Embankment Loading Research Articles

Role of piles in mitigating the movement of pipes in soft grounds during embankment loading

Pipes buried in soft ground can be damaged due to the vertical and lateral movement of the ground during the construction of the embankment. To investigate such a movement of the soft ground, full-scale tests using embankment piles and stabilizing piles were conducted for 70 days. A pile-supported embankment has been used to reduce the deformation of soft ground by transferring the embankment load through piles to the firm layer below the soft ground, whereas stabilizing piles have been employed to resist the lateral earth pressure that is induced in soft ground by embankment loads. The Coupling Area (CA), which was defined as the quantitative index to determine the resistance effect of both settlement and lateral flow of the soft ground when the embankment was reinforced, is adapted. The analysis results of the CA indicate that the piled embankment was more effective for preventing the damage to buried pipe installed near the embankment, while the stabilizing piles had almost the same effect as the piled embankment when the pipe was buried far away from the embankment.

Behavior of an Embankment on Column–Slab Improved Clay Deposit

The performance of an embankment constructed on a cement deep mixing-formed column–slab system improved soft clay deposit was analyzed using field measurements and finite element simulation results. By back-fitting the measured surface settlement curve, it was interpreted that parts of the columns might have failed in compression, and the field mobilized compressive strength was lower than the designed value. Further, the numerical results indicate that some of the columns under the toe of the embankment failed by bending, but the current design method used in Japan does not check for this failure mechanism. In addition, for a soil–cement slab constructed on the ground surface, under a relatively high embankment load, tensile cracks will most likely form in the slab. Therefore, it is suggested that in design, the main function of the slab can be considered for reducing the differential settlement between columns and the surrounding soils; the strength of the slab may be ignored in stability analysis.

Evaluation of Vertical Superimposed Stress in Subsoil Induced by Embankment Loads

Evaluation of Vertical Superimposed Stress in Subsoil Induced by Embankment Loads

Comparative performances of two- and three-dimensional analyses of soil-cement mixing columns under an embankment load

This research presents measurements and simulations of the full-scale behavior of a test embankment built on a soft marine clay deposit improved using soil–cement mixing (SCM) columns in Bangkok, Thailand, using both two-dimensional (2D) and 3D finite element analyses (FEAs). Fixed SCM columns with two different installation patterns, that is, column groups and column rows, were constructed in the soft clay foundation prior to the construction of the embankment. Three column wall methods, namely, equivalent width, equivalent axial rigidity, and equivalent flexural rigidity approaches, were used to convert the 3D individual columns into 2D plane strain column walls. A comparison of the results obtained through the 3D and 2D FEAs revealed that the 2D analyses provide inaccurate results in terms of the column lateral movements, bending moments, and axial loads induced in the SCM columns in addition to the factors of safety against slope failure. This outcome occurred because the actual columns in the 2D FEA were modeled using extended walls, which essentially prevent the movements of soil between two columns or column rows. Correction factors used to convert the 2D analysis results into 3D analysis results were also proposed in this study.

Influence of cement-fly ash-gravel pile-supported approach embankment on abutment piles in soft ground

Abutment piles in soft ground may be subjected to both vertical and horizontal soil movements resulting from approach embankment loads. To constrain the soil movements, the soft soil ground beneath the approach embankment is often improved using composite pile foundations, which aim at mitigating the bump induced by high-speed trains passing through the bridge. So far, there is limited literature on exploring the influence of the degree of ground improvement on abutment piles installed in soft soil grounds. In this paper, a series of three-dimensional (3D) centrifuge model tests was performed on an approach embankment over a silty clay deposit improved by cement-fly ash-gravel (CFG) piles combined with geogrid. Emphasis is placed on the effects of ground replacement ratio (m) on the responses of the abutment piles induced by embankment loads. Meanwhile, a numerical study was conducted with varying ground replacement ratio of the pile-reinforced grounds. Results show that the performance of the abutment piles is significantly improved when reinforcing the ground with CFG piles beneath the approach embankment. Interestingly, there is a threshold value of the replacement ratio of around 4.9% above which the effect of CFG pile foundations is limited. This implies that it is essential to optimize the ground improvement for having a cost-effective design while minimizing the risk of the bump at the end of bridge.

Free strain analysis of the performance of vertical drains for soft soil improvement

Improvement of soft clay deposit by preloading with vertical drains is one of the most popular techniques followed worldwide. These drains accelerate the rate of consolidation by shortening the drainage path. Although the analytical and numerical solutions available are mostly based on equal strain hypothesis, the adoption of free strain analysis is more realistic because of the flexible nature of the imposed surcharge loading, especially for the embankment loading used for transport infrastructure. In this paper, a numerical model has been developed based on free strain hypothesis for understanding the behaviour of soft ground improvement by vertical drain with preloading. The unit cell analogy is used and the effect of smear has been incorporated. The model has been validated by comparing with available field test results and thereafter, a hypothetical case study is done using the available field data for soft clay deposit existing in the eastern part of Australia and important conclusions are drawn therefrom.

