Madhav, M R

Sireesh, Saride

Umashankar, B

Research Archive of Indian Institute of Technology Hyderabad

Discussions and ClosuresClosure to “Influence of Geogrid Properties on Ruttingand Stress Distribution in Reinforced Flexible Pavementsunder Repetitive Wheel Loading” by Ramu Baadiga,Umashankar Balunaini, Sireesh Saride, andMadhira R. MadhavRamu Baadiga, S.M.ASCEDoctoral Student, Dept. of Civil Engineering, Indian Institute of Technology,Hyderabad, Kandi, Telangana 502284, India. Email: ce17resch11002@iith.ac.inUmashankar BalunainiProfessor, Dept. of Civil Engineering, Indian Institute of Technology,Hyderabad, Kandi, Telangana 502284, India (corresponding author).ORCID: https://orcid.org/0000-0003-0813-7872. Email: buma@ce.iith.ac.inSireesh Saride, M.ASCEProfessor, Dept. of Civil Engineering, Indian Institute of Technology,Hyderabad, Kandi, Telangana 502284, India. ORCID: https://orcid.org/0000-0002-7380-0880. Email: sireesh@ce.iith.ac.inMadhira R. MadhavVisiting Honorary Professor, Dept. of Civil Engineering, Indian Instituteof Technology, Hyderabad, Kandi, Telangana 502284, India. Email:madhavmr@gmail.comhttps://doi.org/10.1061/(ASCE)MT.1943-5533.0003972The writers would like to thank the discusser for sharing his viewson our technical article. The conclusions drawn from this studywere based on the subgrade and geogrid types considered in thestudy. Based on Sarsby’s (1985) study, the discusser pointed outthat the highest frictional efficiency of the geogrid occurs whenthe geogrid aperture width is 3.5 × d50 (average particle size).However, many factors influence the frictional efficiency of geo-grids used to stabilize pavements. Aperture size, nominal or aver-age aggregate size, polymer type, subgrade condition, pavementlayer thickness, and reinforcement location significantly influenceoptimal pavement performance (Berg et al. 2000; Hufenus et al.2006; Kwon et al. 2005; Al-Qadi et al. 2011; Byun and Tutumluer2017; Goud and Umashankar 2018; Baadiga et al. 2021c, b).Baadiga et al. (2021a) investigated the performance of geogridsin relation to nominal aggregate size considering three aperturesizes: polypropylene (PP) geogrids PP30S, PP30M, and PP30L(where S, M, L indicate small, medium, and large). These gridshad aperture sizes of about 40 × 40 mm, 65 × 65 mm, and 80×80 mm, respectively, and the nominal size of the aggregates was40 mm. The ratio of geogrid aperture size to nominal aggregate sizecorresponded to 1.0, 1.63, and 2.0 for PP30S, PP30M, and PP30L.The writers observed that the interlocking mechanism was signifi-cant when the normalized ratio ranged between 1 and 1.63. A 2.0ratio of aperture to aggregate size was found to cause internal slip-page of aggregates, leading to improper interlocking. The geogridwith a larger aperture gave the lowest pavement performance be-cause the ribs of the geogrid carry most of the applied loads withminimal particle strikethrough of aggregates within the geogridopenings. In the present study, the normalized ratios of GG1 (poly-propylene), GG2 (polyester), and GG3 (polyester) corresponded to1.0, 0.7, and 0.6, respectively. Interlocking is a significant contribu-tor to resistance in polypropylene geogrids, whereas polyester geo-grid performance is mainly governed by frictional interaction withthe surrounding material (Venkateswarlu et al. 2018; BIS 2020).Therefore, given the polyester geogrids were able to transfer shearstress predominantly through frictional interaction. The discusserpointed out that the aperture sizes of GG2 and GG3 with normalizedratios of 0.7 and 0.6 may not lead to the highest shear stress transferefficacy. However, a point to be noted is that, unlike geogrids, poly-ester materials are flexible, and that manufacturing biaxial geogridswith larger openings can lead to instability in pavement applica-tions. The closer spacing between the opening sizes of a polyesterbiaxial geogrid can lead to