Unreinforced Embankments Research Articles

Load Carrying Mechanism of Geocell Reinforced Embankment on Soft Soil

This paper investigates the influence of geocell reinforcement on the load carrying mechanism of embankments over soft soil. Using a geocell mattress beneath an embankment on soft soil, the size of the rupture zone in the foundation bed is found to have increased significantly, leading to increase in the mobilized shear resistance, and giving rise to enhanced bearing capacity. While the unreinforced embankment, owing to differential settlements, tends to crack and disintegrate, the geocell reinforced embankment continues to behave as a monolith up to a high surcharge pressure/fill height. The performance improvement tends to increase with increase in height of the geocell mattress. Strain variation in the geocell mattress indicates that its reinforcing efficacy is the largest at the central crest region of the embankment and decreases toward the toe. As the geocell mattress behaves as a semirigid slab, when it is present, the stress dispersion angle tends to increase significantly. Considering the stress dispersion zone as an equivalent rigid footing, the bearing capacity of unreinforced and geocell reinforced embankments are analyzed. The predicted bearing capacities are found to be in close agreement with the experimentally observed ones. Three-dimensional numerical analyses indicate that the pressure–settlement behavior of the embankments observed in the model tests is reproduced at large scale.

Large-scale Field Tests of the Performance of Geogrid-reinforced Piled Embankment over Soft Soil

When constructing superstructures on soft soils, geogrid-reinforced embankments and pile-supported embankments are used widely to improve the soft foundation and prevent issues including excessive settlements and large lateral displacements, so it is crucial to understand and evaluate their performance systematically. This study focuses on a case of piled embankments for a motor-racing circuit under construction in China. Two large-scale field tests of pile-supported embankments with and without reinforcement were carried out to investigate the effect of geosynthetic reinforcement on the improvement of embankments. During long-term monitoring, instruments in the test sites measured earth pressures, settlements, lateral displacements, and pore water pressures, and the performances of the reinforced or unreinforced embankments were examined. Test results from the two test sites under similar loading are compared, and it is concluded that the geosynthetic-reinforcement considerably influences the improvement of load transfer and diminishment of total and differential settlements. The lateral restraint provided by the geogrids also reduced the lateral soil displacement and the influence of subsoil depth. The smaller excessive pore water pressures in the site with reinforcement were associated with the enhanced load transfer due to the geogrids. This study provides an important reference for the design and construction of this circuit and other related projects.

Mechanical Behavior of Reinforced Embankment with Different Recycling Waste Fillers

The application of construction and demolition (C&D) waste and used tires in geotechnical engineering contributes to the demand of the sustainable development. This study mainly compared the mechanical behavior of pure sand embankment (PSE), C&D material embankment (CDME), sand-tire shreds mixture embankment (STSME) through a scale model test. Effects of tire shreds content, the first layer geocell reinforcement burial depth, geocell reinforcement depth and compaction degree on the bearing capacity of embankments were investigated. Moreover, embankment load-settlement ratio, the reinforced bearing capacity ratio, the bearing capacity improvement factor (IF), the embankment surface deformation, and the vertical earth pressure distribution inside the embankment were discussed. Results indicate that both C&D material fillers and sand-tire shreds mixture can improve the bearing capacity and stability of embankment slopes. However, C&D material is better than sand-tire shreds mixture in the improvement. The optimum value of tire shreds content is 5%. The reinforcement effect of geocell decreases with the increase of reinforcement depth. With the increase of the buried depth of the first layer, it first increases and then decreases. With the increase of compaction degree increases. The minimum earth pressure appears near the slope. The bearing capacity of CDME is greater than STSME. The ultimate bearing capacity of CDME under the action of the geocell is twice that of the unreinforced embankment.

