Pullout Resistance Of Reinforcement Research Articles

Analytical assessment of pullout capacity of reinforcements in unsaturated soils

The effective interaction mechanisms in the pullout resistance of reinforcements include skin friction mobilized at the soil-solid surface, soil-soil shear resistance, and compressive resistance created against transverse elements. The third component is obtained from passive lateral pressure (LPM) or bearing capacity (BCM) methods. An analytical solution is proposed to determine the pullout capacity of geocell, geogrid, and strengthened geogrids embedded in ordinary and unsaturated soils. For unsaturated soils, the effective stress approach was employed. The solution-predicted results were compared with those obtained from large-scale pullout tests reported in the literature. Results indicated that considering LPM for 2D and 3D reinforcements better agrees with experimental results. The mobilized frictional rib-soil interfaces and the soil-soil shear resistance components generally contribute more to the pullout capacity of the geocell and geogrid, respectively. For the extensibility represented by mpi and flexibility of geocell denoted by αpi, the values of mpi = 1, 0.7, and 0.3 for the first, second, and third row of geocell, αpi= 0.4 for the first row of geocell and 0.25 for the second and subsequent rows are suggested to be considered. Parametric studies showed that the optimum transverse rib spacing is over 50 times the equivalent rib thickness (Beq).

Stiffness-based approach of pullout resistance factors of reinforcements embedded in soil

The design and construction of mechanically stabilised earth (MSE) walls is widespread and stiffness-based MSE wall designs are becoming popular. In MSE wall design, the pullout resistance of reinforcement plays a major role. For various field conditions, properties such as the normal stress and stiffness of reinforcement are hard to determine in the laboratory. In this study, a numerical model, developed using finite-element software, was used to assess pullout behaviour by varying other parameters such as normal stress, soil friction angle and, especially, the stiffness of reinforcements. Pullout resistance factors (F*) were developed based on the stiffness of the reinforcements considered in this study, which were in the range 100−10 000 kN/m for normal stresses of 10–300 kPa (equivalent to a maximum MSE wall height of 17 m). The developed design chart can be used for the optimistic design of MSE walls.

Numerical investigation of reinforcement pullout resistance effects on behavior of geosynthetic-reinforced soil (GRS) piers

In this study, three-dimensional numerical analyses were carried out to investigate the effects of reinforcement pullout resistance including facing connection strength on the behavior of geosynthetic-reinforced soil (GRS) piers under a service load condition. Three different piers were investigated in this study, which simulated different levels of reinforcement pullout resistance. Each pier had two cases with different reinforcement stiffness J and reinforcement spacing Sv but the same ratio of J/Sv. Numerical results showed that reinforcement pullout resistance had a significant effect on the behavior of GRS piers. When the pullout mode prevailed, the case with small Sv and low J had smaller lateral facing displacements and vertical strain of the pier under the same applied pressure as compared to the case with large Sv and high J when the ratio of J/Sv was kept constant. When the pullout mode did not prevail, two cases with the same ratio of J/Sv showed similar performance despite different combinations of Sv and J were used. To more effectively mobilize reinforcement strength and improve GRS pier performance, small reinforcement spacing or high-strength facing connection should be considered when sufficient reinforcement pullout resistance cannot be guaranteed otherwise.

Development of a Unique Test Apparatus to Conduct Axial and Transverse Pullout Testing on Geogrid Reinforcements

In the design of reinforced soil structures, the pullout resistance of reinforcement embedded in the fill material is an important input parameter. Different pullout test setups have been proposed previously to determine the axial pullout resistances of reinforcements. In the present study, the details of a unique test apparatus with the ability to conduct both axial and transverse pullout testing of different types of reinforcement was highlighted. The pullout resistances of different geogrids embedded in uniform dense sand beds were presented. Based on extensive axial pullout testing on five different geogrids of varying tensile strengths and aperture sizes under three different normal stresses, empirical equations were proposed to estimate the axial pullout resistances of geogrids at two front-end pullout displacements. The estimated pullout resistances from the proposed equations were found to be in close agreement with the pullout resistances of a sixth geogrid considered in the present study and with the two other studies reported in the literature. A sensitivity analysis was carried out to determine the key parameters influencing the pullout resistance of the geogrid. For the different geogrids tested in dense sand, the axial pullout resistance factors were found to range from 0.34 to 1.97 and 0.52 to 2.05, corresponding to the reinforcement front-end displacements of 30 and 50 mm.

Pullout Behavior of Different Geosynthetics—Influence of Soil Density and Moisture Content

Geosynthetics have increasingly been used as reinforcement in permanent earth structures, such as road and railway embankments, steep slopes, retaining walls and bridge abutments. The understanding of soil-geosynthetic interaction is of primary importance for the safe design of geosynthetic-reinforced soil structures, such as those included in transportation infrastructure projects. In this study, the pullout behaviour of three different geosynthetics (geogrid, geocomposite reinforcement and geotextile) embedded in a locally available granite residual soil is assessed through a series of large-scale pullout tests involving different soil moisture and density conditions. Test results show that soil density is a key factor that affects the reinforcement pullout resistance and the failure mode at the interface, regardless of geosynthetic type or soil moisture content. The soil moisture condition may considerably influence the pullout response of the geosynthetics, particularly when the soil is in medium dense state. The geogrid exhibited higher peak pullout resistance than the remaining geosynthetics, which is associated with the significant contribution of the passive resistance mobilised against the geogrid transverse members to the overall pullout capacity of the reinforcement.