predominantly effective frictional inter-actions, followed by strikethrough of particles between the geogridopenings. Also, the aperture sizes of the polyester geogrids consid-ered in the study corresponded to geogrids commonly available inthe market. Hence, the conclusions drawn in this study based on theconsidered polypropylene and polyester geogrids are reasonable.Further, the discusser pointed out that the observed stress reduc-tion levels at the subgrade level due to geogrid reinforcement withGG1, GG2, and GG3 were the same for pavements overlying the1%- and 5%-CBR subgrades. However, maximum vertical stressesinduced at the subgrade level are a function of pavement base layerthicknesses, subgrade condition, and reinforcement type (Abu-Farsakh et al. 2015; Giroud and Han 2004; Han et al. 2011; Qianet al. 2013). The reported reductions in subgrade stresses of 21%,33%, and 42% due to GG1, GG2, and GG3 geogrids correspondedto pavements overlying the 1%-CBR subgrade, and the percentagereductions differed for pavements overlying the 5%-CBR subgrade.For example, along the axis of loading, measured contact stresses atthe subgrade level at the end of the loading cycles (N ¼ 100,000)were on the order of 149, 109, 66, and 56 kPa, respectively, for thecontrol, GG1, GG2, and GG3 reinforced pavements [Fig. 10(b) inthe original paper]. The corresponding stress reductions due tothree reinforcement types were 27%, 56%, and 62%, respectively,for the 5%-CBR subgrade. As indicated earlier, the total thicknessof the base and asphalt layers considered in the study were of 650and 490 mm for the 1%- and 5%-CBR subgrades, respectively.Relatively thin pavement sections experienced relatively highstress levels under the induced contact pressure through repetitiveload action. The writers intended to convey similar trends inthe observed behavior of reinforced pavements. As opined by thediscusser, the GG3 geogrid exhibited higher reductions in stresslevel due to the higher stiffness of the material. Between GG1and GG2, the identical ultimate tensile strength geogrids, GG2 per-formed better than GG1 due to superior resilience under repetitiveload action.© ASCE 07022017-1 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2023, 35(2): 07022017 Downloaded from ascelibrary.org by "Indian Institute of Technology, Hyderabad" on 08/20/23. Copyright ASCE. For personal use only; all rights reserved.Regarding Tables 5 and 6 in the original paper, the discusserpoints out that compared with the higher stiffness geogrid (GG3),the lower stiffness geogrid (GG2) performed better in controllingrut depth at the pavement surface but not at the subgrade for pave-ment overlying the 5%-CBR subgrade. From Table 6, it can be seenthat the differences in rut depth reduction at the subgrade level weremarginal for reinforced pavements overlying a relatively fair sub-grade. The higher rut depth reductions measured at the subgradelevel for GG2 and GG3 could be due to distribution of applied loadsover a wider area. The writers used vertically placed rutting rods tomeasure rut depth levels at the subgrade level. This procedure wasnot straightforward. Certainly, there is scope to investigate rut depthvariation at the subgrade level due to identical reinforcement andreinforcement of varied stiffness over different subgrades. The writ-ers also agree with discusser that the study findings are worthwhilein determining a suitable geogrid for pavement applications.ReferencesAbu-Farsakh, M., I. Akond, and Q. Chen. 2015. “Evaluating the perfor-mance of geosynthetic-reinforced unpaved roads using plate loadtests.” Int. J. Pavement Eng. 17 (10): 901–912. https://doi.org/10.1080/10298436.2015.1031131.Al-Qadi, I. L., S. Dessouky, E. Tutumluer, and J. Kwon. 2011. “Geogridmechanism in low-volume flexible pavements: Accelerated testing offull-scale heavily instrumented pavement sections.” Int. J. PavementEng. 