Behaviour of geosynthetic reinforced column supported embankments

PurposeThis paper aims to investigate the behaviour of geosynthetic reinforced deep cement mixed (DCM) column-supported embankments constructed over soft soils.Design/methodology/approachCoupled consolidation analyses based on the finite element method are carried out assuming that the soil and DCM columns are fully saturated porous mediums. In the first part of the paper, a case study of an embankment constructed over a very soft soil deposit in Finland is presented. Two- and three-dimensional finite element models for the case study are developed including isolated and attached DCM columns beneath the embankment to capture the arching mechanism between DCM columns. The model simulations were carried out considering the actual staged construction procedure adopted in the field. Finite element predictions show good agreement with field data and confirm that the load transfer is mainly between attached columns beneath the embankment. Next, the significance of geosynthetic reinforcement on the load transfer mechanism is investigated. Finally, the influence of permeability of columns and soft soil on the performance of geosynthetic reinforcement column-supported embankments is studied.FindingsResults demonstrate that the excess pore pressure dissipation rate is fast in DCM column-improved ground compared to the same case without any columns, although the same permeability is assigned to both DCM columns and surrounding soft soil. When DCM column permeability exceeds soil permeability, excess pore pressure dissipation rate shows a remarkable increase compared to that observed when the DCM column permeability is less than or equal to the permeability of surrounding soft soil. [ ]Originality/valueThis paper investigates the contribution of permeability and geosynthetic layer on the vertical load transfer mechanism of the embankment and modelling issues related to application of the embankment load and the properties of the cement-improved columns.

Properties of geogrid-reinforced marine slope due to the groundwater level changes

ABSTRACTEvaluation of slope stability, especially in the absence of a proper bed such as marine soils, is one of the most important issues in geotechnical engineering. Using geogrid layers to enhance the strength and stability of embankments is regarded as a commendable stabilization method. On the other hand, groundwater level erratically fluctuates in coastal areas. Therefore, the aim of this research is to study the effects of groundwater level changes on stability of a geogrid-reinforced slope on loose marine soils in Qeshm Island, Iran. At first, geotechnical properties of the site were obtained by comprehensive series of geotechnical laboratory and in situ tests. Then, by simultaneous changes of groundwater level and several parameters such as embankment slope, loading, geogrid length, geogrid number, and tensile strength of geogrid, different characteristics such as embankment safety factor (SF), vertical and horizontal displacements at embankment top and embankment base were studied. It was observed that groundwater level had significant effects on behavior of the embankment. For most of the observations, by decreasing the groundwater level, the displacements decreased and consequently safety factor increased. Increasing the length, number, and tensile strength of geogrid led to the reduction of displacements and an increase in the safety factor.

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.

Predicting bending failure of CDM columns under embankment loading

The mechanism of bending failure and the magnitude of the bending moment in a column formed by cement deep mixing (CDM) under an embankment load were investigated by a series of three-dimensional (3D) finite element analyses. Based on the numerical results, a design method to consider the bending failure of the CDM column has been established. The usefulness of the proposed methods was verified using the results of two centrifuge model tests of the embankments on the CDM column improved soft model ground model reported in the literature, and the columns had tensile cracks or showed complete failure.

Settlements and Consolidation Rates under Embankments in a Soft Soil with Vertical Drains

In this paper, a study was carried out in order to estimate settlements and consolidation rates under embankments constructed on Moroccan soft soils. Settlement measurements in several embankments in High Speed Railway project between two Moroccan cities, Tangier and Assilah, were analyzed. The objective of this study is to estimate settlement values and settlement rates, with sufficient precision, in soft soils under embankment loadings. It was found that the elastic method using the pressuremeter modulus results in more accurate settlement values than the oedometric method. Furthermore, settlement rates could be determined with fair accuracy by using a correlation between the vertical coefficient of consolidation and the liquid limit, and also by considering an isotropic behavior of soil.

Effect of matric suction and initial static loading on dynamic behaviour of unsaturated cohesive soil

Unsaturated soils are frequently encountered in various civil engineering projects; however, their dynamic behaviour is still unexplored. Present study evaluates the influence of matric suction, initial static loading, and load repetition on dynamic response of unsaturated cohesive soil (CH type). A series of cyclic triaxial tests have been performed on Ahmedabad-based cohesive soil under as-compacted conditions (unsaturated). Matric suction of soil is obtained using filter paper method at varying dry density and water content to characterise the behaviour of unsaturated soil. Application of initial static axial strain exhibited a unique stiffness response in loading and unloading phases of cyclic testing, and significantly impacted the cyclic strength response of unsaturated cohesive soil. The initial static axial strain in cyclic triaxial testing represents the conditions of a highway/railway embankment, where the embankment load on soil acts like initial static loading and passing vehicles like cyclic loading on soil. Load repetition exhibited significant degradation in shear modulus of cohesive soil under cyclic loading conditions.

