No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Pullout Behavior of the L-Shaped Anchorage of Geogrid Under Static and Cyclic Loading
Abstract
Geogrid as a reinforcing element is used in various soil structures such as reinforced walls and slopes, soft soil fills, and base layers of railway and roads. Due to space restrictions, geogrid often cannot be implemented horizontally, and different shapes of anchors should be used, where the L-shaped form is very common. Additionally, the geogrids used in reinforced soil are exposed to cyclic surcharges, along with permanent loads during the operation period. Thus, the present study provides the results of pullout tests on sandy soilburied geogrid with L-shaped anchorage under static and cyclic pullout force in order to assess the effect of different factors such as load amplitude and the number of replicating loading. Based on the results, adding the amplitude of cyclic loading resulted in mobilizing more pullout force compared to static conditions and enhancing cumulative displacements along the geogrid specimen. Further, adding the number of replicating cyclic loading resulted in diminished pullout force related to the anchorage of geogrid and safety margin of the operating structure under the condition of displacement control.
Supplementary resource (1)
Data
September 2023
... In addition, there are some scholars who have studied the influence pull-out load has on interactions with a reinforced soil interface [17][18][19]. For example, the interaction between the geogrid and the soil can be analyzed by pull-out tests [20][21][22][23][24], and the mechanisms of pull-out limit state and anchorage zones can be studied with a large pull-out facility [25,26]. Abdi [27] analyzed the size, distribution and displacement of particles at the interface of reinforcement and soil by pull-out test. ...
The geogrid flexible reinforced soil wall is widely used in engineering practice. However, a more comprehensive understanding of the dynamic behavior of reinforced soil wall is still required for a more reasonable application. In order to explore the mechanical behavior of a geogrid flexible reinforced soil wall, the model test was carried out to investigate the dynamic deformation of geogrid reinforced soil wall subjected to a repeated load. The numerical simulation was also conducted for comparison and extension with regards to the earth pressure and the reinforcement strain. The change rules for the deformation of the wall face, the vertical earth pressure and the reinforcement strain subjected to dynamic load with four frequencies (4, 6, 8 and 10 Hz) and four amplitudes (30–60, 40–80, 50–100 and 60–120 kPa) were obtained. The factors that affect the mechanical behavior of geogrid flexible reinforced soil wall were analyzed. The results show that the dynamic deformation characteristics of reinforced soil wall are affected by the number of vibrations, the amplitude of dynamic load and the frequency of vibration. The maximum lateral displacement of the reinforced soil wall occurs on the third to the fifth layer. With an increase in dynamic load amplitude, the development of dynamic deformation gradually increases, and after a cumulative vibration of 200 × 10⁴ times, the cumulative lateral deformation ratio and the cumulative vertical deformation ratio of the wall face is less than 1%. The vertical earth pressure of geogrid flexible reinforced soil wall increases partially along the length of the reinforcement, and the vertical earth pressure of the third layer is basically unchanged when subjected to a dynamic load. With an increase in vibration number, the change in the reinforcement strain of the third layer is more complex, and the change rules of the reinforcement strain of each layer are different. The reinforcement strain is small, with a maximum value of 0.1%.
The problem of improving foundation bases in strongly deformable and structurally unstable soils is examined. A design is proposed for a sand cushion reinforced with horizontal geosynthetic elements. The results of the operation of the proposed structure with basal soil as well as approaches to determining the maximum resistance force and the deformation of a base improved by such a structure are presented.
The soil reinforcement by geosynthetic is widely used in civil engineering structures:
reinforced slopes and walls, embankments on compressible and soft soils, slope on a stable
foundation, embankments on cavities and retaining structures, reinforcement in the base layers of
railroads and road constructions, bridging over sinkholes or reinforced abutments, piled
embankment, reinforced foundation mattresses.
The stability of these structures specially depends on the efficiency of the anchors holding the
geosynthetic sheets. The anchorages simple run-out and with wrap around are two most commonly
used approaches. Designing the required dimensions of the anchorage with wrap around remains
problematic. In order to improve the available knowledge of the anchorage systems behaviour, the
experimental and numerical studies were performed jointly. This paper focuses on the physical and
numerical models of the geosynthetics behaviour in two anchors (simple run-out and with wrap
around). Laboratory pull-out tests, performed with two experimental tanks under controlled
conditions, consisted in the pull-out of three reinforced non-woven needle-punched geotextiles
(uinaxial or biaxial with different stiffness) anchored following various geometries in different kind
of soil.In order to confirm and to complete the experimental studies presented in these anchorage systems,
a two-dimensional discrete-element model (DEM) was performed. The advantage of the numerical
model is its ability to reproduce the behaviour of the geosynthetic and the soil/geosynthetic
interaction. The parameters deduced from physical model are used in this numerical study.
