Geosynthetic-reinforced Soil Research Articles

Earthquake Response of Connected and Unconnected Back-to-Back Geosynthetic-Reinforced Soil Walls

A two-dimensional finite-element analysis based on PLAXIS 2D was used to study the behavior of connected and unconnected back-to-back mechanically stabilized earth walls under earthquake loading. The numerical model was first validated with the results from the full-scale dynamic centrifuge tests on reinforced soil-retaining walls. The behavior of connected and closely spaced unconnected back-to-back mechanically stabilized earth walls (BBMSE) was compared in terms of tensile forces mobilized in geogrids, and the lateral earth pressures and maximum displacements of the wall. The total seismic earth thrusts at the end of the reinforced zone and at the facing of BBMSE walls and their points of application were presented. These results were compared with the widely used Mononobe–Okabe method. The connected walls were found to significantly reduce the dynamic loads on the walls compared with those on unconnected walls.

Analysis of Layered Geogrids–Sand–Clay Reinforced Structures under Triaxial Compression by Discrete Element Method

Compared with the commonest geosynthetics-reinforced soil structures, layered geogrids–sand–clay reinforced (LGSCR) structures (School of Architecture and Civil Engineering, Shenyang University of Technology, Shenyang 110870, China) can replace granular materials with clay as the primary backfill material. Up until now, the performance of LGSCR structures under triaxial compression has been unclear. In this paper, the discrete element method was used to simulate the triaxial compression test on the LGSCR samples. Based on the particle flow software PFC3D, three types of cluster particle-simulated sand and the reinforced joints of the geogrid were constructed by secondary development. The effects of the geogrid embedment in sand layers, the number and thickness of sand layers in relation to the deviatoric stress, and the axial strain and the shear strength index of the LGSCR samples were analyzed. The results showed that laying the sand layers in the samples can improve their post-peak strain-softening characteristics and increase their peak strengths under a high confining pressure. A geogrid embedment in sand layers can further enhance the ductility and peak strength of the samples, and in terms of the shear strength index, there is a 41.6% to 54.8% increase in the apparent cohesion of the samples.

Stochastic seismic analysis of geosynthetic-reinforced soil slopes using the probability density evolution method

This paper presents a stochastic seismic analysis of geosynthetic-reinforced soil slopes (GRSS) using the probability density evolution method (PDEM). The combination of the uncertainties of seismic ground motions (SGM), soil properties and reinforcement parameters was considered. The stochastic SGM was generated from a random function based on the spectral representation method. The present method is proved to be more precise than the pseudo-static method and pseudo-dynamic method due to the consideration of the uncertainty of frequency spectrum of seismic excitations, and more efficient than the Monte Carlo simulation method for reducing the number of samples by 39 times. Without involving the stochastic earthquake, the result of the estimated performance would incur large errors since it greatly depends on the selected earthquakes, which may be one of the major reasons for GRSS failure. The slope displacement and the reinforcement strain occur at a relatively narrow region at the beginning, then increase and fluctuate intensively with large uncertainty, and finally become steady in the earthquake decay phase. The reinforcement length has a more substantial influence on the failure probability of the reinforcement than other parameters in the studied ranges. The reinforcement strain increases but the slope displacement decreases with the reinforcement length because of the variation of failure mechanisms.

Physical Modelling of a Strip Footing on a Geosynthetic Reinforced Soil Wall Containing Tire Shred Subjected to Monotonic and Cyclic Loading

In this study, the mechanical behavior of geosynthetic reinforced soil (GRS) walls has been investigated through physical modeling subjected to strip footing monotonic and cyclic loads at various stress paths. The influence of footing location, stress level, post-cyclic behavior and sand-tire shred admixture on the lateral deformations of the wall facing, bearing capacity and the settlement beneath the footing were assessed. To this aim, 12 physical model tests were conducted with a scale of 1: 4. Results indicated that the bearing capacity has increased with the increase in the offset distance of the strip footing to the wall facing and adding tire shred to the backfill material, but the increase is more prominent by adding tire shred to the backfill material. The location of the footing from the wall facing was a crucial parameter on the deformation of facing and the failure mode of the footing. Failure in the facing was the predominant mode of failure in the near facing footing. However, a rupture in the geosynthetic caused failure in the footing far from facing footing. Also result of cyclic loading tests showed both permanent displacement and residual settlement accumulated with load cycles and a majority of them occurred over the first fifteen cycles. Depending on where strip footing was located, it may or may not induce a magnifying effect on subsequent cyclic loading responses.

