Available online at ScienceDirect. Procedia Engineering 189 (2017 )

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1 Aville online t ScienceDirect Procedi Engineering 189 (2017 ) Trnsporttion Geotechnics nd Geoecology, TGG 2017, My 2017, Sint Petersurg, Russi Evlution of lod trnsfer in geogrids for se stiliztion using trnsprent soil Xin Peng, Jorge G. Zornerg * Deprtment of Civil, Architecturl nd Environmentl Engineering, the University of Texs t Austin, 301 E. Den Keeton St. Stop C1700, Austin, Texs, , USA Astrct The design of rodwys with geosynthetic-stilized se lyers requires proper evlution of the lod-trnsfer mechnisms etween soil prticles nd geosynthetics. In the cse of geogrid reinforcements, the resistnces moilized on ri elements re key fctors tht determine the mechnicl responses for oth: (1) the ultimte pullout strength; nd (2) the in-plne stiffness. Geogrids with different perture shpes hve ri elements long different orienttions, nd different ri orienttions could generte different lod trnsfer mechnisms. In this study, new experimentl testing progrm using trnsprent soil ws conducted to visulize the lod trnsfer of geogrids with different perture shpes (e.g. rectngulr, tringulr). Specificlly, smll-scle soilgeosynthetic interction tests were conducted using high-definition cmers. Consequently, imge-processing techniques were used to otin the displcements nd deformtions of geogrid specimens from digitl imges. The soil-geogrid interction ehviors for geogrid specimens with different perture shpes were evluted nd compred. Overll, multiple mechnisms for lod trnsfer etween soil nd geogrids with different geometric chrcteristics could e chrcterized nd quntified using new techniques involving trnsprent soil nd digitl imge nlysis The The Authors. Pulished y Elsevier y Elsevier Ltd. This Ltd. is n open ccess rticle under the CC BY-NC-ND license ( Peer-review under responsiility of the scientific committee of the Interntionl conference on Trnsporttion Geotechnics nd Peer-review Geoecology. under responsiility of the scientific committee of the Interntionl conference on Trnsporttion Geotechnics nd Geoecology Keywords: geosynthetics; geogrid; trnsprent soil; stiliztion; lod trnsfer; imge nlysis * Corresponding uthor. Tel.: ; fx: E-mil ddress: zornerg@mil.utexs.edu The Authors. Pulished y Elsevier Ltd. This is n open ccess rticle under the CC BY-NC-ND license ( Peer-review under responsiility of the scientific committee of the Interntionl conference on Trnsporttion Geotechnics nd Geoecology doi: /j.proeng

