Instability of Sand and its Implications for the Design of Tailing Dams

Tuesday, March 1, 2016 – 11:00 – 12:00 pm, 2312 Yeh Student Center

Jian Chu, Ph.D.
Nanyang Technological University, Singapore

Static liquefaction or flowslide is considered as one of the most common failure mechanisms for granular slopes or tailings dams. One of design approaches adopted is to use the residual strength or the so-called post-liquefaction undrained shear strength. However, there are a number of problems associated with this approach. One of them is that the post-liquefaction strength cannot be determined properly experimentally. The assumption of an undrained condition is also questionable for sand or tailings with relatively high permeability under static loading conditions. In this seminar, instability behavior of sand under undrained, drained, and other than undrained conditions are presented to illustrate that instability does not have to occur under an undrained condition and “undrained” does not have to be taken as a design assumption. Based on the new findings, a different design approach to use the stress ratio of instability line or the peak strength ratio is suggested.

Please view the flyer and bio attached for further details: Jian Chu, PhD

 

Problematic Soils in Australia and New Zealand

Thursday, March 3, 2016 – 12:00pm, B02 Coordinated Science Laboratory (CSL)

Sergei Terzaghi , Principal at ARUP

Australia and New Zealand contain many unusual and/or problematic soils.  Failure tounderstand the properties and behavior of these materials will lead to major cost overrunsand substantial difficulties in projects involving these materials.  Conversely, designingthe projects to take into account the unusual properties can lead to significant costsavings.  A number of case histories from both countries will be presented to illustrate theunique properties and how these properties can either lead to an economical design or toproblems. In New Zealand, there are two groups of soils that lead to fairly unusualproblems. The first is the pumiceous materials of the Central Volcanic Zone and theirallophane rich weathered materials, and the second are the residual soils of Auckland andNorthland.  All of these materials have high void ratios, but contrary to expectation, theyare often quite strong and stiff. Once a critical yield stress (or strain) is reached however,their behavior changes quite radically.  The reasons and consequences will be discussed.

Please view the flyer and bio attached for further details: GESO Guest Speaker -Sergei Terzaghi