Toe Of Embankment Research Articles

Effects of soil inhomogeneity on seepage behavior within embankments

Heavy rain events that accompany recent climate change, have triggered disasters of embankment structures, such as road embankment and levee. Internal erosion, which is the migration of soil particles following seepage flow, causes inhomogeneity of the soil properties of the embankment. However, there are very few studies investigating the effects of soil inhomogeneities on the seepage behavior of groundwater within embankment. In this study, small-scale modelling tests were performed under repeated seepage flow histories. As a result, the groundwater table gradually increased in accordance with the number of seepage repetition. Modelling the fluctuation of permeability due to internal erosion following seepage flow was additionally performed using the soil/water/air coupled finite element analysis, and seepage behavior was investigated. In these analyses, the lower permeability of the toe of embankment was shown to possibly cause an increase in upward water pressure.

Effect of Different Reinforced Load Transfer Platforms on Geosynthetic-Reinforced Pile-Supported Embankment: Centrifuge Model Test

Geosynthetic-reinforced pile-supported (GRPS) embankment has been widely utilized in the railways and highways subgrade of soft clay area. The load transfer platform (LTP), consisting of sand layers and one or more layers of geosynthetic, is constantly used at the base of embankment to increase the load transfer to piles and reduce the differential settlement of embankment surface. However, the effect of different reinforced LTPs on the performances of GRPS embankment has not been fully understood. Eight centrifuge model tests were conducted to investigate the effect of five influence factors on deformation and load transfer of embankment, and tensile force of geogrid: placing geogrid or not, the number of geogrid layers, geogrid reinforced position, geogrid stiffness, wrapped-back geogrid setting in LTP. The results showed that the wrapped-back geogrid setting in the LTP was equivalent to anchoring the geogrid at the slope toe of embankment, which strengthened the reinforcement-soil interaction and restricted the pull-out displacement of geogrid to enhance the stiffness for LTP. The LTP reinforced with stiffer geogrid or multi-layer geogrid contributed to increase the stability and load transfer of embankment due to the increase of the integrity stiffness for LTP. When the geogrid was set at the middle of LTP, the performances of the GRPS embankment was enhanced due to the more interfaces between the geogrid and soil to improve the integrity stiffness of the LTP. The two-layer geogrid reinforced in the LTP could be the best choice to enhance the performance of the GRPS embankment under the comprehensive consideration of the performance and economy. The five setting ways of the reinforcement in LTP increased the integrity stiffness of LTP, which provided more methods to enhance the performances of the GRPS embankment.

Centrifuge study on behavior of rigid pile composite foundation under embankment in soft soil

The rigid pile composite foundation is widely used in highway projects in soft soil area as it can effectively increase the bearing capacity and stability of the foundation. While the research on the behavior and failure mode of rigid pile composite foundation under embankment is not enough, instability failure of rigid pile composite foundation often occurs in practical projects. This paper presents a centrifuge model test to investigate the load transfer mechanism, settlement characteristic and failure mode of rigid pile composite foundation under embankment. The test results show that: the soil displacement of different region in rigid pile composite foundation was different, obvious vertical displacement occurred in the soil under the center of embankment and the horizontal displacement was very small in this region; both vertical and horizontal displacement occurred in the soil under the shoulder of embankment; and obvious horizontal displacement occurred in the soil under the slope toe of embankment; moreover, ground heave also occurred near the slope toe of embankment. The soil displacement in rigid pile composite foundation had a large influence on the stress characteristic and failure mode of rigid piles, the compressive failure and bending failure would probably occur for the piles under the center and shoulder of the embankment, respectively, and the tension-bending failure would probably occur for the piles under the slope toe of embankment. The different failure modes of piles at different regions should be considered in the design of rigid pile composite foundation under embankment. The test results can be used to improve the design method for rigid pile composite foundation under embankment in practical projects.

