Geogrid-reinforced Soil Research Articles

3d Numerical Analysis of Bearing Capacity of Square Foundations on Geogrid Reinforced Soil

Results of numerical simulations on square footing supported by reinforced and unreinforced sand bed are presented and discussed. The primary objective of this study is to evaluate the performance of geogrid layers in improving the bearing capacity of the square footings and to study the influence of different parameters such as the width and embedment depth of the foundation, on the overall performance improvement of the footing. The optimum values of reinforcement parameters (such as vertical spacing between top layer of reinforcement and bottom of the foundation, the width of the reinforcement layers, the distance between consecutive reinforcement layers and the depth of reinforcement zone) have been obtained from previous experimental studies, and was applied in numerical modeling. The results of the numerical simulations are compared with the experimental and analytical results published by different authors. It was found that with increasing the width and embedment depth of the foundation, the rate of increment of bearing capacity due to reinforcing with geogrid, was reduced.

장기간 강우특성 변화에 따른 국내 사면의 안정성

Shallow landslides and debris flows are a common form of soil slope instability in South Korea. These events may be generally initiated as a result of intense rainfall or lengthening rainfall duration because of the effects of climate change. This paper presents the evaluation of rainfall-induced natural soil slope stability and reinforced soil slope instability under vertical load (railway or highway load) throughout South Korea based on quantitative analysis obtained from 58 sites rainfall observatories for 38 years. The slope stability was performed for infinite and geogrid-reinforced soil slopes by taking an average of maximum rainfall every ten years from 1973 to 2010. Seepage analysis is carried out on unsaturated soil slope using the maximum rainfall at each site, and then the factor of safety was calculated by coupled analysis using saturated and unsaturated strength parameters. The contour map of South Korea shows four stages in 10-year-time for the degree of landslide hazard. The safety factor map based on long term observational data will help prevent rainfall-induced soil slope instability for appropriate design of geotechnical structures regarding disaster protection.

Three-Dimensional Analysis of Geogrid-Reinforced Soil Using a Finite-Discrete Element Framework

AbstractThree-dimensional analysis of soil-structure interaction problems considering the response at the particle scale level is a challenging numerical modeling problem. An efficient framework that takes advantage of both the finite- and discrete-element approaches to investigate soil-geogrid interactions is described in this paper. The method uses finite elements to model the structural components and discrete particles to model the surrounding soil to reflect the discontinuous nature of the granular material. The coupled framework is used in this study to investigate two geotechnical engineering problems, namely, strip footing over geogrid-reinforced sand and geogrid-reinforced fill over a strong formation containing void. The numerical model is first validated using experimental data and then used to provide new insights into the nature of the three-dimensional interaction between the soil and the geogrid layer.

Numerical Simulation of Geogrid-Reinforced Soil Barriers Subjected to Differential Settlements

AbstractA numerical simulation of centrifuge model tests was carried out to develop an understanding of the behavior of geogrid-reinforced soil barriers (GRSBs) of landfill covers subjected to differential settlement. The influence of the axial stiffness of the geogrid, soil-geogrid interface friction, overburden pressure, and thickness of the soil barrier on the overall performance of GRSBs was investigated. Results from the study indicate that unreinforced soil barriers (URSBs) experience tensile stresses and strains throughout their thickness at the zone of maximum curvature; however, with the inclusion of geogrid within the soil barrier, the depth of the tension zone was found to be reduced significantly. A significant reduction in the magnitude of tensile stresses and strains in particular below the location of the geogrid was noticed with an increase in the axial stiffness of the geogrid. The results demonstrate that the geogrid layer mobilizes higher tension and thereby transfers lesser bending str...

Numerical Study on Seismic Performances of Geogrid Reinforced Soil Retaining Walls in Liquefiable Backfill Sand

Numerical Study on Seismic Performances of Geogrid Reinforced Soil Retaining Walls in Liquefiable Backfill Sand

Laboratory Performance of Geogrid-reinforced Soils Subjected to Freezing and Thawing

Abstract This paper reports results from bench-scale plane-strain laboratory tests conducted in order to investigate the behavior of geogrid-reinforced silt specimens during freezing and thawing cycles. Soil–geogrid interaction was analyzed through comparison of the soil and geogrid strains. Vertical and lateral pressures were applied to the specimens to simulate anisotropic loading conditions in the field. Reinforced and unreinforced specimens were subjected to cycles of freezing (−25°C) and thawing (+23°C) temperatures inside a walk-in temperature-controlled environmental chamber. Measured geogrid strains at the end of 12 freezing-thawing cycles were on the order of 0.57 %. An additional strain of this magnitude in the reinforcement due to the freezing-thawing cycles would have only minimal effect on working strain levels in the design, which range from 1 % to 2 %. However, the strains induced by freezing and thawing can approach working design strains as the number of cycles increases. This could have significant long-term implications if accumulated strains were to overstrain the geogrid. The soil deformations were observed to be mostly horizontal. This pattern of deformations during the freezing and thawing of silt could result in shallow sliding at the face of slopes and embankments. The soil strains were higher than the geogrid strains, indicating relative movements between soil and reinforcement, mostly during thawing.

