Geosynthetic-reinforced Soil Structures Research Articles

Pull-out response of a geogrid buried in recycled sands

Recycled construction and demolition waste (RCDW) has demonstrated geotechnical properties that encourage it to be used in reinforced soil structures (RSS) with geosynthetics. However, the interaction between RCDW and reinforcements needs to be better understood, given its importance for design. This paper presents a qualitative study on the interaction between geogrid and recycled sands by means of pull-out tests performed on small equipment. Tests with the same degree of compaction and a geogrid buried in different types of recycled and natural sands (for comparison purposes) were performed. The characterisation of the materials was carried out in the laboratory and the variability of their geotechnical properties was evaluated. In addition, fill material moisture content was investigated as another potential factor influencing soil-geogrid interface shear. The results of the pull-out tests demonstrated the specific influences of the factors investigated. The comparative study showed that recycled sands can be suitable materials to be used as backfill in geosynthetic reinforced soil structures, meeting physical, mechanical and environmental requirements for this kind of work.

Assessing Numerical Simulation Methods for Reinforcement–Soil/Block Interactions in Geosynthetic-Reinforced Soil Structures

The purpose of this study is to assess effects of two different simulation methods (i.e., interfaces with a single spring-slider system and interfaces with double spring-slider systems) for interactions between reinforcement and the surrounding medium on the performances of geosynthetic-reinforced soil (GRS) structures when conducting numerical analyses. The fundamental difference between these two methods is the number of the spring-slider systems used to connect the nodes of structural elements simulating the geosynthetic reinforcement and the points of solid grids simulating the surrounding medium. Numerical simulation results of pull-out tests show that both methods reasonably predicted the pullout failure mode of the reinforcement embedded in the surrounding medium. However, the method using the interfaces with a single spring-slider system could not correctly predict the interface shear failure mode between the geosynthetics and surrounding medium. Further research shows that these two methods resulted in different predictions of the performance of GRS piers as compared with results of a laboratory load test. Numerical analyses show that a combination of interfaces with double spring-slider systems for reinforcement between facing blocks and interfaces with a single spring-slider system for reinforcement in soil resulted in the best performance prediction of the GRS structures as compared with the test results. This study also proposes and verifies an equivalent method for determining/converting the interface stiffness and strength parameters for these two methods.

Geosynthetic Reinforced Soil Structures: Forensic Investigation on Failures and Remedial Measures

Geosynthetic Reinforced Soil Structures: Forensic Investigation on Failures and Remedial Measures

Evolutionary artificial intelligence in the Industry 4.0 to simulate static loads in railway tracks for geosynthetic-reinforced soil structures based geogrid

Evolutionary artificial intelligence in the Industry 4.0 to simulate static loads in railway tracks for geosynthetic-reinforced soil structures based geogrid

Test and DEM study on cyclic hysteresis characteristics of stereoscopic geogrid–soil interface

The bearing resistance provided by the geogrid's transverse ribs is a non-negligible aspect of the strength mechanism in mobilizing the geogrid–soil interface. Therefore, studying its influence on the response mechanism of geosynthetic-reinforced soil structures under cyclic loading is crucial. The stereoscopic geogrids were manufactured using 3D printing technology by quantitatively thickening the transverse ribs of planar geogrids. To investigate the cyclic hysteresis relationship and stress–dilatancy phase-transformation characteristics of the stereoscopic geogrid–coarse particle interface, cyclic direct shear tests were conducted. Additionally, a discrete element method (DEM) was employed to study the evolution of shear bands and fabric anisotropy at the interface under cyclic loading. The results of the study indicate that the stress–displacement phase angle of the stereoscopic geogrid in the horizontal direction of cyclic shear is smaller compared to the planar geogrid. Furthermore, thickening the transverse ribs decreases the stress–dilatancy phase-transformation angle of the interface. The thickness of the interface shear band in the stereoscopic geogrid is greater than that of the planar geogrid. Moreover, as the transverse-rib thickness increases, the principal direction of the average normal contact force and average tangential contact force under cyclic loading also increases.

