Tailings Sub-committee of the SAICE Geotechnical Division presents a 3-day workshop.
Venue: The Maslow Hotel, Sandton
Date: 7, 8 and 9 March 2018
Presented by:
Mr. Mike Jefferies
Dr. Dawn Shuttle
Developing confidence in critical state soil mechanics: A practical approach.
Background
Critical state soil mechanics (CSSM) is the only framework that predicts/quantifies the effect of void ratio on the mechanical behaviour of soil. CSSM is built on a century of developments in theoretical soil mechanics, but these developments are posed in both unfamiliar form and require background in aspects of mechanics that are not commonly taught in civil engineering degrees. In addition, pre-1985 developments in CSSM were over-idealized to the extent that they were verging on useless for real soils. These issues appear to have constrained adoption of CSSM in engineering practice (and indeed limited even the teaching of CSSM).
CSSM has its origins in static liquefaction failures (going back more than 100 years), and the recent history of large tailings dam failures involving liquefaction has renewed interest in CSSM. This renewed interest also builds on comprehensive further developments to CSSM during the past 25 years. CSSM has subsequently become the dominant framework for understanding, and quantitatively modelling soil behaviour from coarse sands through to clays, with particular relevance to liquefaction.
Workshop Outline
The aim of this workshop is for all attendees to become confident in using CSSM across a spectrum of applications, from assessing laboratory data through to developing design parameters and evaluating CPT data. A workshop setting is desired because most engineers will not develop true understanding in CSSM from studying papers or listening to lectures. The unfamiliar nature of work hardening plasticity requires people to implement CSSM from âfirst principlesâ to truly understand the theory. Such a âtutorialâ rather than âlectureâ setting was insisted on three decades ago by Peter Wroth as the only way to grasp CSSM – and is still valid today.
Part 1 â Theory and guided tutorials
The first part of the course is presented as a series of short lectures presenting aspects of the theory, each of which is then followed by a guided tutorial for implementation. The tutorials take the form of Excel spreadsheets that participants put together to implement CSSM models of progressively increasing generality and leading to the simulation of static liquefaction. Once the ideas have been grasped, the course will move on to applying the ideas.
Part 2 â Determination of soil properties*
The second part of the course will introduce test data, on both a sand and a silt, for participants to determine the soil properties and to model the tests. The intention is for participants to convince themselves of the accuracy and power of CSSM.
Part 3 â Assessment of CPT data*
The third part of the course looks to the practical question of determining the state parameter in-situ, which comes down to evaluating CPT data. The background to the CPT (and its stress normalization) will be covered. Participants will be introduced to the âwidgetâ, which is an open-code executable that generates soil-specific CPT calibrations. This final part of the course will cover using the widget and processing CPT data to recover the in-situ state.
* Note for Part 2 and Part 3 participants are encouraged to bring their own data sets in digital format (compatible with Excel) for additional practice.
Requirements
1. Workshop participants will need to bring a laptop computer with Microsoft Excel installed, to participate in the exercises.
2. Participants will need to be familiar with using Excel for engineering calculations (i.e. for implementing simple equations) and with graphing/charting in Excel. Other advanced aspects of Excel (i.e. VBA) will be taught as part of the course.
3. No pre-requisite reading about CSSM is required.
4. The needed theory will be taught, with hand-outs for the needed equations, and the course content has been found suitable to people with both a civil engineering and engineering geology background. The level of mathematics involved is roughly a first-year undergraduate standard. Participants who have forgotten about the first-order differential equation governing an in-situ falling head test may find it useful to refresh their knowledge of this math before the course; CSSM requires similar mathematics.
Instructors
The workshop will be taught by Mike Jefferies and Dr. Dawn Shuttle. Mike is the originator of NorSand (and author of a widely-cited text on critical state soil mechanics).
Dawn has implemented the NorSand in various finite element applications as well as developed the methodology for recovering state parameter from CPT data.
Related References
The course approximately covers Chapters 2 â 4 of the Soil Liquefaction book by Jefferies and Been (2015). Most people will find it more insightful to refer to these chapters after the course, rather than before.
Ken Beenâs ISC5 Keynote is a helpful overview to the issues explored and covered in the course.
The workshop is limited to 30 participants.
Contact: Yolandé van den Berg | info@selahproductions.co.za | 082 323 3910