Visualization of the formation and features of soil arching within a piled embankment by discrete element method simulation

Piled embankments are widely used in highway and railway engineering due to their economy and efficiency in overcoming several issues encountered in constructing embankments over weak soils. Soil arching, caused by the pile-subsoil relative displacement (Δs), plays an important role in reducing the embankment load falling on weak soil, however, the fundamental characteristics (e.g., formation and features) of soil arching remain poorly understood. In this study, a series of discrete element method (DEM) modellings are performed to study the formation and features of soil arching with the variation of Δs in piled embankments with or without geosynthetic reinforcement. Firstly, calibration for the modelling parameters is carried out by comparing the DEM results with the experimental data obtained from the existing literature. Secondly, the analysis of the macroand micro-behaviours is performed in detail. Finally, a parametric study is conducted in an effort to identify the influences of three key factors on soil arching: the friction coefficient of the embankment fill (f), the embankment height (h), and the pile clear spacing (s−a). Numerical results indicate that Δs is a key factor governing the formation and features of soil arching in embankments. To be specific, soil arching gradually evolves from two inclined shear planes at a small Δs to a hemispherical arch at a relatively large Δs. Then, with a continuous increase in Δs, the soil arching height gradually increases and finally approaches a constant value of 0.8(s−a) (i.e., the maximum soil arching height). For a given case, the higher the soil arching height, the greater the degree of soil arching effect. The parametric study shows that the friction coefficient of the embankment fill has a negligible influence on the formation and features of soil arching. However, embankment height is a key factor governing the formation and features of soil arching. In addition, pile clear spacing has a significant effect on the formation of soil arching, but not on its features.

Piled embankment to prevent damage to pipe buried in soft grounds undergoing lateral flow

ABSTRACTLateral flow of soft ground occurs when embankment filling is performed on reclaimed land of foreshore. If a utility pipe is buried in soft ground undergoing the lateral flow, severe damage to the pipe can be caused. A pile-supported embankment has been used to support embankment to minimize lateral flow of the soft soil by transferring the embankment loads through the piles to the firm layer. To prevent damage to the buried pipe subjected to lateral force of the soft ground, full-scale field experiments on the piled embankment were conducted for 70 days. The test results show that the piled embankment effectively reduces both the settlements of the ground and the lateral displacements of the buried pipe. Although additional load was not imposed on the embankment after finishing embankment filling, the settlement and lateral displacement of soft ground simultaneously increased. This coupling behavior was observed at the toe of the embankment and the back of the buried pipe. To quantitatively evaluate the coupling effect of the movement, the coupling area (CA) was coined and analyzed with the efficiency of load transfer. The efficiency evaluated by the CA was in good agreement with the efficiency by the soil arching mechanism.

Field studies of a technique to mitigate ground settlement of operating highways

In the eastern coastal region of China, many operating highways built over soft ground are vulnerable to severe post-construction settlement. In this study, a technique using jet grouted piles is developed to mitigate post-construction settlement. The piles are installed by drilling boreholes throughout the embankment. The principal stages of the construction process are described, and two field tests in China, on the Lianyan and Linhai highways, are presented. The results revealed that ground heaves of up to 219 mm and 337 mm induced during a short construction period were able to mitigate the settlement of the embankment. The average settling rate was significantly reduced from 60 mm/y to 9 mm/y on the Lianyan highway. Lateral ground displacement on the Linhai highway increased with time during construction, but after construction showed a slight reduction associated with the dissipation of excess pore water pressure. An analytical method was adopted to describe the ground heave due to the jet grouted piles. The ground heave increased with grout pump pressure, but decreased as the embankment load and distance from the pile center increased.