Numerical Analyses on the Behavior of Geosynthetic-Reinforced Soil: Integral Bridge and Integrated Bridge System

Geosynthetic-reinforced soil (GRS) technology has been used worldwide since the 1970s. An extension to its development is the application as a bridge abutment, which was initially developed by the Federal Highway Administration (FHWA) in the United States, called the GRS—integrated bridge system (GRS-IBS). Now, there are several variations of this technology, which includes the GRS Integral Bridge (GRS-IB) developed in Japan in the 2000s. In this study, the GRS-IB and GRS-IBS are examined. The former uses a GRS bridge abutment with a staged-construction full height rigid (FHR) facing integrated to a continuous girder on top of the FHR facings. The latter uses a block-faced GRS bridge abutment that supports the girders without bearings. In addition, a conventional integral bridge (IB) is considered for comparison. The numerical analyses of the three bridges using Plaxis 2D under static and dynamic loadings are presented. The results showed that the GRS-IB exhibited the least lateral displacement (almost zero) at wall facing and vertical displacements increments at the top of the abutment compared to those of the GRS-IBS and IB. The presence of the reinforcements (GRS-IB) reduced the vertical displacement increments by 4.7 and 1.3 times (max) compared to IB after the applied general traffic and railway loads, respectively. In addition, the numerical results revealed that the GRS-IB showed the least displacement curves in response to the dynamic load. Generally, the results revealed that the GRS-IB performed ahead of both the GRS-IBS and IB considering the internal and external behavior under static and dynamic loading.

Noncircular Deterministic and Stochastic Slope Stability Analyses and Design of Simple Geosynthetic-Reinforced Soil Slopes

Abstract The purpose of this study is to examine the behavior of simple soil slopes reinforced with geosynthetics using deterministic and stochastic as well as circular and noncircular limit equili...

Finite element analysis and design method of geosynthetic-reinforced soil foundation subjected to normal fault movement

This paper presents a series of finite element analyses to investigate the performance and reinforcing mechanism of geosynthetic-reinforced soil (GRS) foundations subjected to normal fault movement. Numerical and experimental results of unreinforced and reinforced foundations were first compared for model validation. Parametric studies were then conducted to evaluate the influence of soil and reinforcement parameters on the performance of reinforced foundations. The total height of the baseline reinforced foundation was 3 m in the prototype scale, and this foundation was subjected to fault movement of up to 1 m (S/H = 33%). The variables considered in the parametric studies included reinforcement length, stiffness, ultimate tensile strength, vertical spacing, foundation height, and soil–reinforcement interface property. The numerical results revealed that FE analysis satisfactorily predicted the deformation behavior of unreinforced and reinforced foundations subjected to normal fault movement. Two main reinforcing mechanisms identified in this study were tensioned membrane and shear rupture interception effects. Based on the numerical results, regression equations for predicting the maximum angular distortion and the mobilized reinforcement tensile strain induced by normal fault movement were established. Design methods were also developed for determining the reinforcement length (against significant pullout) and failure strain (against breakage).

Case history on failure of geosynthetics-reinforced soil bridge approach retaining walls

Six geosynthetic-reinforced soil (GRS) retaining walls supporting bridge approach roads of an overpass bridge in China exhibited a series of structural problems after 18 years of service. Field investigations demonstrated that the major structural problems consist of excessive lateral facing displacement, settlement and damage of facing panels, and pavement cracks above the GRS retaining walls. The structural problems were mainly caused by inadequate backfill compaction behind the facing, rain water infiltration, the settlement of foundation soil, and reinforcement ageing. Among the six GRS walls, a 22-m-long section collapsed after mild rain in July 2016, and the failure surface in the collapsed zone was mainly located 0.5–0.9 m away from the back of facing panels along the wall height. The field investigation found that external water filtration into the backfill behind the facing panels, and the breakage of connection between reinforcement and facing panels were the main causes of the failure. The connection breakage resulted from the ageing of PP reinforcement strips, and the critical issue of PP reinforcement ageing in complex backfill environment was pinpointed. Remedial measures of the failed section and reinforcing techniques of the remaining GRS walls were briefly presented in the end.