Analysis of the Stability of Reinforced Plastic Waste Treated Clay as Embankment Fill on Soft Soils

The purpose of this study is to analyze the suitability and stability of clay soil treated with plastic waste as an embankment fill. Plastic wastes are used to stabilize the locally found weak clay. The locally found weak clay soil is stabilized with plastic waste. The stability analyses of the proposed slope have been done by finite element method using geotechnical software PLAXIS 2D. The stability analyses were performed for different conditions considering the geometry of the embankment, characterization of fill material, and the strength of reinforcement. Different models were analyzed to determine the safe height, side slope, and tensile strength of geogrid required to stabilize the embankment in addition to that of unreinforced embankments. The factor of safety of each trial is taken to check the stability of the modeled embankments. Accordingly, the factor of safety increases as geogrid axial stiffness increases greater than 500 kN/m. The analysis results revealed that with increasing slope height and slope angle the factor of safety decreases. This study found that plastic waste treated clay could be used as embankment fill when reinforced with geogrid.

Experimental Study on Embankment Failure Law and Reinforcement Technology for Highway Widening Project over Silt Soils

Abstract In the highway widening project, it is of great importance to take measures to control the differential settlement between the new and old embankment, therefore improving the stability of the new embankment. This article presents a series of model tests to analyze the failure law of the new embankment and compare the reinforcement effects of different reinforcement technologies. The test results show that the new embankment is unstable because of the slope slippage under ultimate load. In the reinforcement test of gravel pile, reaming phenomenon occurred at the top of the pile, and both of the values in pavement settlement and embankment lateral deformation are similar to those of the unreinforced embankment. In the geogrid reinforcement test, the embankment settlement can be reduced by restricting the lateral deformation of the new embankment with geogrid, where the settlement is 41 % less than that of the unreinforced scenario. In the cement fly ash gravel (CFG) reinforcement test, the pavement load is transferred to a deeper layer of the embankment by CFG piles, a soil arch effect with the surrounding soil is formed to restrict the lateral deformation and slippage, and the pavement settlement is 46 % less than that of the unreinforced scenario. According to the test results, the order of effectiveness for the reinforcement methods is CFG piles > geogrid > gravel pile.

DEM Simulation of the Load Transfer Mechanism of a GRPS Embankment with a Fixed Geogrid Technique

As a new technique, a fixed geogrid in a geogrid-reinforced and pile-supported (GRPS) embankments has been used to reduce the total and differential settlement. To investigate the load transfer mechanism of the fixed geogrid technique of a GRPS embankment, three discrete element method (DEM) models of pile-supported embankments were established, including an unreinforced embankment, a geogrid reinforced embankment, and a fixed geogrid reinforced embankment. The efficacy of the pile, the evolution law of the contact force chain and the axial force of the reinforcement, and the microscopic load-bearing structure of the soil were investigated. Numerical simulation results showed that the embankment self-weight and surcharge load were transferred to the pile through the soil arching and tensile membrane effect. The settlement could be effectively reduced via the addition of the reinforcement, and the fixed geogrid technique was more conducive to improving the load-bearing ratio of the pile than the traditional reinforcement technique. Compared with the traditional technique of a GRPS embankment, the fixed geogrid technique had a better effect on reducing the total and differential settlement. With the increase in the surcharge load and the settlement of the soft subsoil, the reinforcement transferred a greater load to the pile. The results also showed that the stress of the embankment fill was concentrated at the pile top in all three models. The GRPS embankment with a fixed geogrid technique had a lower soil stress concentration than the other two cases. The contact force chain and stress in the embankment also showed that the reformation of the microscopic load-bearing system of the embankment fill was the internal mechanism that caused the development of the soil arching and the redistribution of stress. Furthermore, the evolution of the fabric parameters in the arching area could reflect the evolution of the soil arching structure. In the fixed geogrid case, the proportion of the load transferred to the pile from the soil arching effect was reduced, and the vertical load transferred to the pile top by the tensile membrane effect accounted for 22–28% in this study. Under the combined effect of the tensile membrane and the soil arching, the efficacy of the pile could increase by 10%.

