Performance Of Embankment Research Articles

Application of a modified structural clay model considering anisotropy to embankment behavior

Natural clays exhibit features such as structural and anisotropy. In this work, a constitutive model that is able to replicate these two salient features of natural clays is presented. The proposed model is based on the classical S-CLAY1 model, where the anisotropy of the soil is captured through the initial inclination and rotation of the yield surface. To account for the structural of the soil, the compression curve of the reconstituted soil is taken as the reference. All parameters of the proposed constitutive model have clear physical meanings and can be conveniently determined from conventional triaxial tests. This proposed model has been used to simulate the behavior of soft soil in the undrained triaxial tests and the performance of Murro embankment in terms of settlement and horizontal displacements during embankment construction and consolidation stage. Results of numerical simulations using proposed model have been compared with the field measurement data. The comparisons show that the two features significantly influence the prediction results.

Shake Table Tests to Measure the Dynamic Performance of Geotextile-reinforced Embankment

Using geosynthetics in highway embankments can reduce theimpact of hazardous earthquakes by transmitting less excitationto improve the seismic performance. This study uses a 1-greduced scale (1/50) approach and subjects the model embankmentto an earthquake time history as well as several levelsof uniform cyclic loading. The main focus of comparison isbetween an unreinforced embankment and a one, reinforcedwith two levels of geosynthetics material. Results reveal thatgeotextile reinforced highway embankment models performmuch better under the applied motions. Larger amplitudes causemore severe deformations as a result of the increased dynamicloads. It is also revealed that the effectiveness of the geosyntheticsis dominated by the seismic frequency. Deamplificationis observed within the geotextile reinforced embankment but thedegree of deamplification is highly depended on the predominantfrequency of the dynamic load.

Hydromechanical behavior of an embankment during inundation

The paper presents a comprehensive analysis of the hydromechanical response of an embankment subject to inundation. The modified Cam clay model extended to unsaturated conditions and formulated in terms of Bishop’s effective stress is used to predict the mechanical behavior of the sand–clay mixture. The model’s ability to accurately reproduce the embankment response is evaluated by comparing the numerical predictions with the results of the physical model. Time evolution and spatial distribution of the wetting-induced displacements are analyzed together with the stress paths resulting from the imbibition process. The influence of after-compaction conditions on the embankment performance is examined focusing on the occurrence of the volumetric collapse.

Influence of gradation and proportion of sand on stress–strain behavior of clay–sand mixtures

To investigate the influence of proportion of sand as well as its gradation on the undrained strength behavior of soils, undrained tests on statically compacted specimens of clay–sand mixtures were carried, with two extreme clay minerals, namely commercially available kaolinite and bentonite mixed with specimens of three grades of sand fractions, and also varying their proportion from 10 to 80%. This work was extended to two natural soils, viz., Red earth (kaolinitic type) and B.C. soil (montmorillitic type) by using fractionized fine portion from these soils obtained by sedimentation process, and later mixed with different proportions and grades of sand fractions. Results from this experimental investigation reveals that, at optimum sand content in clay–sand mixtures, use of medium sand fractions is more beneficial to improve the undrained strength of the mixtures irrespective of the clay mineral type being present in the mixture. It thus implies that proper selection of grade of sand is also important along with the optimum content to obtain higher strength of a clay–sand mixture. This has practical implications in understanding the performance of embankments or any ground improvement applications involving strength of clayey natural soils for better load carrying capacity, stability, and good performance of the structure supported by soil. It is also very useful in the geo-environmental applications like proper selection of proper grade of clay–sand mixtures as liners for better performance.