When determining the dimensions of a geosynthetic lining system, it is important to have knowledge of the behaviour of the anchorage of the geotextile sheets. In order to optimise the geometry of the structures in question and then reduce the area taken up by the anchorage, anchorage solutions using trenches of varying forms are sometimes used. This paper focuses on two types of anchors (simple run-out and wrap around). The first author has previously performed some pull-out tests using an anchorage bench under controlled conditions using three types of geosynthetics and two types of soil. The results obtained from that study showed that there is an optimum length for the upper part of the geosynthetic for the wrap around anchorage. A more detailed analysis which describes the behaviour of a geosynthetic for the wrap around anchorage, the influence of the geosynthetic and of the soil types is presented herein.
Geosynthetics are used as reinforcing elements in a wide variety of structures: reinforced slopes and walls; embankments on soft soils; piled embankment; reinforcement in the base layers of railroad and road constructions; reinforced foundation mattresses; bridging of sinkholes or reinforced abutments. In some cases, these reinforced structures require anchorage areas. Designing the required dimensions of this anchorage remains problematic. This paper focuses on the simple run-out and wrap around anchorages. Laboratory tests, performed with these two anchorage benches, consisted of the pull-out of three geotextiles (uniaxial or biaxial with different stiffness) anchored following various geometries in different kinds of soil. In order to confirm and to complete the experimental studies presented in these anchorage systems, a specific two-dimensional discrete-element model has been used. The soil was described by discrete elements and the geosynthetic behaviour was taken into account by the use of thin finite elements. The interface behaviour between the soil particles and the geosynthetic elements was considered at each contact point by using a Coulomb contact law. The numerical model reproduced the experimental campaign and the anchorage mechanisms reasonably. The load transfer between the geosynthetic and soil was visualised by the force and displacements distribution along the geosynthetic sheet. The numerical procedure could also be used to define the conditions of stability for reinforced slopes or walls.
Nowadays, geosynthetics are used as reinforcing elements in a wide variety of structures: Reinforced
slopes and walls, embankments on soft soils, piled embankment, reinforcement in the base layers of railroad and road constructions, reinforced foundation mattresses, bridging of sinkholes or reinforced abutments.
In most cases, these reinforced structures require anchorage areas where the friction forces between the soil and the sheet equilibrate the horizontal tensile force induced in the geosynthetic sheet. Depending on the space available and on the loads applied, the anchorage systems may be configured with different shapes: simple run-out, anchorage or trenches of different geometries, and anchorage with wrap around. Designing the required dimensions of this anchorage remains problematic. In order to improve the knowledge of the behaviour of different kinds of anchorage, experimental and numerical studies were developed jointly.
This paper focuses on the simple run-out and anchorage with wrap around. Laboratory tests consisted in the
pullout of a reinforced non-woven needle-punched geotextile anchored following various geometries.
Pullout tests of linear and non linear geosynthetic sheets were simulated using a two-dimensional discrete-element model (DEM). In the DEM, the soil was modelled with elementary particles which are assembled together to make clusters that interact with one another via their contact points. The constitutive behaviour of the soil is defined via micro-mechanical parameters of the contact laws. The geosynthetic was modelled by means of a dynamic spar elements method (DSEM). The advantage of DSEM elements is their ability to reproduce the behaviour of the geosynthetic and its interface directly.
With the parameters selected, numerical results of pullout calculations compare well with experimental data.
Comparisons were made on the values of displacements obtained on particular points of the sheet, on tensile force in the sheet and on failure behaviour.