2 308 Xin Peng nd Jorge G. Zornerg / Procedi Engineering 189 ( 2017 ) Introduction The use of different types of geogrids in the design of reinforced soil retining structures nd stilized rodwys requires proper evlution of the lod trnsfer mechnisms etween soil nd reinforcement. A numer of experimentl [1,2,3,4,5] nd numericl [5,6,7] studies investigting these mechnisms were conducted over the pst decdes. Bsed on these studies, the resistnce moilized on the geogrid specimen is typiclly considered to result from two contriutions: (1) resistnce generted from longitudinl ris; nd (2) pssive resistnce developed t the frontl surfce of the trnsverse ris. In the ppliction of pvement stiliztion, the improved stiffness ehviors of geogrid-stilized se lyers were evluted vi lortory nd field tests [8,9,10]. However, the lod trnsfer mechnisms etween soil prticles nd geogrid elements is still not fully understood to explin the incresed stiffness performnce of the soil-geogrid composite lyer. Trnsprent soils, such s those contining morphous silic mterils, nd pore fluids with mtching refrctive index hve recently een utilized in typicl geotechnicl studies to mesure continuous sptil deformtions in soils. Isknder [11], Ezzein nd Bthurst [12] introduced severl types of trnsprent soils, nd documented their geotechnicl properties nd opticl mesurement methods. Ezzein nd Bthurst [13] used lrge-scle pullout test pprtus with trnsprent grnulr soil to evlute the moiliztion of the geogrid joints displcement t different pullout lod levels. Ferreir nd Zornerg [14] conducted smll-scle pullout tests with trnsprent grnulr soil nd geogrids with mrkers to trck geogrid displcements s well s the movement of soil prticles during pullout loding. Unixil nd ixil geogrids hve een widely utilized to stilize rodwys. In recent yers, geogrids with tringulr pertures hve een introduced into the mrket for their potentil geometric dvntges, s compred to trditionl unixil nd ixil geogrids. These include: (1) offering three principl directions of stiffness insted of one or two; (2) comprtively lrger ri depth to fcilitte confinement of soil prticles; nd (3) hexgonl junction shpe with comprtively high junction strength nd stiffness. Dong et l. [15] conducted numericl evlutions to compre the tensile ehvior of geogrids with rectngulr pertures ginst tht of geogrids with tringulr pertures. They concluded tht under tensile loding trixil geogrids hve fr more uniform stress nd strin distriutions thn geogrids with rectngulr pertures. Sun et l. [16] indicted tht in comprison to unstilized sections, trixil geogrid-stilized pvement sections exhiited reductions in surfce nd sugrde permnent deformtions, s well s reduction in the horizontl pressures within the sugrde. 2. Mterils nd methods 2.1. Trnsprent grnulr soil The solid mteril used in this study ws crushed fused qurtz. According to the Unified Soil Clssifiction System (USCS) the prticle size rnge of this mteril is poorly grded snd (SP). Some sic geotechnicl properties mesured ccording to ASTM stndrds re summrized in Ошибка! Источник ссылки не найден. Tle 1. Geotechnicl properties of crushed fused qurtz. Property Test method Vlue Specific grvity (20 C) Wter Pycnometer Test (ASTM D854) Mximum index dry density (g/cm3) Virtory Tle Test (ASTM D4253) Minimum index dry density (g/cm3) Virtory Tle Test (ASTM D4254) Friction ngle, dry (o) Direct Sher Test (ASTM D3080) 45 Friction ngle, oil sturted, drined (o) Direct Sher Test (ASTM D3080) 44 The pore fluid used with the trnsprent soil contined mixture of two cler minerl oils: Puretol 7 nd Prflex HT4. Puretol 7 hs higher refrctive index (RI) thn the solid fused qurtz (RI: ), while Prflex HT4 hs lower refrctive index. Therefore, for the given volume rtio of these two liquids, the finl comintion imed t

3 Xin Peng nd Jorge G. Zornerg / Procedi Engineering 189 ( 2017 ) hving the sme refrctive index s tht of fused qurtz. Bsed on the direct sher tests shown in Ошибка! Источник ссылки не найден., due to the potentil luriction of the pore fluid, the friction ngle of the oilsturted soil is one degree less thn tht of the dry prticles. A trnsprent soil smple (pproximtely 2/3 of the fused qurtz from the ottom ws fully sturted with the oil mixture nd the top 1/3 of the fused qurtz ws in dry condition) with n inserted ixil geogrid is displyed in Fig. 1. Fig. 1. () Frontl view nd () side view of trnsprent soil smple nd inserted ixil geogrid Geogrid type The geogrids used in this study were mnufctured y punching out holes in polypropylene sheets, nd then heting nd stretching them long different directions. To evlute nd compre lod trnsfer mechnisms etween soil prticles nd different geogrids, two geogrid types one with rectngulr nd one with tringulr perture shpes were used in experimentl tests. The nominl geometric chrcteristics of oth geogrids re presented in Tle 2. For G2 (with tringulr pertures), ll ris re oriented in three sustntilly equilterl directions. Tle 2. Geometric properties of the geogrids used in this study (from mnufcturer s specifiction sheet). Geogrid Aperture shpe Ri Ri pitch (mm) Mid-ri depth (mm) Mid-ri width (mm) G1 G2 Rectngulr Tringulr Longitudinl Trnsverse Longitudinl Digonl Smll-scle soil-geosynthetic interction test setup Fig. 2 illustrtes the test pprtus used in this study. The loding system nd dt cquisition system were the sme s those reported y Ferreir [17]. A high-definition cmer ws used to cpture deformtions of the entire geogrid in the confined portion of the smple. The smpling rte ws 5 seconds, nd loding displcement rte of 1 mm/min ws pplied during testing. Frontl unit tension nd cptured imges were synchronized y the dt cquisition system. A light system, composed of two 160 W photo studio soft oxes, ws used to provide uniform light on the trnsprent pullout ox. The internl dimensions of the trnsprent ox were 300 mm 250 mm 150 mm (width length height), nd the dimensions of the confined portion of the trixil geogrid were out 210 mm 230 mm (width length).

