Geotechnical failure modelling is becoming ever more sophisticated, with the launch of LimitState:Geo’s latest programme. NCE reports.
Computational limit analysis techniques can now be used to rapidly determine the critical failure mechanism and margin of safety for almost any type of geotechnical construction.
This allows engineers to move beyond simple “automated hand calculations” and predefined mechanisms - without needing to resort to significantly more complex and potentially time-consuming techniques such as non-linear finite element analysis.
LimitState:Geo claims to have developed the only commercially available computational limit analysis software. It is a tool which is being used across the world to solve a wide range of industry problems. It can help the decision making process for temporary works, verifying and optimising ultimate limit state (ULS) designs, and performing detailed parametric studies for geometrically complex offshore problems.
Key to the operation of LimitState:Geo’s program is the powerful “discontinuity layout optimisation” (DLO) limit analysis procedure, which is used to directly produce accurate solutions in the form of slip line collapse mechanisms, familiar to all geotechnical engineers. With DLO, the critical collapse mechanism is determined from a wide range of possible layouts. Even on a modest desktop PC, problems containing over 21 trillion potential slip line layouts can be considered.
A key feature is the highly visual animated display of the critical failure mechanism identified. The speed of solution and interactive user interface also allows “what if” scenarios to be rapidly investigated, allowing users to quickly build up a good understanding of the likely mode of response of the geotechnical construction under consideration, and the key parameters influencing safety.
However, unlike more complex analysis methods, problems can be set up quickly and without the need for extensive training or previous numerical modelling expertise.
The adoption of Eurocode 7, which became mandatory in Europe in 2010, marked a significant change in the way geotechnical design is performed.
Eurocode 7 specifies a general set of partial factors that are not problem specific, meaning that general purpose computational limit analysis tools can be applied to a wide range of geotechnical stability problems.
The engineer particularly benefits from the ability to model all possible ULS failure modes, rather than only a narrow subset, as is often the case when using automated hand calculations.
Computational limit analysis is fully compatible with the Eurocode 7 philosophy, and tools such as LimitState:Geo can include:
- Built in Eurocode 7 “problem-agnostic” partial factor sets
- Eurocode 7 load descriptions (permanent, variable, accidental)
- Favourable and unfavourable load classifications
- The ability to check multiple design approaches/combinations in a single analysis
Furthermore, compatibility with the Eurocode 7 framework enables computational limit analysis procedures to readily be used with other limit state design methodologies.
The launch of LimitState:Geo 3.0 this summer marks a real step change in computational limit analysis.
Previously the ultimate limit state had to be reached by automatically factoring one or more loads in the system.
This can now also be achieved by automatically factoring down material strengths, making the analysis of slope stability problems much more straightforward.