structure functions and the k-type pseudo null helices are discussed completely. Based on the theories of pseudo null curves, a class of embankment surfaces are constructed and characterized by the structure functions of the pseudo null base curves.

Mapping of leakage paths in damaged embankment using modified resistivity array method

The cause and path of leakage in a damaged embankment in Korea were interpreted through integrated 3-D resistivity inversion. Data from a modified electrical resistivity survey were analyzed for cross potential array, direct potential array, and D-Lux array. These proposed modified arrays used line source, point source, and borehole source for data acquisition in the embankment. The modified electrical resistivity survey is a method to predict the path of a leakage by connecting the regions where the current flow gathers, and the potential difference is reduced when the current flows through the embankment. Therefore, this method takes the potential differences as data and calculates the potential distribution for the target area to interpret the path of the current flow. Analysis of the modified survey data revealed the existence of two zones suspected of leakage in the downstream slope. One region was identified as an end drainage pipe, and the other was the right abutment, where the leakage occurred. The 3-D inversion model was built through modified electrical resistivity tomography. In the 3-D model, the resistivity anomaly at the right abutment matched a low-resistivity zone in the modified survey data, and it means that the results of traditional 3-D survey support those of the modified electrical resistivity survey. For reliability of interpretation, we verified the findings based on the evidence of actual leakage on the embankment surface. Through comparative analysis, the cause and route of leakage of the fill dam could be predicted and verified.

Embankment Surfaces in Euclidean 3-Space and Their Visualizations

In the present paper, we obtain the parametric representation of an embankment surface and give an example for it. We define the notions of embankmentlike surfaces and tubembankmentlike surfaces. Furthermore, we create some embankmentlike and tubembankmentlike surface examples with the aid of different directrix and draw these directrix and surfaces. Also, we find the Gaussian, mean and second Gaussian curvatures of these surfaces and draw the Gaussian, mean and second Gaussian curvature functions’ graphics and the variations of Gaussian, mean and second Gaussian curvatures on related surfaces with the aid of Mathematica.

Characteristics of wave attenuation due to roughness of stepped obstacles

ABSTRACT In this study, we investigated the energy dissipation characteristics of stepped obstacles by using both the regular and irregular waves in a physical wave flume. The stepped obstacle used in this study is different from those of traditional stepped dikes with fixed horizontal and vertical stage surfaces; here, the angle of the stepped surface varies with the slope of the embankment surface, with various interaction angles between the incident waves and the rough stepped surfaces. The stepped embankments were composed of six types of stepped arrangements and were used to analyse the wave run-up heights and reflection coefficients; in addition, the variations in energy dissipation effects were also studied. The results identify two of the six roughness types that have better mitigation effects on the investigated the energy dissipation characteristics of stepped obstacles. The reflection coefficient is larger for a submerged dike with a rough surface than for one with a smooth surface.

Settlement and Vertical Load Transfer in Column-Supported Embankments

Column-supported embankments (CSEs) with or without a load-transfer platform (LTP) can reduce settlements, improve stability, and prevent damage to adjacent facilities when embankments are constructed on ground that would otherwise be too weak or compressible to support the new load. CSEs function by transferring the embankment load to the columns through stress redistribution above and below the foundation subgrade level. Mobilization of load-transfer mechanisms to the columns requires differential settlement at the base of the embankment between the stiff columns and foundation soils. This paper presents the load-displacement compatibility (LDC) analysis method, which estimates the transfer of vertical loads by (1) arching within the embankment fill, (2) the vertical component of tension developed in the geosynthetic reinforcement within the LTP, and (3) negative skin friction acting along the column. The LDC method incorporates the vertical displacements that accompany load transfer by considering nonlinear consolidation of the soft foundation soil, elastic compression of the columns, out-of-plane deformation of geosynthetic layers, and settlement of the embankment surface in compliance with the differential settlement at the embankment base. This paper also presents recommendations for estimating the critical height of the embankment, which is the minimum embankment height above the columns to avoid poor ride quality resulting from differential settlement at the surface of the embankment produced by differential settlements at the base of the embankment. Estimates of load transfer and reinforcement strain using the LDC method are compared to measurements from 15 full-scale embankments.

Identification of the Causes of a Landslide in Koronowo (Polish Lowlands)

Abstract The paper discusses difficulties of identifying the causes of a landslide. These difficulties are illustrated in the example of a catastrophic landslide on the embankment of the western bank of the Brda River, which affected a bridge abutment of a disused narrow-gauge railway line from Bydgoszcz to Koronowo (Polish Lowlands). The railway was closed in 1992, and after the removal of the track, the bridge served as a pedestrian overpass. The landslide occurred in February 2011. Investigations revealed that the first signs of the landslide were cracks and subsidence that appeared at the embankment crest. Then, an initially slow movement accelerated suddenly, resulting in an over 45 m total displacement of the soil mass. The primary passive cause of the landslide movement resulted from the geology of the mass (loose soils underlain by cohesive soils) and from the steep inclination of the embankment surface. Active causes, however, are often ambiguous. In this case, no significant apparent phenomena which could trigger the movement occurred in the days preceding its initiation. Therefore, a detailed analysis of atmospheric conditions was carried out to identify and explain the causes. It was proved that the fundamental triggering cause of the landslide was a combination of rainfall, snowfall, snow-melting and air temperature. Moreover, an important cause was a faulty construction of a ditch with a sewage pipe on the crest of the embankment.

