Geotechnical Engineering Journal of the SEAGS & AGSSEA ISSN 0046-5828
Vol. 42 No.1 March 2011
Some Issues in Geosynthetic Reinforced Walls and Slopes
D. Leshchinsky
ABSTRACT: Current design of geosynthetic reinforced soil is well-established, rendering safe and economical structures. However, there are some issues that need attention so as to improve the economics or to avoid pitfalls. This paper presents three such issues suggesting possible solutions and commentary. The first issue deals with the artificial definition of reinforced walls and reinforced slopes. The distinction is based on an arbitrary slope angle. Such division results in two incompatible design methodologies. For reinforced walls the required strength of reinforcement is as much as twice as that needed for slopes; however, the trade off is simpler and more transparent calculations. With the availability of computer codes and with entrusting geotechnical engineers (as opposed to structural engineers) to design walls, it is expected that the less conservative and more consistent approach for reinforced slopes will be adopted for walls. One possible approach is using the safety map approach. The second issue deals with the current seismic design of geosynthetic reinforced walls. This design actually inhibits the use of such walls in seismic areas. However, field experience indicates that such walls actually behave very well under seismic loads. Its inherent flexibility produces a ‘shock absorbing’ type of structure that can dissipate seismic energy. Presented are the results of large scale shake table tests demonstrating the performance of geosynthetic reinforced retention structures. An alternative pseudostatic design approach, including reduced seismic coefficients, is proposed as a conclusion. The third issue deals with observations of ‘smaller than expected’ field measured load in geosynthetic reinforcement. These measurements have resulted in ‘calibration’ of a new design methodology that completely ignores statics and entirely relies on statistics. While the motivation to improve very conservative designs is understandable, the alternative of completely discarding the principles of static may result in unsafe structures. It is shown that a clear and simple explanation for the apparent conservatism is due to apparent cohesion which is generated by soil matrix suction. Without this cohesion, which is likely to disappear during the life span of the reinforced structure, the statistically-based approach yields a structure that is globally unsafe. Hence, in the context of design, the statistical approach without a benchmark based on statics, is unsafe. To get the full perspective of all three issues, references giving further elaboration are provided.
KEYWORDS: Some Issues, Geosynthetic Reinforced Walls, Slopes
