Clay Geosynthetic Barriers

H. Zanzinger, R.M. Koerner, E. Gartung, H. Zanzinger, R.M. Koerner, E. Gartung

• Editore: CRC Press
• Anno: 2022
• ISBN:
  9781000151213
• Edizione: 1
• Argomento: Technology & Engineering
• Categoria: Civil Engineering

Clay geosynthetic barriers are most frequently used in environmental areas, such as landfill cover systems. This work discusses the durability and lifetime aspects of clay geosynthetic barriers related to the synthetic yarns and fibres.

1.APPLICATION/CASE HISTORIES

DOI: 10.1201/9781003078777-1

Geosynthetic clay liner performance in geotechnical applications

DOI: 10.1201/9781003078777-2

G. HeertenNaue Fasertechnik GmbH & Co. KG, Luebbecke, Germany

ABSTRACT: Since the late 1980s, geosynthetic clay liners (GCLs) have been specified and used by design engineers, agencies and owners as an alternative to soil barriers in various applications. The growing interest in these products stems from the unique properties and advantages they offer. They are very effective as a hydraulic barrier even under high gradient conditions; they are easy to install; show a high robustness against installation stresses and they can withstand elongation as well as settlement stresses without significant impact on their hydraulic performance. The wide range of GCL use includes landfill caps and base liner applications, environmental protection barriers under roads and railways, within various containment structures such as dams, canals, ponds, rivers and lakes, even for waterproofing of buildings and similar structures. However, their potential in other applications is only limited by convention. Numerous laboratory studies have shown the excellent performance capable with natural sodium bentonite geosynthetic clay liners. In more recent years, field conditions have been replicated in large-scale simulations to study the complex environmental effects such as wet/dry and freeze/thaw cycles as well as ionic exchange. The aim of this paper is to document the design requirements for various GCL applications, summarize the latest large-scale field trials and to illustrate that a GCL is equivalent if not superior to the prescriptive compacted clay liner.

1 INTRODUCTION

The main purpose of a geosynthetic clay liner (GCL) in any geotechnical application is to reduce/limit the flow of liquid through the GCL or barrier system. GCLs are mostly used to replace a compacted clay liner (CCL) or soil barrier. Natural sodium bentonite typically acts as the primary sealing element. In many applications, GCLs are also used in combination with a geomembrane and replace the CCL, such as landfill base seals or landfill caps, to achieve a composite-lined sealing system with two independent liners which complement each other, e.g. to act as a barrier against polar and non-polar contaminants. For the purposes of this paper, a geomembrane is considered to have a thickness of ≥1mm (40 mils). Thinner membranes are termed more accurately as a plastic sheeting, foil, film or tarp. It should be stated, however, that German landfills require a minimum thickness of 2.5 mm (100 mils).

Observation of various products in the geosynthetic industry illustrates that over a period of years, a product will undergo further development with specific characteristics changed due to market requirements. Table 1 shows such a product evolution for a selected GCL brand from 1988 to 2000 (modified according to Reuter 1999). The transition illustrated in Table 1 clearly shows three major product aspects that have changed over the years:

The change to the mass per unit area of bentonite used in a GCL product from 3,000 g/m² to 5,000 g/m² is logical due to the fact that the bentonite is the active sealing component. The rational for this bentonite increase was likely that a higher bentonite mass in a GCL is associated with better sealing characteristics, assuming that the quality of the bentonite is the same or better.

Daniel (2000) mentioned that another key to achieving consistent hydraulic integrity over the long-term is to prevent loss of bentonite and to avoid penetrations or fracturing of the GCL. Estornell et al. (1992) have recognized bentonite migration into anunderlying geonet was not observed whenaheavier (356 g/m²) nonwoven geotextile was used as a filter layer between the GCL and the geocomposite.

Examining the geotextile mass per unit area for one GCL (see Table 1), it can be seen that the mass per unit area for the underlying carrier geotextile component of the GCL was much heavier during the early days of GCL development – in the range of 300 to 800 g/m². In all cases, a scrim (slit film woven) reinforcement was incorporated in the carrier layer of this product. This concept (use of the slit film woven) evolved from turbulence tests to simulate high hydraulic loading that indicated a scrim reinforced nonwoven prevented bentonite loss better than thin nonwovens by themselves. It is for this same reason that one manufacturer generally recommends the slit-film woven or scrim reinforced nonwoven geotextile be installed down-gradient.

Table 1 Component evolution in a needle-punched GCL from 1988 to 2000.

	1988–2000
Cover	300 g/m^2 PPNW	300 g/m^2 PPNW	300 g/m^2 PPNW	300g/m^2 PPNW	300g/m^2 HDPE NW	200 g/m^2 PPNW	220 g/m^2 PPNW
Bentonite	3000 g/m^2 act. Ca^++	3000g/m^2 act. Ca^++	3000g/m^2 act. Ca^++	4000 g/m^2 nat. Na^+	4000 g/m^2 nat. Na^+	4200g/m^2 nat. Na^+	4500–5000g/m^2 nat. Na^+
Carrier	400 g/m^2 PP NW/W	300 g/m^2 PP NW/W	300 g/m^2 PP NW/W	300g/m^2 PP NW/W	300g/m^2 HDPE NW/W	300 g/m^2 PPNW 800 g/m^2 bent. impr	110g/m^2 PPW

(i) The bentonite component changed from Na-activated calcium-bentonite to natural sodium bentonite.

(ii) The mass per unit area of the bentonite was increased from 3,000 g/m² to 5,000 g/m².

(iii) The encapsulating geotextile components decreased from 300 g/m²/800 g/m² to 110 g/m²/300 g/m².

Gilbert et al. (1997) have also witnessed bentonite extrusion through thinner nonwovens and select wovens and state as follows:

“… for GCLs with bentonite encased between geotextiles, the bentonite passes through to the geotextiles into adjacent interfaces and affects the interface strength. Bentonite extrusion is normally associated with woven geotextiles although ithas been observed for thin (i.e. mass per unit area less than 220 g/m²) nonwoven geotextiles as well… Not only did bentonite extrude through the woven geotextile, but a smooth geomembrane that was adjacent to the woven geotextiles was also smeared with bentonite after hydration.”

Generalizing, there are two probable causes for all bentonite extrusion. One is the bentonite extrusion through thin geotextile components due to the simple swelling pressure of the bentonite. In this case, the extrusion could cause surface lubrication and reduce the interface friction angle to adjacent surfaces such as a geomembrane and eve...