Laboratory Pullout Tests Research Articles

Influence of rigid and flexible face on geogrid pullout tests

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.

Predictions of the uplift response of model belled piles in geogrid-cell-reinforced sand

Breakout factors from a series of laboratory pullout tests on model-belled piles (or enlarged base footings) in geogrid-cell-reinforced sand, which included tests on various model geometries and sand densities, are examined. The concept of effective diameter and effective embedment ratio based on the diameters of both belled piles and geogrid-cell-reinforcement is introduced which provides a pattern of uplift behaviour consistent with previous findings for anchor-type foundations. A unique relationship between effective breakout factor and effective embedment ratio is derived for a given sand density. Experimental breakout factors compare well with predictions from some existing theories for anchor foundations, while a simple approach based on the vertical slip surface model incorporating an uplift coefficient K=0.8√ K P yields close overall agreement with the laboratory data. A hyperbolic relationship is established between pullout load and displacement, which can be used to determine soil stiffness for use in non-linear analyses.

Numerical simulation of pullout response for planar soil reinforcements

This paper presents a series of numerical simulations for laboratory and field pullout tests. A nonlinear differential expression for interface pullout from simple equilibrium of forces and hyperbolic interface model for shear displacement variation along the length of the planar reinforcement is utilised. Finite difference numerical method and nondimensional expressions are adopted for wider application. The relative stiffness and relative displacement parameters are defined and related to the interface pullout interaction mechanism. A parametric study to develop computer-simulated interface design charts for a practical range of relative stiffness and relative bond resistance is theoretically illustrated. The pullout model is capable of simulating the responses of inextensible as well as highly extensible planar reinforcements. The model responses compared satisfactorily with the available theoretical and experimental pullout test results for steel straps, polymer strips, geotextiles, geomembranes, nylon geosynthetics, and geogrid reinforcements.Key words: geosynthetics, extensible reinforcement, numerical simulation, parametric study, pullout testing, reinforced soil.

Changes in Interface Stresses During Pullout Tests on Geogrid Strip Reinforcement

Abstract For a strip geogrid reinforcement, pullout resistance per unit width is known to increase with decreasing specimen width at low applied normal stresses. This phenomenon can be explained by a conceptualized model for a pullout interaction mechanism consisting of combined 2-D and 3-D interaction mechanisms, and the results obtained from laboratory pullout tests can be extended to the field. In this paper, a series of pullout tests on stiff extruded geogrid specimens embedded in dense sandy gravel was carried out and the normal stresses at the soil-reinforcement interface were measured by small-diameter earth pressure cells. On the basis of these tests, the fundamental behavior of soil-geogrid reinforcement interaction is explained and the conceptualized pullout interaction model is corroborated. It is shown that restrained positive dilatancy, observed at low applied normal stresses, results in an increase in actual normal stresses at the soil-reinforcement interface at the edges of the geogrid, thereby increasing the pullout resistance of the reinforcement.

Pullout Simulation of Postinstalled Chemically Bonded Anchors

Chemically bonded postinstalled anchors have seen tremendous growth over the past few years for retrofits, as well as new construction. Currently, they are designed from proprietory tables provided by adhesive manufacturers based on laboratory pullout tests. Recently, Doerr et al. in 1989, Cook in 1993, and Eligehausen et al. in 1984 have developed equations to predict pullout resistance of anchors. Since chemically bonded anchors result in the failure of both the concrete and adhesive-concrete interface, the equations attempt to predict the ultimate resistance of the anchor through the sum of the contributions from the concrete-failure cone and adhesive-concrete interface. However, this approach requires an estimate of both the average or maximum shear stress within the adhesive bond layer and the concrete-failure cone depths. To shed more light on the development of failure for these types of anchors, a state-of-the-art elastoplastic finite-element analysis was performed and compared to experimental results. Besides being able to predict pullout resistance, concrete-failure cone depths, and orientations, the analysis revealed that failure initiates as a tension zone below the concrete surface at the anchor-adhesive interface and propagates with load toward the surface. In the process, both the concrete and adhesive material dilate increasing the confinement and shear resistance within the adhesive layer. Once the tension zone reaches the surface, the confinement is lost, resulting in a diminished shear resistance within the adhesive layer and anchor failure. After comparing a number of proposed methods to predict resistance to the experimental data, it was found that a simplistic, uniform bond stress applied over the whole anchor did an excellent job of predicting pullout capacity.

The pull-out resistance of geogrids in reinforced soil

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.

An Interface Pullout Formula for Extensible Sheet Reinforcement

Pullout tests have been widely used to evaluate soil reinforcement interface properties for the design and analysis of reinforced soil structures. However, there are difficulties interpreting pullout test results particularly when extensible materials, such as geotextiles, are used as reinforcement. In this study, an analytical model (an “interface pullout formula”) is presented for predicting and interpreting pullout test results in a unified and consistent manner. The model is based on three postulates that were deduced from the measured behavior of laboratory pullout tests and numerical results from finite element analyses. A number of applications of the interface pullout formula for predicting and interpreting the results of pullout tests are presented, including: how to predict the active length at a given applied pullout force; how to predict the pullout failure force for reinforcement of a given length; how to determine the coefficient of friction from results of a pullout test; and, how to predict the displacement at any point along the reinforcement for a given applied pullout force. Results using the interface pullout formula are shown to be in good agreement with the results of an instrumented pullout test and finite element analyses.