Seismic effects on reinforcement load and lateral deformation of geosynthetic-reinforced soil walls

Seismic effects on reinforcement load and lateral deformation of geosynthetic-reinforced soil walls

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

In the current paper, using experimental studies and numerical analyses, the effect of surcharge width on the behavior of geosynthetic-reinforced soil (GRS) walls is evaluated under working stress conditions. Experimental tests were performed at the Geotechnical Laboratory of COPPE/UFRJ, using block and wrapped-face walls. Four well-instrumented GRS walls were examined considering different facing type and surcharge width. The numerical analysis of GRS walls was carried out using the two-dimensional computer program PLAXIS. Parametric studies were carried out with different combinations of surcharge width, wall height, compaction induced stresses (CIS) and face inclination. The results indicate the effect of the surcharge width in combination with other investigated factors on the magnitude and the position of the maximum reinforcement load and the lateral facing displacement of GRS walls.

Experimental study of a geosynthetic-reinforced soil bridge abutment

The article presents an experimental study of a geosynthetic-reinforced soil (GRS) bridge abutment (BA). The BAs are seated on a saturated soft foundation layer and support a 16 m long concrete bridge. Laboratory tests were conducted on the foundation soil, geogrid, and fill material. The BA is constructed from 14 geogrids and has a total height of 4.2 m. The strain values in the geogrids were measured and recorded during the construction of the abutments and after installation of the bridge structure. The test results show that more than 50% of the total strain in the geogrids was developed during the construction of the BAs, mostly embedded in the ground. The remainder of the measured strain was a consequence of installing the prefabricated bridge girders, back fill placement, concreting the top slab, and placing the asphalt concrete. The strain distribution along the geogrids shows that the maximum strain was recorded below the sill, and was 50% higher than at the center of the BA. Based on an analysis of the construction costs, it can be concluded that conventional reinforced concrete abutments could cost up to five times the amount of optimally designed GRS-BAs.

A new apparatus for the study of pullout behaviour of soil-geosynthetic interfaces under sustained load over time

At present, the design of geosynthetic-reinforced soil structures is executed with reference to the tensile strength of the reinforcement obtained from in-air short-term tensile tests, decreasing this value by means of several factors. Among these, the creep effect resulting from in-air tensile creep tests reduces tensile strength the most. Consequently, this procedure does not take into account the effects of soil confinement and interaction on the tensile response of the reinforcements. This paper illustrates a new large-scale pullout prototype apparatus, with the capacity to investigate the behaviour of a geosynthetic reinforcement embedded in a compacted soil and subject to a tensile load kept constant over time. The apparatus allows the verification of how the soil can modify the prediction of the long-term behaviour of geosynthetics. Results in terms of confined tensile strains were analysed, and the comparison of those values with the strains obtained by in-air tensile creep tests has led to the conclusion that the creep reduction factor might be conservative. Moreover, the confined tensile strains were related to the apparent coefficients of friction to propose a new procedure capable of determining the design interaction parameter under long-term pullout load as a function of the allowable reinforcement strains.

Dynamic Analysis of Machine Foundation with and without Geosynthetic Reinforced Soil Beds

Most of the machine foundations are located in the regions with poorly graded soil including loose sand. Hence, the experimental studies are undertaken to evaluate the dynamic parameters of geosynthetics using cyclic PLT. This paper presents the results of the 10 m2 area of the model cyclic plate load test conducted on geosynthetics reinforced soil beds with similar density, supporting square footing, the results of cyclic PLT from the laboratory-model tests on square footings resting on a sand bed. The various intensity of cyclic load (loading-unloading) applying on the footing and then the elastic recovery of the footing alike to each intensity of loading obtains during the tests to determine the coefficient of elastic uniform compression (Cu) of sand. Results showes that the provision of geosynthetics like geogrid and jute the value of Cu decreases due to elastic recovery increases as compared to unreinforced soil bed, by 06% to 94% and natural frequency 03% to 76% . Introduction of planer geogrid at the base of the geosynthetic matress not only enhance the load carrying capacity but also increasing the elastic recovery to making them more elastic and prevents footing to failure due to vibration. In addition to the experiments also analyses various dynamic parameters of the machine foundation using cyclic PLT on the geosynthetics

Time-Dependent Response of a Recycled C&D Material-Geotextile Interface under Direct Shear Mode.