Field test of a geogrid-reinforced and floating pile-supported embankment

A well-designed field experiment was carried out to enhance the understanding of a geogrid-reinforced and floating pile-supported (GRFPS) embankment constructed on alluvial soil with medium–low compressibility (ASMLC). Two test sections with identical reinforcement solutions and fill load were chosen for field monitoring which lasted approximately 32 months. The measurements, including pore water pressure, settlement, soil stress, strain in geogrid, and lateral displacement during and after the embankment filling, were reported and the performance of GRFPS embankment was examined. The results indicate that the downward movement of the floating pile allowed the fill load to transfer from the pile (cap) to the subsoil and mobilised more counter support from the subsoil. Less soil arching effect and tensioned membrane effect were observed, and so were the stress concentration ratio and strain in the geogrid. The floating pile with limited embedment depth is sufficient to control both the total settlement and lateral displacement. The existing design procedures are expected to be overly conservative for GRFPS embankment constructed on alluvial soil with medium–low compressibility, and some recommendations are proposed to help with the design.

Performance of Road Embankments on Seasonally-Frozen Peat Foundations with and without Corduroy Bases

AbstractTwo test sections along a newly constructed road embankment on peat foundations were instrumented to investigate their performance and to develop more economical means of construction method. The peat deposit in the study area has an average thickness of 4 m. One test section is an embankment with geotextile only at its base, and the other is with geotextile and timber logs (corduroy). Settlements were measured using monitoring plates and pins. Ground temperatures were measured using thermistor strings. Pore water pressures were measured using vibrating wire piezometers. This paper presents the monitoring results of the two fully-instrumented sections. Results show that adding timber logs near the toe of the slope reduced the settlement of the peat foundation and therefore reducing the requirement for fill material to maintain road elevation.

1st Proctor Lecture of ISSMGE:

Abstract Ballasted rail tracks are widely used throughout the world because they are economical, readily drained, and have sufficient load bearing capacity. Despite these advantages, geotechnical concerns such as ballast degradation, fouling (e.g. coal and subgrade soil), poor drainage of soft subgrade, pumping of clayey subgrade, differential track settlement and track misalignment due to excessive lateral movements exacerbate the cost of track maintenance. Globally, billions of dollars are spent annually on the construction and maintenance of rail tracks. Existing industry design standards are often unable to address these problems because they ignore true cyclic loading patterns, track vibrations, and the onset of plasticity and degradation of track materials. The mechanisms of ballast breakage and deformation, understanding the interface behaviour using geosynthetics, the need for effective track confinement using geocells, time-dependent drainage and filtration properties of track materials require further research to improve existing design guidelines. In view of this, large scale laboratory tests have been carried out using state-of-the-art facilities designed and built at the University of Wollongong and in other proactive rail institutes worldwide in Europe, America, Japan and China. Based on these tests, various factors governing the stress–strain behaviour of ballast, the strength and degradation of ballast, the ability of various geosynthetics and synthetic energy absorbing mats to minimise ballast breakage and track settlement, the effectiveness of subballast as a granular filter and its stabilisation with geocell have been analysed. In Australia, field studies on instrumented tracks at Bulli (near Wollongong), Singleton and Sandgate (near Newcastle), have been carried out to assess the performance of railroad embankments stabilised with geosynthetic grids, rubber mats, and prefabricated vertical drains. This inaugural Ralph Proctor Lecture focuses on the current state of research encompassing deformation and degradation assessment of railroads and the benefits of geo-inclusions, highlighting examples of innovations from theory to practice, predominantly based on the own experience of the Author.

Seismic response analysis of GRPS embankment under oblique incident P wave

In order to investigate the seismic performance of geosynthetic reinforced and pile supported (GRPS) embankment under seismic loads, an input method for three-dimensional oblique incidence of P wave was proposed. This method is based on the explicit finite element method while considering the viscous-spring artificial boundary (VSAB) condition. Using the proposed method, a numerical study was conducted, and the influence of oblique incidence on the seismic response of GRPS embankment under the oblique incident P waves was analyzed. The results indicate that in comparison with vertical incidence, the oblique incidence can significantly increase the displacement, velocity and acceleration of key locations in the GRPS embankment. The existence of geosynthetics can alleviate the impact of seismic load on the response of the embankment to a certain degree. Moreover, the number of reinforcement layers and modulus of geogrid also greatly influence the seismic performance of GRPS embankment.