On the Potential of Using Random Forest Models to Estimate the Seismic Bearing Capacity of Strip Footings Positioned on the Crest of Geosynthetic-Reinforced Soil Structures

Geosynthetic-reinforced soil structures are often used to support shallow foundations of various infrastructure systems including bridges, railways, and highways. When such infrastructures are located in seismic areas, their performance is linked to the seismic bearing capacity of the foundation. Various approaches can be used to calculate this quantity such as analytical solutions and advanced numerical models. Building upon a robust upper bound limit analysis, we created a database comprising 732 samples. The database was then used to train and test a model based on a random forest machine learning algorithm. The trained random forest model was used to develop a publicly available web application that can be readily used by researchers and practitioners. The model considers the following input factors: (1) the ratio of the distance of the foundation from the edge and the width of the foundation (D/B), (2) the slope angle (β), (3) the horizontal seismic intensity coefficient (kh), and (4) the dimensionless geosynthetic factor, which accounts for the tensile strength of the geosynthetic. Leveraging the model developed in this study, we show that the most important features to predict the seismic bearing capacity of strip footings positioned on the crest of geosynthetic-reinforced soil structures are D/B and kh.

Durability of geogrid in a sloped reinforced soil wall after 25 years in service

The durability of geogrid reinforcement exhumed after 25 years from a sloped wall structure was examined through a comparison of the material properties of exhumed samples with technical data for the original product type. Visual and microscopic inspections found no evidence of installation damage. Analysis of strain increments in rapid loading creep tests to 10 000 h showed excellent agreement between the exhumed and original materials. The results of this study lend confidence in the use of isochronous load–strain–time data for predicting the long-term strain of geosynthetic-reinforced soil structures in design to a serviceability limit state.

Evolutionary artificial intelligence in the Industry 4.0 to simulate static loads in railway tracks for geosynthetic-reinforced soil structures based geogrid

Evolutionary artificial intelligence in the Industry 4.0 to simulate static loads in railway tracks for geosynthetic-reinforced soil structures based geogrid

Research on the Effect of Particle Size on the Interface Friction between Geogrid Reinforcement and Soil

For projects such as roads and railways, different fillers are often selected, and these also relate to the area where the project is located, so the characteristics of the filling soil should be considered in the design. However, the characteristics of the soil used in geosynthetic-reinforced soil (GRS) structure design are routinely simple soil properties and are not based on testing of soil with reinforcement. In order to study the influence of fillers with different particle sizes on the interface friction characteristics between the geogrid and soil, a self-developed large-scale pull-out testing machine was used. Under the action of a normal static load, pull-out tests were carried out with different fillers, such as sand, silt and gravel. According to the test results, the greater the stress applied in the normal direction, the greater the maximum pull-out force. As for the different fillers, shear stress from material with a larger particle size, such as gravel, was larger than that of sand and silt. Finally, to reveal the pattern of how the soil particles moved during the pull-out test, from a microscopic point of view, and the effect on particle–mesh size ratio, a series of discrete element method (DEM) analyses were conducted by PFC2D. The results indicated that a larger particle is more likely to rotate and move during the test, and this makes the interlocking effect greater between the geogrid and the soil, which leads to a larger pull-out force in the laboratory test.

A hyperbolic model for mechanical behaviour of marginal soil-geosynthetic interface

Locally available marginal soils are of great interest to use as backfill material in geosynthetic reinforced soil structures due to their cost-effectiveness. The advanced stress–strain analysis of these structures necessitates the correct evaluation and the accurate description of marginal soil-geosynthetic interface behaviour. Therefore, the primary objectives of this study are numerical and analytical analysis of the soil-geosynthetic interface behaviour with application of a hyperbolic nonlinear elastic perfectly plastic constitutive model. In this investigation a series of large-scale direct shear tests was performed to evaluate the shear stress-displacement interface behaviour considering two types of marginal soils in contact with five types of geosynthetic materials in different soil moisture conditions. Accordingly, the hyperbolic model was used to simulate the soil-geosynthetic interface behaviour. Moreover, a three-dimensional finite element model of the direct shear test was developed using ABAQUS software and a user-defined subroutine was implemented to consider the hyperbolic interface model. The results indicated a very good agreement between the experimental data and the predicted finite element simulations of the direct shear tests and analytical solutions. Finally, a numerical simulation of a pullout test is presented in this paper with application of the hyperbolic interface model.

