Geosynthetic-reinforced Soil Walls Research Articles

FEM and ANN analyses of short and tall geosynthetic reinforced soil walls: Evaluation of various effective aspects and ASSHTO acceptable design methods

FEM and ANN analyses of short and tall geosynthetic reinforced soil walls: Evaluation of various effective aspects and ASSHTO acceptable design methods

Seismic analysis of geosynthetic-reinforced soil walls in tiered configuration

Research on geosynthetic-reinforced soil (GRS) walls in tiered configurations is increasing gaining attention, with numerical methods being predominantly used in the past. In recent years, there has been a growing trend in conducting shaking table tests to further explore this area. However, traditional limit equilibrium (LE) methods are more preferred for design purposes. This study utilized a modified top-down approach, which is based on LE and pseudo-static methods to investigate the horizontal seismic force on the distribution of required tension along each reinforcement layer. The approach is initially extended from static analysis to seismic analysis for multitiered GRS walls. Parametric analyses are conducted to study the impacts that horizontal seismic coefficient, reinforcement length and spacing, internal friction angle of soil, height ratio of upper/lower tier, offset distance have on the internal stability of two-tiered GRS walls. Meanwhile, influences of wall batter and number of tiers on the critical offset distance for different seismic coefficients are assessed. Results indicate that the internal stability differs between the upper and lower tiers under seismic conditions, particularly with higher seismic forces, where the lower tier requires greater reinforcement tension to enhance its stability. Additionally, the critical offset distance grows with the increase in seismic coefficient, and it is sensitive to the internal friction angle of soil and the height ratio.

Numerical investigations of GRS wall performance with tiered configurations

Geosynthetic Reinforced Soil (GRS) walls have become increasingly popular as a result of their numerous advantages. In some cases these structures are constructed in a multi-tiered configuration, which makes their behavior more complicated. Nevertheless, the response of the multi-tiered walls is insufficiently explained by the existing design manuals and literature studies. This paper investigated the performance of GRS walls with multi-tiered configurations using two-dimensional (2D) finite element numerical models. This study compares the performance of two-tiered GRS walls with simple GRS walls (single-tiered). It also examines the impact of offset distance, backfill strength properties, and reinforcement parameters (vertical spacing and reinforcement length) on horizontal deformations and reinforcement tensile loads in two-tiered GRS walls. Adopting a multi-tiered configuration for GRS walls can significantly reduce both the horizontal wall deformation and the maximum reinforcement tensile loads. Additionally, the critical offset distance found in this study is significantly smaller than that recommended by the Federal Highway Administration (FHWA) guidelines. The finite element results also demonstrate that using high-quality backfill soil can minimize interaction between lower and upper tiers. Using a uniform reinforcement length of 0.6H for both tiers significantly reduces horizontal deformation compared to the FHWA recommendation of 0.6H and 0.35H for the lower and the upper tier respectively.

Effect of facing stiffness on reinforced soil walls under surcharge loading–unloading

This paper investigates the impact of facing stiffness on the performance of geosynthetic-reinforced soil (GRS) walls under surcharge loading–unloading. Data from two instrumented physical model tests are utilised considering two different facing stiffness (block and wrapped). After the end of construction, the physical models were loaded and unloaded, step by step. They were comprehensively instrumented to monitor the load mobilised along with the reinforcements, horizontal toe load, lateral facing displacement, vertical displacement at the top of the walls and horizontal stress behind the block faces. In addition, a simplified analytical procedure is proposed in order to determine the maximum reinforcement load under surcharge unloading. The results show that the toe restraint at the base of the block-faced wall highly controls the performance of GRS wall with structural facing. When there is no toe resistance, irrespective of the facing type, the walls present, in general, similar performance under surcharge loading and unloading. Furthermore, during surcharge unloading, the reinforcement load near the face may be less affected in the wrapped-face wall compared with the block-faced wall. Moreover, the maximum reinforcement loads during surcharge unloading were fairly captured using the proposed procedure.