Reinforced Gravel Foundation for Box Culvert Construction on Soft and Subsiding Ground

The paper investigates the performance of box culverts supported on geogrid reinforced gravel foundations overlying soft Ariake clay of the Saga Plain in Japan. The study focuses on: the reinforcing function of geogrids in large scale laboratory load and pullout tests; field observations of prototype box culvert structures; and numerical analyses. Large scale laboratory load tests were performed to determine which geogrid configuration (two horizontal layers, or geocells) would resist settlement the most. The laboratory results showed that settlements were comparatively less for two horizontal geogrid layers; thus, this geogrid configuration was used in the numerical analyses and for the prototype box culvert structures. Although the field observations indicated large values of total settlement for box culverts on reinforced gravel fill overlying clay, the differential settlements were small and no cracks or serious damage to the culverts occurred.

Interaction of lateritic soil and steel grid reinforcement

Laboratory and field pullout tests were carried out to study the interaction of welded steel grid reinforcements embedded in lateritic residual soil backfill. The laboratory pullout tests were conducted on various reinforcement sizes, mesh geometries, normal pressures, and compaction conditions of the backfill material. Field pullout tests were conducted at representative overburden, field-moisture, and density conditions. From the test results, it was found that the longitudinal members yielded frictional resistance from 8 to 15% of the total grid pullout resistance. Thus, the major contribution to the pullout resistance of grid reinforcements consists of the passive resistance mobilized in front of the transverse members. The maximum pullout resistance is shown by a bilinear curve which displayed similarity with the failure envelope from direct shear tests of the backfill material. This bilinear envelope reinforced the previous observation regarding the effect of particle breakage phenomenon inherent to lateritic residual soils subjected to high normal pressures. Comparisons between laboratory and field pullout resistances and between the predicted passive resistance and the laboratory test data are also presented. Key words : reinforcement, laboratory test, earthfill, compaction, friction resistance.

Pullout Tests Using Steel Grid Reinforcements with Low‐Quality Backfill

Both laboratory and field pullout tests are conducted using steel grid reinforcements with cohesive-frictional backfill soils. The laboratory pullout tests are performed using a large-scale pullout apparatus designed especially for this study. The field pullout tests are performed on the dummy welded-wire reinforcements embedded in a full-scale reinforced test wall/embankment system that utilize three different locally available, low-quality, cohesive-frictional backfill soilds, namely, clayey sand, lateritic soil, and weathered clay, in the three sections along its length. It is observed that the magnitudes of the mobilized field pullout resistances as well as the strains induced in the reinforcing elements are strongly influenced by the response of the wall/embankment system to the subsoil movements and the resulting arching effects due to the presence of the inextensible reinforcements. Meanwhile, the laboratory pullout test results generally seem to provide a conservative approximation of the field pullout resistances of the grid reinforcements in cohesive-frictional backfills. Using the finite element method to model the laboratory pullout tests, the analytical results are observed to agree fairly well with the experimental results.

Pullout Resistance of Steel Geogrids with Weathered Clay as Backfill Material

Abstract The pullout resistance of welded steel geogrid reinforcement embedded in poor-quality, cohesive-frictional backfill material such as weathered clay was investigated. Laboratory pullout tests were conducted on various reinforcement sizes, mesh geometry, and compaction conditions of the backfill material. Field pullout tests were also conducted to investigate the pullout resistance of reinforcements embedded at representative overburden, field moisture, and density conditions. The soil-reinforcement interaction indicated the dominant role of passive or bearing resistance contributed by the transverse members to the total pullout resistance. The frictional resistance of the longitudinal members was found to contribute only about 5 to 15% of the total pullout resistance. It was observed that the reinforcement moved nearly as a rigid body and that the pullout resistance along the reinforcement is uniformly mobilized. The field pullout test provided higher pullout resistance compared to that of the laboratory test. Comparison of the predicted pullout bearing resistance with the observed data indicated that the prediction based on the bearing failure model formed the upper boundary while the prediction associated with the punching failure model provided the lower boundary. An empirical equation was proposed to predict the bearing resistance of the transverse members with reasonable accuracy.

Steep reinforced embankment using geogrid — laboratory pullout test of geogrid and its finite element analysis : Proc 4th International Conference on Geotextiles, Geomembranes and Related Products, The Hague, 28 May–1 June 1990 V1, P45–51. Publ Rotterdam: A A Balkema, 1990

Steep reinforced embankment using geogrid — laboratory pullout test of geogrid and its finite element analysis : Proc 4th International Conference on Geotextiles, Geomembranes and Related Products, The Hague, 28 May–1 June 1990 V1, P45–51. Publ Rotterdam: A A Balkema, 1990

Deformation of Geotextile confined in Soil

The laboratory pull-out test of the nonwoven fabric confined in sand was performed to examine the deformation of the geotextile confined in soil. As a result, because the lateral contraction of the nonwoven fabric decreases as normal stress increases, it was able to estimate that the lateral contraction will not develop as the lateral contractible force of the nonwoven fabric is equal to the friction between soil and nonwoven fabric. In additions the distribution of shear stress occurred between the geotextile and the soil was examined by the mechanical model. As the result of analysis, it is examined that the distribute condition of shear stress will be controlled strongly by the modulus of rigidity of the geotextile.