Investigation of drainage function of geosynthetics for basal-reinforced embankments

This study investigates the behaviour of basal-reinforced embankments under seepage flow. For this purpose, physical embankment models with dimensions of 195 cm long, 100 cm wide and 110 cm high were constructed in the laboratory. The seepage gradient within the embankment was generated by applying a constant water head of 100 cm at the water compartment located behind the models. The unreinforced embankment experienced seepage erosion at the toe section which triggered deep-seated global failure. Due to the limited transmissivity of the non-woven geotextile, the geotextile-reinforced embankment exhibited similar pore-water pressure distribution to that of the unreinforced embankment, which resulted in lateral spreading failure between the base of the embankment and the non-woven geotextile. In contrast, the geocomposite drain, which has a higher in-plane flow capacity compared to that of the geotextile, significantly alleviated the pore-water pressures within the embankment. The behaviour of the physical models was verified numerically by variably saturated flow modelling conducted for a wide range of in-plane permeabilities for the basal reinforcement. The effect of increasing in-plane permeability of the basal reinforcement layer on pore-water pressure reduction was quantified irrespective of the geosynthetic type.

Model Test Study on Dynamic Response of Expressway Plastic-Reinforced Earth Embankment under Earthquake

Aiming at the seismic response of plastic geogrid-reinforced embankments, with Zhounan Expressway as the research engineering background, a self-designed seismic-rainfall coupled slope model test system was designed and used to produce 1 : 20 scale plastic geogrid-reinforced embankments. Moreover, the physical model of the unreinforced embankment under Hanshin wave, Wenchuan wave, Tianjin wave, etc. was also studied to carry out comparative analysis on seismic response and dynamic response on test model. The dynamic characteristics and dynamic response of the embankment model were tested from low to high seismic intensity; the changes of the embankment’s natural frequency, damping ratio, acceleration at the measuring point, and dynamic earth pressure were analyzed; and the main influencing factors and damage to the embankment seismic response feature were discussed herein. The test results showed that the initial natural frequency of the reinforced embankment was 42.4% higher than that of the unreinforced embankment, and its initial damping ratio reduced by 19.4%. The attenuation effect of the natural frequency and damping ratio of the reinforced embankment with the loading history was significantly lower than that of the unreinforced embankment. Embankment reinforcement exhibited a very good inhibitory effect on the PGA amplification effect of the embankment, and the inhibitory effect on the interior of the slope was more significant than that on the slope. Moreover, the type of seismic wave, the amplitude of the seismic wave, and the frequency of the seismic wave significantly influenced the PGA amplification effect of the embankment. The peak dynamic soil pressure of the unreinforced embankment at the same location was significantly greater than that of the reinforced embankment. The two embankment models showed significantly different antivibration damage performance. After the peak acceleration of 2 m s-2 was loaded, no cracks were seen on the surface of the embankment model. When the peak acceleration of 3 m s-2 was loaded, on the slopes of the two embankment models, smaller cracks were observed in the middle and upper parts of the face. When the peak acceleration of 4 m s-2 was loaded, the failure of the unreinforced embankment model was obvious. Large cracks on the top of the slope could reach 16 mm in width, and 27 mm settlement appeared at the top, and the slope was convex. The reinforced embankment model was only on the slope shoulder. Moreover, there were fine cracks on the top, and the slope top settlement was less than 5 mm. The research results provide theoretical support for preventing and controlling the road embankment vibration diseases and improving highway durability design.

Influence of geocell on bearing capacity and settlement of railway embankments: an experimental study

ABSTRACT Despite using geocell for many geotechnical purposes, the application of geocell on the mechanical behaviour of railway embankments have been less investigated in the technical literature. To this end, this paper aims to investigate the effect of geocell layers on both bearing capacity and settlement of railway embankments. In this regard, six 1:20 scaled down railway embankments were constructed in the lab environment. The embankments consisted an unreinforced embankment and four geocell-reinforced embankments including 1, 2, 3, 4 and 5 geocell layers reinforcement in which geocell layers were placed non-spacing in the embankment body from the crest to down. After installation of linear variable differential transformers (LVDTs) and load cells, each embankment was subjected to a gradually uniform load on the crest until the occurrence of the failure while the data were recorded simultaneously. The results have shown that adding geocell layers up to 4 layers results in improving both bearing capacity and settlement of the embankments while adding the fifth geocell layer represented a performance almost such as reinforced embankments with 4 layers. However, embankment reinforced using four geocell layers showed the maximum bearing capacity and minimum settlement by 38.6 and 37%, respectively, in comparison with the unreinforced model.

