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The global check as implemented in D-Flow Slide comprises the following steps, which are strongly based on Annex 9.4 of the VTV-2006can also be found in Toetsmethode zettingsvloeiing (version 2, 22 febr. 2016).
Step 1a : Would flow slide lead to damage on levee (i.e. is the "schadelijksheidscriterium" met)?
The damage criterion ("schadelijksheidscriterium" in Dutch) is met if at the so-called assessment level ("beoordelingsniveau") the actual slope lies landward of the so-called assessment profile ("signaleringsprofiel"), see Figure below, which is adopted from Annex 9.4 of the VTV-2006 Toetsmethode zettingsvloeiing (version 2, 22 febr. 2016).
1) Determination of the assessment profile
The required margin (the horizontal part from the "invloedslijn" of the dike) depends on the presence of a revetment and is determined by the relation:M
- in case no revetment: M = 2 Hgeul
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- in case
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- a revetment: M = Max [ Mbestorting - Linfluence; 2 H
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- onbest) ]
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- (see also figure below)
where:
Hgeul is the channel depth in case no revetment is present and Hgeul = Honbest in case a revetment is present
Honbest is the depth of the channel below the top revetment.
Mbestorting is the horizontal projection of the length of the top revetment starting at the outer dike toe
Linfluence is the length of the influence zone from the outer dike toe
The influence zone is defined as follows: if this zone is damaged by an indirect failure mode, for example a flow slide, the safety of the dike drops below the required safety level, considering all direct failure modes. At surface level the influence zone is confined by the influence lines (in Dutch: "invloedslijnen").
Schadelijksheidscriterium - Determination of the observation profile ("signaleringsprofiel") when a top revetement is present
In case no slope protection is present, if over the entire channel depth softening sensitive sand is present, this this margin is thus equal twice the fictive channel depth (M = 2 H), assuming that entire submerged consists of sand that is sensitive to liquefaction and/or breach flow.
The inclined part of the observation profile in line with the horizontal portion. The inclination of the slope depends on the channel depth:
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If the liquefaction point SZV is situated landwards of the observation point Ssign, the (so as in figure above), the criteria is not met, which means that the Global check PASSES. so go to step 1c.
If the liquefaction point SZV is not situated landwards of the observation point Ssign, the criteria is not met, so go to step 1c which means that the Global check PASSES.
Step 1b: Criterion on slope protection met (<1:2,5)?
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If this occurrence criterion not met, go to step 1e.
Step 1e: Is flow slide possible based on the occurrence criterion based on average geometry?
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Liquefaction flow criteria:
HR [m] is the fictitious height of the submerged slope in its most unfavourable situation during the assessment period and determined with:
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Other symbols in the figure below are (in Dutch):
LLWS LLWS meerjarig gemiddelde van het laagste springlaagwater ten opzichte van NAP, geldig in het kustgebied en de estuaria.
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OLR Overeengekomen Lage Rivierstand ten opzichte van NAP, geldig in het bovenrivierengebied (in Waal stroomopwaarts van Tiel), hetgeen overeenkomt met de Overeengekomen Lage Afvoer bij Lobith.
Breach flow criteria:
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- a slope with or without horizontal steps ("berms")
- the sand type:
- very fine sand with D50,5m ≤ 200 μm and D15,5m ≤ 100 μm
- medium fine sand with 200 < D50,5m ≤ 500 μm and 100 < D15,5m ≤ 250 μm
- coarse sand and gravel with Dwith D50,5m > 500 μm and D15,5m > 250 μm
where D15,5m and D50,5m 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.
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- the calculated diameter D50;5m if a Detailed check is performed
- the calculated diameter D15;5m and D5D50;5m is if an Advanced Breach flow check is performed
In case of a incoherence, the Overall result gives a Warning message.
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.
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NOTE: In case the user-defined sand type is "very fine sand", the breach flow criteria cannot be checked and the program gives always that . The program indicates breach flow is possible and a warning message will be given in the Overall Results window.
NOTE: Only the case "without horizontal steps" is implemented in D-Flow Slide.
Table A.4.2a from CUR113b, profile without horizontal steps:Table with th average and local slope
from depth | to depth z [m +GL(a)] | Average slope | |||
|---|---|---|---|---|---|
Medium fine sand D50 > 200 μm and D15 > 100 μm | Coarse sand/Gravel D50 > 500 μm and D15 > 250 μm | ||||
| Local slope | Average slope 0 - z | Local slope | Average slope 0 - z | ||
0 | -5 | 1:2 | 1:2 | 1:2 | 1:2 |
-5 | -10 | 1:3 | 1:2.5 | ||
-10 | -15 | 1:4 | 1:3 | 1:3 | 1:2.5 |
-15 | -20 | 1:5 | 1:3.5 | ||
| -20 | -25 | 1:6 | 1:4 | 1:4 | 1:3 |
| -25 | -30 | 1:8 | 1:4.67 | ||
| -30 | -35 | 1:10 | 1:5.43 | 1:6 | 1:3.75 |
| -35 | -40 | 1:10 | 1:6 | ||
(a) In D-Flow Slide, the ground surface level (GL) (maaiveld in Dutch) is the lowest level between the water level and the top of the channel slope (called "Insert river channel").
NOTE:
The above table is based on Table A.4.2a from CUR113b, In D-Flowslide only "without horizontal steps" are implemented, as defined in the CUR-report.