This paper presents the results of pullout tests on uniaxial geogrid embedded in silica sand under monotonic and cyclic pullout forces. The new testing device as a recently developed automated pullout test device for soil-geogrid strength and deformation behavior investigation is capable of applying load/displacement controlled monotonic/cyclic forces at different rates/frequencies and wave shapes, through a computer closed-loop system. Two grades of extruded HDPE uniaxial geogrids and uniform silica sand are used throughout the experiments. The effects of vertical surcharge, sand relative density, extensibility of reinforcement and cyclic pullout loads are investigated on the pullout resistance, nodal displacement distributions, post-cyclic pullout resistance and cyclic accumulated displacement of the geogrid. Tell-tale type transducers are implemented along the geogrid at several points to measure the relative displacements along the geogrid embedded length. In monotonic tests, decrease in relative displacement between soil and geogrid by increase of vertical stress and sand relative density are the main conclusions; structural stiffness of geogrid has a direct effect on pullout resistance in different surcharges. In cyclic tests it is observed that the variation of post-cyclic strength ranges from minus 10% to plus 20% of monotonic strength values and cyclic accumulated displacements are increased as normal pressure increase, but no practical specific comment can be made at this stage on the post-cyclic strength of geogrids embedded in silica sand. It is also observed that in loose sand condition, the cyclic accumulated displacements are considerably smaller as compared to dense sand condition.
Anchored geosynthetics are able to withstand higher tension and provide higher anchorage capacity. The simple run-out and wrap-around anchorages are two commonly used configurations in anchored geosynthetics. However, the influence of geometric parameters of different anchorage configurations on pull-out performance is still problematic. To study the influence of anchorage angles on pull-out resistance of the geotextile wrap around anchorage, two geometric control variables, namely, the top and bottom anchorage angles, were introduced and investigated experimentally and theoretically. A series of pull-out tests were carried out on the geotextile anchorages with varying configurations embedded in sand, including simple run-out and wrap around anchorages that were configured at varying top and bottom anchorage angles. Three stages were summarised to interpret the mobilisation of pull-out resistance of the geotextile wrap around anchorage during the pulling process. It was found that the smaller the bottom angle, the higher the initial pull-out resistance achieved at the early and middle stages, while the larger the top angle, the higher the final pull-out resistance achieved at the final stage. In addition, theoretical studies on pull-out resistance of the geotextile wrap around anchorage with varying anchorage angles were also carried out based on the static equilibrium analysis.
The pullout resistance of reinforcement is an important parameter in the design of reinforced earth structures. Existing design procedures consider the pullout resistance of reinforcement from axial pull. However, the kinematics of failure clearly establish that the reinforcement is pulled obliquely along the slip surface. The response of reinforcement to oblique pull is equivalent to an application of axial and transverse components of oblique pull. In this study, details are provided of a novel experimental test setup used to examine the response of smooth-metal-strip reinforcement subjected to transverse pull at one end. A large-size test chamber of dimensions (length, width, and depth) with an arrangement to conduct transverse pullout of reinforcement is developed. The pullout response of smoothmetal- strip reinforcements to transverse pull is obtained for three different normal stresses of 17, 52, and 87 kPa. Transverse pullout resistance factors of smooth-metal-strip reinforcements corresponding to different transverse displacements of the reinforcement are proposed and found to range from 0.6 to 2.9, corresponding to transverse displacements of 20-30 mm.
The pullout test is one of the methods commonly used to study pullout behavior of reinforcements. In the current research, large pullout tests (i.e. 100 × 60 × 60 cm) have been conducted to investigate the possibility of pullout resistance enhancement of clays reinforced with HDPE geogrid embedded in thin layers of sand. Pullout tests on clay–geogrid, sand–geogrid and clay–sand–geogrid samples have been conducted at normal pressures of 25, 50 and 100 kPa. Numerical modeling using finite element method has also been used to assess the adequacy of the box and geogrid sizes to minimize boundary and scale effects. Experimental results show that provision of thin sand layers around the reinforcement substantially enhances pullout resistance of clay soil under monotonic loading conditions and the effectiveness increases with increase in normal pressures. The improvement is more pronounced at higher normal pressures and an optimum sand layer thickness of 8 cm has been determined for maximum enhancement. Results of numerical analysis showed the adequacy of the box and geogrid length adopted as well as a relatively good agreement with experimental results.
Interaction between soils and geosynthetics is of utmost importance in applications of these materials as reinforcement in geotechnical engineering. That is also the case for some applications of geosynthetics in environmental protection works. The mechanisms of soil–geosynthetic interaction can be very complex, depending on the type and properties of the geosynthetic and the soil. This paper presents and discusses some experimental, theoretical and numerical methods for the study and evaluation of interaction between soils and geosynthetics, with particular reference to the applications of these materials in soil reinforcement. The main advantages and limitations of some traditional experimental and theoretical methods for the study of soil–geosynthetics interaction are presented and new applications of these methods are addressed. The need for improvements in experimental and theoretical techniques for a better understanding of soil–geosynthetic interaction is highlighted.
