Volume 42 Issue No. 1 March 2011 – SEAGS

Some Issues in Geosynthetic Reinforced Walls and Slopes

itsupport installer — Sat, 24 Oct 2015 15:29:34 +0000

Geotechnical Engineering Journal of the SEAGS & AGSSEA ISSN 0046-5828

Vol. 42 No.1 March 2011

Some Issues in Geosynthetic Reinforced Walls and Slopes

D. Leshchinsky

ABSTRACT: Current design of geosynthetic reinforced soil is well-established, rendering safe and economical structures. However, there are some issues that need attention so as to improve the economics or to avoid pitfalls. This paper presents three such issues suggesting possible solutions and commentary. The first issue deals with the artificial definition of reinforced walls and reinforced slopes. The distinction is based on an arbitrary slope angle. Such division results in two incompatible design methodologies. For reinforced walls the required strength of reinforcement is as much as twice as that needed for slopes; however, the trade off is simpler and more transparent calculations. With the availability of computer codes and with entrusting geotechnical engineers (as opposed to structural engineers) to design walls, it is expected that the less conservative and more consistent approach for reinforced slopes will be adopted for walls. One possible approach is using the safety map approach. The second issue deals with the current seismic design of geosynthetic reinforced walls. This design actually inhibits the use of such walls in seismic areas. However, field experience indicates that such walls actually behave very well under seismic loads. Its inherent flexibility produces a ‘shock absorbing’ type of structure that can dissipate seismic energy. Presented are the results of large scale shake table tests demonstrating the performance of geosynthetic reinforced retention structures. An alternative pseudostatic design approach, including reduced seismic coefficients, is proposed as a conclusion. The third issue deals with observations of ‘smaller than expected’ field measured load in geosynthetic reinforcement. These measurements have resulted in ‘calibration’ of a new design methodology that completely ignores statics and entirely relies on statistics. While the motivation to improve very conservative designs is understandable, the alternative of completely discarding the principles of static may result in unsafe structures. It is shown that a clear and simple explanation for the apparent conservatism is due to apparent cohesion which is generated by soil matrix suction. Without this cohesion, which is likely to disappear during the life span of the reinforced structure, the statistically-based approach yields a structure that is globally unsafe. Hence, in the context of design, the statistical approach without a benchmark based on statics, is unsafe. To get the full perspective of all three issues, references giving further elaboration are provided.

KEYWORDS: Some Issues, Geosynthetic Reinforced Walls, Slopes

DOI: 10.14456/seagj.2011.26

Advance in Geogrid Reinforced Slopes in Malaysia

itsupport installer — Sat, 24 Oct 2015 15:28:56 +0000

Geotechnical Engineering Journal of the SEAGS & AGSSEA ISSN 0046-5828

Vol. 42 No.1 March 2011

Advance in Geogrid Reinforced Slopes in Malaysia

T.A. Ooi and C.H. Tee

ABSTRACT: Geogrid product was formally introduced into and developed in Malaysia after Pilecon Holdings Sdn Bhd signed a distributorship agreement with Netlon Ltd (now Tensar International Ltd) United Kingdom in 1985. Prior to that Star Art Sdn Bhd was the distributor of Netlon product in Malaysia. Ooi &Tee (2004) examines the various case histories of slope repair and the role of geosynthetic reinforcement used in slope reconstruction and their performances for the last twenty years since the introduction of geogrids to Malaysia. Slope failure is not uncommon in many parts of Malaysia. Asahari (2009) reported more than 100 landslide incidences a year in Malaysia at a seminar on safe hill-site development in Kuala Lumpur. The frequency of occurrence of slope failure increases during the monsoon seasons where incessant rain extended over long period of time caused the slope to fail despite the fact that it may be stable for a long time. The infiltration of rainwater causes the reduction of soil suction, rise in water table and reduction of the shear strength of soil. In the case of uncompacted fill slope massive failures have occurred and lives and properties were lost. The Landmark case Highland Towers Condominium collapse in December 1993 and the high profile December 2008 Bukit Antarabangsa massive landslide are the worst landslides that have happened in Malaysia. The Public Works Department set up Slope Engineering Branch in 2004 to specifically manage and control the landslide problems faced by Malaysia. Many natural slopes are in fact in limiting equilibrium. Cutting in slope reduces the stability of slope and yet it is a common practice. Of course surface water is an important factor in causing instability of slope. Surface runoff must be taken away from the slope as quickly as possible in order to ensure the safety of slope. Over the last forty years, various methods of slope repair have been used. The stability of slope can be increased by the introduction of geosynthetics as soil reinforcement so that steep engineered slope can be formed. This paper presents the various case histories of slope repair and the role of geosynthetic reinforcement in the slope reconstruction and their performances.

