A

Level of analysis and investigation

Level of analysis and investigation

Figure 6. PERD process flow chart (after PERD, 1998).

Consequences (X)

Figure 6. PERD process flow chart (after PERD, 1998).

Avalanche defence structure

(Hydropower, Tailings)

Shallow foundation Ski lift mast on fractured/

weathered bedrock

Building on solid rock

Temporary foundation access road

_low_high_

Failure consequences

Figure 7. Examples of mountain permafrost infrastructure.

Failure Mode and Effects Analyses (FMEAs: Nahir et al., 2005; Robertson and Shaw, 2005) are an additional important pillar during a design process. The result of the analysis is to be incorporated into the screening process as it identifies sensitivities as well as consequences. This should be an unreserved process with various experts involved. The earlier an FMEA is carried out, the better it can be used to guide the project design.

Fischer and Huggel (2008) present a methodical design for stability assessments of permafrost affected rock walls that provides additional information when dealing with structures in rock.

Adaptational Design

Design for adaptation is an important element in the design of structures when either high sensitivity or high consequences are expected, or even both. As it is not economical to design for all possible scenarios, best estimates of changes in soil properties and climate boundary conditions should be investigated and accounted for in the design. A "high" case and extreme years should also be looked at, as will be described below. Although climate models are improving, it is practically impossible to predict the foundation conditions in 50+ years time. Measures should therefore be incorporated into the design so that they can be implemented based on monitoring results and pre-defined thresholds. Such measures could include anchor redundancies, access for anchors to be installed if rock masses could become unstable, or the installation of pipes that can be used for later installation of thermosyphons or an active refrigeration system. Flexible systems need to have ample room so that possible movements of the foundation can be adjusted accordingly.

In his Rankine lecture, Professor Ralph B. Peck (1969) made the following comments: "if the governing phenomena are complex, or are not yet appreciated, the engineer may measure the wrong quantities altogether and may come to dangerously incorrect conclusions". This is a situation often encountered in alpine environments and where the observational method, as introduced by Terzaghi and Peck (1969), is an ideal approach. However, in contrast to its original concept, monitoring, evaluating and modifying or adapting is not limited to the construction phase but more importantly it should be carried out continuously during the service life of the structure and even for a certain time after abandonment depending on the design purpose (e.g. tailings facilities).

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