Misleading results of pull-out tests have often been reported. Factors such as soil dilatancy or the effects of boundary conditions are usually given as causes. This Paper attempts to group the results of pull-out tests of grids to show a consistent pattern of variation independent of the scale of the test. This has been accomplished by identifying some of the usual causes of misleading results and by considering the grid reinforcement as a succession of bearing elements, buried in the soil, that can interfere with each other. If boundary influences are avoided, the interference between bearing elements is the main factor that affects the results of pull-out tests of grids. It is also observed that, despite its practical advantages, the comparison of a grid to a perfectly rough material, as an upper limit for grid performance, seems not to be the most appropriate.
En général des facteurs tels que la dilatance du sol ou les effets des conditions aux limites sont donnés pour expliquer les résultats souvent erronés des essais d'arrachement de grilles. L'article groupe les résultats de tels essais pour démontrer un système conséquent de variation indépendant de l'échelle de l'essai. À cette fin on a identifié certaines causes classiques des résultats errones, en considérant le renforcement à grille comme une succession d'éléments portants enfouis dans le sol qui peuvent interférer les uns avec les autres. Si on néglige les influences de bord, l'interférence entre les éléments portants constitue le facteur principal qui influence les résultats des essais d'arrachement de grille. On a trouvé aussi que malgré des avantages pratiques il paraît peu justifié de comparer la grille à un matièriau de rugosité parfaite pour obtenir une limite supérieure de la performance de la grille.
Pullout and direct shear tests have been conducted to investigate the soil-reinforcement interaction behavior in pullout and direct shear mechanisms. An apparatus-discussed in this paper-has been developed that is capable of performing both pullout and direct shear tests, displacement measurements to monitor dilatancy on the backfill soil during pullout tests are incorporated in the apparatus. Test results for the geogrid type of reinforcement embedded in dense granular soil are discussed. The devised testing program provides valuable information on the appropriate interaction models and parameters that will be employed in the design and analysis of reinforced soil structures. The dilatancy measured in the laboratory may also provide useful information on the increase of interface shear resistance when dilatancy is restrained under field conditions
Mobilization of the pullout resistance of geosynthetics in monotonic and cyclic modes is described from both displacement- and load-controlled tests performed at normal stresses in the range 4-17 kPa. The tests were performed on three geogrids and two geomembranes embedded nearly 1.0 m in a uniformly graded sand. Results for load-controlled tests at a constant rate of 0.25 kN/(m ·min-1), followed by several series of load cycles of increasing amplitude, are compared with displacement-controlled tests at a constant rate of 0.5 mm/min. In general the geogrids behave as an equivalent textured sheet. Pullout behaviour, and especially the incremental displacement mobilized at cyclic loads close to the maximum resistance, is found to vary with type of geogrid. In only one case was cyclic pullout resistance of a grid found to exceed the monotonic resistance. A comparison of the cyclic and monotonic response yields a constant ratio of pullout resistance at large displacement, but one which is not unique to a particular specimen. Cyclic strains of decreasing amplitude are mobilized along a test specimen, with most of the necessary relative displacement occurring close to the loaded end and the embedded end showing little response.Key words: pullout testing, monotonic, cyclic, dynamic, geosynthetics, reinforced walls.
This paper deals with some results of a wide experimental research carried out in order to study factors affecting cyclic and post-cyclic pullout behaviour of different geogrids embedded in a granular soil. The new test procedure developed (multistage pullout test) and the relative results are described. In particular, test results obtained using the constant rate of displacement (CRD) and the multistage pullout tests highlighted the influence of the different factors involved in the research (cyclic load amplitude and frequency, vertical confining stress, geogrid tensile stiffness and structure) both on the peak pullout resistance and on the peak apparent coefficient of friction mobilized at the interface.