4 310 Xin Peng nd Jorge G. Zornerg / Procedi Engineering 189 ( 2017 ) Moving hed of lod frme Geogrid Dt cquisition system Trnsprent pullout ox Trnsprent soil Light system I Bse of lod frme Light system II Digitl cmer 2.4. Imge processing techniques Fig. 2. Soil-geosynthetic interction test setup with trnsprent soil. Greyscle imges cptured during testing were used to trck deformtions of the geogrid. An open source imge processing tool pckge ImgeJ ws utilized for some sic imge processing, nd further deformtion cpturing nd dt nlysis were conducted using Mtl progrming codes. Oil- nd friction-resistnt white mrkers were used to trck displcements nd deformtions of G1(). The Digitl Imge Correltion (DIC) technique ws used to oserve the displcements of the ri junctions nd deformtions of ris (Fig. 3). Fig. 3. () Frontl view of the center section of undeformed G1 in the trnsprent pullout ox with trnsprent soil nd () displcement field of this section of deformed G1 long pullout direction from DIC nlysis.

5 Xin Peng nd Jorge G. Zornerg / Procedi Engineering 189 ( 2017 ) Test Results nd Discussion Results from tests using trnsprent soil with geogrids G1 nd G2 re presented in this section. Tests were conducted using n pplied norml pressure of 27.6 kn/m 2 t constnt displcement rte of 1 mm/min. DIC codes were used to trck the junction displcement for G1 nd G2. Junction displcement profiles long the pullout direction for G1 nd G2 t different frontl unit tensions re shown in Fig. 4. Fig. 4. Junction displcement profiles long the pullout direction for () G1 nd () G2 t different levels of frontl unit tension. Junction displcement profiles for G1 nd G2 t similr frontl unit tensions long the pullout direction re compred in Fig. 5. Two min oservtions cn e mde sed on Fig. 5: (1) for ech of the four plots, even though the frontl unit tension of G2 ws slightly higher thn G1, ll G2 junctions still hd fewer displcements long the pullout direction thn G1; (2) for the given frontl unit tensions, G1 generlly hd steeper nd more curved junction displcement profiles thn G2. The tngent slopes of the displcement profiles re strins t corresponding loctions. Fig. 5 lso illustrtes tht G2 typiclly hd fewer strins (slopes) in t lest the first hlf of the specimen length from the frontl confined oundry s compred to G1, nd hd significntly fewer chnges in strins (chnges in slopes) long the specimen s entire emedment length. More uniform strins long G2 could e explined s more uniform lod distriution generted on the specimen.

6 312 Xin Peng nd Jorge G. Zornerg / Procedi Engineering 189 ( 2017 ) c d Fig. 5. Comprisons of junction displcement profiles etween G1 nd G2 t different levels of frontl unit tension. For comprison of the confined stiffness performnce etween G1 nd G2, junctions t the front, middle nd end loctions of the geogrid specimens were selected. The distnces from the frontl confined oundry to these three junction loctions re tulted in Tle 3. Comprisons of the reltionships etween frontl unit tension nd junction displcement t these three loctions re plotted in Fig. 6. Tle 3. Junction loctions of G1 nd G2 for the comprison of confined stiffness performnce. Geogrid Distnce from the frontl confined oundry to junction t Loction A (mm) Distnce from the frontl confined oundry to junction t Loction B (mm) G G Distnce from the frontl confined oundry to junction t Loction C (mm) Fig. 6 shows tht G2 consistently hd fewer junction displcements for the given frontl unit tensions t ll selected loctions thn G1, which indictes etter confined stiffness performnce for G2. When exmined together, results from Fig. 5 nd Fig. 6 indicte more uniform lod trnsfer long the entire soil-geogrid interfce for G2 thn for G1, nd reltively stiffer confined ehviors for G2 thn for G1.

