Sarsby Geosynthetics in Civil Engineering

1. Auflage 2006
ISBN: 978-1-84569-249-0
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, 312 Seiten

Reihe: Woodhead Publishing Series in Textiles

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

Autoren/Hrsg.

Sarsby, R W

Leseproben

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





Grab strength ASTM D4632 N 1400 900 1100 700 800 500 Sewn seam strengthc ASTM D4632 N 1200 810 990 630 720 450 Tear strength ASTM D4533 N 500 350 400d 250 300 180 Puncture strengthe ASTM D4833 N 500 350 400 250 300 180 Burst strengthf 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 D4833 to ASTM D6241 with higher values. f Burst strength will probably be omitted in the near future. • Class 1. For severe or harsh survivability conditions where there is a greater potential for geosynthetic damage. • Class 2. For typical survivability conditions; this is the default classification to be used in the absence of site-specific information. • Class 3. For mild survivability conditions where there is little or no potential for geosynthetic damage. The second step is to select one of several different tables according to the specific function. These functions follow the intended application. They are filtration, separation, stabilization, erosion control, temporary silt fences and prevention of reflective cracking. Table 1.2 presents the appropriate table for filtration applications. See Koerner (2005b) for the remaining tables and a more complete description together with example problems. It should be mentioned that many federal agencies worldwide have similar generic specifications. Table 1.2 AASHTO M288 subsurface filtration (called ‘drainage’ in the actual specification) geotextile requirements Geotextile class Class 2 from Table 1.1b Permittivityc,d ASTM D4491 s-1 0.5 0.2 0.1 Apparent opening sizec,d ASTM D4751 mm 0.43 maximum average roll value 0.25 maximum average roll value 0.22 maximum average roll value Ultraviolet stability (retained strength) ASTM D4S55 % 50% after exposure for 500 h For cohesive soils with a plasticity index greater than 7, the geotextile maximum average roll value for the apparent opening size is 0.30 mm. a Based on the grain size analysis of in situ soil in accordance with AASHTO T88. bDefault geotextile selection. The engineer may specify a Class 3 geotextile from Table 1.1 for trench drain applications based on one or more of the following. 1. The engineer has found Class 3 geotextiles to have sufficient survivability based on field experience. 2. The engineer has found Class 3 geotextiles to have sufficient survivability based on laboratory testing and visual inspection of a geotextile sample...