Evaluation of the effect of compaction on the behavior of geosynthetic-reinforced soil walls

This paper presents a physical model study of the influence of compaction on the behavior of geogrid-reinforced soil walls. Experiments were accomplished in a facility at the Geotechnical Laboratory of COPPE/UFRJ. For soil compaction, two different types of hand-operated compactors were used: a vibrating plate and a vibratory tamper. Equivalent vertical stresses for the vibrating plate (referred to as the “light compactor”) were much lower than the corresponding value of the vibratory tamper (referred to as the “heavy compactor”). Mobilized tension along the reinforcements and external and internal displacements of the wall were monitored. The results showed that the effect of soil compaction is not limited to a reduction of the soil void ratio. Compaction has led to a significant increase in the horizontal stress inside the reinforced soil mass and generates a kind of pre-consolidated material. Analyses of results showed that compaction has played a decisive factor in terms of the reinforcement tensions and post-construction displacements. The connection load was much less in a wall with heavy compaction than that in a wall with light compaction. Results also showed that the position of maximum tensile force mobilized in the reinforcements was nearer to the face in the wall with heavy compaction. On the other hand, the mobilized tension measured along the reinforcement layers at the end of construction in the wall where heavy soil compaction was used was much higher than the values of tension measured in the wall where light soil compaction was applied. Nevertheless, it was observed that the difference in the mobilized tensions in the reinforcements of these two walls decreased with increase in the value of the external surcharge load.

Behavior of 22m Two Tiered Geogrid Reinforced Soil Wall

Behavior of 22m Two Tiered Geogrid Reinforced Soil Wall

LRFD Calibration of the Ultimate Pullout Limit State for Geogrid Reinforced Soil Retaining Walls

AbstractThe results of load and resistance factor design (LRFD) calibration are reported for the pullout limit state in geogrid reinforced soil walls under self-weight loading and permanent uniform surcharge. Bias statistics are used to account for the prediction accuracy of the underlying deterministic models for load and pullout capacity and the random variability in the input parameters. The paper shows that the current AASHTO simplified method to calculate reinforcement loads under operational conditions is overly conservative leading to poor prediction accuracy of the underlying deterministic model used in LRFD calibration. Refinements to the load and default pullout capacity models in the AASHTO and Federal Highway Administration guidance documents are proposed. These models generate reasonable resistance factors using a load factor of 1.35 and give a consistent probability of pullout failure of 1%. A comparison with the allowable stress design (ASD) past practice shows that the operational factors ...

Evaluation of Direct Shear Tests on Geogrid Reinforced Soil

This paper presents a program of direct shear tests in soil reinforced with geogrids, carried out with large-scale equipment. A woven geogrid was placed in sandy soil and positioned with different inclinations inside the shear box. The strength parameters of the soil-geogrid interface were obtained from shear tests with the geogrid positioned horizontally in the sand. The direct shear tests with inclined reinforcement revealed the strength differences related to the reinforcement inclination, seeking to define the most favorable positioning of the geogrid for construction works in reinforced slopes. An analysis of the deformed configuration of the geogrid is presented, based on the measured position of the grid at the end of the shear tests. Finally, numerical simulations of the direct shear tests were carried out, allowing an assessment of the tensile forces acting on the inclined reinforcement. These studies allowed a clear definition of the soil region that is not distorted during the direct shear test, being subject to a simple translation only. The geogrid’s displacements were found to be anti-symmetrical in relation to the failure plane. Shearing was concentrated at the central region of the specimen’s height, with the upper and lower regions being simply subjected to translation, with no distortion. The inclination of the reinforcement within the soil has a significant influenc

Vertical earth pressure increments due to vibratory roller on geogrid-reinforced embankments

ABSTRACT: There is an increasing demand for geogrid-reinforced soils in geotechnical areas. Geogrid-reinforced soils have been used to minimise the settlement and to increase the bearing capacity of roadway constructions, especially embankments. In this study, field tests have been performed to investigate the effects of geogrid reinforcement under various conditions of embankment heights, the number of reinforced layers of the geogrid, and the mechanical properties of the soils and the geogrid. Dynamic loading generated by a vibratory roller was applied to the ground surface of the embankment and the dynamic vertical earth pressures were measured using an electrical dynamic pressure cell. The results of these measurements indicate that the dynamic vertical earth pressure increment from the vibratory roller decreases for greater embankment heights above the measuring location, which is expected, and the geogrid has little or no effect on the dynamic vertical earth pressures induced by the vibratory roller.

