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Developments in landfill

EDGE Consultants' Eugene Gallagher - the only UK delegate at the Braunschweig Landfill Conference in March - reports on the event.

In March Braunschweig Technical University hosted the ninth landfill symposium in a series that has run since 1985. This year's theme was vertical and horizontal sealing systems. Previous years' themes have included landfilling of high environmental impact wastes (1985), sealing walls and basal seals (1987), stability of landfill (1990 and 1992), landfill geotechnics (1994) and developments in landfill and cut-off wall construction (1998).

Braunschweig (the anglicised name is Brunswick), near Hannover in northern Germany, is a popular venue for geotechnical and landfill engineers who come to learn of the latest research developments in the field, to network and to soak up the friendly welcome.

The university's Institute for Geotechnical Engineering and Soil Mechanics, headed by Professor Walter Rodatz, also organises two other biannual symposia on piling and measurement in geotechnics. The institute's other landfill related research interests include cylinder testing of geoprotectors to HDPE membranes, frost effects on landfill and deformation monitoring at the base of land raise.

The conference attracted 200 delegates and 24 papers from Germany, Austria, Switzerland and the UK. The first day's papers were related to aspects of new landfill construction and capping seals while the second day focused on remediation/encapsulation of historical landfills (ie cut-off wall technology).

The design and construction of new landfills and treatment of unlined (historic) landfills in Germany is largely governed by rules set out in the three publications: TA Abfall (1991), TA Siedlungsabfall (1993) and the German Geotechnical Society's Geotechnics of Landfill and Contaminated Land . These rules gained wider dissemination to UK and other European practitioners through the work of European Technical Committee 8 (ETC8) of the then International Society for Soil Mechanics and Foundation Engineering.

At its first meeting in 1989, the committee decided to adopt recommendations made by the German Geotechnical Society as the basis for its work. German engineers have been in the vanguard of developments in landfill technology and have benefited from significant federal funding of research programmes. German design guidance has had a significant impact on European landfill practice.

Landfill construction and capping seals

Most of the papers (see box) presented referred to parts of the various guidance documents listed above. This is partly a reflection on a codified approach to design, which could be described as typical of German engineering practice.

Although providing a baseline and point of reference for best practice, the fact that use of prescriptive design codes can limit the ingenuity of the individual engineer, was a subtext to the paper by Ruppert & Brockhaus.

Landfill engineering practice in the UK differs from Germany in that a risk-based approach, with regard to site-specific hydrogeological risk assessment in particular, is much more the norm. Two papers considered risk assessment. Schaupp & Walz introduced a fuzzy logic-based model for assessing site location and/or quality of liner components for various standard classes of site, developed using the program fuzzyTECH for Business.

Essentially this compares actual designs against reference systems. The user is required to assess an appropriate distribution for each parameter from a selection of up to five linguistic terms.

I was the sole UK representataive and my paper described hydrogeological risk assessments being used in the context of design decisions in UK practice related to various patented steep sidewall lining solutions (vertical barrier system, reinforced soil with polystyrene formers and various revetment systems).

Risk assessment did not feature significantly in the vocabulary of other delegates and speakers at the conference. The introduction of the European Landfill Directive will require a change in German practice towards a more risk-based approach and there was much interest in UK experience in this area.

Other papers of note included an authoritative review of innovative systems of capping by Hoins, case histories covering the use of bentonite and asphaltic capping materials, and cap design incorporating capillary layers by Steinert & Melchior.

Cut-off wall technology

Historical (unlined) landfills are often encapsulated with deep cutoff walls and then capped, probably more often than is the case in the UK. There is a significant body of experience in Germany of cutoff technology in this context and some innovations in technique were described. Many papers showed a rather conservative approach to engineering solutions for historical landfills or contaminated areas, rather than a riskbased strategy.

The Braunschweig conference has been the forum for debating many novel ideas in landfill design (such as developments in geoprotector testing methods) and is one of which the UK landfill design community needs to be aware.

The presentation on UK experience in steep sidewall liner systems was well received in the context of little direct experience of such issues in Germany.

Questions covered safety during construction, details of basal and sidewall integration and testing of materials, demonstrating genuine interest.

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