Analisis Perkuatan Timbunan Di Atas Tanah Lunak Menggunakan Dinding Turap dengan Pendekatan Model Numerik

Embankment on soft clay may be affect settlement at subgrade, causing lateral deformation and vertical deformation around embankment. Therefore, reinforcement is needed to overcome the effects caused of the embankment. This research was conducted to find out the influence of sheet pile wall of embankment using PLAXIS 2D program based the finite element method. The analysis was done by varying of two condition, they are installation of sheet pile wall under the embankment and the sheet pile wall outside embankment. Sheet pile wall installation is carried out before embankment construction and length of sheet pile wall in this model is 15 m. The soil layers beneath the embankment consist of 10 m layer of soft clay layer and 5 m of sand layer. The height of embankment in this analysis is 8 m, where the constructing of the embankment was done in stages. The distance of sheet pile wall position under embankment from toe of embankment are -9 m, -6 m, -3 m, 0 m, 3 m dan 6 m. The results of analysis show the effective position for displacement are toe of embankment. The Installation of sheet pile walls below the embankment will reducing deformation up to 78% and the safety factor will increase up to 10%.

Liquefaction and Earthquake Response Analysis of Panipat Pond Ash Embankment in India

In this study, liquefaction and earthquake response analysis of Panipat pond ash embankment in India has been carried out considering saturated and natural water table conditions. Laboratory and field studies have been carried out to obtain the material properties required for the nonlinear response analysis of the Panipat pond ash embankment. Nonlinear finite element analysis has been carried out by using open system for earthquake engineering simulation (OpenSees). Three earthquakes namely Chamba, Chamoli and Uttarkashi earthquakes have been considered for liquefaction and earthquake response analysis. The standard penetration test (SPT)-[Formula: see text] value indicates that the ash deposit in Panipat pond ash embankment is in loose to medium dense state. The excess pore pressure ratio obtained from the analysis is found to be one or more than one below upstream and downstream locations of the pond ash embankment for both saturated and natural water table conditions. The horizontal and vertical displacement is found to be maximum near the toe and first rise slope of pond ash embankment. Hence, ash embankment in Panipat is prone to liquefaction under the excitation of moderate to high earthquake loading.

Experiment and Simulation of Earthen Embankment Breach

Many studies of earthen embankment failure from overtopping flow have been conducted in various aspects. Most of them focused on the mechanism of breach, depth and width of erosion, and breach hydrograph. The results were obtained either from both physical and numerical modeling and/or coupling techniques. However, a physical hydraulic model of the effect of breach mechanism under three types; overtopping, beneath structure and piping hole have not been studied. Fixed embankment slopes with scale of 1:8.5 were employed to perform the experiment. It was found that the piping hole case at the toe of embankment was the most severe damage. The iRIC Nays2D numerical model shows a good performance of simulated results in both water flow and breach morphological characteristics, indicating that the model simulation is reasonable.

APPLICATION OF MICROTREMOR MEASUREMENT FOR ESTIMATE OF OVERALL STIFFNESS OF LEVEES

This study explores the feasibility of estimating overall shear wave velocity for levees to detect weak sections by using microtremor measurement. Microtremor measurement is carried out on the crest and near the toe of the levee embankment simultaneously by placing servo-type velocity sensors perpendicular to the levee axis. Then, transfer functions are calculated using the horizontal motions. Finally, overall shear wave velocity structure is identified so that the peak frequency of the transfer function and the fundamental frequency of finite element model of the levee that has the same cross section coincide. The identified shear wave velocities are mostly consistent with shear wave velocities estimated based on SPT blow counts. Hence, this method is feasible to detect weak sections along levees.

