Dr Bob Semple
In many parts of the world, including Australia, the state of practice in assessing if liquefaction will occur is based on the recommendations of Youd et al (2001) which arose from workshops convened in the United States by NCEER. However, the final publication did not so much represent a consensus view as a compromise between conflicting opinions within the expert group. Since then, arguments over key aspects of liquefaction assessment in North America have increased such that there is “a state of chaos” (Youd, 2011).
There is perhaps limited awareness in Australia of this situation nor appreciation of the NCEER limitations in applying their recommendations. Poorly informed decisions increase costs and delay projects.
The purpose of this discussion is to point out some problematic aspects of the NCEER liquefaction criteria and of current recommendations in the literature. The objective is to encourage consideration of reasonable adjustments or alternatives to the de facto standard approach of the NCEER criteria. Some suggestions are made in this regard.
Dr Bob Semple has experience in geotechnical engineering consulting practice in several geographic locations including Australia, North America, Britain, Africa and the Middle-East. He has directed geotechnical engineering studies for large-diameter and cryogenic storage tanks, pipelines, ports and harbours, offshore structures, multistorey buildings, vibrating equipment, deep excavations, bridges, multi-stage embankments on soft clay, hydrocarbon processing and chemical plants, nuclear reprocessing facilities, seismic retrofit projects, and ground improvement.
In the course of these projects, Dr Semple has dealt with a variety of issues including foundation engineering in difficult ground conditions, residual and calcareous soils, pile load testing, design and monitoring of thick fills, slope stabilization, liquefaction and lateral spread evaluation, static and seismic soil-structure interaction analyses, deformation analysis of deep shoring systems, dewatering and acceleration of consolidation, swelling clays, dredging and placement of hydraulic fill, field instrumentation, and construction feasibility.
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