Upper bound stability analysis of tiered geosynthetic-reinforced soil wall

The tiered geosynthetic-reinforced soil (GRS) walls have been increasingly applied in the high and steep retaining soil structures. However, very little is known about the design method for the tiered GRS wall in practice. This study is aimed at proposing an upper-bound stability analysis method of a tiered GRS wall. The proposed method was firstly validated by the existing results from the centrifuge test and the numerical method, and then a parametric study was performed to investigate the effects of the cohesionless backfill friction angle ϕ1 and the wall geometric parameters including the offset distance, the total wall height, the batter angle δ, the number of tiers n, and wall height ratio of adjacent tiers on the dimensionless equivalent earth pressure coefficient KT. The analysis results demonstrated that as the ϕ1 increases, the shear strength of backfill is enhanced and thus the KT or the total reinforcement tensile force decreases, and the KT decreases with the increase of the offset distance at the initial stage and then becomes stable when it reaches a certain critical value. For a fixed offset distance, the KT or the total reinforcement tensile force decreases with the increase of the δ. For the two-tiered GRS walls having the offset distance less than the critical value, the wall with the smaller wall height ratio has a larger KT. Further, the variation of the location of the critical failure surfaces of tiered GRS walls was presented in this study with the variation of the ϕ1 and the wall geometry.

A Framework for Analyzing the Stability of Geosynthetic Reinforced Soil Walls under Unsaturated Conditions

A Framework for Analyzing the Stability of Geosynthetic Reinforced Soil Walls under Unsaturated Conditions

Influence of secondary reinforcements on the behavior of geosynthetic reinforced soil walls

This paper presents numerical simulations to investigate the influence of secondary reinforcements on the behavior of geosynthetic reinforced soil (GRS) walls under static loading. Simulations were conducted using a finite difference program to model an instrumented field GRS wall with secondary reinforcements. Simulated results are in good agreement with field measurements, including facing displacements, lateral soil stresses, and tensile strains of the primary and secondary reinforcement. A parametric study was then conducted to investigate the influences of secondary reinforcement length, backfill soil friction angle, and wall height on the static behavior of GRS walls with secondary reinforcements. Results indicate that the maximum facing displacement and the required reinforcement tensile force of primary reinforcements generally decrease with increasing secondary reinforcement length up to a critical value. The decreasing effect is more pronounced for GRS walls with lower soil friction angle and higher wall height. The K-stiffness method is overconservative for the calculation of required tensile force of primary reinforcements for GRS walls with secondary reinforcements, and the overestimation increases with increasing secondary reinforcement length. A design method that accounts for the influence of secondary reinforcements on the internal stability of GRS walls is provided.

Effects of the tier arrangement and reinforcement length on the deformation behavior of a two-tiered geosynthetic-reinforced soil wall

Effects of the tier arrangement and reinforcement length on the deformation behavior of a two-tiered geosynthetic-reinforced soil wall

Experimental evaluation of geosynthetic-modular block connection loads

The design of segmental geosynthetic mechanically stabilized walls with masonry block facing is often governed by the loads that develop at the connection between the facing and geosynthetic. Yet the current understanding of the mechanisms involved in the mobilization of such connection loads is, at best, incomplete. The testing apparatus developed as part of this study facilitates simulating the transference of stresses at the face and evaluating the facing connection loads in geosynthetic-reinforced soil walls. This study assesses the connection loads between a geogrid reinforcement connected frictionally to modular concrete blocks. A comprehensive instrumentation program was implemented to capture lateral earth pressures, geosynthetic strains and loads acting at the geogrid-block connection in a geosynthetic-reinforced unit cell subjected to incremental surcharge stages. Results indicate that conventional calculations, based on earth pressure theory, may underestimate the facing connection loads, mainly when the connection loads are triggered by the differential settlement of the backfill relative to the block facing. When this mechanism dominates the mobilization at the connection, reinforcement loads increase as the differential settlement increases, developing down-drag forces at the connection between the geogrid and modular blocks.

