Conferencia Nabor Carrillo
CARRILLO LECTURE Geosynthetic-reinforced soil structures: TATSUOKA, F. The theory, history, current practice and perspective of the technology of geosynthetic-reinforced soil (GRS) retaining structure, mainly for retaining walls (RWs), are described. Firstly, based on theoretical considerations as well as results from researches and lessons learned from case histories, it is shown that this technology is a much more cost-effective solution with a much less total amount of CO2 emission than the conventional technology in the construction of soil retaining structures (i.e., walls, steep slopes and backfill structures for bridges and others). A number of representative case histories showing the above are presented. The followings are also shown. GRS retaining wall having a stage-constructed full-height rigid facing is now the standard RW technology for railways (including those for high-speed trains), replacing the conventional RW. A total length of this new type GRS RW is now more than 100 km (as of January 2008). A number of embankments and RWs for highways, railways and residential areas that failed by recent major earthquakes, floods and seashore wave actions were reconstructed to GRS RWs in Japan. Rehabilitation of an old earth dam by using geosynthetic-reinforced steep-sloped embankment is also described. A new type low-height irrigation earth fill dam with a geosynthetic-reinforced down-stream slope allowing temporary over-flow of flood water is also described. Several new bridge abutment types comprising of GRS RWs that have been developed as a much more cost-effective solution to alleviate a number of technological problems with the conventional type bridge, including a low seismic stability, are described. As the latest development, GRS integral bridge comprising of a continuous girder integrated without using bearings to full-height rigid facings to which geosynthetic reinforcement layers are connected is proposed. Facebook Status - Secondly, it is shown that Geosynthetics Engineering combines two engineering disciplines: Material Engineering, specific to polymer materials, and Geotechnical Engineering. The paramount importance of this feature in proper development and practice of GRS structure technology is demonstrated. The following are shown. It is misleading to predict the long-term behaviour, in particular creep deformation, of polymer reinforcement arranged in the backfill solely based on results from tensile tests on specimens in air. Results of laboratory model tests as well as full-scale field behaviour revealed that, with ordinary GRS structures, in particular when adequately designed against seismic and heavy rainfall loads, the tensile force activated in the polymer reinforcement decreases with time without showing a sign of creep failure. This is because both geosynthetic reinforcement and backfill exhibit creep deformation due to their viscous properties. This behavior can be analysed and predicted in the consistent manner only by a relevant elasto-viscoplastic model, not isochronous models. Based on lessons learned from case histories, it is also emphasized that long-term residual deformation of GRS soil structures, as well as soil structures reinforced with so-called inextensible reinforcement, can be restrained much more effectively by better compacting better backfill than by using significantly stiffer reinforcement members. Furthermore, arrangement of a relevant drainage system to prevent the development of high positive excessive pore water pressure in the backfill is essential to keep the residual deformation of reinforced soil structures sufficiently small and to ensure a high stability during heavy rainfalls and seismic events. |
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