Numerical study on load transfer effect of Stiffened Deep Mixed column-supported embankment over soft soil

A new composite column technique referred to as Stiffened Deep Mixed (SDM) column has been adopted to support embankment over soft soil to mitigate the post-construction settlement, increase bearing capacity and enhance stability. The SDM column was formed by inserting a precast concrete core pile into the center of a Deep Mixed (DM) column immediately after the construction of DM column. Due to the complicate interaction between concrete core pile, DM column and surrounding soil, the load transfer mechanism between SDM column and surrounding soil has not been well understood yet. This paper presents a series of three- Dimensional (3-D) finite-element analyses to investigate the load transfer effect of SDM column-reinforced ground under embankment. First, the numerical method was validated by a comparison with field data in terms of settlements and vertical stress on the head of SDM column. Then, based on the validated simulation method, the 3-D numerical model of the SDM column-supported embankment over soft soil was established, and the influence factors of length of DM column and concrete core pile, cross section area of concrete core pile, column spacing and embankment height on the load transfer effect were investigated, respectively. The results showed that the column spacing and height of embankment fill had significant effects on the load transfer between SDM column and surrounding soil, while the influences of length of DM column and concrete core pile, and cross section area of concrete core pile on the load transfer effect were minor. Finally, four current commonly-used design methods were assessed in the prediction of the efficacy of SDM-reinforced soil under embankment loading. The current commonly-used design methods showed great differences in the load transfer predictions of the SDM column-supported embankment over soft soil due to the existence of outer DM column socket. A modified method was proposed for the use of EBGEO (2011) in the design of SDM column-supported embankment over soft soil.

Model test and numerical simulation on rigid load shedding culvert backfilled with sand

For reducing embankment load on box culvert, a new culvert structure called load shedding culvert (LSC) is proposed. First, model tests were conducted to investigate the performance of LSC, which was compared with embankment-installation box culvert (EBC) and imperfect-trench-installation box culvert (IBC). Then, numerical simulations were performed to investigate the stress states of the three culvert structures and associated important influencing factors. This study reveals that the LSC, compared with EBC and IBC, can not only reduce the vertical earth pressure on the top slab but also reduce the horizontal earth pressure on the culvert sidewall.

토목섬유로 보강된 성토지지말뚝 구조에 적합한 말뚝재료의 개발

ABSTRACT It is a current trend that the concrete track is applied for high speed railway. In the case of the railway embankment constructed on soft ground, the damage to concrete track which is sensitive to settlement such as distortion and deflection could be caused by very small amount of long term settlement. Pile Supported Embankment method can be considered as the effective method to control the residual settlement of the railway embankment on soft ground. The Geosynthetics is used inside of the embankment to maximize the arching effect transmitting the load of the embankment to the top of the piles. But, PHC piles that are generally used for bridge structures are also applied as the pile supporting the load of embankment concentrated by the effect of the Geosynthetics. That is very low efficiency in respect of pile material. So, in this study, the cast in place concrete pile was selected as the most suitable pile type for supporting the embankment by a case study and the optimum mixing condition of concrete using a by-product of industry was induced by performing the mixing designs and the compressive strength designs. And it is shown that the cast in place pile with the optimum mixing condition using the by-product of industry is 2.8 times more efficient than the PHC pile for the purpose of Pile Supported Embankment by the finite element analysis method.

Modelling of anisotropy and consolidation effect on behaviour of sunshine embankment: Australia

This paper investigates the time-dependent behaviour of Sunshine embankment on soft clay deposit with and without prefabricated vertical drains. An elasto-viscoplastic model was used to investigate the influence of anisotropy and creep effect on the settlement behaviour of the embankment. The constitutive model, namely ACM accounts for combined effects of plastic anisotropy and creep. For comparison, the problem is also analysed with isotropic Modified Cam Clay model which does not consider creep effect. To analyse the PVD improved subsoil, axisymmetric vertical drains were converted into equivalent plane strain conditions using two different mapping approaches. The results of the numerical analyses are compared with the field measurements. The numerical simulations suggest that the anisotropic creep model is able to give a better representation of soft clay response under an embankment loading. The isotropic model which neglects the effects of anisotropy and creep may lead to inaccurate predictions of soft clay response. Additionally, the numerical results show that the mapping method used for PVD improved soft clays can accurately predict the consolidation behaviour of the embankment and provide a useful tool for engineering practice.

Finite-Element Analysis on the Effect of Subsoil in Reinforced Piled Embankments and Comparison with Theoretical Method Predictions

AbstractThis paper presents a finite-element (FE) analysis of the effect of subsoil in a reinforced piled embankment and compares the findings with predictions from a theoretical method. It shows that the subsoil can carry as much as 75% arching embankment load for the present standard model (pile spacing of 2.5 m, geogrid stiffness of 6 MN/m, embankment height of 6 m, and subsoil compression index of 0.7). Also, the proportion is much larger for the lower value of pile spacing, geogrid stiffness, embankment height, and subsoil compression index. The maximum settlement of subsoil is found to be more sensitive to the pile spacing than to the geogrid stiffness. The theoretical method shows reasonable agreement with the FE results and can therefore be used to predict the effect of subsoil in reinforced piled embankments. The geogrid has a significant role in carrying the entire embankment load without the subsoil support. However, this effect may lead to intolerable geogrid strain due to relatively large set...