Analysis of the stability and seismic behavior of the geosynthetic-reinforced embankments under earthquake

The stability and seismic behavior of geosynthetic-reinforced embankments during the earthquake is not well known. In this paper, the damage types of embankments were summarized, and the seismic stability of reinforced embankment were analyzed through an earthquake damage investigation in the Wenchuan earthquake region. Then, large-scale shaking table model tests were performed on the geosynthetic-reinforced embankment. The results show that the damage level of the reinforced embankment was almost less than that of the unreinforced embankment. The peak seismic earth pressure was nonlinear along the height of the embankment, the largest peak seismic earth pressure was roughly in the middle of the embankment slope. The peak ground accelerations (PGA) amplification factor first showed an increasing pattern and then a decreasing pattern with the increase of elevation, but there was a final increasing trend along the height of the reinforced embankment. The results can help to establish the proper design of the reinforcement embankments under earthquake conditions.

Centrifuge model studies on the settlement response of geosynthetic piled embankments

The paper aims at comparing the deformation behaviour of unreinforced embankments, basal reinforced embankments and geosynthetic reinforced embankments with floating and end bearing piles. The floating piles were terminated within the soft foundation soil, while the end bearing piles transfer the loads to a hard stratum. Four series of centrifuge model tests were conducted at gravity g = 40, using the 4.5 m radius large beam centrifuge facility at the Indian Institute of Technology Bombay. The tests were performed at constant pile spacing, and the embankment was constructed using an in-flight sand hopper. The deformations were measured using Linear Variable Differential Transformers (LVDTs). A digital image analysis technique was employed to arrive at the surface displacements, displacement vectors, and displacement contours. The geogrid reinforced embankments resting on end bearing piles and floating piles showed 88% and 44% lesser settlements respectively, compared to the unreinforced embankments. The geogrid reinforcement helps to distribute the load uniformly. A deep-seated slope failure was observed for unreinforced embankments. The piled embankments proved to be a practical solution for construction without prolonged waiting periods for pre-consolidation of the foundation soil.

Effect of vibration frequency on settlement characteristic of reinforced embankment by geogrid with strengthened nodes using DEM simulation

Geogrid with strengthened nodes (GSN) is a new reinforcement system that is formed by attaching blocks of a certain thickness to the joints of the longitudinal and transverse ribs of an ordinary biaxial geogrid to form strengthened nodes. A series of discrete element method (DEM) simulations were performed to investigate the dynamic response of GSN-reinforced embankment at various vibration frequencies and compare the reinforcing effect of GSN with that of the ordinary geogrid. It was concluded that the settlement ratio of the loading platen at the top of the unreinforced and reinforced embankment decreases with the increase of the vibration frequency. As the frequency increases, the difference between the settlement ratios decreases, which is especially evident in the reinforced embankment. At the same frequency, GSN performs better in restricting the settlement ratio than the ordinary geogrid, and as the frequency increases, the reinforcing effects of both the ordinary geogrid and GSN decrease. The displacement fields of the simulated embankments were analyzed. It was found that the movement of soil particles below the loading platen is restricted due to the presence of the geogrid, resulting in less settlement of the loading platen and smaller lateral deformation of the embankment slope, compared with the unreinforced embankment. As for the GSN-reinforced embankment, the strengthened nodes provide resistance to soil particles, leading to a more effective reinforcing effect, so that the displacement vectors are even smaller.