Laboratory testing and model calibration of a crushed stone backfill in a geosynthetic reinforced soil wall

The objective of this study was to understand the effect of the choice of backfill constitutive models on the numerical simulation of a geosynthetic reinforced soil-integrated bridge system (GRS-IBS). The #89 material, a crushed angular granite stone, characterized by maximum particle sizes of 9 mm, was used for the reinforced backfill for the retaining wall. Consolidated drained triaxial tests were conducted at confining stresses of 48 kPa, 83 kPa, and 117 kPa. The average friction angle was 42 degrees. Two soil models (the linear-elastic perfectly-plastic and the Hardening Soil) were calibrated using the laboratory test results. The calibrated soil models were then used to model the reinforced backfill material in finite element simulations of the abutment. Results of the calculated vertical stresses at the instrument position showed reasonable agreement with the field measurement. The non-linear model predicted about twice the deformation (lateral displacement and bridge seat settlement) compared to the linear-elastic perfectly plastic model. Settlement results showed maximum values corresponding to 0.22% and 0.45% of the abutment height for linear-elastic perfectly-plastic model and Hardening-Soil model, respectively, which are less than 0.5% limit recommended by US FHWA, while the lateral displacements were 0.22% and 0.44% of the abutment height for linear-elastic perfectly-plastic model and Hardening Soil model, respectively, both less than the 1% limit recommended by the US FHWA.

Study of environmental impact from geosynthetic reinforced soil walls

Reinforced soil walls (RSWs) have proven to be a reliable and resilient solution in many geotechnical applications (e.g., bridge abutments, highway and railway embankments, soil retaining walls, dikes, among others). Moreover, the reduced impact of these types of structures over traditional solutions has been compared using life cycle analysis (LCA) and sustainability assessment methodologies. Nowadays, RSWs are often constructed with geosynthetic materials as reinforcement elements due to their ease of use, cost, and technical viability. The use of geosynthetic materials can assist to meet the global challenges of the United Nations global sustainability goals and to adapt to the effects of climate change. The LCA methodology allows designers to determine the environmental impact of different candidate solutions or structures for a given design life. By providing comparable score-based results, a LCA permits objective decision making. The present work describes the environmental impact assessment of idealized polymer strap geosynthetic RSWs using the LCA methodology. Case studies are focused on the use of different backfill material (granular soil from a quarry or riverbed, recycled construction aggregate, and low quality locally available soil). Analysis boundaries include cradle-to-gate considerations and a 100-year design life. Results indicate the reduced environmental impact of using on-site backfill.

Evaluation of the effect of constant and non-constant Poisson’s ratio on reinforcement load of reinforced soil walls

This study analytically and numerically investigates the impact of constant and non-constant Poisson’s ratio on the mobilized maximum load in the reinforcements, Tmax, of reinforced soil walls with vertical facing under working stress conditions. This assessment is carried out considering different controlling factors including reinforcement stiffness, wall height, backfill friction angle, and compaction-induced stress. The analytical procedure and the numerical model are validated against data from an instrumented, large-scale, geosynthetic-reinforced soil wall under working stress conditions. Considering the key factors evaluated in the current study, the results show that the impact of the reinforcement stiffness is dominant over the approach used to consider Poisson’s ratio. A maximum difference of about 20% was obtained between the values of Tmax calculated using constant and variable Poisson’s ratios. This implies that, from a practical standpoint, it may be appropriate to adopt a simpler approach that utilizes a constant Poisson's ratio for the determination of Tmax under operational conditions.

Deformation behaviour of rigid faced GRS walls in numerical simulation with bonded and frictional soil-reinforcement interfaces

ABSTRACT The response predictions for the Rigid Faced (RF) Geosynthetic Reinforced Soil (GRS) wall depend significantly on the considered modelling approach for soil-reinforcement interfaces. Bonded soil-reinforcement modelling is an inadequate approach in many situations like high walls. The selection of interface shear stiffness for frictional contacts is critical under working stress conditions to estimate displacements precisely. Finite Element analysis of RF-GRS wall has been conducted for frictional and bonded interfaces. The results at the end of construction show that the bonded soil-reinforcement interface underpredicts the total fascia displacements and external displacements of the RF-GRS wall compared to the frictional interface. The effect is 2–6 times in a 6 m high wall and 1.5–3 times in a 3 m high wall. The surface settlement of the wall with bonded soil-reinforcement interface is 2–3 times less than the frictional interface. The bonded interfaces produce local stress concentrations at the end of reinforcements.

