Design Block
Prior to carrying out modeling an appropriate design block needs to be defined. The guideline provides two methods of selecting the design block: a “Simplified Approach” and a “Standard Approach”.
The simplified approach may only be carried out if at least one of the following applies:
| Event Frequency Class | Occurrence Frequency n (1/a) | Design Block Size Fractile |
| EF 4 (very high) | n ≥ 10 (> 10 occurrences per year) | V98 |
| EF 3 (high) | 1 ≤ n <10 (1 to 10 occurrences per year) | V97 |
| EF 2 (low) | 0.03 ≤ n <1 (1 occurrence per 1 - 30 years) | V96 |
| EF 1 (rare) | n <0.03 (<1 occurrence per 30 years) | V95 |
Otherwise the standard approach must be used to determine the block size.
Simplified Approach
For the simplified approach, an expert can define the block size based on their experience and information obtained during the site investigation.
Standard Approach
The standard approach involves carrying out a statistical analysis of measured block sizes in the initiation and/or deposition zones. The design block is obtained as a fractile value of the block size distribution as shown in the above table, based on the event frequency. Thus, where there are 10 or more occurrences per year, the 98th-fractile is used as the design block and the 97th-fractile is used for sites having frequencies between 1 and 10 occurrences.
The design block is to be determined for each homogeneous area.
Step-by-Step
Guide
Consequence Class
What level of risk is there?
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How is the design block selected?
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What system capacity is sufficient?
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What system height is required?
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How is an anchor verified?
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What other performance criteria are there?
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How can the system be safely adapted to a site?
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What recommended maintenance protocols exist?
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