...
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
- in case
...
- a revetment: M = Max [ Mbestorting - Linfluence; 2 Honbest) ]
...
- (see also figure below)
where:
Hgeul is the channel depth in case no revetment is present and H = 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:
...
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)?
...
This check should be performed only if the damage criterion (step 1a) is not met (i.e. a flow slide does not lead to damage). The result of this check will not result in a "failure" in the safety assessment, but only indicates that the slope protection may become unstable.
As this check has no influence on the final answer, it is therefore not performed and the answer is always "Not available".
Step 1c: Artificially underwater installed and non-compacted sandy foreland ?
...
A flow slide can occur if one of the two following conditions is met:
- The Liquefaction is possible: the total slope (channel edge-channel bottom) is on average steeper than or equal to 1 : [7 × (HR/24)(1/3) ], in which HR is defined below.
- Breaching is possible (: see paragraph below called "Breaching Breach flow criteria")
If the criteria of occurrence is met, the Global check FAILS and it should be switched to the Detailed method.
If the criteria of occurrence is not met, the Global and the Overall checks SUCCEED.
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:
in which:
(with hdijk is dike height)
In which::
Hgeul depth of the channel [m]
Δhonder height of the slope above the water level during extreme low water: “niveau van geulrand” – “niveau LLWS/OLW/OLR” [m]
hdijk height of the levee with respect to the outer toe of the levee [m]
B width of the foreland. In case of a so-called "schaardijk", B = 0 [m]
cot(α) cotangent of the slope α [-]
αR slope angle of the schematized fictitious under water profile [degrees]
αboven slope of the outer slope of the levee [degrees]
α’boven slope between incision of channel and the fictitious outer crest of the levee with a height of 2.hdijk In case of a "schaardijk", α’boven = αboven [degrees]
Other symbols in the figure below are (in Dutch):
LLWS meerjarig gemiddelde van het laagste springlaagwater ten opzichte van NAP, geldig in het kustgebied en de estuaria.
OLW Overeengekomen Laag Water ten opzichte van NAP, geldig in het benedenrivierengebied (in Waal stroomafwaarts van Tiel).
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:
This criterion is adopted from step 5 of CUR Aanbeveling 113, 2008.
...
- 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.
...
- 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.
...
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: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.4.2b 2a from CUR113b, profile with flat berms:
...
from depth
[m +GL(a)]
...
to depth z
[m +GL(a)]
...
0
...
Z1
...
10
...
1:2.5
...
15
...
1:3
...
20
...
1:3.5
...
25
...
1:4
...
30
...
1:4.67
...
35
...
1:5.43
...
40
...
, In D-Flowslide only "without horizontal steps" are implemented, as defined in the CUR-report.