Geosynthetics International: Vol. 8, No. 2, 2000

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Technical Paper by C.A. Finley and R.D. Holtz

INVESTIGATION AND MODELING OF TWO COMPOSITE LANDFILL COVERS

ABSTRACT: The performance of two municipal solid waste landfill final covers was
investigated. A field investigation of each landfill was performed, with test pits excavated
and soil and geotextile samples collected. The investigation and analysis showed
that the cover components were generally in good condition and performing their
intended function in the field. Differential settlements that had occurred at both landfills
were modeled with a finite difference code. The model results were used to calculate
geomembrane strains and relate them to surface settlement characteristics. Using
this method, two areas of differential settlement at one of the landfills were evaluated,
and the geomembrane strains were found to be well below yield strains. In addition, a
general design method for composite landfill covers spanning voids was developed
with the finite difference model.

KEYWORDS: Landfill cover, Geomembrane, Geotextile, Differential settlement.

AUTHORS: C.A. Finley, Ph.D. Candidate, Department of Civil Engineering, The
University of Texas at Austin, ECJ 9.227, Austin, Texas 77812, USA, Telephone: 1/
512-471-4929, Telefax: 1/512-471-6548, E-mail: finleyca@alpha62.ce.utexas.edu;
and R.D. Holtz, Professor, Department of Civil and Environmental Engineering, University
of Washington, Box 352700, Seattle, Washington 98195-2700, USA, Telephone:
1/206-543-7614, Telefax: 1/206-685-3836, E-mail: holtz@u.washington.edu.

DATE: Original manuscript submitted 26 July 2000, revised version received and
accepted 3 December 2000. Discussion open until 1 October 2001.

REFERENCE: Finley, C.A. and Holtz, R.D., 2001, “Investigation and Modeling of
Two Composite Landfill Covers”, Geosynthetics International, Vol. 8, No. 2, pp. 97-112 .

Technical Paper by G.P. Karunaratne, S.H. Chew, S.L. Lee, and A.N. Sinha

BENTONITE:KAOLINITE CLAY LINER

ABSTRACT: Conventional geosynthetic clay liners (GCLs) contain bentonite. Since
high-quality bentonite is not easily available in Southeast Asia in comparison to kaolinite,
an alternative cost-effective method is necessary. The concept of creating a GCL
with a bentonite and kaolinite mixture on a biodegradable jute base is discussed in the
present paper. The hydraulic conductivity and consolidation behaviour of bentonite:
kaolinite mixtures was investigated. It was revealed that at least 30% bentonite was
required in the mixture to result in the same decreasing coefficient of consolidation trend
with pressure as shown using pure bentonite. The 50:50 bentonite:kaolinite (50:50 B:K)
ratio yielded approximately the same hydraulic conductivity, k, as pure bentonite;
hence, the remainder of the study focused on the 50:50 B:K mixture. For the 50:50 B:K
mixture hydraulic conductivity measurements, the following permeants were used: (i)
distilled water, (ii) 0.25M calcium chloride, (iii) 0.1M hydrochloric acid, and (iv) 0.1M
sodium hydroxide. With the calcium chloride permeant, the hydraulic conductivity of
the mixture was found to be in the range of 10-10 m/s, whereas the hydrochloric acid
and sodium hydroxide permeants yielded values near 10-11 m/s. It was also found that
the liquid limit and swell index tests carried out on bentonite and the B:K mixture were
significantly affected by the presence of a large amount of calcium chloride. A jutebased
clay liner was then created with the 50:50 B:K mixture. Its effectiveness in the
landfill liner system was investigated for equivalency and was found to be satisfactory
when using distilled water as the permeant. The biodegradability of jute and the effect
of organic chemicals on the clays are beyond the scope of the present paper.

KEYWORDS: Geosynthetic clay liner, Bentonite, Kaolinite, Hydraulic conductivity,
Jute.

AUTHORS: G.P. Karunaratne, Associate Professor, S.H. Chew, Assistant Professor,
S.L. Lee, Emeritus Professor, and A.N. Sinha, Research Scholar, Department of Civil
Engineering, National University of Singapore, Block E1A, #07-03, 1 Engineering
Drive 2, Singapore 117576, Telephone: 65/8742170, Telefax: 65/7791635, E-mail:
cvegpk@nus.edu.sg.

DATE: Original manuscript submitted 22 April 2000, revised version received and
accepted 27 November 2000. Discussion open until 1 October 2001.

REFERENCE: Karunaratne, G.P., Chew, S.H., Lee, S.L., and Sinha, A.N., 2001, “Bentonite:
Kaolinite Clay Liner”, Geosynthetics International, Vol. 8, No. 2, pp. 113-133.