Laboratory pull-out tests using bamboo and polymer geogrids including a test study : Bergado, D T; Bukkanasuta, A; Balasubramaniam, A S Geotext GeomemV5, N3, 1987, P153–189

Laboratory pull-out tests using bamboo and polymer geogrids including a test study : Bergado, D T; Bukkanasuta, A; Balasubramaniam, A S Geotext GeomemV5, N3, 1987, P153–189

Performance of epoxy-coated reinforced earth strips

The laboratory pull-out test results of epoxy-coated and galvanised ribbed reinforcing strips are reported and compared. The results have been used to predict the developed tensile stresses within the reinforcing strips of recent reinforced earth retaining wall construction using a numerical finite element method of analysis. Comparisons with field measurements have also been made.

Laboratory pull-out tests using bamboo and polymer geogrids including a case study

This study investigates the interaction between soil and geogrids by using both direct shear and pull-out tests and applied the results to a case study. A polymer geogrid and bamboo grids were used with clayey sand and weathered clay as backfill since these materials are readily available in Thailand. The results indicated that the interaction between soil and reinforcement consists of: (a) the adhesion between soil and reinforcement on the solid surface area of the geogrid; and (b) the bearing capacity of soil in front of all transverse members of the geogrids which behaved as a strip footing embedded in the soil. The proposed design procedure for pull-out resistance agreed fairly well with the laboratory pull-out test results. In addition, it was observed that bamboo grids have higher pull-out resistance per unit area than the polymer geogrids. Moreover, the cohesive fill proved to be quite effective when used with geogrid reinforcement. Finally, the proposed design procedure and test results were applied to a case study on an irrigation canal bank repaired by the Public Works Department of Thailand using cohesive backfill and Tensar SS2 geogrids resulting in much improved slope stability.

Pull-out Friction Test of Geotextiles Embedded in Sand

Series of laboratory pull-out tests were carried out using fore samples of geotextile and two sands. When the pullout force acts on geotextiles embedded in sand, two critical modes that are pullout failure and tensile failure of geotextile are observed. It seems that these two failure modes are closely related to confining pressure and deformation modulus of geotextiles. Also, in the pull-out test the nonuniform shear stress distributions occur along the specimen, so in this paper effective shear length that is obtained from the pull-out experiments introduced to consider the pullout resistance.

Performance of an earthwork reinforcement system constructed with low-quality backfill : Hannon, J B; Forsyth, R A Trans Res RecN965, 1984, P55–66

A preliminary evaluation is presented of a retaining-wall system constructed on Interstate 80 at Baxter, California, using lowquality backfill materials. Four mechanically stabilized embankments were constructed. Two of these walls were instrumented to monitor performance over a 3-year period. Dummy bar-mats of different configurations were installed during construction and were subject to field pullout testing. These field pullout results are compared with laboratory tests conducted with the same backfill material at representative overburden and field moisture and density conditions. Field pullout test results are also compared with laboratory tests conducted before the project design. The results of these tests suggest that the laboratory pullout test values provide a conservative design. The transverse bars governed the pullout capacity of the bar-mat and the overburden stress did not significantly affect the pullout capacity in cohesive backfill. The contractor's method of construction significantly influenced the overall response of the soil-reinforced wall system. The satisfactory performance of this wall system after one severe winter season suggests that mat- (or mesh-) type soil reinforcement systems can be constructed successfully by using low-quality on-site materials as backfill.

Laboratory pull-out testing of grid reinforcements in sand : Ingold, T S Geotech Test JV6, N3, Sept 1983, P101–111

Laboratory pull-out testing of grid reinforcements in sand : Ingold, T S Geotech Test JV6, N3, Sept 1983, P101–111

Laboratory Pull-Out Testing of Grid Reinforcements in Sand

Abstract In many reinforced soil applications the critical mode of failure involves pull-out of the reinforcement from the soil. Although grid reinforcement is known to be very efficient in resisting pull-out failure, very little is published on the mechanisms of soil-grid interaction. To investigate soil-grid behavior, several series of pull-out tests were conducted using both metallic and plastic grids embedded in sand. The results of these tests are presented in this paper together with details of the apparatus and testing techniques used. Results are also given for ancillary testing carried out to assess the effects of grid member orientation with respect to the direction of the applied pull-out load. These tests clearly demonstrate that pull-out resistance is a function of the cumulative embedded area of the grid members normal to the direction of pull-out and not the embedded plan area of the reinforcement. Based on these observations an analytical model is developed for strong inextensible grids. Analytical and test results are compared and found to be in good agreement for both metallic and plastic grids.