12 (2): 121–135. https://doi.org/10.1080/10298436.2010.535534.Baadiga, R., U. Balunaini, and S. Saride. 2021a. “Influence of geogridaperture size on the behavior of mechanically stabilized pavements.” InProc., Int. Airfield and Highway Pavements Conf., 271–282. Reston,VA: ASCE. https://doi.org/10.1061/9780784483510.025.Baadiga, R., U. Balunaini, S. Saride, and R. M. Madhira. 2021b. “Influenceof geogrid properties on rutting and stress distribution in reinforcedflexible pavements under repetitive wheel loading.” J. Mater. Civ.Eng. 33 (12): 04021338. https://doi.org/10.1061/(ASCE)MT.1943-5533.0003972.Baadiga, R., S. Saride, U. Balunaini, and R. M. Madhira. 2021c. “Influenceof tensile strength of geogrid and subgrade modulus on layer coeffi-cients of granular bases.” Transp. Geotech. 29 (Jul): 100557. https://doi.org/10.1016/j.trgeo.2021.100557.Berg, R. R., B. R. Christopher, and S. W. Perkins. 2000. Geosyntheticreinforcement of the aggregate base/subbase courses of pavementstructures. Roseville, MN: Geosynthetic Material Association.BIS (Bureau of Indian Standards). 2020. Geosynthetics: Geogrids forflexible pavements: Specifications. IS 17371. New Delhi: BIS.Byun, Y.-H., and E. Tutumluer. 2017. “Bender elements successfully quan-tified stiffness enhancement provided by geogrid–aggregate interlock.”Transp. Res. Rec. 2656 (1): 31–39. https://doi.org/10.3141/2656-04.Giroud, J. P., and J. Han. 2004. “Design method for geogrid-reinforcedunpaved roads. I. Development of design method.” J. Geotech. Geoen-viron. Eng. 130 (8): 775–786. https://doi.org/10.1061/(ASCE)1090-0241(2004)130:8(775).Goud, G. N., and B. Umashankar. 2018. “Interface shear strength propertiesof gravel bases and subgrades with various reinforcements.” Int. J. Geo-synth. Ground Eng. 4 (7): 1–14. https://doi.org/10.1007/s40891-017-0124-4.Han, J., S. K. Pokharel, X. Yang, C. Manandhar, D. Leshchinsky,I. Halahmi, and R. L. Parsons. 2011. “Performance of geocell-reinforced rap bases over weak subgrade under full-scale moving wheelloads.” J. Mater. Civ. Eng. 23 (11): 1525–1534. https://doi.org/10.1061/(ASCE)MT.1943-5533.0000286.Hufenus, R., R. Rueegger, R. Banjac, P. Mayor, S. M. Springman, andR. Brönnimann. 2006. “Full-scale field tests on geosynthetic reinforcedunpaved roads on soft subgrade.” Geotext. Geomembr. 24 (1): 21–37.https://doi.org/10.1016/j.geotexmem.2005.06.002.Kwon, J., E. Tutumluer, and M. Kim. 2005. “Development of a mechanisticmodel for geosynthetic-reinforced flexible pavements.” Geosynth. Int.12 (6): 310–320. https://doi.org/10.1680/gein.2005.12.6.310.Qian, Y., J. Han, S. K. Pokharel, and R. L. Parsons. 2013. “Performance oftriangular aperture geogrid-reinforced base courses over weak subgradeunder cyclic loading.” J. Mater. Civ. Eng. 25 (8): 1013–1021. https://doi.org/10.1061/(ASCE)MT.1943-5533.0000577.Sarsby, R. W. 1985. “The influence of aperture size/particle size onthe efficiency of grid reinforcement.” In Proc., 2nd Canadian Symp.Geotextiles and Geomembranes, 7–12. Edmonton, AB, Canada: TheGeotechnical Society of Edmonton.Venkateswarlu, H., K. N. Ujjawal, and A. Hegde. 2018. “Laboratory andnumerical investigation of machine foundations reinforced with geo-grids and geocells.” Geotext. Geomembr. 46 (6): 882–896. https://doi.org/10.1016/j.geotexmem.2018.08.006.© ASCE 07022017-2 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2023, 35(2): 07022017 Downloaded from ascelibrary.org by "Indian Institute of Technology, Hyderabad" on 08/20/23. Copyright ASCE. For personal use only; all rights reserved.

Closure to "influence of Geogrid Properties on Rutting and Stress Distribution in Reinforced Flexible Pavements under Repetitive Wheel Loading"

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Closure to "influence of Geogrid Properties on Rutting and Stress Distribution in Reinforced Flexible Pavements under Repetitive Wheel Loading"

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