Geotechnical Teaching Resources

Limit State Analysis and Design

LayeredSlopeExistingSlip.gif GravityWall.gif

buried_footing.gif

Stability analysis problems such as slope stability, retaining wall design and foundation capacity are traditionally taught using predetermined formula for restricted problem types.

While it is important for students to appreciate the core principles of geotechnical stability analysis, often they find it hard to

  • get a feel for the type of collapse mechanism involved with e.g. a Rankine style analysis of a retaining wall.
  • appreciate the sensitivity of a problem to input parameters.

Additionally analysis of all but the simplest problems rapidly become too complex to handle by hand calculation, and lead to somewhat unsatisfactory semi-empirical modifications.

In the past few years, the Sheffield geotechnics group has been applying the maxim of 'research led teaching' by utilizing new numerical analysis techniques and software in undergraduate and MSc classes that have been developed as the result of recent research projects.

These web pages will detail a number of resources developed by the group that may be freely used by academics. Some of the resources described here were developed with the support of a Sheffield University Learning and Teaching Development Grant.

 

Discontinuity Layout Optimization and LimitState:GEO

Discontinuity Layout Optimization is a new technique for determining the collapse load and associated mechanism for a broad range of plasticity problems. Unlike Finite Element techniques, it is formulated entirely in terms of discontinuities and produces highly precise solutions in the form of easily interpreted slip-line mechanisms.

The advantages for teaching are that once the basics of the upper-bound sliding block mechanism analysis method are understood by students then any solution generated by the software is easy to interpret. In addition the DLO solution method is easily described with little complex mathematics.

Following development of the DLO technique at Sheffield, it has been incorporated into a full commercial analysis package LimitState:GEO by Sheffield spinout company LimitState Ltd. LimitState Ltd make this software freely available for academic use in research and teaching.

The following is intended to give a flavour of the usage that the software can be put to in teaching.

  1. Illustration of lecture presentations
  2. Student led exploration of soil-structure interaction problems
  3. Student projects
  4. Eurocode 7

Illustration of lecture presentations

A simple use is to make illustrations of slip line mechanisms come alive. For example an animated version of the Prandltl fan mechanism illustrated below makes the kinematics of the problem much clearer to students and can be generated using LimitState:GEO in a few minutes.

prandtl_mechanism.gif

Equally even the kinematics of simple single wedge sliding block mechanisms for retaining walls can be difficult for some students to conceptualise, particularly the relative movement between wall and wedge. An animated diagram can make this much clearer:

single_wedge_wall.gif

Student led exploration of soil-structure interaction problems

The ability to rapidly set up, modify and solve problems with LimitState:GEO facilitates student led exploration of soil-structure interaction problems. Examples include:

  1. Footing stability on undrained soils
  2. Footing stability on drained soils
  3. Slope stability

(Click on the link for further details and to access resources).

Students may be given worksheets guiding them through a range of parametric studies and asking them to draw conclusions about the general principles of soil structure interaction.

In order to introduce students to the basics of using LimitState:GEO, they can be directed to work through Chapter 3 Quickstart Tutorial of the LimitState:GEO manual. This typically takes the order of 1 hour and an be self directed teaching in the students own time, or preferably run as a timetabled class with demonstrators.

Student projects

The general purpose capabilities of LimitState:GEO allow investigation of a wide range of geotechnical limit analysis problems using the software.

These can range from e.g.:

  1. parametric studies of specific problems e.g. stepped slopes.
  2. generation of yield surfaces for a range of foundations (eg combined sliding/bearing of footings)
  3. investigation of the use of different factor of safety approaches in different design codes such as Eurocode.

Eurocode 7

LimitState:GEO was designed specifically with the Eurocode approach to partial factors in mind. It thus facilitates exploration of the Eurocode 7 design approach and comparison of different design approaches.

LimitState:GEO - use by academics

LimitState Ltd make the geotechnical software package LimitState:GEO freely available for use by academics in research and teaching. For further information follow this link to the LimitState website.