Projects and Optimized Engineering with Geogrids from 'Non-Usual' Polymers
A perfect geosynthetic reinforeerneut should have from the point of view of geotechnical engineers following proper lies: appropriate tensile module, low creep, high coefficient of interaction, low installation damage, high chemical resistance, low price. This perfect reinforeerneut is not available yet. NeverthcHess, the use of modern polymers - additionally to the common used PP, PET and HDPE- allows for optimized solutions quite close to the "ideal case". Projects with new geogrids made from aramid and polyvinylalcohol during the last years are presented and discussed. Three of them are projects with high-strength geogrids from aramid: for overbridging sinkholes at a highway in Germany; to ensure slope stability at a waste disposal in Austria and to reinforce embankment on piles for a new high-speed train in Germany. The projects require high tensile forces at minimized strains. Further, two projects are reported with geogrids made of polyvinylalcohol: for a waste disposal and for a retaining wall in Germany. In both cases low creep had to be combined with high alkaline resistance. Typical project cross-sections, the final solutions, characteristic properties ofreinforcement and photos are presented, demonstrating the broaden geotechnical engineers's options today.
The properties of the geotechnical engineer's "ideal" geosynthetic reinforeerneut are described, although no such product ex ists as yet. However, present-day "common" polymers (high tenacity polyester: PET, polyethylene: PE and polypropylene: PP) already provide some possibility for optimal choice of rein foreerneut products depending on the raw material, because im portant properties of reinforeerneut are in fact largely determined by the polymer used.
The general advantages of geogrids (woven, knitted and extruded) as a reinforeerneut material are explained briefly.
Which is more important (being the focal point ofthe paper): the ongoing development of polymers and, based on that, of reneer's scope for project-specific optimisation.
In this connection, use of the "latest" polymers such as aramid (AR) and polyvinylalcohol (PVA) has often proved appropriate.
In the context of project optimisation there is a brief discus sion on properties of these novel polymer geogrids, which are relevant to the engineer, namely modulus, creep behaviour, du rability, etc.
The paper includes recent, more important projects, in which geogrids in AR and PVA have provided a useful solution, some times the only one.
Three of these projects involve aramid geogrids in road engi neering, landfill construction and railway engineering (including the first use of any kind of aramid geogrid), and two have used PVA geogrids for landfill and retaining wall construction, being the firsttime that PVA geogrids have been installed in Germany. Tensile strengths of geogrids in the projects presented range from 110 kN/m to 1200 kN/m and strains from about 2.5% to araund 5.0%.
For reasons of space, problems posed, solutions, characteristic values, experience and design methods have been presented rather briefly, with emphasis on graphic information on project details and reinforeerneut behaviour.
Reference is made to the literature on the subject, in so far as it is available, given the novelty of the subject matter.
In conclusion it can be said that the above-mentioned applications of novel polymers geogrids noticeably broaden the civil engineer's options for an optimal solutionon asound base.