In order to study the factors affecting the behaviour of reinforcement geogrids embedded in granular compacted soils, a large-scale pullout test apparatus has been designed. More than 40 pullout tests have been performed, at constant displacement rate, on three different HDPE extruded geogrids embedded in a compacted granular soil by varying the specimen lengths and the applied vertical effective pressures. The different geogrids used in the research have been tested using unconfined tensile tests performed at different speeds, and, in particular, at the same speed of the pullout tests; granular soil have been characterized through classification, Proctor and shear tests.The pullout test results showed the influence of the different parameters studied on pullout behaviour. Moreover, on the basis of the test results it was possible to evaluate the peak and the residual pullout resistance and the apparent coefficient of friction mobilized in the same conditions.
A series of laboratory pullout tests was carried out to investigate the pullout behavior of geogrid in sand under rigid and flexible boundary conditions at the front of a pullout test apparatus. Furthermore, non-destructive X-ray radiography method was used to examine the sand behavior during the pullout of the geogrid. The front boundary condition, overburden pressure, relative density and stiffness of geogrid were considered test parameters. Based on the measurements of geogrid displacement distribution, pullout force, lateral force on the rigid front face and displacement of the flexible front face, it is made clear that the geogrid pullout behavior with the rigid front face is different from that with the flexible front face. Furthermore, the mechanism of each geogrid behavior is discussed.
The design methods used for soil mass structures, such as mechanically stabilised earth (MSE) structures, are based on soil/reinforcement anchorage models which require the knowledge of the soil/reinforcement interface friction capacity. However, different types of reinforcements are used in these structures and present different behaviour. This study concerns two types of strips reinforcements. The first one is metallic and is classically designed using elasto-plastic models (
[21] and [22]). The second type is geosynthetic. The classical anchorage models do not take into account the extensibility of this materiel and do not reproduce its complex behaviour.In the first part this paper presents pull-out tests carried out on the two types of strips reinforcements (metallic and synthetic) subjected to several levels of vertical stresses. The tests are carried out in a metallic tank in controlled and instrumented conditions. In the second part, three modelling processes of the pull-out tests are implemented. The first method takes classical anchorage models into account. The second method improves the friction model using the analysis of the experimental tests. The last method adds the real tensile behaviour of the synthetic reinforcement to the second and assumes an initial strain threshold ɛ0 (Bourdeau et al. 1990) in order to simulate the delayed mobilisation. This analysis leads to parameters which qualify the interaction between metallic or synthetic strips and the soil mass, and enable a better understanding of the behaviour of the structures.
The testing equipment, specimen preparation and testing procedures are described for a series of pull-out tests on geogrids in granular soil.The interaction between a well graded very gravelly sand and a uniaxial geogrid made of high density polyethylene is studied in a pull-out box with dimensions of 1.53 m length, 1·00m width and 0·80m height.The influence of the confinement pressure, soil density and displacement rate on the pull-out resistance of the geogrid is discussed by analysing the results of the pull-out tests.
Pull-out resistance has been evaluated using pull-out tests on geogrids in soils. Both field and laboratory pull-out tests were carried out in order not only to make clear the pull-out mechanism but also to determine the parameters for design and analysis of the reinforced soil structures. When the geogrid in the soil is subjected to a pulling force, the geogrid is pulled out of the soil as the grid itself elongates. In order to evaluate the pull-out resistance, two elevation methods which are called ‘Mobilizing Process Method’ and ‘Average Resistance Method’ are newly defined. These are implemented using the test results. Recommendations for laboratory pull-out tests are also proposed.
Factors affecting the interface apparent coefficient of friction mobilised in pullout conditions
- N Moraci
- G Romano
- F Montanelli
N. Moraci, G. Romano, and F. Montanelli, "Factors affecting the interface apparent coefficient of friction mobilised
in pullout conditions," Third European Geosynthetics Conference, Munich, Germany, 313-318 (2004).
Modeling of the behavior of geosynthetic composite structures by discrete elements-application to anchors in trenches at the head of the slope
- B Chareyre
B. Chareyre, "Modeling of the behavior of geosynthetic composite structures by discrete elements-application to
anchors in trenches at the head of the slope," Thesis, Grenoble I-Joseph Fourier University (2003).
Design of anchoring at the top of slopes for geomembrane lining systems
- L Briançon
- H Girard
- D Poulain
- N Mazeau
L. Briançon, H. Girard, D. Poulain, and N. Mazeau, "Design of anchoring at the top of slopes for geomembrane lining
systems," 2nd European Geosynthetics Conference, 645-650 (2000).