Technical Paper by R.P. Hillman and T.D. Stark

SHEAR STRENGTH CHARACTERISTICS OF PVC GEOMEMBRANE-GEOSYNTHETIC INTERFACES

ABSTRACT: Torsional ring shear and large-scale direct shear tests were conducted
to investigate the shear behavior of polyvinyl chloride (PVC) geomembrane-geosynthetic
interfaces. Specifically, the smooth and faille-finished sides of a 0.75 mm-thick
PVC geomembrane were sheared against five different nonwoven geotextiles, a drainage
composite, a geonet, and an unreinforced geosynthetic clay liner (GCL). Test
results indicate that the smooth side of the PVC geomembrane yields a higher interface
shear resistance than the faille-finished side due to the larger contact area and higher
pliability of the smooth side. The interface shear behavior of the PVC geomembrane is
compared to that of a high density polyethylene (HDPE) geomembrane and two very
flexible polyethylene (VFPE) geomembranes. Faille-finished PVC geomembrane-nonwoven
geotextile interfaces experience a post-peak strength loss of less than 25% at
normal stresses between 100 and 400 kPa and no post-peak strength loss at normal
stresses of 50 kPa and below. This behavior is attributed to the pliability of the PVC
geomembrane, which enables (i) the geomembrane surface to be roughened, (ii) the
other interface component to embed into the geomembrane as shearing progresses, and
(iii) no texturing to be used that can damage the overlying geosynthetic. The effects of
nonwoven geotextile fiber type, mass per unit area, and calendering on PVC geomembrane-
nonwoven geotextile interface strength are also investigated.

KEYWORDS: PVC, Geomembrane, Geotextile, Geosynthetic clay liner, Drainage
composite, Direct shear test, Ring shear test, Shear strength, Slope stability.

AUTHORS: R.P. Hillman, Project Engineer, Golder Associates, Inc., 10 Chrysler,
Suite B, Irvine, California 92618, USA, Telephone: 1/949-583-2700, Telefax: 1/949-
583-2770, E-mail: rhillman@golder.com; and T.D. Stark, Professor of Civil and Environmental
Engineering, 2217 Newmark Civil Engineering Laboratory, University of
Illinois, 205 N. Mathews Ave., Urbana, Illinois 61801, USA, Telephone: 1/217-333-
7394, Telefax: 1/217-333-9464, E-mail: t-stark1@uiuc.edu.

DATE: Original manuscript submitted 29 December 1999, revised version received 3
January 2001, and accepted 4 January 2001. Discussion open until 1 October 2001.

REFERENCE: Hillman, R.P. and Stark, T.D., 2001, “Shear Strength Characteristics
of PVC Geomembrane-Geosynthetic Interfaces”, Geosynthetics International, Vol. 8,
No. 2, pp. 135-162.

Technical Paper by J.P. Gourc, R. Arab, and H. Giraud

CALIBRATION AND VALIDATION OF DESIGN METHODS FOR GEOSYNTHETIC-REINFORCED RETAINING STRUCTURES USING PARTIAL FACTORS

ABSTRACT: The technique for constructing geosynthetic-reinforced soil retaining
structures is now in widespread use. Since its first use in the late 1960s, construction
processes have become more technologically advanced, and the number of alternatives
has reduced, with most of the construction techniques being standardised. This type of
reinforced structure has been in use for nearly 30 years, during which time its reliability
has been proved. At the same time, work is in progress to standardise the design of
these structures using the new international format of Ultimate Limit States and Serviceability
Limit States calculations and associated partial factors. This study presents
the procedure currently being prepared for the future standard in France. First, a preliminary
parametric calibration based on typical structure profiles is described, comparing
different stability calculation methods and different partial factor combinations.
Second, design validation of instrumented case histories is performed.

KEYWORDS: Soil reinforcement, Geosynthetic, Standard, Design, Case history,
Partial factor.

AUTHORS: J.P. Gourc and R. Arab, Lirigm, University J.F. Grenoble 1, 38041
Grenoble Cedex 9, France, Telephone: 33/4-76-82-80-90, Telefax: 33/4-76-82-80-70,
E-mail: gourc@ujf-grenoble.fr and rarab@ujf-grenoble.fr; and H. Giraud, SNCF,
Direction Ingénierie, rue des Poissonniers, Paris 18, France, Telephone: 33/1-55-31-
11-61, Telefax: 33/1-55-31-82-63, E-mail: hubert.giraud@sncf.fr.

DATE: Original manuscript submitted 10 August 2000, revised version received 27
November 2000, and accepted 3 December 2000. Discussion open until 1 October 2001.

REFERENCE: Gourc, J.P., Arab, R., and Giraud, H., 2001, “Calibration and Validation
of Design Methods for Geosynthetic-Reinforced Retaining Structures Using Partial
Factors”, Geosynthetics International, Vol. 8, No. 2, pp. 163-191.