International Geosynthetics Society

Geosynthetics International: Vol. 9, No. 4, 2002

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Foreword

Most of the contents of the technical paper by J.G. Zornberg published in this issue (Zornberg, J.G., 2002, “Peak Versus Residual Shear Strength in Geosynthetic-Reinforced Soil Design”, Geosynthetics International, Vol. 9, No. 4, pp. 301-318.) were presented at the 15th GRI Conference, in December 2001. Prof. Robert M. Koerner, the organizer of the Conference, has kindly allowed publication of that material in Geosynthetics International.

Following the session in which the contents of the paper were presented (Session I: Peak versus Residual Shear Strength, 13 December 13 2001), the session panelists were involved in a heated exchange of electronic mail communications. Geosynthetics International is pleased to provide these communications as discussions and responses to the technical paper. It should be noted, though, that the e-mail communications were not originally intended for publication. Accordingly, the style of the text is more informal than in typical discussions.

T.S. Ingold R.J. Bathurst J.P. Giroud

Peak Versus Residual Shear Strength In Geosynthetic-Reinforced Soil Design

Technical Paper by J.G. Zornberg

ABSTRACT: Current design guidelines for geosynthetic-reinforced soil structures disagree over the shear strength parameters that should be selected to characterize the backfill material. Most geosynthetic reinforcing materials are classified as extensible inclusions for almost all practical applications. The extensible nature of geosynthetic reinforcements has led to the recommendation by several agencies and reinforced soil designers toward the use of the residual shear strength instead of the peak shear strength for design. However, common practice in the US has been the use of the peak shear strength. The main purpose of this paper is to provide experimental evidence regarding selection of either peak or residual shear strength to characterize the backfill material for the design of geosynthetic-reinforced soil structures. Specifically, experimental results from reduced-scale models tested in a geotechnical centrifuge indicate that the stability of geosynthetic-reinforced slopes is governed by the peak soil shear strength.

KEYWORDS: Soil reinforcement, Shear strength, Centrifuge, Design.

AUTHOR: J.G. Zornberg, Assistant Professor, Department of Civil, Environmental and Architectural Engineering, University of Colorado at Boulder, Campus Box 428, Boulder, Colorado 80309-0428, USA, Telephone: 1/303-492-4699, Telefax:1/303-492-7317, E-mail: zornberg@colorado.edu.

DATE: Original manuscript submitted 2 June 2002, revised version received 10 December 2002, and accepted 11 December 2002. Discussion open until 1 September 2003.

REFERENCE: Zornberg, J.G., 2002, “Peak Versus Residual Shear Strength in Geosynthetic-Reinforced Soil Design”, Geosynthetics International, Vol. 9, No. 4, pp. 301-318.

Development Of A General Time-Dependent Model For Geogrids

Technical Paper by V.N. Kaliakin and M. Dechasakulsom

ABSTRACT: A simple yet general time-dependent mathematical model for geogrid reinforcement is presented. The model is based on the assumption that the time-dependent behavior of the reinforcement can be represented by creep isochrones. The model is capable of simulating the general time-dependent response of geogrids subjected to monotonic loading, which includes creep and relaxation as special cases. The model is formulated, calibrated, implemented, and its predictive capabilities verified. The range of applicability and limitations of the model are noted.

KEYWORDS: Geogrid, Relaxation, Creep, Polyethylene, Polypropylene, Isochronous curve, Constitutive model.

AUTHORS: V.N. Kaliakin, Associate Professor, Department of Civil and Environmental Engineering, University of Delaware, Newark, Delaware 19716, USA, Telephone: 1/302-831-2409, Telefax: 1/302-831-3640, E-mail: kaliakin@ce.udel.edu; and M. Dechasakulsom, Road Research and Development Center, Department of Highways, Sriayuthaya Road, Rachathevee, Bangkok, Thailand 10400, Telephone: 246-1122-30 Ext. 4417, Telefax: 246-1122-30 Ext. 4423, E-mail: montri@ce.udel.edu.