KEYWORDS: Soft Ground; Geo-synthetics; Slope failure; Slope rehabilitation

DOI: 10.14456/seagj.2011.27

Embankment Construction with Saturated Clayey Fill Material Using Geocomposites

itsupport installer — Sat, 24 Oct 2015 15:28:19 +0000

Geotechnical Engineering Journal of the SEAGS & AGSSEA ISSN 0046-5828

Vol. 42 No.1 March 2011

Embankment Construction with Saturated Clayey Fill Material Using Geocomposites

J.-C. Chai, T. Hino, Y. Igaya, and Y. Yamauchi

ABSTRACT: To design an embankment using saturated clayey backfill with a dual function (drainage and reinforcement) geocomposite, predicting the undrained shear strength (S u) of the backfill during construction is an essential requirement. A method of predicting the S u value has been proposed, in which the effects of discharge capacity (Q w) of the geocomposite, spacing (2B) between geocomposite layers, construction speed (V), and the coefficient of consolidation (C v) of the backfill are considered. Then Q w values of four geocomposites were measured by laboratory tests under the confinement of clayey soils. The test results indicate that to maintain a higher long-term (about 1 month) Q w value (> 100 m 3 /year/m), for a geocomposite confined in clayey soil, it must have a drainage core and a strong filter. Finally, example analysis was conducted on predicting S u values and evaluating the factor of safety (FS) of an assumed geocomposite reinforced 5 m height embankment with saturated clayey backfill. A parametric study was carried out to investigate the effects of Q w , 2B, as well as V.

KEYWORDS: Embankment Construction, Saturated Clayey Fill Material, Geocomposites

DOI: 10.14456/seagj.2011.28

Numerical Modeling of Geosynthetic-Reinforced Earth Structures and Geosynthetic-Soil Interactions

itsupport installer — Sat, 24 Oct 2015 15:27:33 +0000

Geotechnical Engineering Journal of the SEAGS & AGSSEA ISSN 0046-5828

Vol. 42 No.1 March 2011

Numerical Modeling of Geosynthetic-Reinforced Earth Structures and Geosynthetic-Soil Interactions

J. Huang, A. Bhandari, and X. Yang

ABSTRACT: Nowadays geosynthetics have been used as a routine reinforcement in earth structures such as mechanically stabilized earth (MSE) walls, column-supported embankments, soil slopes, and paved/unpaved roads. In those applications, reinforcement mechanisms of the geosynthetics are vaguely described as confinement, interlocking, and load shedding respectively but not fully understood. The uncertainties of the mechanisms have been reflected as overconservativeness, inconsistence and empiricism in current design methods of those applications. Various researches have been widely carried on to investigate the mechanisms of reinforcement of the above mentioned applications, especially the geosynthetic-soil interactions and then quantitatively consider them into design methods. Numerical modeling characterized as cost-and time-saving, is preferred in many circumstances. An appropriate modeling strategy is vital to yield reliable results. This paper reviewed and summarized the modeling techniques used to model modular-block MSE walls, reinforced embankments/slopes, and reinforced paved/unpaved roads, which include conventional continuum modeling based on constitutive relationships as well as micro-mechanical modeling based on Newton’s law of motion, i.e., modeling the soil mass as an assembly of soil particles governed by universal physics principles. The review of conventional continuum modeling includes constitutive models for soils, geosynthetics and other components (e.g., modular blocks), interface models for contacts between dissimilar materials, and simulation of construction, while the review of the micro-mechanical modeling is extended to the principle of the micro-mechanical modeling and how the micro-mechanical modeling is implemented to model the geosynthetic-soil interaction by using the most popular micro-mechanical scheme-PFC as an example. The objective of this paper is to provide a state-of-art review of the various numerical modeling techniques and consequently promote the usage of numerical modeling in research and practice of geosynthetic-reinforced earth structures.