Required strength of geosynthetic-reinforced soil structures subjected to varying water levels using numeric-based kinematic analysis

This work developed a numeric-based kinematic approach for evaluating the required strength of three-dimensional (3D) geosynthetic-reinforced soil structures (GRSSs) with different water levels. Instead of directly employing the pore-water pressure coefficient ru, this work utilizes numerical simulations to obtain the distribution of pore-water pressures. The presented method avoids to determine the value of ru, which is uncertain as the variation of water tables. A 3D horn-like failure mechanism is discretized to describe the collapse of GRSSs. On this basis, the seepage forces acting on each element of the discretized mechanism are determined by using an interpolation technique. Thanks to the principle of work rate balance, the required reinforcement of geosynthetics is determined through optimization. Sets of design charts are provided for simplicity of practical use, followed by a sensitivity analysis. Results of this paper indicate that the presence of a seepage flow increases the required strength of reinforcements, whereas the inclusion of 3D effects has an opposite effect. The variation of water levels significantly impacts the required strength and the failure pattern of GRSSs. The proposed method in this paper can provide an insight into the design of GRSSs subjected to seepage forces.

Embodied energy and carbon emissions analysis of geosynthetic reinforced soil structures

The significant role of geotechnical engineering in achieving sustainable development is often neglected. Geosynthetic reinforced soil (GRS) technology brings promising prospects for embracing sustainable practices. In this study, the embodied energy (EE) and embodied carbon (EC) of three design options for a hypothetical large retaining structure project in China are investigated. The purposes are (1) to capture the relative impact contributions of the process stages in each design; (2) to determine whether GRS technology has significant merits regarding environmental impact among various structures; (3) to understand the distribution characteristics of the environmental impact indicators of the collected materials; and (4) to compare the difference in environmental impacts caused by geographical factors of carbon coefficient (CC). Results show that the stage of raw material production for various design options has the greatest impact on the environment. GRS technology could reduce the total embodied energy (TEE) and TEC of large retaining structures by an average of 30% and 60%, respectively. The embodied energy coefficient (EEC) and CC values of geosynthetics exhibit significant variety. Recycled steel can drastically reduce its impact on the environment. The results of the assessment can be affected by the spatial variability of CC, but its influence is limited.

Influence of cyclic load on pullout stiffness of geogrid embedded in well-graded gravel

Railway structures applied to high-speed railways must achieve high performance in terms of strength and deformation characteristics. This requirement has led to the widespread use of geosynthetic-reinforced soil (GRS) structures. For the design of GRS structures, it is important to evaluate not only the tensile strength of the geosynthetic but also the pullout stiffness (spring constant of geosynthetic). Hence, a series of cyclic pullout loading tests were conducted to evaluate the pullout characteristics of various types of reinforcement embedded in the soil. Moreover, these test results were compared with the results of in-isolation tensile tests with the same loading histories. The experiments revealed that the pullout stiffness increased with an increase in the confining pressure and in-isolation tensile stiffness, but decreased with an increase in the relative displacement between the soil and reinforcement. Although the pullout stiffness was found to be affected by factors such as experimental conditions and type of reinforcement, a similar trend was observed in the results of several other tests when examining the relationship between the normalized pullout stiffness and the average strain generated in the reinforcement. This interesting correlation can be taken into account during the design of GRS structures that support bridge girders.

Stability assessment of 3D reinforced soil structures under steady unsaturated infiltration

Internal stability assessment of geosynthetic-reinforced soil structures (GRSSs) has been commonly carried out assuming plane-strain conditions and dry backfills. However, failures of GRSSs usually show three-dimensional (3D) features and occur under unsaturated conditions. A procedure based on the kinematic limit-analysis method is proposed herein to assess 3D effects and the role of steady unsaturated infiltration on the required geosynthetic strength for GRSSs. A suction stress-based framework is used to describe the soil stress behavior under steady unsaturated infiltration. Based on the principle of energy-work balance, the required geosynthetic strength is determined. A comparison analysis with the prior research is conducted to verify the developed method. Two kinds of backfills, i.e., high-quality backfill and marginal backfill, are considered for comparison in this work. It is shown that accounting for 3D effects and the role of unsaturated infiltration considerably reduces the required geosynthetic strength. The 3D effects are primarily affected by the width-to-height ratio of GRSSs, and the contribution of unsaturated infiltration is mainly influenced by the soil type, flow rate, GRSS's height, and location of the water table.

Reliability Analysis of High Concrete-Face Rockfill Dams and Study of Seismic Performance of Earthquake-Resistant Measures Based on Stochastic Dynamic Analysis

The randomness of earthquake excitation has a significant impact on the seismic performance of high earth-rock dams. In this paper, the seismic performance of geosynthetic-reinforced soil structures (GRSS) of high concrete face rockfill dams (CFRDs) is evaluated from the stochastic perspective. Multiple groups of seismic ground motions are generated based on spectral expression-random function non-stationary model. Taking Gushui CFRD as an example, this study calculates the failure probability of each damage level of non-reinforce slopes and reinforce slopes based on generalized probability density evolution method (GPDEM) and reliability analysis is presented though multiple evaluation indicators. The result shows that GRSS can reduce the mild damage of CFRDs during earthquake and restrain the moderate and severe damage. The influence of vertical spacing and length of GRSS on the seismic performance is obtained, which provides a reference for the seismic design and risk analysis of CFRDs.

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.

1-g Shaking table tests to determine the behavior of geosynthetic reinforced soil walls under seismic loads

Geosynthetic reinforced soil structures are widely used to support and enable transportation infrastructure. Given the importance of the transportation infrastructure within the context of disaster resilience, it is crucial to fully understand the response of the elements which constitute and support the infrastructure assets. This study presents and discusses the results of four heavily instrumented large scale geosynthetic reinforced soil walls which were subjected to seismic loading under 1-g conditions. The walls were constructed with different reinforcement arrangements, backfill materials, and batter angles to study the effects of these parameters on the behaviour and seismic performance of model walls. The test results indicate an interplay with the wall response and Arias Intensity which is an earthquake intensity measure.

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.

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.

Geosynthetic reinforcement stiffness for analytical and numerical modelling of reinforced soil structures

Many analytical and numerical analysis and design methods for geosynthetic-reinforced soil structures require a single-value (constant) estimate of reinforcement stiffness. However, geosynthetic reinforcement products are rate-dependent polymeric materials meaning that they exhibit time and strain-dependent behaviour under load. Hence, the appropriate selection of a constant (elastic) stiffness value requires careful consideration. A simple hyperbolic stiffness model is shown to be a useful approximation to the constant-load isochronous creep-strain behaviour of these materials at low load levels applicable to operational (serviceability) conditions of geosynthetic-reinforced soil structures. A large database of 606 creep tests on 89 different geosynthetic reinforcement products falling within seven different product categories was collected. From these data, isochronous stiffness values were determined for different combinations of duration of loading and strain level. Data from products falling within the same category were collected together to provide approximations linking the isochronous load-strain (creep) stiffness to the ultimate tensile strength of the material. These approximations are useful for analytical and numerical modelling particularly when parametric studies are undertaken to identify the sensitivity of model outcomes to reinforcement stiffness. Finally, three different geosynthetic-reinforced soil application examples are provided to demonstrate the important role of tensile stiffness on analysis and design outcomes.