Study on the effects of vegetation density in reducing bed shear stress on the downstream slope of earthen embankment

River bank, coastal erosion and embankment failures are endemic and recurrent natural hazards, causing loss of lands and livelihoods along major rivers and coastlines. Overflow is the most damaging factor for earthen embankments on the downstream (d/s) slope due to the erosion of surface material which is caused by the high bed shear stress and supercritical flow over the entire d/s slope. Vegetation planted on d/s slope may have a considerable effect in reducing bed shear stress which makes erosion. However,the influence of vegetation for flow resistance as well as bed shear stress control has been studied a little. Therefore, the aim of this research is to introduce the use of natural resources like vetiver grass for controlling bed shear stress which actually causes embankment erosion starts from the high flow region that is, in supercritical flow state. A small-scale experiment is performed with four different densities of vegetal cover considering different discharges on d/s slope. Vegetative barrier affect the mean flow rate by induced drag force against hydraulic forces. Hydraulic characteristics and mechanism of vegetation in open channel during overflow are studied through flume experiment. Results demonstrated that vegetation markedly reduced the effective bed shear stresses which are the influencing factor for causing erosion on the d/s slope, toe and bed of embankment. Results also revealed a significant reduction of damage due to erosion and risk of failure from overtopping flow can be achieved by providing dense vegetation cover on the d/s slope of earthen embankment. Key words: Embankment, downstream slope, drag force, bed shear stress, vegetation density.

Effect of Geotextile and Prefabricated Vertical Drains Used in Soft Soil Foundation

Based on the generalized formulation of two dimensional Biot′s theory of consolidation, the effect of geotextile and prefabricated vertical drains (PVDs) using in soft soil foundation was studied with nonlinear finite element method. The dissipation of excess pore pressure, vertical settlement and lateral displacement of foundation were contrasted between foundations with and without PVDs. It is found that the vertical settlements become lager, the lateral displacements become less and the bulges at the toe of embankment become less at the same time of consolidation when PVDs are used. And the stability of embankment improved for the bearing capacity of soil enhanced with excess pore pressure dissipated fast. Meanwhile, the axial force of geotextile become less when PVDs are used. Those changes showed that the design of foundation can be optimized by shortening the time of consolidation when PVDs are used.

ANALYSIS OF GEOTEXTILE EMBANKMENT BY ANSYS

The major objectives of this research are to analyze the behavior of road embankmentsreinforced with geotextiles constructed on soft soil and describe the finite element analysis by usingANSYS program ver. (5.4). The ANSYS finite element program helps in analyzing the stability ofgeo- structure (embankment) in varied application of geotextiles reinforcement to enhance the bestdesign for embankment.The results of analysis indicate that one of the primary function of geotextiles reinforcement was toreduce the horizontal displacement significantly. With the inclusions of reinforcement, the horizontaldisplacement reduced by about (81%), while the vertical displacement reduced by (32%). The effectof geotextiles stiffness modulus on horizontal and displacement is quite significant even a very highmodulus of geotextile will have relatively little effect on vertical displacement. Also it is observedfrom the obtained results that the maximum displacement occurred at the toe of embankment for bothhorizontal and vertical movement, then decrease gradually to a negligible value for the layerreinforced case. Also the reinforcement reduces the shear stress developed in the foundation soil.

Character of Embankment Reinforced with Geotextile on Sloping Weak Foundation

Based on nonlinear finite element method, the character of embankment reinforced with geotextile on sloping weak foundation has been studied. It is shown that the lateral displacement of embankment has been distinctly effected by the sloping of foundation, the value of lateral displacement on sloping foundation is greatly bigger than that of horizontal foundation. The peak value of lateral displacement can be effectively reduced by geotextile. With the same condition, geotextile in sloping foundation acts a more important effect than that of horizontal foundation. The development of plastic zone of embankment has been impeded and separated by geotextile, which enhanced the stability of embankment. The results also indicated that, if necessary, reinforcement such as anti-slide pile should be layout at lower toe of embankment on sloping weak foundation.

Case Study of Degrading Permafrost beneath a Road Embankment

This paper reports on a case study of degrading permafrost beneath a road embankment in Northern Manitoba, Canada. Field measurements of ground temperatures for a three-year monitoring period have been used in calibrating the geothermal model developed to reproduce the conditions and trends in the subsurface thermal regime beneath the embankment. The numerical model was used to investigate the future ground thermal regime of the foundation and evaluate the potential impacts of embankment construction and climate change. Particular interest was paid to the foundation soil near the toe of embankment where relatively rapid permafrost degradation was occurring.