Evaluation of Extent of Damage to Geogrid Reinforced Soil Walls Subjected to Earthquakes

ABSTRACT The aim of this study is to establish a simple method for evaluating the extent of damage to geogrid reinforced soil walls (GRSWs) subjected to earthquakes. Centrifuge tilting and shaking table tests were conducted to investigate the seismic behaviour of GRSWs, with special focus on the effects of the tensile stiffness of the geogrids, the pullout characteristics and the backfill materials. As a result, it was found that GRSWs showed large shear deformation in the reinforced area after shaking, that such deformation was influenced by the tensile stiffness of the geogrids, the pullout resistance and the deformation modulus of the backfill material, and that finally slip lines appeared. However, the GRSWs maintained adequate seismic stability owing to the pullout resistance of the geogrids, even after the formation of slip lines. It is considered that such slip lines appeared due to the failure of the backfill material. Since the maximum shear strain occurring in the backfill can be roughly estimated from the inclination of the facing panels, using a simple plastic theory, it is possible to evaluate whether the backfill has reached its peak state or not. The formation of slip lines observed in the centrifuge model tests could be well explained by this method. Finally, the method is proposed to estimate the failure sections in the GRSWs using a Two Wedge analysis.

Field Behavior of a Geogrid Reinforced Soil Retaining Wall with a Wrap-Around Facing

Abstract The earth pressure and deformation characteristics of a geogrid reinforced soil retaining wall were monitored during and for a period of 1.5 years after construction. Both vertical and lateral soil stresses were recorded with vibrating-wire earth pressure cells, and the reinforcement deformations were measured using flexible displacement sensors. The maximum vertical foundation pressure along the wall’s reinforcements occurred at the center of the reinforcement, gradually decreasing towards the front and back ends. The measured lateral earth pressure within the reinforced soil wall is non-linear along the wall height, and the value is less than the theoretical active lateral earth pressure. The distribution of tensile strain along the reinforcements within the lower portion of the wall has two peak values. The potential failure surface of the wall closely follows the theoretical Coulomb failure surface of an unreinforced backfill.

CENTRIFUGE TESTS ON SEISMIC STABILITY OF THE DAMAGED GEOGRID REINFORCED SOIL WALL

Recent huge earthquakes have caused severe and small damage to a number of geogrid-reinforced soil walls. For proper repair or reconstruction, it is necessary to evaluate degree of damage of those structures. In this research, the pullout test of geogrid subjected to the unloading-reloading process was carried out to learn its effects on the pullout resistance. The results were then used to evaluate the factor of safety and sliding surface of the damaged geogrid reinforced soil wall. GRSW models in centrifuge shaking and tilting table tests under 50G were performed. The damaged GRSW models were first achieved by both shaking and tilting. The damaged GRSW were then subjected to unloading-reloading process until the full collapse occurred. The pullout peak value and residual value using in current design of GRSW were also discussed.

Development of rational seismic design method for geogrid-reinforced soil wall combined with fibre-mixed soil-cement and its applications

ABSTRACT: The combined use of a geogrid-reinforced soil wall with a fibre-mixed soil-cement wall (GRSW-FSC) has recently been developed, and its application has grown rapidly. The results of previous centrifuge shaking-table tests have clearly shown the effectiveness of the GRSW-FSC to achieve a higher seismic stability than conventional reinforced soil walls. The current research investigates the effect of geogrid arrangement and the width of the soil-cement wall in order to develop a new rational design method for GRSW-FSCs in field applications. To achieve this goal, a series of centrifuge shaking-table tests was conducted. The results show that even if the width of the fibre-mixed soil-cement wall is reduced by 20%, the GRSW-FSC has enough seismic stability to resist severe seismic motions. Moreover, the effect of the length of the geogrid located at the upper part of the wall plays a more important role in seismic stability than that at the lower part. Based on these two results, a new design concept was developed. The procedure for this new design method is addressed in detail in this paper, and some examples of case studies using this new design concept are given.