The Performance of Road Embankments on Glacial Deposits in Ireland

Glacial deposits are very common as foundation soils supporting road embankments in Ireland and are typically present in almost all road projects. Despite this there is limited research data linking the settlement performance of embankments to the compressibility and consolidation properties of such soils. This is largely due to the difficulties in obtaining representative, high quality undisturbed samples and laboratory testing of glacial deposits, which exhibit a large range of gradation particle sizes including gravels, cobbles and boulders.The paper presents the results of several case histories of foundations and monitored road embankments supported on glacial deposits located throughout Ireland. In situ field compressibility and consolidation parameters are back calculated from field performance and correlated to standard index properties such as liquid limit, plasticity index, particle size gradations and SPT N values. Some general conclusions plus recommended ways to predict embankment performance from commonly obtained geotechnical test data are suggested. Identification of difficult glacial soil types requiring special investigation and treatment or improvement are suggested.

Effect of Geosynthetic on the Performance of Road Embankment over Sabkha Soils in Algeria: Case Study

This paper focuses on the construction technique of road embankment which crosses a section of about 11 km on sabkha soils of Chott El Hodna in Algeria. Due to the poor bearing capacity of sabkha surface and the rising water table over the surface, serious difficulties were encountered during the investigation of the subsurface soil and the construction of the first embankment layers. In this construction site, the use of basal geosynthetic layer to maintain the performance of embankment was found to have relevant reinforcing effect by increasing the soil bearing capacity to allow safe construction of the first layers and improving the compaction quality. Based on the in situ observations and the geotechnical investigation, numerical simulations were performed using the software PLAXIS. The results have shown the contribution conditions of geosynthetics to improve the bearing capacity of sabkha soils.

Performance of reinforced, DMM column-supported embankment considering reinforcement viscosity and subsoil’s decreasing hydraulic conductivity

It has been widely accepted that reinforcement made of polyethylene and polypropylene is susceptible to creep and soil’s hydraulic conductivity varies with its void ratio. However, unfortunately there is no available sensitivity analysis on time-dependent embankment behaviour taking either reinforcement viscosity or time varying hydraulic conductivity of subsoil into consideration. The influence of geosynthetic reinforcement viscosity and decreasing hydraulic conductivity with consolidation on the time-dependent performance of embankments with floating columns is investigated using a fully 3D coupled model. For an embankment at the working height corresponding to a post-consolidation polypropylene geotextile strain of about 5%, it is shown that the assumption of constant hydraulic conductivity and the failure to consider the viscous behaviour of geosynthetic reinforcement can underestimate time-dependent embankment deformations (including differential crest settlement and horizontal toe movement). The effects of factors including the foundation soil, reinforcement stiffness, column stiffness, column spacing, column type (floating and fully penetrating), and construction rate, on the time-dependent behaviour of column supported embankments are explored.

Numerical study of the effects of geosynthetic reinforcement viscosity on behaviour of embankments supported by deep-mixing-method columns

The influence of reinforcement viscosity on the post-construction performance of embankments with floating columns and fully penetrating columns is explored. It is shown that the viscous behaviour of geosynthetic reinforcement can increase the long-term shear deformations of foundation soil and increase the horizontal toe movement. The effects of reinforcement strain at the end of construction of embankments over two soft clay deposits are investigated. The deep-mixing-method column supported embankments with viscous and with inviscous reinforcement are numerically constructed to identify the effect and magnitude of reinforcement creep and stress relaxation.