DATE: Original manuscript submitted 30 May 2002, revised version received and accepted 17 January 2003. Discussion open until 1 September 2003.

REFERENCE: Kaliakin, V.N. and Dechasakulsom, M., 2002, “Development of General Time-Dependent Model for Geogrids”, Geosynthetics International, Vol. 9, No. 4, pp. 319-344.

A "Pouch Test" For Characterizing Gas Permeability Of Geomembranes

Technical Paper by P. Pierson and M. Barroso

ABSTRACT: To characterize the gas permeability of seamed or non-seamed geomembranes, laboratory tests were carried out using a new permeability test: the gas permeability pouch test. Circular and rectangular “pouches” made of two pieces of high density polyethylene (HDPE) geomembrane were tested. To study the permeability of the geomembrane itself, the pouch was made of two circular geomembrane sheets welded together (the percentage of the seamed area is negligible compared to the non-seamed area). To study the permeability of the HDPE seams, two rectangular pieces of geomembrane were welded together using the thermal-hot dual wedge method (where the percentage of the seamed area is predominant). For this test, specimens are pressurized with a gas (e.g., nitrogen, in this case), and immersed either in air or in water. The flow of gas is indicated by a decrease in the pressure inside the pouch. The test results obtained are in agreement with results reported in the literature and show that the gas permeability pouch test can be used to characterize geomembrane permeability, with the advantages of being easy to carry out and allowing the assessment of the seam quality by quantitative measurement of their permeance.

KEYWORDS: HDPE geomembrane, Seam, Gas Permeability, Pouch test, Gas flow and permeance.

AUTHORS: P. Pierson, Professor, LIRIGM, University Joseph Fourier, BP 53 - 38041 Grenoble Cedex 9, France, Telephone: 33/476825330 Telefax: 33/476824476, E-mail: patrick.pierson@ujf-grenoble.fr; and M. Barroso, Ph.D. Student and Research Assistant, Laboratório Nacional de Engenharia Civil, Avenida do Brasil, 101, 1700-066 Lisboa, Portugal, Telephone: 351/218443327, Telefax: 351/218443021, E-mail: Mbarroso@lnec.pt.

DATE: Original manuscript submitted 30 July 2002, revised version received 21 February 2003, and accepted 11 March 2003. Discussion open until 1 September 2003.

REFERENCE: Pierson, P. and Barroso, M., 2002, “A ‘Pouch Test’ For Characterizing Gas Permeability of Geomembranes”, Geosynthetics International, Vol. 9, No. 4, pp. 345-372.

Shear Strength Parameters Of Soil-Geosynthetic Interfaces Under Low Confining Pressure Using A Tilting Table

Technical Note by H.I. Ling, C. Burke, Y. Mohri, and K. Matsushima

ABSTRACT: Tilting table tests are typically used to determine the friction angle between soils and structures. A procedure is presented to determine both the adhesion and frictional properties of soil-geosynthetic interfaces under very low confining pressures using a tilting table test. A simple tilting table device was developed and a series of tests were conducted on three different types of sand in contact with smooth and textured geomembranes under dry and moist conditions. The study showed the relevance of the proposed procedure and device especially when residual state is concerned.

KEYWORDS: Tilting table test, Geosynthetic, Sand, Interface, Shear strength.

AUTHORS: H.I. Ling, Associate Professor, Department of Civil Engineering and Engineering Mechanics, Columbia University,500 West 120th Street, New York, New York 10027, Telephone: 1/212-854-1203, Telefax: 1/212-854-6267, E-mail: Ling@civil.columbia.edu; C. Burke, Graduate Research Assistant, Department of Civil Engineering and Engineering Mechanics, Columbia University, 500 West 120th Street, New York, NY 10027, Telephone: 1/212-854-4153, Telefax: 1/212-854-6267, E-mail: cburke@civil.columbia.edu; Y. Mohri, Research Manager, Soil Laboratory, National Research Institute of Agricultural Engineering, Tsukuba, Japan, Telephone: 81/298-38-7575, Telefax: 81/298-38-7609, E-mail: accord1@ss.nkk.affrc.go.jp; and K. Matsushima, Soil Laboratory, National Research Institute of Agricultural Engineering, Tsukuba, Japan, Telephone: 81/298-38-7575, Telefax: 81/298-38-7609, E-mail: kenichi@ss.nkk.affrc.go.jp.