Pullout response of strengthened geosynthetic interacting with fine sand

This research describes results of pullout tests performed on two new systems to reinforce the fine-grained silica sand classified as SP in the Unified Soil Classification System. The first system is composed of geogrid on which transverse steel bars are tied to make a 3-D strengthened geogrid, here called Geogrid-Bar (GGB). In the second system, plastic push pins are attached to geocomposite and a strengthened geocomposite is made, here called Geocomposite-Pin (GCP). Eighteen pullout tests were conducted with the soil relative density of 80% revealed that the use of GGB and GCP systems causes the reinforcement pullout resistance to increase by about 37% and 46%, compared with normal planar geogrid and geocomposite, respectively.

Transverse Pullout Response of Smooth-Metal-Strip Reinforcements Embedded in Sand

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 smooth-metal-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.

Experimental analysis of large-scale pullout tests conducted on polyester anchored geogrid reinforcement systems

The pullout resistance of reinforcement, such as geogrids in mechanically stabilized earth (MSE) walls, includes the skin friction between the soil and solid geogrid surfaces. It also includes the bearing resistance against the transverse ribs, which has a greater influence on the production of pullout resistance. Taking the current limitations involved in producing woven polyester geogrids into consideration (i.e., the limited thickness of the transverse ribs), the amount of bearing resistance developed in front of transverse ribs is limited in the pullout mechanism. Thus, along with introducing an innovative and applied system, this research has endeavoured to demonstrate the effective performance of this new system in increasing the passive resistance — and thereby the pullout resistance — of standard geogrids. This new system, which is formed by adding steel transverse elements (a set of steel equal angles) to the ordinary polyester geogrids by means of nuts and bolts, is called an anchored geogrid (AG). The experimental results show that a spacing-to-height ratio of transversal elements equal to 5 gives the maximum pullout resistance for a polyester AG system in sandy soil used in the study. With an optimum arrangement, this system is capable of increasing the pullout resistance of the ordinary geogrid system by 65%. In addition, based on the plasticity solution, the pullout bearing failure mechanisms of a single isolated transverse element in the polyester AG system depend on overburden pressures.

Evaluation of oblique pullout resistance of reinforcements in soil wall subjected to seismic loads

Pullout resistance is one of the most important factors governing seismic stability of reinforced soil walls. The previous studies on the seismic stability of reinforced soil walls have focused on the axial resistance of the reinforcement against the pullout. However, the kinematics of failure causes the reinforcement to be subjected to the oblique pullout force and bending deformation. Considering the kinematics of failure and bending deformation of the reinforcement, this paper presents a pseudo-static seismic analysis for evaluating the pullout resistance of reinforcements in soil wall subjected to oblique pullout forces. A modified horizontal slice method (HSM) and Pasternak model are used to calculate the required force to maintain the stability of the reinforced soil wall and shear resistance mobilized in the reinforcements, respectively. In addition, this paper studies the effect of various parameters on the pullout resistance of the reinforcements in soil wall subjected to seismic loads. Results of this study are compared with the published data and their differences are analyzed in detail.

浸透流を受ける補強盛土の崩壊機構について

A series of centrifuge model tests were carried out to investigate effectiveness of toe drainage as countermeasureagainst failure of embankment and behavior of slopes reinforced with geotextile due to seepage flow, and to evaluatethe contribution of reinforcement to the stability of these slopes. It was found that the toe drainage contributes for thestability of the slopes and the embankment which reinforced with toe drainage fails suddenly along a well-defined andlarge slip surface. In the case with reinforced with geotextiles, smaller shear deformation in the toe area ofembankment and the smaller settlement at the top of embankment were observed. It indicate that the pull-outresistance of reinforcements make the slope stability increase. Especially, the embankment that installed non-wovenfabrics, which has lager tensile stength, with less reinforcement spacing is highly stable in this study. The factor ofsafety that obtained by means of limit equilibrium could not accurately evaluate the stability of embankments whichinstalled geotextiles. The reason is that in the stability analysis that on the basis of limit equilibrium, the deformation ofembankment that is required to produce the reinforcement force of geotextile was not taken into account

Prediction of Pullout Resistance and Pullout Force-Displacement Relationship for Inextensible Grid Reinforcements

A new analytical method is proposed for determining the inextensible grid reinforcement pullout resistance and pullout force/pullout displacement curve by using basic backfill soil and grid reinforcement properties. The pullout skin friction resistance/pullout displacement relationship is simulated by linear elastic-perfectly plastic model. A hyperbolic model has been proposed to represent the pullout bearing resistance/pullout displacement relationship in which the maximum bearing resistance of a single bearing member is determined using a new bearing capacity equation proposed in this paper. The influences of the grid bearing member spacing ratio, S/D, the bearing member deflection rigidity, and the pullout softening behavior on the mobilization of pullout bearing resistance are explicitly included in the proposed model. Good agreement has been obtained between calculated values and laboratory test 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.