Secondary reinforcement effect on the value and location of maximum reinforcement load

This paper numerically evaluates the effect of secondary reinforcement on the value and location of the maximum reinforcement load along the primary reinforcement layers (Tmax) in geosynthetic-reinforced soil (GRS) walls under working stress conditions. Data from three instrumented sections of a well-instrumented GRS wall were used for model validation. A parametric study was carried out considering different controlling factors (i.e. the vertical reinforcement spacing, facing type and secondary reinforcement stiffness and length). The results show that for a constant relative soil-reinforcement stiffness index, the variation of the vertical reinforcement spacing and stiffness may not affect the location and normalised value of Tmax. In general, for the conventionally used type of reinforcement, the secondary reinforcement inclusion reduces Tmax to values lower than those corresponding to the active condition (Ka). For a given facing type, the combined effect of the secondary reinforcement length and stiffness is the main factor that controls the Tmax location. In general, increasing the secondary reinforcement stiffness and length moves the location of Tmax from the back of the facing to a distance corresponding to the length of the secondary reinforcement layers. In addition, for this condition, a flexible face model performs similarly to a block face model.

Failure Mechanism and Deformation-Based Design of Narrow Geosynthetic Reinforced Soil Walls

In recent years, the working performance of mechanically stabilized earth (MSE) walls has shown their outstanding stability and capacity to accommodate large deformation. The behavior and failure mechanisms of conventional MSE walls have been carefully examined. In cases where space is limited, such as in mountainous regions, in coastal regions, and for road expansion, the conventional MSE wall can be modified by adjusting the length of reinforcement to conform the construction area. For narrow geosynthetic reinforced soil (GRS) wall, the modification and arrangement of reinforcement components, including reinforcement tensile strength, vertical spacing, and aspect ratio, play key roles in the behavior of reinforced earth walls and can also lead to differences in the distribution of lateral earth pressure compared with conventional MSE walls. In this study, a series of geotechnical centrifuge tests are conducted to clarify the failure behaviors, distribution of lateral earth pressure, and deformation progresses of narrow GRS walls. Among the investigated variants, it is verified that improved reinforcement strength leads to a significant decrease in horizontal wall displacement. The relationship among lateral earth pressure, zero-earth-pressure zone, and horizontal displacement can be applied to predict the deformation of a narrow GRS wall.

Effects of concave facing profile on the internal stability of geosynthetic-reinforced soil walls

Effects of concave facing profile on the internal stability of geosynthetic-reinforced soil walls

Comparative assessment of stability of GRS abutments through 1 g physical model tests for field implementation

Geosynthetic reinforced soil (GRS) abutments have emerged as innovative improvement measures over the conventional GRS walls. Being an internally stabilized composite structure subjected to heavy stresses adjacent to facing, proper selection of GRS abutments in field is very important. Over the years, various design philosophies have been formulated in respect of GRS abutments but proper selection to a specific problem remains undiscussed. The present study attempts to conduct comparative analysis of stability of 5 types of chronologically evolved GRS bridge abutments (BA) namely BA I, BA II, BA III, BA IV and BA V through 1 g model tests (5 types are defined later) with special emphasis given to the influence of type of facing and configuration of reinforcements. A total of 75 model tests on 1/5th (N = 5) scaled down abutments have been performed to evaluate the effects of footing width (B), footing offset (x), facing type and abutment type on serviceable bearing capacity, ultimate bearing capacity, footing settlement, horizontal displacement of facing, tilting of footing, rotation and buckling of facing. The serviceability criteria based on FHWA recommendation has been chosen to ascertain field suitability of the model. An interesting mechanism correlating footing tilt (positive and negative) with movement of facing has been hypothesized and validated by the failure mode observed at the facing of the abutments. The abutments with modular facing were found to be more stable as compared to continuous facing. The footing width ratio (B/H) > 0.2 with footing offset ratio (x/H) > 0.3 (where, H is height of abutment) was found to be more suitable for field application. The degree of tilt, facing rotation, buckling behavior and differential settlement of footing were minimum for BA V. Based on all response parameters, BA V having modular facing with secondary reinforcements in the bearing bed performed exceedingly well in withstanding serviceable bearing pressures while sustaining larger footing settlements and resisting horizontal displacements of facing, followed by BA IV, BA III, BA II and BA I.