Several factors affecting seismic behaviour of embankments in dynamic centrifuge model tests

A series of dynamic centrifuge model tests was conducted in order to evaluate some factors affecting the seismic performance of hillside embankments consisting of sandy or silty soils and resting on stiff base slope. The effects of seepage water elevation in embankments, toe drain, embankment height, base slope inclination, soil compaction, and fill materials on the seismic behaviour of embankments were investigated. The test results showed that: (1) the seepage water was one of the most important factors for earthquake-induced embankment failure; (2) the seismic performance of both the smaller and higher embankments was remarkably improved by installing the toe drain; (3) larger base slope inclination produced larger earthquake-induced deformation of embankments; (4) well-compacted embankments were not vulnerable to earthquake-induced damage; and (5) the seismic performance of well-compacted embankments consisting of well-graded silty soils with large fines content was higher than that of poorly graded sands under otherwise the same condition. In some tests, as observed during past strong earthquakes, delayed flow failure occurred due possibly to the multiple effects of upward seepage associated with the redistribution of excess pore water pressures generated during main shaking, continued small vibration after main shaking, and driving static shear stresses caused by the embankment weight. A series of triaxial compression and cyclic triaxial liquefaction tests was also conducted to evaluate undrained behaviour of the fill materials. The correlation between the model and laboratory element test results was presented.

The Optimized Dynamic Behavior of Short Embankment Based on Frequency Performance

Due to the performance of embankment under the earthquake, relative displacement at both edges of the crest is very important for body cracks. It can be computed by dynamic analysis. In this way, response spectrum analysis and Rayleigh damping coefficient are dependent factors to dominant frequency. Based on the new technology using advanced programs to compute frequency, free vibration analysis as the basic technique and considering of different vibration modes is accessible. This research tried to evaluate the distribution of dominant frequencies for short embankment (H=30 meter) using Finite-Element Method (ANSYS 13). To evaluate of the frequency, elasticity modulus ratio and foundation depth ratio were the main objectives. Both were defined by the ratio between the embankment and foundation. As a result, maximum and minimum vertical displacements were located on both slopes, and maximum horizontal displacement was exposed at the crest. The dominant frequency increased as the modulus ratio decreased. In addition, dominant frequency decreased as the depth ratio increased. The impact of the modulus ratio to enhance frequency was greater than the depth ratio. In terms of contributing engineering, the amplitude of the dominant frequency (Hz) was finally optimized for modulus ratios (0.25-1.00) and depth ratios (0.1-1.00). For critical situation, modulus ratio was more than three, and the depth ratio was half of the unit. More research about medium embankment is recommended.

Deformation performance of cement-fly ash-gravel pile-supported embankments over silty clay of medium compressibility: a case study

This paper presents a special case study on the performance of geosynthetics-reinforced and pile-supported embankments (GRPS) over silty clay of medium compressibility. A full-scale high-speed railway embankment with four instrumented subsections over medium silty clay was constructed in three stages. Three of the sections were reinforced by geosynthetics and cement-fly ash-gravel (CFG) piles with different configurations, while the other section was only reinforced by geosynthetics, which was used as a reference. The discussion mainly focused on the deformation behaviors of test embankments. The results show that (1) both the vertical settlements and the lateral displacements slightly increased until a certain fill height. Afterwards, they increased rapidly due to the transformation from the over-consolidated state to partly or entirely normally consolidated state of the foundation soil. (2) CFG pile reinforcement performed well in terms of reducing settlements and lateral displacements. (3) The lateral displacement is a useful indicator for evaluating external stability of GRPS embankments. Moreover, the comparison of soil stiffness obtained from in situ and laboratory suggests that an appropriate equivalent modulus may be obtained based on the stiffness-strain curve from a triaxial test with local strain measurements while considering the correct strain level obtained from field measurements of vertical settlements.

An experimental study on the compaction and collapsible behaviour of a flood defence embankment fill

With renewed interest in the performance of flood embankments globally, it is important that the performance of fills in conditions similar to ‘as-constructed’ are scrutinised. The fill material investigated in this study was sampled from flood embankments located along the Bengawan Solo River in East Java, Indonesia. The recurrent history of overtopping and stability issues in these embankments provided the motivation for developing a better understanding of the behaviour of this compacted fill under different loading and wetting conditions. The site investigation revealed that the embankment fill was compacted at low dry densities and that there was local variation in the dry densities determined. A detailed study highlighted that at low compactive efforts this fill material exhibits an irregular double-peak compaction curve, which can be explained by the tendency of this fill to form aggregates on wetting. To cover different plausible operational conditions of these embankments, saturated and unsaturated compression oedometer tests and one-dimensional collapse tests were performed under different initial conditions. Specimens compacted at conditions similar to ‘as-constructed’ exhibited significant collapse deformation (up to 13.6%) on wetting. Evolution of the microstructure during loading and wetting paths was investigated using MIP and ESEM. A physically-based framework proposed by Romero (2013) was used to explain the changes in the macroscale collapse behaviour observed in the oedometer tests based on the evolution of microporosity. Using this model the evolution of the microporosity with dry density and water content was presented. This microstructural approach could be used as a tool for specifying appropriate compaction conditions for earthworks where fill material is susceptible to volumetric collapse.