Experimental study of embankments with different reinforcement materials and spacing between layers

Worldwide, waste tires are being discarded in landfills at a huge environmental cost, therefore, their use as a three-dimensional reinforcement material is a wise solution to reduce their environmental impact, and fire risk in the case of shredded tires. In this research a series of experimental model tests of embankments reinforced with Geocell and tires were conducted to compare the performance of these types of reinforcement. The models tested had different Geocell embedment depths, number of Geocell layers, vertical spacing between Geocell layers and density or soil stiffness. Testing consisted of applying pressure at the crest of the embankment and monitoring the pressure distribution, as well as the vertical and horizontal deformations inside of the embankment. The results suggested that when compared with unreinforced embankments, reinforced embankments effectively improve the bearing capacity, thereby, reducing vertical and lateral displacements. This study also showed that an optimal embedment depth and spacing between Geocell reinforcement layers can further improve the slope performance. Comparisons between Geocell reinforced embankments and waste tire reinforced embankments, showed that waste tire reinforcement has a superior performance over the Geocell-reinforced embankments. This difference in performance between the two types of reinforcement is more apparent if the embankment backfill has lower stiffness. i.e. lower density.

Experimental and 3-D Finite Element Analyses on Geocell-Reinforced Embankments

Abstract This article presents an improvement in performance that is due to the inclusion of geocell in the embankment base overlying a soft foundation bed. Firstly, model tests were conducted on embankments over soft clay, in which a mattress of geocell reinforcement was placed at the interface between the embankment and soft foundation bed, which was trimmed at the embankment’s toe. Parameters like type of infill material and aspect ratio (pocket-size) of the geocell layer were varied during the experimental program to observe their effects on the performance of geocell-reinforced embankments. A model test on unreinforced embankment was also carried out to show influence on performance and improvement as a result of the presence of geocell reinforcement. A significant percentage of decrease in vertical settlements, lateral deformations, and heaving—with a percentage of increase in the load-bearing capacity of embankments reinforced with geocell—were observed from the test results, as compared to unreinforced embankments. The experimental results were validated using three-dimensional finite element analyses of geocell-reinforced embankments. The results of the finite element method (FEM) showed good agreement with that of the model tests. The displacement and vertical stress distributions of geocell-reinforced embankment were also studied using FEM. Lastly, a parametric study was carried out to observe the influence of the stiffness of subgrade soil, tensile strength of geocell material, stiffness of infill material, effective friction angle of infill material, and effective cohesion of embankment soil on the performance of geocell-reinforced embankment base.

Investigating the effect of geogrid on stabilization of high railway embankments

This paper investigates the effect of geogrid on controlling the stability and settlement of high railway embankments using laboratory testing and finite element modeling. To do this, five series of embankments with 50 cm height were constructed, at a scale of 1:20 and then were uniformly loaded on the crest in a loading chamber in dimensions of 240 × 235 × 220 cm. In this regard, the embankments of the first series were constructed without geogrid reinforcing layers. Following to preliminary numerical simulations for determining the appropriate level of geogrid layers installation, the second to fifth series of embankments were constructed. These embankments were reinforced with one to four layers of geogrid respectively and finally, the results of their load in terms of settlements were compared. In these studies, the reinforced embankments with a single geogrid layer had 7.14% raise in bearing capacity and 11.24% reduction in settlement respectively, in comparison with the unreinforced embankment. The obtained results for the third to fifth series of embankments were respectively in order of (19, 36.14), (26.3, 52.8) and (28.9, 53.42)%. In the next stage, by modeling the embankments in the PLAXIS 2D software, the results were validated by the values obtained through laboratory models. In continuation of the study, real embankments with heights of 5, 10, 15, and 20 m were simulated and placed under LM71 loading pattern (Eurocode, 2003). In this respect, the impact of important effective parameters such as number of geogrid layer, soil characteristics, embankment dimensions, interface coefficient between soil and geogrid and tensile strength of geogrid on bearing capacity and settlement have been studied. The numerical results like the experimental ones, confirmed the increase in bearing capacity and settlement diminishing with definite increase in the geogrid layers, so that more geogrid layers do not affect these parameters. With respect to improving the soil characteristics and reducing the height of embankments, the FEM models showed decreasing effect of geogrid tensile strength on embankment crest settlement. On the other side, the value of geogrid-soil interface coefficient has minor effect on both settlement and sliding safety factor.

