The determination of seismic earth pressures acting against retaining walls is a complex soil-structure interaction (SSI) problem. Factors which affect these earth pressures include:
- The nature of the input motions which includes the amplitude, frequency, directivity and duration of the motion.
- The response of the soil behind, in front & underlying the wall.
- The characteristics of the wall, which includes the strength and bending stiffness of the wall.
The pseudo-static class of analysis is most commonly used in design and makes use of the free-field Peak Ground Acceleration (PGA ) expressed as a Seismic coefficient, C (/g) typically obtained from national design standards (e.g., NZTA Bridge Manual, 2014).
1. Flexible (Mononobe-Okabe)
2. Stiff (Matthewson et al., 1980)
3. Rigid (Matthewson et al., 1980)
Question: Can Co be optimized for New Zealand?
- Perform two-dimensional dynamic finite element analyses using OpenSees Consider 2 soil classes (Classes C &D) (NZS 1170.5:2004)
- Use appropriate NZ acceleration-time histories for two zones in North Island & one for South Island, and allowance for magnitude scaling
- Analyses for two embedded cantilever wall heights (2m and 3m) & one double propped wall height (3m, with two different prop stiffnesses)
- Carried out 946 dynamic analyses run
Example results for Christchurch, Shallow Soils, Soil Class C
Last updated: 24/09/15
LAST THREE MONTHS
• Project completed on budget and a final report was issued on 21/8/15. A further revised copy of the report was submitted due to typographical revisions and was submitted on 9/9/15.