Experimental and DEM investigation of geogrid–soil interaction under pullout loads

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Abstract

Geogrid–soil interaction is a key issue to describe geogrid reinforcement mechanisms. In order to investigate the geogrid–soil interface behaviour, both experimental and numerical pullout tests have been carried out with modified geogrid samples embedded in granular soil. In the laboratory tests, two different failure modes have been observed depending on the number of geogrid transverse members in this study. Obviously, the maximum pullout resistance increased with increasing number of geogrid transverse members. In the numerical investigations, discrete element software PFC2D has been used. The geogrid–soil interaction under pullout loads has been investigated not only by the qualitative force distributions along the geogrid and in the specimen but also by the quantitative geogrid force, displacement and strain distributions along the geogrid with different numbers of geogrid transverse members. The numerically obtained contributions of transverse members to the total pullout resistance have been used to explain the different failure modes in the laboratory pullout tests. Based on the Fourier Series Approximation (FSA) method, reorientations of contacts and forces in the specimen were presented at different clamp displacements. Moreover, normal stress distributions in the geogrid plane, which is a decisive parameter that can only be evaluated indirectly in the experimental pullout tests, have been obtained directly using the FSA method in the numerical modelling. The experimental and DEM investigation results in this study provide researchers an improved understanding of the geogrid–soil interaction under pullout loads.

Introduction

As an important reinforcing material in practice, geogrids have been widely used in dealing with various geotechnical problems, e.g. stabilizing the earth structures, increasing the bearing capacity of base courses, reducing the rut depth in flexible pavements, etc. (Yoo and Kim, 2008, Leshchinsky et al., 2010, Al-Qadi et al., 2011, Al-Qadi et al., 2012, Heerten, 2012, Yang et al., 2012, Indraratna et al., 2013, Koerner and Koerner, 2013, Qian et al., 2013, Santos et al., 2013, Allen and Bathurst, 2014, Santos et al., 2014, Abdesssemed et al., 2015). The geogrid reinforcing effects are performed via the interaction of geogrids together with the surrounding soil. Hence, the geogrid–soil interface behaviour has been regarded as a significant factor to investigate geogrid reinforcement mechanisms (Lopes and Ladeira, 1996, Palmeira, 2009).

Fig. 1 shows a typical application of geogrids in reinforcing an earth wall in practice. Failure might happen within the geogrid reinforced structure along the potential slip plane. In order to investigate the failure mechanisms of geogrid reinforced structures, many researchers have conducted various laboratory tests on the interface behaviour between geogrid and soil as well as the general compound behaviour of the composite material (Palmeira and Milligan, 1989, Ochiai et al., 1996, Moraci and Recalcati, 2006, Naeini et al., 2013, Ruiken, 2013, Arulrajah et al., 2014, Liu et al., 2014, Ferreira et al., 2015, Qian et al., 2015). Among all the experimental approaches, the pullout test has been regarded as a better way to investigate the geogrid–soil interface behaviour (Yogarajah and Yeo, 1994). Plenty of pullout tests have been carried out based on various geogrid and soil types (e.g. Bergado and Chai, 1994, Palmeira, 2004, Teixeira et al., 2007, Moraci and Cardile, 2009, Palmeira, 2009, Sieira et al., 2009, Giang et al., 2010, Abdi and Arjomand, 2011, Esfandiari and Selamat, 2012, Moraci and Cardile, 2012, Zhou et al., 2012, Mosallanezhad et al., 2016). Those studies have illustrated the influences of various factors on the geogrid responses under pullout loads, which provides helpful hints in designing geogrid reinforced earth structures. Besides the conventional pullout tests, Ezzein and Bathurst (2014) developed a novel pullout test apparatus to evaluate the geogrid–soil interaction using transparent granular soil, which allows to visualize the relative horizontal displacement between geogrid and its surrounding soil.

