ISSN / EISSN : 1072-6349 / 1751-7613
Published by: Thomas Telford Ltd. (10.1680)
Total articles ≅ 1,072
Latest articles in this journal
Geosynthetics International pp 1-31; https://doi.org/10.1680/jgein.21.00032a
Understanding the tensile behavior of geosynthetic reinforcement materials at different temperatures is essential for the design of reinforced soil structures in seasonally cold regions. This study describes a series of tensile tests performed on two polypropylene geogrid materials, namely a biaxial geogrid and a geogrid composite. A total of 84 tests were performed in an environmental chamber with temperatures as low as −30°C and as high as +40°C. The response of each material is examined over the range of investigated temperatures to evaluate the effect of temperature changes on the tensile strength of the two geogrid materials. The response of the biaxial geogrid is found to be sensitive to temperature variations, with samples tested at low temperatures exhibiting brittle behavior characterized by high rupture strength and small ultimate strain while samples tested at elevated temperatures displayed ductile behavior with large elongation at failure and comparatively small rupture strength. Similar response was found for the geogrid composite, however, the rupture strength seemed to be less sensitive to temperature changes. The modes of failure observed at each temperature are examined based on photographic evidence taken during the experiments.
Geosynthetics International pp 1-42; https://doi.org/10.1680/jgein.21.00021a
Pullout behaviour of geogrids is critical to understand in the design of mechanically stabilized earth walls. The pullout coefficients are determined through laboratory testing on geogrids embedded in structural fill. Random forest (RF) is a data-driven ensemble learning method that uses decision trees for classification and regression tasks. In the present study, the use of random forest regression technique for estimation of pullout coefficient of geogrid embedded in different structural fills and at variable normal stress based on 198 test results has been investigated using five-fold cross-validation. 80 % of the data has been trained on the model algorithm and the accuracy of the model is then tested on 20 % of the remaining dataset. The performance of the model has been checked using statistical indices, namely R2, mean square error, as well as external validation methods. The validity of the model has also been checked against laboratory tests conducted on geogrid embedded in four different fills. The results of the RF model have been compared to results obtained with three other regression models namely, Multivariate Adaptive Regression Splines, Multilayer Perceptron, and Decision Tree Regressor. The results demonstrate superiority of the RF-based regression model in predicting pullout coefficient values of geogrid.
Geosynthetics International pp 1-63; https://doi.org/10.1680/jgein.21.00046
This paper addresses unpaved and paved roads improved with geosynthetics, such as geotextiles, geogrids and geocells. The paper examines the mechanisms associated with the use of geosynthetics to improve roads, describes the principles of the design methods used to quantify the benefits of geosynthetics used in unpaved and paved roads, presents case histories to demonstrate the use of geosynthetics to solve challenging road problems, and discusses the relevance of tests and trials to real roads. This paper is supplemented by four presentations in pdf format that contain more than 800 slides. These four presentations are updated versions of the four presentations made during a one-day short course at the 11th International Conference on Geosynthetics held in Seoul, Korea, in September of 2018. The paper that follows contains a summary of each of the four presentations, with special emphasis on key issues.
Geosynthetics International pp 1-33; https://doi.org/10.1680/jgein.21.00016a
The seismic stability of geosynthetic structures incorporating soil-geomembrane interfaces depends largely on their response to dynamic loads caused by earthquakes or traffic. The present study investigates the dynamic shearing response of sand-smooth geomembrane interface through fixed–block type shake table tests. The influence of dynamic loading parameters, like, sliding velocity, loading frequency, normal stress, displacement amplitude and the number of cycles, and relative density of sand on the shearing behavior of the sand-geomembrane interface are examined. Results show that the peak cyclic shear stress is significantly influenced by normal stress, shear displacement amplitude, loading cycles, and relative density of sand. The dynamic coefficient of friction of the sand-geomembrane interface displays an increasing trend with an increase in loading frequency, shear displacement amplitude, and relative density of sand but decreased for the rest of the considered parameters. The shape of the hysteresis loops is dependent on the normal stress and displacement amplitude. The dynamic coefficients of friction are also compared with the corresponding values under static conditions. The results from the present study emphasize the importance of considering the design basis value of the dynamic coefficient of friction for each parameter during the design stage of geosynthetic structures involving sand and geomembrane.
Geosynthetics International pp 1-31; https://doi.org/10.1680/jgein.21.00015a
Analytical solutions for geosynthetic reinforced fills over a void have appeared in the literature starting in the 1980s. Current solutions pay little or no attention to the influence of the creep-reduced stiffness of the geosynthetic reinforcement under tensile loading. This paper addresses this gap by introducing a reinforcement stiffness limit state in the design of these systems. The choice of reinforcement stiffness is based on a simple two-parameter hyperbolic isochronous load-strain model developed by the authors and applied to a large database of uniaxial and biaxial geogrids and woven geotextiles. The paper provides a design chart procedure that can be used with four well-known analytical solutions to compute the maximum reinforcement load. In addition to the stiffness limit state, the design chart approach includes vertical deformation and reinforcement strain serviceability limit states, and a tensile strength limit state. A novel feature of the design charts is a quantitative link to the ultimate strength of the reinforcement to estimate the isochronous stiffness of the reinforcement for different elapsed loading times and strains. There are many instances in the literature where the reinforcement stiffness was taken from a constant rate-of-strain tensile test. The paper shows that this is non-conservative for design.