7 Xin Peng nd Jorge G. Zornerg / Procedi Engineering 189 ( 2017 ) Fig. 6. Comprisons of confined stiffness performnces etween G1 nd G2 t () Loction A, () Loction B nd (c) Loction C. 4. Conclusions Lod trnsfer mechnisms of geogrids with different perture shpes nd ri dimensions were evluted using trnsprent soil nd integrted imge processing techniques. Bsed on results from smll-scle soil-geosynthetic interction tests, the following conclusions were drwn: 1) The use of trnsprent soil nd imge processing techniques dopted in this study were found to e dequte to cpture displcements nd deformtions without creting physicl disturnces t the soilgeosynthetic interfce (s trditionl sensor mesurements typiclly hve). 2) Junction displcement profiles long the pullout direction for G1 nd G2 were compred t selected frontl unit tensions, nd ll G2 junctions exhiited fewer displcements thn those for G1. 3) For the given frontl unit tensions, G1 generlly hd steeper nd more curved junction displcement profiles thn G2, which indictes tht G1 generted lrger strins nd lrger strin chnges long the pullout direction thn G2. 4) The confined stiffness performnce etween G1 nd G2 t three different junction loctions long the specimens were compred throughout testing. G2 consistently showed fewer displcements thn G1 t those loctions, regrdless of frontl unit tension levels, which demonstrtes tht the confined stiffness ehvior ws generlly etter for G2 thn G1. Acknowledgements The uthors gretly pprecite Tensr Interntionl Corportion who provided the geogrids used in this study. The uthors lso grtefully cknowledge Dr. Julio Ferreir who finished the initil design of the soil-geosynthetic interction test setup. References [1] H. Ochii, J. Otni, S. Hyshic, T. Hiri, The pull-out resistnce of geogrids in reinforced soil. Geotext Geomemr. 1996;14(1): [2] A.M.N. Algiywnn, M. Sugimoto, S. Sto, H. Toyot, Influence of longitudinl nd trnsverse memers on geogrid pullout ehvior during deformtion. Geotext Geomemr. 2001;19(8): [3] S.H. Teixeir, B.S. Bueno, J.G. Zornerg, Pullout resistnce of individul longitudinl nd trnsverse geogrid ris. J Geotech Geoenvironmentl Eng. 2007;133(1):37 50.

8 314 Xin Peng nd Jorge G. Zornerg / Procedi Engineering 189 ( 2017 ) [4] A.C.C. Sieir, D.M. Gerscovich, A.S. Syo, Displcement nd lod trnsfer mechnisms of geogrids under pullout condition. Geotext Geomemr. 2009;27(4): [5] Z. Wng, F. Jcos, M. Ziegler, Experimentl nd DEM investigtion of geogrid soil interction under pullout lods. Geotext Geomemr Jun;44(3): [6] R.F. Wilson-Fhmy, R.M. Koerner, Finite element modelling of soil-geogrid interction with ppliction to the ehvior of geogrids in pullout loding condition. Geotext Geomemr. 1993;12(5): [7] V.D.H. Trn, M.A. Meguid, L.E. Chouinrd, A finite discrete element frmework for the 3D modeling of geogrid soil interction under pullout loding conditions. Geotext Geomemr. 2013;37:1 9. [8] J.G. Collin, T.C. Kinney, X. Fu, Full scle highwy lod test of flexile pvement systems with geogrid reinforced se courses. Geosynth Int. 1996;3(4): [9] Q. Chen, M. Au-Frskh, M. To, Lortory evlution of geogrid se reinforcement nd corresponding instrumenttion progrm. ASTM Geotech Test J. 2009;32(6): [10] M.Y. Au-Frskh, Q. Chen, Evlution of geogrid se reinforcement in flexile pvement using cyclic plte lod testing. Int J Pvement Eng. 2011;12(3): [11] M. Isknder, Modelling with trnsprent soils: Visulizing soil structure interction nd multi phse flow, non-intrusively. Springer Science & Business Medi; [12] F.M. Ezzein, R.J. Bthurst, A Trnsprent Snd for Geotechnicl Lortory Modeling. ASTM Geotech Test J. 2011;34(6): [13] F.M. Ezzein, R.J. Bthurst, A new pproch to evlute soil-geosynthetic interction using novel pullout test pprtus nd trnsprent grnulr soil. Geotext Geomemr. 2014;42(3): [14] J.A. Ferreir, J.G. Zornerg, A Trnsprent Pullout Testing Device for 3D Evlution of Soil Geogrid Interction. Geotech Test J. 2015;38(5): [15] Y-L Dong, J. Hn, X-H Bi, Numericl nlysis of tensile ehvior of geogrids with rectngulr nd tringulr pertures. Geotext Geomemr. 2011;29(2): [16] X. Sun, J. Hn, M.H. Wyne, R.L. Prsons, J. Kwon, Experimentl Study on Resilient Behvior of Trixil Geogrid-Stilized Unpved Rods. In: Ground Improvement nd Geosynthetics. ASCE; p [17] J.A.Z. Ferreir, Evlution of soil-geogrid interction t different lod levels using pullout tests nd trnsprent soil (Doctorl disserttion) Aville from: