Geosynthetics International: Vol.8, No. 4, 2001

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Technical Paper by Y.S Jang, Y.W. Kim, and J.Y. Park

CONSOLIDATION EFFICIENCY OF NATURAL AND PLASTIC GEOSYNTHETIC BAND DRAINS

ABSTRACT: Consolidation efficiency of natural and plastic geosynthetic band drains is examined using laboratory tests and a three-dimensional numerical flow model. The numerical model is first validated by comparing its results with the laboratory consolidation data and then the influence of the drain installation depth on the consolidation time is estimated. The drains used in the analysis are circular and bandshaped natural drains and a band-shaped plastic drain. The results of discharge capacity tests show that the discharge capacity of the plastic drain is larger than those of the natural drains. Despite the difference in discharge capacity of the plastic and natural geosynthetic drains, the degree of consolidation versus time relationships obtained from laboratory consolidation tests were similar and the numerical model predicted the consolidation behavior quite well. The numerical simulation results of the effect of installation depth showed that the degree of consolidation versus time relationship for the circular-shaped natural and plastic geosynthetic drains was not significantly influenced by increases in installation depth. However, the consolidation-time relationship for the band-shaped natural geosynthetic drain, having a smaller discharge capacity, was influenced by well resistance with increased installation depth.

KEYWORDS: Natural geosynthetic drain, Plastic geosynthetic band drain, Well resistance, Numerical flow program, Drain length, Consolidation.

AUTHORS:
Y.S. Jang, Associate professor, Department of Civil and Environmental Engineering, Dongguk University, 3-26 Pildong, Chunggu, Seoul, Korea, Telephone: 82/2-2260-3355, Telefax: 82/2-2266-8753, E-mail: ysjang@dgu.ac.kr;
Y.W. Kim, Junior Engineer, Department of Civil and Infrastructures, DaeWoo Engineering, Seoul, Korea, Telephone: 82/31-738-0339, Telefax: 82/31-738-0309, E-mail: ywkim@dweng.co.kr; and
J.Y. Park, Graduate Student, Department of Civil and Environmental Engineering, Dongguk University, 3-26 Pildong, Chunggu, Seoul, Korea, Telephone: 82/2-2260-3355, Telefax: 82/2-2266-8753, E-mail: jiban@chollian.net.

DATE: Original manuscript submitted 3 December 2000, revised version received 1 June 2001, and accepted 9 June 2001. Discussion open until 1 April 2002.

REFERENCE: Jang, Y.S, Kim, Y.M., and Park, J.Y., 2001, “Consolidation Efficiency of Natural and Plastic Geosynthetic Band Drains”, Geosynthetics International, Vol. 8, No. 4, pp. 283-301.

Technical Paper by A.S. Dhar and I.D. Moore

LINER BUCKLING IN PROFILED POLYETHYLENE PIPES

ABSTRACT: Thermoplastic pipes are often manufactured with profiled walls to maximize the flexural stiffness of the pipe for a given amount of polymer. Thin elements in the profile can buckle under the influence of large earth pressures associated with deep burial or other extreme loading conditions. Earth load tests have been conducted on high density polyethylene pipes with a number of different wall profiles. Two highpressure pipe test cells have been used to conduct these tests. Observations of local buckling in the internal liners of these products have been examined and compared to stability assessments based on the conventional equation for buckling in stiffened plate structures (following modification of that equation to an equation that defines critical strain instead of critical stress). The strain levels that develop in the liner are, however,dependent on three-dimensional bending within the pipe profile. Provided the effects of three-dimensional bending in the pipe profile are considered, the modified Bryan equation appears to be a useful tool for quantifying liner stability and should be considered for inclusion in limit-state design procedures for these structures.

AUTHORS:
A.S. Dhar, Graduate student, Department of Civil and Environmental Engineering, The University of Western Ontario, London, Ontario, Canada N6A 5B9,Telephone: 1/519-661-2111, Ext. 88517, Telefax: 1/519-661-3942, E-mail: asdhar@engga.uwo.ca; and
I.D. Moore, Professor and Canada Research Chair, Department of Civil Engineering, Queen’s University, Kingston, Canada K7L 3N6, Telephone: 1/613-533-3160, Telefax: 1/613-553-2128, E-mail: moore@civil.queensu.ca.

KEYWORDS: Thermoplastic pipe, HDPE, Culvert, Deep burial, Local buckling, Plate-buckling model, Limit state design.

DATE: Original manuscript submitted 18 July 2000, revised version received 9 April 2001, and accepted 12 April 2001. Discussion open until 1 April 2002.

REFERENCE: Dhar, A.S. and Moore, I.D., 2001, “Liner Buckling in Profiled Polyethylene Pipes”, Geosynthetics International, Vol. 8, No. 4, pp. 303-326.

Technical Paper by P.C. Lopes, M.L. Lopes, and M.P. Lopes

SHEAR BEHAVIOUR OF GEOSYNTHETICS IN THE INCLINED PLANE TEST – INFLUENCE OF SOIL PARTICLE SIZE AND GEOSYNTHETIC STRUCTURE

ABSTRACT: This paper reports the investigation of the shear behaviour of six geosynthetics with two granular soils. The test equipment, soils, and geosynthetics properties are described and the soil-geosynthetic interaction behaviour is studied. The influence of soil particle size, geosynthetic structure, and test method are discussed by analysing the results of inclined plane tests. The main conclusions of the study are as follows: geosynthetic structure has an important influence on the soil-geosynthetic interface friction angle; higher soil-geosynthetic interface friction angles are measured when the geosynthetic surface has significantly sized apertures (e.g., geogrids) or allows the penetration of soil particles into the geosynthetic (e.g., nonwoven, spunbonded geotextiles); geosynthetic surface roughness (e.g., geomembranes) is associated with higher soil-geosynthetic interface friction angles; soil particle size has an important influence on the soil-geosynthetic interface friction angle; broadly graded soils with large average soil particle sizes allow an increase in the soil-geosynthetic interface resistance; the method of test does not significantly influence the soil-geomembrane or soil-geotextile interface friction angles (geosynthetics with continuous surfaces); and the validity of evaluating the soil-geogrid interface resistance using a rigid support (Test method 1) depends on the structure of the geogrid. It is suggested that site conditions is the greatest factor to consider when selecting the most appropriate test method.

KEYWORDS: Inclined plane shear, Geogrid, Geotextile, Geomembrane, Interaction, Particle size, Geosynthetic structure, Test method.

AUTHORS:
P.C. Lopes, Ph.D. candidate, M.L. Lopes, Associate Professor, Department of Civil Engineering, Geotechnical Division, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal, Telephone: 351/22 5081729, Telefax: 351/22 6053868, E-mail: costa@fe.up.pt; and
M.P. Lopes, Ph.D. candidate, Civil Engineering Division, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal,Telephone: 351/234 370941, Telefax: 351/234 370094, E-mail: mlopes@civil.ua.pt.

DATE: Original manuscript submitted 4 April 2001, revised version received 25 July 2001, and accepted 28 July 2001. Discussion open until 1 April 2002.

REFERENCE: Lopes, P.C., Lopes, M.L., and Lopes, M.P., 2001, “Shear Behaviour of Geosynthetics in the Inclined Plane Test – Influence of Soil Particle Size and Geosynthetic Structure”, Geosynthetics International, Vol. 8, No. 4, pp. 327-342.

Technical Paper by D. Leshchinsky and C. Vulova

NUMERICAL INVESTIGATION OF THE EFFECTS OF GEOSYNTHETIC SPACING ON FAILURE MECHANISMS IN MSE BLOCK WALLS

ABSTRACT: The analysis used in design of mechanically stabilized earth (MSE) block walls is based on the premise that a failure surface will develop within the reinforced soil zone defining an active soil mass. Limit equilibrium analysis of this mass renders the reactive force in the reinforcement and connections. The objective of this work was to identify the effects of reinforcement spacing on failure mechanisms in block walls. A computer program, based on continuum mechanics and capable of dealing with soil at failure, was utilized. Geosynthetic connection to the blocks was purely frictional. Interfaces between stacked blocks, reinforcement and confining blocks, soil and blocks, and soil and reinforcement were modeled. In addition to spacing effects, computer simulations were conducted to study the effects of factors such as backfill strength, foundation strength, reinforcement stiffness, interface strength, and intermediate reinforcement layers. Results of the parametric studies on a surcharge-free wall show that, as the reinforcement spacing decreases, the likelihood of developing a failure or active zone entirely within the reinforced soil zone decreases. Nonexistent such failure zones, for closely spaced reinforcement, imply that current limit-equilibrium formulations and designs might be unrealistic leading to excessive reinforcement load and related length. However, based on the parameters used, it was observed that conventional failure modes, such as direct sliding and toppling, deep-seated failure, and compound instability, may occur. Current “external stability” design addresses the same identified modes and mechanisms; hence,reinforcement dimensioning based on these mechanisms seems appropriate.

KEYWORDS: Block wall, External stability, Failure mechanism, FLAC, Interface effect, Internal stability, MSE wall.

AUTHORS:
D. Leshchinsky, Professor, and C. Vulova, former graduate student, Department of Civil and Environmental Engineering, University of Delaware, Newark, Delaware 19716, USA, Telephone: 1/302-831-2446, Telefax: 1/302-731-1001, Email: dov@ce.udel.edu and chrisvul@yahoo.com, respectively.

DATE: Original manuscript submitted 10 April 2001, revised version received 8 August 2001, and accepted 25 August 2001. Discussion open until 1 April 2002.

REFERENCE: Leshchinsky, D. and Vulova, C., 2001, “Numerical Investigation of the Effects of Geosynthetic Spacing on Failure Mechanisms in MSE Block Walls”, Geosynthetics International, Vol. 8, No. 4, pp. 343-365.