Geosynthetics International pp 1-43; https://doi.org/10.1680/jgein.21.00052
The influence of backfill type and material properties on the performance of field-scale GRS abutment models is investigated. Two alternative types of backfill as recommended in the FHWA guidelines (called open graded and well graded) were used to build two field-scale model abutments and compare their load-bearing performance under a loading beam. Results are presented and discussed relative to the loading beam settlement, facing deformation and reinforcement strains. The well-graded backfill was found to result in smaller beam settlements and facing lateral deformations, especially at smaller loads that were comparable to service load levels. However, it was significantly faster and easier to compact the open-graded aggregate to the unit weight recommended in the guidelines. Nevertheless, performances of both abutment models were found to be satisfactory relative to the limiting requirements on the beam settlement and facing deformations at service load levels.
Geosynthetics International pp 1-46; https://doi.org/10.1680/jgein.21.00043
Back-to-back mechanically stabilized earth (MSE) walls are being widely utilized as bridge abutments and highway ramps, considering their cost effectiveness and ease of construction. Though high quality well-graded granular fill is the most appropriate backfill material, owing to its scarcity, locally available low-quality soils are often used as backfill. Nevertheless, numerous failure cases of such walls with low-quality soil are reported, especially subsequent to the rainwater infiltration. The stiffness of reinforcement is a key parameter affecting the overall behaviour of MSE walls. The present study investigates the influence of reinforcement stiffness on the response of select fill, marginal fill, and hybrid-fill back-to-back MSE walls using a finite element (FE) based approach. Results show that stiffness of reinforcement has a significant effect on the overall performance of marginal fill wall upon rainfall infiltration. Specifically, with the increase of reinforcement stiffness, the infiltration induced facing displacement decreases and reinforcement tension increases. However, the performance of select fill and hybrid-fill walls following rainfall infiltration was found to be satisfactory even with low stiffness reinforcements and further improvement with increase of reinforcement stiffness was insignificant. The reduction of safety factors during infiltration was shown to be independent of reinforcement stiffness for all wall types.
Geosynthetics International pp 1-37; https://doi.org/10.1680/jgein.21.00044
This paper presents two-dimensional (2D) and three-dimensional (3D) numerical simulations of a half-scale geosynthetic reinforced soil (GRS) bridge abutment during construction and bridge load application. The backfill soil was characterized using a nonlinear elasto-plastic model that incorporates a hyperbolic stress-strain relationship and the Mohr-Coulomb failure criterion. Geogrid reinforcements were characterized using linearly elastic elements with orthotropic behavior. Various interfaces were included to simulate the interaction between the abutment components. Results from the 2D and 3D simulations are compared with physical model test measurements from the longitudinal and transverse sections of a GRS bridge abutment. Facing displacements and bridge seat settlements for the 2D and 3D simulations agree well with measured values, with the 2D simulated values larger than the 3D simulated values due to boundary condition effects. Results from the 3D simulation are in reasonable agreement with measurements from the longitudinal and transverse sections. The 2D simulation can also reasonably capture the static response of GRS bridge abutments and is generally more conservative than the 3D simulation.
Geosynthetics International pp 1-45; https://doi.org/10.1680/jgein.21.00034
Geosynthetic-reinforced and pile-supported (GRPS) systems already proved their good performance to support embankments constructed over soft soil. The load transfer mechanism in GRPS embankments depends on the complex interaction between the soil in place, the structural elements and, the embankment's soil type (cohesive or cohesionless). However, the cohesion influence of the embankment soil has not been well investigated as it is often not considered in the design of such systems. The main aim of this study is to present an analytical model for GRPS embankments that combine several phenomena such as the concentric arches model in cohesive fill soils, the hyperbolic model for the isochrone geogrid curve, and subsoil's consolidation. Three-dimensional numerical analyses are also conducted to evaluate the embankment soil cohesion influence on the soil arching. Both the numerical and analytical results agree that the cohesive embankment fills strengthen the soil arching effect and, increases the efficacy if compared with cohesionless embankment fills. A comparison of the analytical model with measured data and other design methods for full-scale field tests proved the proposed model efficiency. The proposed analytical model therefore can be applicable for GRPS embankments with cohesive and non-cohesive fill soils.
Geosynthetics International, Volume 28, pp 479-490; https://doi.org/10.1680/jgein.21.00022
The article presents an experimental study of a geosynthetic-reinforced soil bridge abutment. The geosynthetic reinforced soil bridge abutments 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 bridge abutment is constructed from fourteen 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 bridge abutments, mostly embedded in the ground. The rest 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, which is 50% more than at the center of the bridge abutment. 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 optimal designed GRS bridge abutments.