A new optical fibre sensor to assess the stability of geogrid-reinforced soil walls

ABSTRACT: It is not easy to assess the stability of vertical soil walls reinforced by geogrids during and after construction. This paper describes a unique monitoring system called an ‘optical fibre sensor geogrid' in which an optical fibre sensor is installed within a longitudinal member of a geogrid reinforcement material. The structure of the optical fibre sensor and the measuring method to record strain in the geogrid are described. Laboratory tests were first carried out to assess the accuracy of geogrid strain measurements using the optical fibre sensor method. Optical fibre sensor geogrids were then used to measure the strain in embedded geogrid layers in three reinforced soil walls constructed in the field. The system allows the stability of reinforced soil walls to be monitored continuously during and after construction, and a stability evaluation index to be assigned to the walls based on peak strain readings.

Deformation analysis of reinforced soil retaining walls—simplistic versus sophisticated finite element analyses

Over the last two decades, different kinds of modular block have been increasingly used in the geogrid-reinforced soil retaining walls. The simulation of such wall behavior, which involves interactions between different structural components and backfill soils, requires a rigorous numerical procedure. Finite element is usually a preferred method, but this procedure, especially the soil constitutive models, is of different degrees of sophistication. It is always an issue of how simple or sophisticated should an analysis be conducted in replicating the actual behavior. In this article, a full-scale test wall was used to validate simplistic and sophisticated finite element analyses. Different types of finite element and material models were used in the two kinds of analysis to differentiate the level of simplicity or sophistication. The results obtained from stress-deformation analyses are presented and compared. It is shown that for wall construction that involves static loading conditions, simplistic nonlinear elastic and sophisticated elastoplastic analyses produced close and acceptable results.

Evaluation of Rainfall Infiltration and Compaction Effect on Soil-Geogrid Interaction Behavior

The geogrid-reinforced soil structures play important roles in the reinforcement applications since 1980s. Generally in design of the geogrid-reinforced soil structures, the soil-geogrid interaction behavior is not directly considered. Instead, the interaction strength is represented by the consolidation drained strength of soil commonly. However, neglecting the effect of compaction and suction on enhancing soil strength in design possess great conservativeness, leading to the waste in engineering practice. Moreover, along with providing appropriate drainage, the effect of water presence on stability of reinforced soil structures is not specially considered in design. As a result, reinforced soil structures have the possibility to failure caused by rainfall even totally following design code. Therefore, a trend considering the compaction effect and suction influence on the soil structure's behavior has arisen. For such trend, soil-geogrid interaction behavior need to be carefully investigated paying attention to the infiltration to avoid failure due to the rainfall. In this research, improved pullout tests capable of simulating in-suit rainfall infiltration are conducted considering the influence of rainfall infiltration and compaction. In order to survey the infiltration effect on interaction behavior, the pullout behavior of infiltrated soil samples are compared with the pullout behaviors of dry soil sample and soil sample with optimum water content. And the soil samples in pullout test are prepared in different degree of compaction paying attention to the compaction effect. The test results demonstrate that the infiltration dramatically reduces the pullout strength of soil-geogrid interaction. Meanwhile, the compaction could not mitigate the harm of infiltration on the pullout strength although it is able to enhance the peak pullout strength obviously.

Static and seismic numerical modeling of geosynthetic-reinforced soil segmental bridge abutments

This paper presents numerical modeling verification of a block-faced geogrid-reinforced soil bridge abutment (‘segmental bridge abutment’), subjected to construction-induced loads and seismic loads. The static response of the well-instrumented Founders/Meadow segmental bridge abutment, near Denver, USA, during different stages of construction and in-service behavior, and also the static/seismic response of a carefully instrumented reduced-scale reinforced soil-retaining wall tested on a shaking table at the Royal Military College of Canada (RMC), have been used for numerical modeling verification purposes. A 2-D, explicit dynamic finite difference program was used to perform the analyses, with user-defined static/seismic constitutive models. The comparisons between the predicted results from the numerical models and the measured physical results from instrumented prototypes were judged to show good agreement for vertical and horizontal displacements, reinforcement forces, and vertical/horizontal soil pressures. The lessons learned to model the physical structures were used to investigate the seismic response of the Founders/Meadow segmental bridge abutment.

Mechanism of geogrid reinforced soil at bridge approach

Using Geogrid-Reinforced Soil (GRS) we studied the working mechanism and design method of GRS at bridge approach with high backfill by field experiment. In a highway section where the height of backfill is 13.5 meters, geogrids were used at two bridge approaches to address the bumping problems. Some soil pressure cells were used to measure the normal and lateral soil pressure at different locations in the roadbed. The experimental results indicate that geogrids in geogrid-reinforced soil (GRS) could produce an uplift force, the closer the location to the abutment, the larger the uplift force, and the reduction of measured soil pressures compared with theoretical values was the largest at the bottom of roadbed, less at the top than at the bottom, and the least in the mid-height of roadbed than at the bottom. These findings are different from those of the traditional greogrid-reinforced subgrade design method.