Geosynthetic-reinforced Soil Walls Research Articles

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.

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.

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.

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.

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.

Centrifuge modeling on the effect of mechanical connection on the dynamic performance of narrow geosynthetic reinforced soil wall

As people migrate to densely populated cities, the importance of establishing a new transportation infrastructure to meet their needs becomes increasingly critical. The limited space available for construction makes a narrow geosynthetic reinforced soil (GRS) wall a cost-effective alternative. Prior research has primarily examined the performance of narrow GRS walls under static loads, revealing that these structures are highly vulnerable to significant crest displacements. Consequently, multiple studies have recommended incorporating mechanical connections in the upper layer during the construction of narrow GRS walls. However, some places are more susceptible to earthquakes; hence, this research was conducted to investigate the dynamic response of narrow GRS walls and quantify the effect of mechanical connections on increasing the stability of narrow GRS walls. Two sets of narrow GRS wall models were constructed, with and without mechanical connections to a stable wall, and subjected to a similar series of earthquakes. The test results indicate that the mechanical connection can reduce the accumulated normalized horizontal displacement of narrow GRS walls by 30–80% after being subjected to the same dynamic input motion excitation.

Numerical Studies on the Performance of Geosynthetic Reinforced Soil Walls Filled with Marginal Soil

Numerical Studies on the Performance of Geosynthetic Reinforced Soil Walls Filled with Marginal Soil

Estimation of Horizontal Displacements for Geosynthetic Reinforced Soil Wall

Nowadays, the geotechnical design trend is increasingly heading towards the serviceability limit state. However, the current practice in the design of geosynthetic reinforced soil (GRS) walls mostly relies on ultimate limit state. Commonly available design software programs provide typical factor of safety values against various failure modes. With increasing height and variability in GRS walls, the deformation characteristics of the GRS walls also become an important parameter in the design. In this paper, an expression has been developed to predict the horizontal deformation of a GRS wall using a set of data obtained from about sixty-four finite element model configurations. The horizontal deformation expression includes wall-height, internal friction angle and elastic modulus of backfill, length, spacing and stiffness of geosynthetic reinforcements. It has been found out that all these parameters contribute to the horizontal displacement of a GRS wall. In addition, some comparisons have been made to reveal the influence of each individual parameter on the horizontal displacement of the wall.

Flood Hazard Assessment of Water-Front Geosynthetic Reinforced Soil Wall for Dam Regulation Rule Level

The flood hazard parameter of peak discharge and prolonged inundation due to change in dam regulation is estimated for a water front Geosynthetic Reinforced Soil (GRS) wall on the downstream of large dam. Dam regulation rule level is pre-emptying the reservoir with lower peak discharge to protect the expanding downstream city intruding the flood plain. Present study is to test the hypothesis that rule level has significantly changed peak discharge and inundation duration and also to estimate these two important parameters of flood hazard for different flood return periods. The methodology consists of three parts: first is the categorization of flood data according to major event of flood regulation, second is the distribution test and third is the estimation of design maximum peak discharge and duration of flood. The estimated value of peak discharge and flood duration clearly indicate the implication of dam regulation rule level; the estimated value of peak discharge for 200 years return period is 13.9 lakh Cusecs, which is lower than the flood discharge for year 1968, which was 15 lakh Cusecs, and the estimated flood duration for 10 years return period is 41 days. The most important finding of this study is the substantial increase in duration of flood due to implementation of rule level which will add one more flood hazard parameter for water front geotechnical structure that is prolonged inundation.

Model tests of geosynthetic-reinforced soil walls with marginal backfill subjected to rainfall

A series of model tests were conducted to investigate the performance of geosynthetic-reinforced soil (GRS) walls with marginal backfill subjected to rainfall infiltration. The effectiveness of improvement measures—such as decreasing reinforcement spacing and increasing sand cushion thickness—to prevent the GRS wall failure due to heavy rainfall was evaluated. The distribution and variation of the volumetric water content, porewater pressure, wall deformation, and reinforcement tensile strain were monitored during the test. The advancement of the wetting front and the drainage function of sand cushions were visually observed using the fluorescent dyeing technique. For the baseline case, the wall began to deform as rainfall proceeded, causing the potential failure surface to gradually move backward. When the potential failure surface moved beyond the reinforced zone, the pullout of the topmost reinforcement layers occurred, resulting in the collapse of the GRS wall in a compound failure mode. Decreases in reinforcement spacing and increases in sand cushion thickness effectively reduced wall deformation and enhanced wall stability. The placing of sand cushions between the reinforcement layers can also delay water infiltration and reduce the accumulation of porewater pressure inside the wall. Suggestions for designing rain-resistant GRS walls are also proposed based on the findings.

Probabilistic Assessment on the Performance of Tiered Geosynthetic Reinforced Soil Walls Using RLEM and RFEM

Probabilistic Assessment on the Performance of Tiered Geosynthetic Reinforced Soil Walls Using RLEM and RFEM

Numerical evaluation of the influence of compaction and soil strength parameters on GRSW

This paper presents a numerical evaluation, using PLAXIS 2D finite element software, of the effects of varying the distance of the heavy compaction from the face in a geosynthetic reinforced soil wall (GRSW). The main effects studied were the tensions in the reinforcements and the horizontal deformations of the face, including the influence of the type of shear strength envelope (total stresses or effective stresses) of the soil. In this study, a young gneiss residual soil (silty sand) was studied to obtain the grain size distribution, index properties and parameters of strength and deformability. This soil was considered for backfill in hypothetical sections of GRSW. The numerical results contributed to a better understanding of the GRSW behaviour, with evaluations closer to real field conditions. In the analyses carried out, when increasing the heavy compaction distance from the face, there are tendencies pointing to the reduction of the tensions in the reinforcements, displacement toward the interior of the soil mass of the points at which the maximum reinforcement tension occurs and reduction of the horizontal deformations of the face.

Experimental analysis of bearing capacity failure of geosynthetic-reinforced soil walls

Small- and large-scale 1g experiments were conducted to investigate the bearing capacity failure of geosynthetic-reinforced soil walls. The small-scale experiments (1/10) provided fundamental insights into the development of failure based on digital image correlation analysis. Since these tests suffered from scale effects, large-scale tests (1/1.67) were performed to quantify the ultimate load-bearing capacity of a 1.2 m high wall. A vertical load was applied on top of the structures and internal soil movements and stresses, wall deformations and reinforcement strains were measured. The experimental results revealed that the failure was initially triggered at the rear end of the bottom reinforcement. The wall rotated to the backfill and the ground surface in front of the wall was uplifted. The results confirmed the quasi-monolithic behaviour of the reinforced zone. A multi-body failure mechanism was observed below the base of the wall, consisting of an active and a passive wedge connected by a transition zone. Important scaling factors were discussed using the two different scales which has shown important conclusions that are relevant for experimental studies. The analytical calculations revealed that a reduced reinforcement length needs to be considered in the analytical approach to predict a rather conservative load-bearing capacity.