KEYWORDS: Numerical Modeling, Geosynthetic-Reinforced Earth Structures, Geosynthetic-Soil Interactions

DOI: 10.14456/seagj.2011.29

Geosynthetic Tubes and Geosynthetic Mats: Analyses and Applications

itsupport installer — Sat, 24 Oct 2015 15:26:35 +0000

Geotechnical Engineering Journal of the SEAGS & AGSSEA ISSN 0046-5828

Vol. 42 No.1 March 2011

Geosynthetic Tubes and Geosynthetic Mats: Analyses and Applications

J. Chu, W. Guo, and S.W. Yan

ABSTRACT: In recent years, there has been an increasing use of geotextile or geosynthetic materials for the construction of river or coastal structures. In this paper, a review of different applications of geotextile or geosynthetic tubes and geosynthetic mats is presented. The types of geotextile or geosynthetic tubes and geosynthetic mats are classified. A summary of different analytical methods for geosynthetic tubes is also provided. So far, there are few analytical or numerical methods available for geosynthetic mats as it is a relatively new technique. Several new analytical or numerical methods have therefore been developed recently for geosynthetic mats. Some of these methods are presented in this paper.

KEYWORDS: Geosynthetic Tubes, Geosynthetic Mats, Analyses, Applications

DOI: 10.14456/seagj.2011.30

Performance-based Design for Geosynthetic Liner Systems in Landfills

itsupport installer — Sat, 24 Oct 2015 15:25:51 +0000

Geotechnical Engineering Journal of the SEAGS & AGSSEA ISSN 0046-5828

Vol. 42 No.1 March 2011

Performance-based Design for Geosynthetic Liner Systems in Landfills

Y.M. Chen,W.A. Lin, B. Zhu, and L.T. Zhan

ABSTRACT: Municipal solid waste landfill is a new type of geotechnical structures occurring with the urbanization development, the functions of which are to contain municipal solid waste and protect natural environment. The geosynthetic liner system consisting of geomembrane and geosynthetic clay liner is widely used to separate the waste and the associated leachate in landfills from the surrounding environment. This paper addresses some issues for the geosynthetic liner system based on its performances, including: (1) breakthrough time, the contaminants cannot transport through the geosynthetic liner system during the service life; (2) sliding failure along the geosynthetic liner system interfaces; (3) tensile failure in the geosynthetic liner system resulting from the waste deformations. These issues are investigated and their associated design criteria are discussed based on theoretical analysis and experimental results, which would be useful for the state-of-the-practice designs of landfills.

KEYWORDS: Performance-based Design, Geosynthetic Liner Systems, Landfills

DOI: 10.14456/seagj.2011.31

Quantifying the Influence of Geosynthetics on Performance of Reinforced Granular Bases in Laboratory

itsupport installer — Sat, 24 Oct 2015 15:24:46 +0000

Geotechnical Engineering Journal of the SEAGS & AGSSEA ISSN 0046-5828

Vol. 42 No.1 March 2011

Quantifying the Influence of Geosynthetics on Performance of Reinforced Granular Bases in Laboratory

J. Han, Y. Zhang, and R.L. Parsons

ABSTRACT: Interaction between geosynthetics (geogrid and geotextile) and aggregates under traffic wheel loading has been considered as one of high-priority problems by the U.S. Transportation Research Board. The practical use of geosynthetics above a subgrade or within a base course has demonstrated the benefit of reducing rut depths and prolonging pavement life. However, no standard test method is available to appropriately evaluate the geosynthetic-soil confinement effect and distinguish the benefits of the different types of geosynthetics and soils. This paper provides an overview of existing test methods and outlines the advantages and disadvantages of each method. The newly developed test method by the authors is performance-based and modified from the Asphalt Pavement Analyzer to evaluate geosynthetic-soil confinement. In this test, a geosynthetic sheet is placed within a base course to form a reinforced base, which is subjected to wheel loading. The measured rut depth with the number of cycles of wheel loading can be used to evaluate the geosynthetic-soil confinement. In this study, two different base course materials and four different geosynthetics were used. The experimental results clearly show that this newly developed performance-based test method can distinguish the benefits of rut reduction among different types of geosynthetics and base course materials. The experimental tests of geotextile-reinforced bases were analyzed by a two-dimensional discrete element method. The limitations of this experimental method are also discussed.

KEYWORDS: Quantifying, Geosynthetics, Performance, Reinforced Granular Bases, Laboratory

DOI: 10.14456/seagj.2011.32