Response of stone column-improved ground under c-ϕ soil embankment

Problems with stone column-supported embankments are often addressed considering the pure granular soil properties of the embankment material. In practice, however, the embankment material may contain a certain percentage of fines which makes the material c-ϕ in nature. In the present paper, experimental and 3D numerical studies are conducted to investigate the effect of the fines content present in the embankment soil on the response of a stone column-improved ground. The numerical study is carried out using the finite difference software package FLAC3D. The time-dependent behavior of the improved soil is modeled. It is observed that an increase in the fines content in the embankment soil brings about a decrease in the stress concentration ratio and an increase in the vertical displacement and the pore pressure in the soft soil. However, the vertical displacement of the soft soil does not change significantly above a fines content of 20%. The lateral displacement of the stone column increases at the top with an increase in the fines content and the point of the maximum lateral displacement shifts in the downward direction. It is also observed that the differential settlement increases at the ground level as well as at the embankment top with an increase in the quantity of fines in the embankment soil. Thus, the critical height of the embankment (a height where no differential settlement occurs on the embankment surface) increases due to the increase in the fines content.

Analysis of the Embankment Stability in Permafrost Regions based on Double Strength Reduction Finite Element Method

In order to study the embankment stability in permafrost regions, the vertical deepening and horizontal extension of the thaw bulb under the embankment in permafrost regions have been calculated and analyzed based on the double strength reduction finite element method. The vertical depth of the thaw bulb has less impact on the location of longitudinal cracks, and greater impact on the size of cracks on the embankment surface. Moreover, the deeper the vertical depth of the thaw bulb is, the larger the size of cracks becomes. The horizontal extension of the thaw bulb not only impacts on the location of longitudinal cracks on the embankment surface, but also impacts on the size of cracks. There is a critical length for the horizontal extension of the thaw bulb, where the probability of longitudinal cracks is the greatest. When the length is smaller than the critical length, the probability of longitudinal cracks increases with the length increasing; when the length is greater than the critical length, there will be no longitudinal cracks, but the whole embankment tilts to the sunny slope.

Investigation of Arching Effect in Geosynthetic-Reinforced Piled Embankments

Column-supported embankments provide a practical and efficient solution for construction on soft soil due to the low cost and short construction times. In recent years, geosynthetics have been used in combination with column systems to support embankments. The load transfer mechanism in these systems is a combination of soil arching and membrane effect of the geosynthetics. In this paper, numerical method was used to improve the understanding of the long-term performance of geosynthetic-reinforced embankments supported on end-bearing piles. The distribution of skin friction, axial force distribution, settlements on the embankment and foundation soil surface, and vertical stresses on the pile head and foundation surface were studied. Finally, the results from the numerical studies were compared with the results from different analytical methods. Based on the numerical results obtained, modified arching coefficient is presented for end-bearing piles.

Thermodynamic responses of a crushed-rock interlayer embankment on sloping permafrost ground under traffic loads

Crushed-rock embankments (CRE) are widely used engineering structures in permafrost regions, and they can effectively prevent the underlying permafrost from thawing. The heat transfer mechanisms of CREs have been extensively investigated using experimental and numerical methods, but the associated mechanical behavior has been largely ignored. However, the safe operation of an embankment is controlled not only the thermal state but also the mechanical stability and deformation. To comprehensively evaluate the thermomechanical behavior of the CREs in permafrost regions, we build a thermodynamic model of a CRE based on three conservation principles and select a crushed-rock interlayer embankment (CRIE) on sloping permafrost ground to simulate the traffic load-induced responses over four typical seasons in its 20th service year. The numerical results show that the CRIE can actively cool the underlying permafrost, but the CRIE temperature exhibits obviously seasonal differences. Thus its mechanical behaviors are seasonally different. By comparing the acceleration, velocity, displacement and excess pore water pressure characteristics of the CRIE, their amplitudes are the smallest on April 15 and the largest on October 15 in a year. So October 15 is the most unfavorable time, in which the dynamic responses to traffic loads are the most extensive. When the traffic load leaves the CRIE, the residual displacements extrude outward and downward from the centerline of the embankment surface, and the downside part of the embankment moves along the ground slope. Similarly, the residual displacement is higher on October 15 in a year. Therefore, engineers should pay close attention to the most easily damaged zone in the most unfavorable time. Through this study, we hope the numerical model and conclusions of the study can provide theoretical support for CRIE construction and maintenance and a reference for future studies of CREs in permafrost regions.