DATE: Original manuscript submitted 23 January 2002, revised version received 28 October 2002, and accepted 12 December 2002. Discussion open until 1 September 2003.

REFERENCE: Ling, H.I., Burke, C., Mohri, Y., and Matsushima, K. “Shear Strength Parameters of Soil-Geosynthetic Interfaces Under Low Confining Pressure Using a Tilting Table”, Geosynthetics International, Vol. 9, No. 4, pp. 373-380.

Discussion and Response

Peak Versus Residual Shear Strength In Geosynthetic-Reinforced Soil Design

TECHNICAL PAPER UNDER DISCUSSION: Zornberg, J.G., 2002, “Peak Versus Residual Shear Strength in Geosynthetic-Reinforced Soil Design”, Geosynthetics International, Vol. 9, No. 4, pp. 301-318.

DISCUSSER: J.P. Giroud, JP GIROUD, INC., 5837 North Ocean Boulevard, Ocean Ridge, Florida 33435, USA, Telephone: 1/561-737-1642, Telefax: 1/561-733-2809,E-mail: jpg@jpgiroud.com.

REFERENCES FOR DISCUSSION AND RESPONSE: Giroud, J.P., 2002, “Discussion of ‘Peak Versus Residual Shear Strength in Geosynthetic-Reinforced Soil Design’ ”, Geosynthetics International, Vol. 9, No. 4, pp. 381-382.

Zornberg, J.G., 2002, “Response to ‘Peak Versus Residual Shear Strength in Geosynthetic-Reinforced Soil Design’ ”, Geosynthetics International, Vol. 9, No. 4, pp. 382-386.

Discussion and Response

Peak Versus Residual Shear Strength In Geosynthetic-Reinforced Soil Design

TECHNICAL PAPER UNDER DISCUSSION: Zornberg, J.G., 2002, “Peak Versus Residual Shear Strength in Geosynthetic-Reinforced Soil Design”, Geosynthetics International, Vol. 9, No. 4, pp. 301-318.

DISCUSSER: J.P. Giroud, JP GIROUD, INC., 5837 North Ocean Boulevard, Ocean Ridge, Florida 33435, USA, Telephone: 1/561-737-1642, Telefax: 1/561-733-2809, E-mail: jpg@jpgiroud.com.

Zornberg, J.G., 2002, “Response to ‘Peak Versus Residual Shear Strength in Geosynthetic-Reinforced Soil Design’ ”, Geosynthetics International, Vol. 9, No. 4, pp. 387-390.

Discussion and Response

Peak Versus Residual Shear Strength In Geosynthetic-Reinforced Soil Design

TECHNICAL PAPER UNDER DISCUSSION: Zornberg, J.G., 2002, “Peak Versus Residual Shear Strength in Geosynthetic-Reinforced Soil Design”, Geosynthetics International, Vol. 9, No. 4, pp. 301-318.

DISCUSSER: R.B. Gilbert, Associate Professor, Department of Civil Engineering, University of Texas at Austin, Austin, Texas, USA, Telephone: 1/512-471-4929, Telefax: 1/512-471-6548, E-mail: bob_gilbert@mail.texas.edu.

REFERENCES FOR DISCUSSION AND RESPONSE: Gilbert, R.B., 2002, “Discussion of ‘Peak Versus Residual Shear Strength in Geosynthetic-Reinforced Soil Design’ ”, Geosynthetics International, Vol. 9, No. 4, pp. 391-392.

Zornberg, J.G., 2002, “Response to ‘Peak Versus Residual Shear Strength in Geosynthetic-Reinforced Soil Design’ ”, Geosynthetics International, Vol. 9, No. 4, pp. 392-393.