Geosynthetic-reinforced soil structures have been used extensively in recent decades due to their significant advantages over more conventional earth retaining structures, including the cost-effectiveness, reduced construction time, and possibility of using locally-available lower quality soils and/or waste materials, such as recycled construction and demolition (C&D) wastes. The time-dependent shear behaviour at the interfaces between the geosynthetic and the backfill is an important factor affecting the overall long-term performance of such structures, and thereby should be properly understood. In this study, an innovative multistage direct shear test procedure is introduced to characterise the time-dependent response of the interface between a high-strength geotextile and a recycled C&D material. After a prescribed shear displacement is reached, the shear box is kept stationary for a specific period of time, after which the test proceeds again, at a constant displacement rate, until the peak and large-displacement shear strengths are mobilised. The shear stress-shear displacement curves from the proposed multistage tests exhibited a progressive decrease in shear stress with time (stress relaxation) during the period in which the shear box was restrained from any movement, which was more pronounced under lower normal stress values. Regardless of the prior interface shear displacement and duration of the stress relaxation stage, the peak and residual shear strength parameters of the C&D material-geotextile interface remained similar to those obtained from the conventional (benchmark) tests carried out under constant displacement rate.

Numerical study of geosynthetic reinforced soil bridge abutment performance under static and seismic loading considering effects of bridge deck

Although the use of Geosynthetic Reinforced Soil (GRS) bridge abutments has been increasing, the seismic performance of such structures has remained a significant concern due to their unknown behavior in load-bearing and stress distribution under bridge load and seismic conditions simultaneously. This paper investigates the static and dynamic response of GRS bridge abutment. A series of numerical models representing the realistic field conditions of these structures, including two reinforced soil walls and a single span deck that restrains the top of walls, rather than equivalent surcharge load, was developed. The calibrated numerical model in FLAC program was used to evaluate the effects of horizontal restraint from the deck on the GRS wall displacements and reinforcement loads at the end of construction and under harmonic base acceleration up to 0.5 g. Results indicated that the restraint mobilized from the bridge deck presence, considerably affected the results at both the end of construction and after the dynamic load was applied. Moreover, a series of the parametric studies were performed to investigate the influences of backfill soil relative compaction, reinforcement stiffness, reinforcement length, and reinforcement vertical spacing on the response of GRS abutments at the end of construction and post dynamic state.

Dynamic Behavior of Geosynthetic-Reinforced Expansive Soil under Freeze-Thaw Cycles

Expansive soil has a significant impact on the stability of many key construction projects in cold regions. To study the physical and mechanical properties of expanded soil under the condition of freeze-thaw cycle, cryogenic cyclic triaxial tests were conducted on the dynamic and the displacement characteristics of geosynthetic-reinforced expansive soil subjected to the freeze-thaw cycles. Compared with the unreinforced expansive soil samples, the effects of freeze-thaw cycles on the soil dynamics were discussed. The dynamic shear modulus (Gd) and damping ratio (λ) of the expansive soil samples are improved by reinforcement. Reinforced soil can inhibit the axial compression of the sample and restrain the frost heave deformation of the sample during the freezing process. Meanwhile, it can delay the structural damage effect caused by frost heave and reduce the rate of change of the Gd and the λ with the freeze-thaw cycle. At the same time, reinforced soil can inhibit the axial expansion, reduce the rate of reduction of the Gd, stabilize it with a higher rate, and reduce the influence of the freeze-thaw cycles on the λ of the expansive soil sample. Finally, the change of mechanical properties of expansive soil under the condition of reinforcement is obtained. The main conclusions of this paper can be used to reinforce the roadbed and foundation engineering of frozen soil in a cold region and provide support for the fiber reinforcement method of expansive soil.

Stability analysis of geosynthetic-reinforced soil structures under steady infiltrations

Conventional approach for evaluation of the stability of geosynthetic-reinforced soil structures (GRSSs) is performed under either completely dry or saturated conditions, whereas soils are usually unsaturated in practice. Owing to the suction-induced effect, the behavior of soil is quite different, consequently leading to various stability conditions of GRSSs. This study presents a useful analytical solution for assessing the reinforcement effect of geosynthetics on the internal stability of unsaturated GRSSs under steady infiltration conditions using the kinematical approach of limit analysis, aiming at determining the reinforcement strength required for preventing slope failure. This analytical solution can take the effect of suction stress, unit weight of soil and tensile strength cut-off simultaneously into account. By comparing with the results of other solutions, the validity of the analytical solution is verified. An extensive parametric study is conducted in this paper. The obtained results show that the suction stress has a more significant effect than the tensile strength cut-off on the required normalized reinforcement; additionally, the required normalized reinforcement obtained by the extended M-C yield criterion is more conservative than that of the tension cut-off model in the presence of suction stress, and the hysteresis effect should be considered in the routine design.

Predicting the settlement of geosynthetic-reinforced soil foundations using evolutionary artificial intelligence technique

In order to ensure safe and sustainable design of geosynthetic-reinforced soil foundation (GRSF), settlement prediction is a challenging task for practising civil/geotechnical engineers. In this paper, a new hybrid technique for predicting the settlement of GRSF has been proposed based on the combination of evolutionary algorithm, that is, grey-wolf optimisation (GWO) and artificial neural network (ANN), abbreviated as ANN-GWO model. For this purpose, the reliable pertinent data were generated through numerical simulations conducted on validated large-scale 3-D finite element model. The predictive power of the model was assessed using various well-established statistical indices, and also validated against several independent scientific studies as reported in literature. Furthermore, the sensitivity analysis was conducted to examine the robustness and reliability of the model. The results as obtained have indicated that the developed hybrid ANN-GWO model can estimate the maximum settlement of GRSF under service loads in a reliable and intelligent way, and thus, can be deployed as a predictive tool for the preliminary design of GRSF. Finally, the model was translated into functional relationship which can be executed without the need of any expensive computer-based program.

Erratum for “Experimental Evaluation of the Interaction among Neighboring Reinforcements in Geosynthetic-Reinforced Soils” by Amr M. Morsy, Jorge G. Zornberg, Dov Leshchinsky, Barry R. Christopher, Jie Han, and Burak F. Tanyu

Erratum for “Experimental Evaluation of the Interaction among Neighboring Reinforcements in Geosynthetic-Reinforced Soils” by Amr M. Morsy, Jorge G. Zornberg, Dov Leshchinsky, Barry R. Christopher, Jie Han, and Burak F. Tanyu

An intelligent approach for predicting the strength of geosynthetic-reinforced subgrade soil

ABSTRACT In the recent times, the use of geosynthetic-reinforced soil (GRS) technology has become popular for constructing safe and sustainable pavement structures. The strength of the subgrade soil is routinely assessed in terms of its California bearing ratio (CBR). However, in the past, no effort was made to develop a method for evaluating the CBR of the reinforced subgrade soil. The main aim of this paper is to explore and appraise the competency of the several intelligent models such as artificial neural network (ANN), least median of squares regression, Gaussian processes regression, elastic net regularisation regression, lazy K-star, M-5 model trees, alternating model trees and random forest in estimating the CBR of reinforced soil. For this, all the models were calibrated and validated using the reliable pertinent historical data. The prognostic veracity of all the tools mentioned supra were assessed using the well-established traditional statistical indices, external model evaluation technique, multi-criteria assessment approach and independent experimental dataset. Due to the overall excellent performance of ANN, the model was converted into a trackable functional relationship to estimate the CBR of reinforced soil. Finally, the sensitivity analysis was performed to find the strength and relationship of the used parameters on the CBR value.