A NUMERICAL MODEL ON GEOSYNTHETIC REINFORCED PILE SUPPORTED EMBANKMENTS

Reinforced pile embankments are started use more commonly because they allow fast construction of highways. When geosynthetics are adopted to piled fills, this kind of structures are then called as geosynthetic reinforced piled structures. When the geosynthetics are used, area of pile caps is reduced because geosynthetic transfers fill load to piles by its membrane effect. In this study, effect of multi – layer reinforcement is investigated using 2D finite element method. For this purpose, settlements, pressures, excess pore water and horizontal displacements are analyzed. Results showed that using two and three layers of reinforcement significantly decreases settlements on foundation soil and embankment surface. Placement of additional layer has great effect on settlements, pressures, excess pore water pressure and horizontal displacements. It is also found out that, two layers of reinforcement is more effective when only settlements are considered.

Stability of railway embankment of China under extreme storms

The stability of railway embankments under extreme storms is important for ensuring the normal operation of the railway network. In this study, the effect of precipitation extremes on the stability of the high-speed railway embankment in China is investigated. Historical records of precipitation in the region along the Xuzhou–Shanghai section are used to estimate the value of probable maximum precipitation. Three extreme storm scenarios are generated by upscaling the base storm event which occurred in July 2016 in Nanjing. The results of the numerical analysis show that the water levels rise up significantly, and the lower part of the embankment near the toe is fully saturated. The slip surface moves to shallow depths, and the factor of safety reduces due to surface infiltration. The effects of track superstructures, filling materials in the substructure and the uncertainties of soil hydraulic properties are also discussed. Under extreme storms, a ballastless embankment can be marginally stable even though the embankment surface is covered with a concrete base. The extreme storm magnifies the effects of the uncertainty of soil properties, and the uncertainty bounds of factor of safety are wider under a more severe storm.

Bench-Scale Test Apparatus for Modeling Column-Supported Embankments

Column-supported embankments (CSEs) with or without basal geosynthetic reinforcement can be used in soft ground conditions to reduce settlement by transferring the embankment load to the columns through stress redistribution above and below the foundation subgrade level. CSEs are typically used to accelerate construction and protect adjacent facilities from settlement induced by the new embankment load. Mobilization of load-transfer mechanisms to the columns in a CSE requires differential settlement at the base of the embankment. When the embankment height is low relative to the clear spacing between columns, poor ride quality can occur because of unsatisfactory differential settlement at the surface of the embankment that result from differential settlements at the base of the embankment. Currently, there is no widespread consensus on the minimum embankment height required to avoid this type of distress. This paper describes a bench-scale test apparatus, materials, test procedures, and instrumentation that were used to improve understanding of how factors such as the spacing between columns, column diameter, presence and tensile stiffness of geosynthetic reinforcement, and loading on the embankment surface affect settlement at the surface of the embankment in response to differential settlement at the base of the embankment. The results of one test performed using a single column, and one test performed using a 5 by 5 square array of columns are presented to illustrate the type of information that can be obtained using the apparatus. Future publications will synthesize the results obtained from the testing program and provide recommendations for CSE design.

Numerical embankment breach modelling including seepage flow effects

The multi-physical processes during embankment breaching due to overtopping are complex and known to depend upon seepage flow through the embankment. A numerical breach model for progressive embankment breaching is proposed, taking the seepage flow into account including its influence on slope stability due to apparent cohesion effects. Overtopping and embankment surface erosion are computed using finite-volume methods applied to the 2D shallow-water and the Exner equations. The seepage flow is modelled using a Lattice–Boltzmann approach solving the 3D Richards’ equation. The modules are executed in a coupled manner with dynamically adapted boundary conditions. The breach side wall failures are considered using a geometrical approach based on critical failure angles. This approach is enhanced to account for apparent cohesion effects by dynamically adapting the critical failure angles as a function of the water saturation in a heuristic way, as a major enhancement compared to previous approaches. The model is successfully applied to a laboratory experiment of a small-scale spatial embankment breach.

Field Testing and Analysis of Embankment Vibrations Induced by Heavy Haul Trains

This paper presents a field testing of track and ground-borne vibration generated by heavy haul trains. The test sites consisted of three embankments with height of 6.6, 8.1, and 11.9, respectively. The acceleration signals of the rail, sleeper, and embankment surface were recorded, and then the propagation characteristics of ground vibration with distance to track center were contrastively analyzed. The test results show that horizontal vibration was dominant for locations near the track but decreased rapidly and became comparable with the vertical levels as the distance from track center increases. The quasi-static excitation dominated the sleeper response, and the dominant frequency range was found in the low-frequency zone corresponding to the fundamental axle passage frequency. For embankment surface, another pronounced dominant frequency zone was observed between 30 and 80 Hz, which was attributed to the dynamic excitation. Moreover, these higher frequency components were more promptly attenuated than low-frequency ones. The reason that vibration levels generated by locomotive were greater than wagon was attributed to the different bogie suspension mode. The relationship between normalized PPV and distance from track center in doubly logarithmic scales can be expressed with exponential function, and the vibration attenuation rates were restrained with increasing the embankment height.