Influence of Heterogeneous Arrangements of Reinforcements’ Length and Stiffness on the Deformation of Instrumented Geosynthetic-Reinforced Retaining Walls Constructed with Sustainable Locally Available Backfill Soils

Sustainable solutions involving geosynthetic-reinforced soil walls have been achieved in projects that use locally available backfill materials and a reduced volume of geosynthetic reinforcements. Different arrangements of reinforcements can be adopted to reduce the volume of geosynthetics. This paper reports the deformation measurements taken from four instrumented geosynthetic-reinforced soil walls constructed with different arrangements of reinforcement layers including different lengths and tensile properties. The deformation of walls with rigid reinforcements at lower elevations and more flexible at upper portions of the wall height was compared to walls with a uniform distribution of reinforcement layers. Similarly, the effect of the nonuniformity of reinforcement lengths along the wall height was also evaluated. Relatively short reinforcements (L/H < 0.7) used at deeper reinforced layers were observed to overload the upper reinforcement layers resulting in mobilized loads higher than expected, resulting in increases of approximately 80% in the wall’s deformation. In contrast, the use of rigid reinforcements at lower layers led to a reduction in facing displacements of 50% at lower instrumented layers and of 60% at upper instrumented layers. The distribution pattern of facing displacements, reinforcement-mobilized loads and strains along the wall height was significantly affected by the adoption of heterogeneous reinforced layers.

Lateral facing deformation versus factor of safety for geosynthetic-reinforced soil walls in a tiered configuration

Geosynthetic-reinforced soil (GRS) walls in a tiered configuration have been used for high earth retaining structures, especially in mountainous areas. More attention has recently been paid to lateral facing deformations and stability of such walls. A validated numerical model of a GRS wall was utilized to calculate the maximum lateral facing deformations and the maximum tensile forces in reinforcement layers in tiered GRS walls. The same model was used to compute their factors of safety (FS), using the shear strength reduction (SSR) method. A parametric study was carried out to assess the effects of backfill and foundation soil properties, reinforcement layout and stiffness, and tiered wall configuration on the maximum lateral facing deformations at the end of construction (EOC) and the FS values of the tiered GRS walls. Moreover, the relationship between the FS value and the normalized maximum lateral facing deformation at EOC was established. The comparison with the existing numerical results demonstrates that the empirical relationship established in this study can reasonably predict the FS values for tiered GRS walls.

Seismic coefficients for pseudo-static analysis of wrap-faced GRS walls with nonlinear soil fills

Pseudo-static seismic design procedure for Geosynthetic Reinforced Soil (GRS) walls includes the selection of a suitable horizontal seismic coefficient for external and internal stability analysis. The present guidelines for the seismic design of GRS walls have been mostly adopted from studies performed on conventional retaining walls. Hence, it is required to study the seismic response of GRS walls. In the present study, a finite element (FE) model of a wrap-faced GRS wall was developed in OpenSees. It was analysed for multiple earthquake time histories to study the variability in earthquake characteristics. The shaking level was also varied from 0.12g to 0.48g to consider the nonlinear response of backfill soil. The acceleration response and dynamic earth pressure increment in the wall were observed to increase with the shaking level but at a lower rate for higher shaking levels. The reinforcement force increments under seismic loading also showed a similar response. The internal failure plane in the GRS wall was slightly inclined, although not completely aligned with Rankine's active failure plane. Seismic coefficients are recommended for wrap-faced GRS walls as a function of PHA. The coefficients were calibrated using the maximum earth pressure and reinforcement forces obtained from FE analysis. The effect of reinforcement stiffness is also incorporated in the recommendation for internal stability analysis. A seismic coefficient greater than PHA is suggested at low shaking levels. It is in direct contrast to many previous studies as the coefficients are calibrated considering the maximum force demand in the GRS wall. Force-based designs need to consider the applicability of maximum earth pressure and reinforcement forces in the GRS wall, which can cause either external or internal instability in the wall. While at higher PHAs, the seismic coefficient should be almost constant to provide reliable estimates of earth pressure and reinforcement forces.