The discrete element method (DEM) (Cundall and Strack, 1979), which has particular advantages in capturing the kinematic behaviour of discontinuous media at a microscopic level (Zhang and Thornton, 2007, Stahl and Konietzky, 2011, Zhang et al., 2013b), has also been used to investigate the geogrid–soil interaction under pullout loads. McDowell et al. (2006) modelled the interaction between ballast and geogrid by simulating pullout tests and the optimum aperture size of geogrids subjected to pullout loads was discussed. Zhang et al. (2007) conducted numerical pullout tests on loose and dense soil samples to study the effect of compaction on the pullout response. Ferellec and McDowell (2012) investigated the influence ballast shapes on the ballast–geogrid interlocking effects. Chen et al. (2013) and Tran et al. (2013) reproduced experimental pullout tests using the DEM and the simulation results provided detailed responses of geogrid and soil. Chen et al. (2014) investigated the effects of clump shapes on both the pullout resistance and the distribution of contact forces. Stahl et al. (2014) investigated the interlocking effect based on modelling the behaviour of soil mobilization and geogrid deformation. All the above DEM investigations provide detailed observations at the geogrid–soil interface. However, due to the varying elastic–plastic properties of geogrids and soils as well as the high sensitivity of their interaction to many influencing factors, the compound stress–strain behaviour of geogrids embedded in soil is very complex. Therefore, the geogrid reinforcement mechanisms up to now have not been described conclusively and it is still an essential issue to investigate the geogrid–soil interface behaviour.

In this paper, the results of both experimental and numerical pullout tests, which were carried out with different modified geogrids embedded in granular soil, have been presented. Those geogrid samples were modified with different numbers of transverse members. Compared with 3D modelling, 2D numerical simulations have particular advantages of providing insights into key mechanisms with less computational time. Hence, the commercial software Particle Flow Code (PFC2D), which was developed by Itasca (2008) based on the DEM, has been used for the numerical investigations. The limitations of 2D numerical modelling are discussed in the later part of this paper. The aim of this study is to investigate the geogrid pullout responses with different numbers of transverse members and to provide researchers more detailed insights into the geogrid–soil interaction at a microscopic scale.

Section snippets

Testing apparatus

Fig. 2 shows the sketch of the pullout apparatus used in this study. The pullout box was made of steel with the inside dimensions of L/W/H = 435/300/200 (unit: mm). Different from the flexible surcharge loading systems recommended in the ASTM test standard (ASTM D6706-01, 2001, Huang and Bathurst, 2009), the vertical load was applied on top of the specimen through a rigid plate in this study. It should be noted that the vertical forces on both the top and the bottom plates were recorded with

DEM investigations and analyses

In order to gain further detailed insights into the geogrid–soil interaction under pullout loads, the discrete element software Particle Flow Code (PFC2D) has been used in this study. PFC2D utilizes rigid entities (particles and walls) and soft contacts in the numerical modelling. Newton's second law of motion is used to update the positions of the rigid entities due to the forces acting on the soft contacts. The contact forces are then updated based on the force–displacement law (Itasca, 2008

Limitations of the numerical modelling

The numerical simulations in this study were carried out using 2D software, which has inherent limitations in investigating the real 3D problems, e.g. a 2D model dilates with a much higher rate than a 3D model since the 2D plane assembly can only dilate in the vertical and horizontal directions but not in the cross-plane direction (Rothenburg and Bathurst, 1992). The granular soil was modelled with circular disks in this study and large frictional coefficients have been used to compensate the

Conclusion

This study investigated the pullout behaviour of geogrid embedded in granular soil with both experimental and numerical approaches. In the laboratory tests, geogrids with different tensile stiffnesses have been used and those geogrid products have been modified into specimens with different numbers of transverse members. In the discrete element modelling, the models and the input parameters of the granular soil and the geogrid have been calibrated by direct shear tests and tensile tests,

Acknowledgements

This work was financially supported by the China Scholarship Council (No. 2010630201) and the geogrids used in this study were provided by NAUE GmbH & Co. KG. The authors appreciate the above supports.

References (85)

  • G. Heerten

    Reduction of climate-damaging gases in geotechnical engineering practice using geosynthetics

    Geotext. Geomembr.

    (2012)
  • B. Indraratna et al.

    The lateral displacement response of geogrid-reinforced ballast under cyclic loading

    Geotext. Geomembr.

    (2013)
  • R.M. Koerner et al.

    A data base, statistics and recommendations regarding 171 failed geosynthetic reinforced mechanically stabilized earth (MSE) walls

    Geotext. Geomembr.

    (2013)
  • H.J. Lai et al.

    DEM analysis of “soil”-arching within geogrid-reinforced and unreinforced pile-supported embankments

    Comput. Geotech.

    (2014)
  • Y.L. Lin et al.

    Experimental and DEM simulation of sandy soil reinforced with H–V inclusions in plane strain tests

    Geosynth. Int.

    (2013)
  • C.-N. Liu et al.

    Behavior of geogrid–reinforced sand and effect of reinforcement anchorage in large-scale plane strain compression

    Geotext. Geomembr.

