Geosynthetics in Civil Engineering

R W Sarsby

• Publisher: Woodhead Publishing
• Year: 2006
• Print ISBN: 9781855736078
• eBook ISBN: 9781845692490
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Geosynthetics are man-made polymer-based materials which facilitate cost effective building, environmental, transportation and other construction projects. Given their versatility, geosynthetics are a vital material in all aspects of civil engineering.The first section of the book covers the fundamentals of geosynthetics. Chapters discuss the design and durability of geosynthetics together with their material properties and international standards governing their use. Building on these foundations, part two examines the various applications of geosynthetics in areas such as filters, separators, landfills, barriers and foundation materials. The book concludes by reviewing methods of quality assurance and the service life of geosynthetics.Written by an international team of contributors, Geosynthetics in civil engineering is an essential reference to all those involved in civil engineering. - Discusses the fundamentals of geosynthetics - Examines various applications in areas such as filters, separators, landfills and foundation materials - Reviews quality assurance and the service life of geosynthetics

Part I

General issues

1

The design principles of geosynthetics

R.M. Koerner Drexel University, USA

1.1 Introduction

As with all new materials design, one adopts and adapts earlier approaches from other and/or similar materials. With geosynthetic materials design, the closest allied fields are construction materials and, in particular, soil materials as encompassed within the discipline of geotechnical engineering. As is to be expected with the gradual maturing of the geosynthetic area, the design methods have advanced from very simplistic to quite detailed and still emerging.

In this regard, the chapter will describe the following:

1 ‘Design by cost’ (exemplifying past practice).

2 ‘Design by specification’ and ‘Design by function’ (exemplifying present practice).

3 ‘Design using probability’ and ‘Load and reduction factor design’ (exemplifying possible future practice).

1.2 Past practice in geosynthetic design

Manufacturers’ specifications appeared almost simultaneously with the development and introduction of each geosynthetic product’s entry into a particular application. Geotextile and geomembrane manufacturers led the way with product specifications accompanying each product throughout the 1960s and 1970s. The downside of such specifications was that, either overtly or by using subtle test methods, the net result was to use that particular product, thereby excluding all others. Of course, the designer was at liberty to ‘cut and paste’, thereby forming a project-specific specification but this was difficult owing to rapid changes in the emerging technology and the general lack of field performance and designers experience. Thus, which tests to include, which minimum or maximum values to select, which test procedures to evoke and which testing frequencies to require were all very subjective issues. As a result, the method often used by the designer could be described as ‘design by cost’.

Design by cost is quite simple. The funds available are divided by the area to be covered, and a maximum available unit price that can be allocated for the geosynthetic product is calculated. The geosynthetic product with the best properties for the site-specific application is then selected within this unit price limit and according to its availability. The method is obviously weak technically but is one that has been practised and very often resulted in adequate performance. It perhaps typified the situation in the early days of geosynthetics, but it is very outmoded by the current standard of practice.

1.3 Present practice in geosynthetic design

A defining point in geosynthetics was the first international conference on the subject in Paris in 1977. This conference spurred the first books on the topic (Koerner and Welsh, 1980; Rankilor, 1981) both of which collected more advanced and generic specifications and laid the groundwork for designing by function. Thus, from 1980 to the present, geosynthetic design has taken two parallel routes, ‘design by specification’, and ‘design by function’. In general, design by specification is used for ordinary and non-critical applications, while design by function is used for site-specific and generally critical applications. Each will be explained.

1.3.1 Design by specification

Design by specification is very common and is used extensively when dealing with public agencies and many private owners as well. In this method, several application categories are listed in association with various physical, mechanical, hydraulic and/or endurance properties. The application areas are usually related to the intended primary function.

A federal agency that has formulated a unified approach in the USA for geotextiles is the American Association of State Highway and Transportation Officials (AASHTO). In its M288 geotextile specifications, AASHTO provides for three different strength classifications (Table 1.1). The classifications are essentially a list of minimum strength properties meant to withstand varying degrees of installation survivability stresses. It is the first step in the process.

Table 1.1

AASHTO M288 geotextile strength property requirements

	Test method	Units	Geotextile Classification^a
			Class 1		Class 2		Class 3
			Elongation < 50%^b	Elongation > 50%^b	Elongation < 50%^b	Elongation > 50%^b	Elongation < 50%^b	Elongation > 50%^b
Grab strength	ASTM D4632	N	1400	900	1100	700	800	500
Sewn seam strength^c	ASTM D4632	N	1200	810	990	630	720	450
Tear strength	ASTM D4533	N	500	350	400^d	250	300	180
Puncture strength^e	ASTM D4833	N	500	350	400	250	300	180
Burst strength^f	ASTM D3786	kPa	3500	1700	2700	1300	2100	950
Permittivity	ASTM D4491	s^−1	Minimum property requirements for permittivity, apparent opening size and ultraviolet stability are based on geotextile application. Refer to separate tables for subsurface filtration, separation, stabilization or permanent erosion control
Apparent opening size	ASTM D4751	mm
Ultraviolet stability	ASTMD4355	%

^a Required geotextile classification is designated in accompanying tables for the indicated application. The severity of installation conditions for the application generally dictate the required geotextile class. Class 1 is specified for more severe or harsh installation conditions where there is a greater potential for geotextile damage, and Class 2 and Class 3 are specified for less severe conditions.

^b As measured in accordance with ASTM D4632. Note that woven geotextiles fail at elongations (strains) less than 50%, while non-woven geotextiles fail at elongation (strains) greater than 50%.

^c When sewn seams are required. Overlap seam requirements are application specific.

^d The required MARV tear strength for woven monofilament geotextiles is 250 N.

^e Puncture strength will probably change from ASTM D...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Contributor contact details
• Part I: General issues
• Part II: Applications
• Index