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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
NOTE: If the average state parameter Ψ5m (as entered in the General Parameters window) is more than -0,05, that means that liquefaction is possible. In such case the Global check fails, whatever the result of the steps described below. An information message will be given in the Overall Results window.
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steps
Step 1a : 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.
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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:
M = 2 Hvw + 1.5 (H - Hvw) H in case no revetment is present
M = Max [ Mbestorting ; 2 Hvw + 1.5 (H - Hvw) ] in case a revetment is present
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H is the channel depth in case no revetment is present and H = Honbest in case a revetment is present
Hvw is the thickness of the sensitive layer(s). The sensitivity is determined using the following criterion: sand (or gravel) layers with Ψ5m > -0.05 (when considering all the layers until 1.5*H below the toe of the submerged slope), are considered as sensitive. (NOTE: For this check, the state parameter Ψ5m entered per layer is used, not the value entered in the General Parameters window.)
Honbest is the depth of the channel below the revetment.
Mbestorting is the horizontal projection of the length of the revetment.
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In case no slope protection is present, if over the entire channel depth softening sensitive sand is present, this margin is thus equal twice the fictive channel depth (M = 2 H).
The inclined part of the observation profile in line with the horizontal portion. The inclinaison inclination of the slope depends on the channel depth:
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If the liquefaction point SZV is not situated landwards of the observation point Ssign, the criteria is met, so go to step 3to step 1c.
Step
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1b: 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 11a) is not met. However, as the result The result of this check has no influence on the result assessment, this check is not performed.
Step
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1c: 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 non-natural deposited slopes, both Global and Detailed Overall checks FAIL and it should immediately be switched to the advanced Advanced methods.
In case of natural deposited slopes, go to step 41d.
Step
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1d: Flow slide possible based on geometry only (i.e. is the "optredingscriterium" met)?
If the previous step (step 31c) has not been passed, a check on criteria of occurrence (“optredingscriterium”) must be performed.
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The answer is "Yes" if D50 < 200 μm or D15 < 100 μm where D15 and D50 are the minimum averaged values (only for sand and gravel soils) 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 breaching possible?
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- a slope with or without flat banks
- for medium fine sand with D50 > 200 μm and D15 > 100 μm
- for coarse sand and gravel with D50 > 500 μm and D15 > 250 μm
where D15 and D50 are the minimum averaged values (only for sand and gravel soils) over a thickness of 5 m between the water line and the toe of the channel slope.
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.
NOTE: The case where the sand is finer than where D50 < 200 μm is not checked because according to question 6 (see above) in this case a detailed check must be performedbut a warning message will be given in the Overall Results window.
NOTE: D50 and D15 are determined in the same way as in question 6 Only the case "without flat blanks" is implemented in D-Flow Slide.
Table A.4.2a from CUR113b, profile without flat berms:
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