    (2014)
  • M.L. Lopes et al.

    Influence of the confinement, soil density and displacement rate on soil–geogrid interaction

    Geotext. Geomembr.

    (1996)
  • Y. Miyata et al.

    Reliability analysis of soil–geogrid pullout models in Japan

    Soils Found.

    (2012)
  • N. Moraci et al.

    Factors affecting the pullout behaviour of extruded geogrids embedded in a compacted granular soil

    Geotext. Geomembr.

    (2006)
  • N. Moraci et al.

    Influence of cyclic tensile loading on pullout resistance of geogrids embedded in a compacted granular soil

    Geotext. Geomembr.

    (2009)
  • N. Moraci et al.

    Deformative behaviour of different geogrids embedded in a granular soil under monotonic and cyclic pullout loads

    Geotext. Geomembr.

    (2012)
  • M. Mosallanezhad et al.

    Experimental and numerical studies of the performance of the new reinforcement system under pull-out conditions

    Geotext. Geomembr.

    (2016)
  • N.T. Ngo et al.

    DEM simulation of the behaviour of geogrid stabilised ballast fouled with coal

    Comput. Geotech.

    (2014)
  • E.M. Palmeira

    Bearing force mobilisation in pull-out tests on geogrids

    Geotext. Geomembr.

    (2004)
  • E.M. Palmeira

    Soil–geosynthetic interaction: modelling and analysis

    Geotext. Geomembr.

    (2009)
  • Y. Qian et al.

    Characterization of geogrid reinforced ballast behavior at different levels of degradation through triaxial shear strength test and discrete element modeling

    Geotext. Geomembr.

    (2015)
  • E.C.G. Santos et al.

    Behaviour of a geogrid reinforced wall built with recycled construction and demolition waste backfill on a collapsible foundation

    Geotext. Geomembr.

    (2013)
  • M. Shinoda et al.

    Lateral and axial deformation of PP, HDPE and PET geogrids under tensile load

    Geotext. Geomembr.

    (2004)
  • A.C.C.F. Sieira et al.

    Displacement and load transfer mechanisms of geogrids under pullout condition

    Geotext. Geomembr.

    (2009)
  • V.D.H. Tran et al.

    A finite-discrete element framework for the 3D modeling of geogrid–soil interaction under pullout loading conditions

    Geotext. Geomembr.

    (2013)
  • Z. Wang et al.

    Visualization of load transfer behaviour between geogrid and sand using PFC2D

    Geotext. Geomembr.

    (2014)
  • R.F. Wilson-Fahmy et al.

    Finite element modelling of soil–geogrid interaction with application to the behavior of geogrids in a pullout loading condition

    Geotext. Geomembr.

    (1993)
  • G. Yang et al.

    Geogrid-reinforced lime-treated cohesive soil retaining wall: case study and implications

    Geotext. Geomembr.

    (2012)
  • I. Yogarajah et al.

    Finite element modelling of pull-out tests with load and strain measurements

    Geotext. Geomembr.

    (1994)
  • C. Yoo et al.

    Performance of a two-tier geosynthetic reinforced segmental retaining wall under a surcharge load: full-scale load test and 3D finite element analysis

    Geotext. Geomembr.

    (2008)
  • T.M. Allen et al.

    Design and performance of a 6.3 m high block-faced geogrid wall designed using the K-stiffness method

    J. Geotech. Geoenviron. Eng.

    (2014)
  • I.L. Al-Qadi et al.

    Geogrid mechanism in low-volume flexible pavements: accelerated testing of full-scale heavily instrumented pavement sections

    Int. J. Pavement Eng.

    (2011)
  • I.L. Al-Qadi et al.

    Geogrid-reinforced low-volume flexible pavements: pavement response and geogrid optimal location

    J. Transp. Eng.

    (2012)
  • A. Arulrajah et al.

    Evaluation of interface shear strength properties of geogrid-reinforced construction and demolition materials using a modified large-scale direct shear testing apparatus

    J. Mater. Civ. Eng.

    (2014)
  • ASTM D6706-01

    Standard test method for measuring geosynthetic pullout resistance in soil

    Annual Book of ASTM Standards

    (2001)
  • R.J. Bathurst et al.

    Investigation of micromechanical features of idealized granular assemblies using DEM

    Eng. Comput.

    (1992)
  • R.J. Bathurst et al.

    Geogrid and soil displacement observations during pullout using a transparent granular soil

    Geotech. Test. J.

    (2015)
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