Evaluation and Utilization of Kuantan Clayey as Material Embankment for Roadway

In general, clayey soil was used as material embankment for increasing road way level before road structure being constructed. Some types of clay are expansive soil, its have been contributing to pavement failures and subsequently causing increased annual maintenance expenditure of the road. The pavements design/redesign methods are found to be the primary cause of these failures. Thus, it is quite important to propose the Kuantan clay engineering properties chart for design criteria that can improve the embankment performance. Thus, it is quite important to investigate the Kuantan clay properties so that can improve the embankment performance. This paper was evaluated and utilized of the engineering properties of Kuantan Clayey as material embankment for roadway. The research were conducted soil engineering properties, standard compaction, four days soaked California Bearing Ratio (CBR) test to ten clayey samples from various sites in Kuantan. The 4 days soaked CBR of clayey samples were prepared at optimum water content. The chemical element was investigated by Integrated Electron Microscope and Energy-Dispersive X-Ray Spectroscopy (SEM-EDS) and linear regression analysis were used to anlyzing relation among engineering properties variables.

EFFECT OF ADDING DOWNSTREAM BERMS ON SEISMIC MITIGATION OF EMBANKMENTS

This paper investigates the performance of embankments subjected to seismic loading. Finite element analysis using Plaxis dynamic software program was carried out to evaluate the crest settlement of a dense sand embankment on rock foundation before and after adding downstream berms. Undraind analysis is carried out using Mohr-Coulomb criteria. The numerical intensities are close to previous studies and the results show that the best embankment performance is when the berm is added in downstream at height equals to half of the embankment total height. The downstream berm slope has no significant effect on crest settlement for slopes less than 1.5H: 1V. It is also found that when adding two downstream berms, the best mitigation is obtained when the top berm is at two third the embankment and the bottom berm is added at one third the total embankment height.

Performance of fixed geosynthetic technique of GRPS embankment

Geosynthetic-reinforced and pile-supported (GRPS) embankment has been increasingly constructed in a large number of regions and for a wide range of projects in the past decades. However, many disadvantages are exposed through a lot of applications on conventional technique of GRPS embankment (called CT embankment), i.e., intolerable settlement and lateral displacement, low geosynthetic efficiency, etc. In view of these disadvantages, the fixed geosynthetic technique of GRPS embankment (called FGT embankment) is developed in this work. In this system, the geosynthetic is fixed on the pile head by the steel bar fulcrum and concrete fixed top. The principles and construction techniques involved in the FGT embankment are described firstly. Then, the numerical analysis method and two-stage analysis method are used to study the performance of FGT embankment, respectively. It is shown that the FGT embankment can provide a better improvement technique to construct a high embankment over soft ground.

Study of the Effect of Pile Type for Supporting Basal Reinforced Embankments Constructed on Soft Clay Soil

This paper studies the effect of the type of pile on the behaviour of basal reinforced pile supported embankments constructed on soft clay. The performance of embankment supported on both end bearing piles and floating piles was studied. 3D column models were used for carrying out the parametric studies to examine the development of arching mechanism, settlements and stresses on the foundation surface and the pile head and the development of tensile forces in the reinforcement layers. Full three-dimensional analyses were performed to study the lateral movement of the soft foundation soil near the embankment toe and the results obtained from the analyses were compared with those from British Standard BS8006-2010.