Deterministic and random FEM analysis of full-scale unreinforced and reinforced embankments

This paper presents the results of numerical simulations of one physical full-scale unreinforced embankment and two reinforced embankments taken to failure using a strip footing. The embankments were 3.4 m in height and were constructed with the same slope using the same sand backfill. One reinforced embankment was constructed with a relatively weak and extensible geogrid material and the other with a relatively stronger and stiffer geogrid product. Deterministic finite element method (FEM) and random finite element method (RFEM) analyses were carried out and the results compared to observed performance. Analyses were performed assuming vertical spatial variability in soil strength at a scale of fluctuation matching the compaction lift thickness of the physical tests and treating the soil as a random (homogeneous) material. Both deterministic and probabilistic analyses showed good agreement with the measured bearing capacity of the footing in each full-scale test. However, the assumption of vertically anisotropic spatial variability in soil strength was shown to achieve a better match with the observed failure mechanism in each of the embankments.

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.

Limit analysis of reinforced embankments on soft soil

Previous research into the stability of reinforced embankments founded on soft soil has presented limited studies based on a narrow range of assumed failure mechanisms. In this paper comprehensive parametric studies of reinforced and unreinforced embankments were conducted using the general purpose computational limit analysis approach Discontinuity layout optimisation (DLO). Comparisons with previous Limit Equilibrium and FE results in the literature showed good agreement, with the DLO analysis generally able to determine more critical failure mechanisms. Simplified, summary design envelopes are presented that allow critical heights and reinforcement strengths to be rapidly determined based on soft soil strength and depth, and show how the balance between soft soil strength and reinforcement strength combines to affect overall stability.

Study of a small scale tyre-reinforced embankment

Tyre-reinforced soil, used to improve slope stability, retaining walls, etc., has an excellent mechanical performance, and has the capability of a wider application and of reducing waste disposal costs. This article studies the stress and deformation characteristics, as well as the influencing factors related to the reinforcing arrangement, through small scale model embankment tests. It is shown that tyre reinforcement highly improved the strength of the model embankments; much higher stresses were mobilised inside the soil mass (around 2 times higher in comparison with the unreinforced embankment). There is an obvious plastic flow in the unreinforced embankment, while the plastic zone, on the reinforced embankments, was difficult to determine. Comparisons between the vertical settlement of the embankments show that the settlement of the reinforced embankment is roughly half of the settlement of the unreinforced embankment, for the same vertical load applied. These results also show that the tests with the top layer of reinforcement nearer the load application area and a smaller distance between the intermediate layers have a better performance, particularly in dense fabrics. The location of the top reinforcement layer seems to dominate the failure modes of the reinforced and unreinforced embankments, the horizontal deformations and the location of the shear bands in the embankment.

Seismic response of embankment slopes with different reinforcing measures in shaking table tests

In order to study the seismic response of the embankment slopes with different reinforcing measures, shaking table tests were performed on three embankment slope models (i.e., unreinforced embankment slope, 2-layer reinforced embankment slope and 4-layer reinforced embankment slope). Wenchuan earthquake motions and white noise excitations were performed to investigate the change of the model parameters, the horizontal acceleration response, the vertical acceleration response and the dynamic earth pressure response of embankment slopes. A comparison was made on the seismic response among the embankment slopes with different reinforcing measures. The results show that the natural frequency of reinforced embankment slope is larger than that of unreinforced embankment slope, and the reinforced embankment slope is less sensitive to seismic excitation. Horizontal acceleration response is obviously amplified by embankment slope. Horizontal acceleration magnification presents a decreasing trend with the increase of the peak value of input horizontal acceleration, and the decreasing ratio is higher for reinforced embankment slope. The vertical acceleration magnification of reinforced embankment slope is much smaller than that of unreinforced embankment slope, and the nonlinear characteristic of embankment slope in vertical direction is not as obvious as that in horizontal direction. Residual earth pressure is mainly induced at the upper part of embankment slope.