1. Global check
The global check as implemented in D-Flow Slide is based on the assessment schema described in VTV-2014 and may comprise the following steps
Step 1 : Would flow slide lead to damage on levee (i.e. is the "schadelijksheidscriterium" met)?
The criteria of harmfulness ("schadelijksheidscriterium" in Dutch) is met if at the so-called assessment level is situated within the slope (i.e. on landward side of) the so-called observation profile, in accordance with Annex 9.4 of the VTV-2006.
1) Determination of the observation profile
The required margin (the horizontal part from the outside toe of the dike) depends on the presence of a revetment and is determined by the relation:
...
- 1:15 if the fictive channel depth is less than 40 m (H < 40 m)
- 1:20 if the fictive channel depth is more than 40 m (H ≥ 40 m)
2) Determination of the assessment level
The assessment level is the lower boundary of the liquefiable sand layer, but has a minimum and maximum of H/3 and H/2 above the bottom of the channel respectively.
3) Comparison of the observation profile with the existing profile at the assessment level
Ssign is the intersection point between the observation profile (from the foreshore) and the assessment level and SZV is the intersection point between the existing profile and the assessment level.
...
If the liquefaction point SZV is not situated landwards of the observation point Ssign, the criteria is met, so go to step 3.
Step 2: Criterion on slope protection met (<1:2,5)?
Directly in front of the toe of the dike or on the outside of the toe dumping or to the outward end of a dumping, the slope 1:2.5 may not be cut by the profile.
This check should be performed only if the criteria on harmfulness (step 1) is not met. However, as the result has no influence on the result assessment, this check is not performed.
Step 3: Artificially underwater installed and non-compacted sandy foreland?
The nature of the submerged slope is given as input by the user in the "General parameters" window.
...
In case of natural deposited slopes, go to step 4.
Step 4: Flow slide possible based on geometry only (i.e. is the "optredingscriterium" met)?
If the previous step (step 3) has not been passed, a check on criteria of occurrence (“optredingscriterium”) must be performed.
...
If the criteria of occurrence is not met, go to step 5.
Step 5: Is liquefaction possible?
Liquefaction is possible if the state parameter Ψ5m > -0.05 .
...
NOTE: for this check, the state parameter Ψ5m as entered in the General Parameters window is used, not the Ψ5m values per layer.
Step 6: Are there layers present with a thickness of minimal 5 m, in which D50 < 200 μm or D15 < 100 μm averaged over a thickness of 5 m?
The answer is "Yes" if D50 < 200 μm or D15 < 100 μm (only for sand and gravel soils) averaged over a thickness of 5 m between the water line and the toe of the channel slope.
NOTE: in the current version of the program, it is not checked if the thickness is minimal 5 m. The average is performed over a thickness of 5 m, by not taking into account the none-sandy layers.
Step 7: Is unstable breaching possible?
This criterion corresponds to step 5 of CUR Aanbeveling 113, 2008.
...