Group 2: Benchmarks from literature (approximate solution)

This section uses the results of a by-hand calculation performed for three profiles of the Spui dike project (see figure below):

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As the details of the calculation performed by hand are not available, those benchmarks are set in group 2.

2.1. Spui dike at km 63.9 (Nieuw Beijerland)

Description

The dike profile at hmp 63.9 is given in the figure below.

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• Water level: 0.9 m
• Required probability of failure of the dike: 1:4000
• Percentage probability of failure byliquefaction: 1 %
• Model factor: 1
• Area ratio (c = A₂/A₁): 1.4
• Standard deviation cot(gamma): 4.6
• Considered dike length: 100 m

Benchmark results

According to the by hand calculation, both Global and Advanced checks fail.

D-FLOW SLIDE results

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By lack of information, the following values are chosen:

• A state parameter (for Global step 5 and Detailed checks) of -0.05
• A critical retrogression length of 1 mlength of 34.353 m (which corresponds to the foreland length = 79.035 m - 44.682 m)
• A migration a migration velocity foreshore of 10 100 mm/year
• For the state parameter per layer, a value of -0.04 is used for sand layers and -0.06 for the other layers.

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Method	Benchmark	D-FLOW SLIDE	Relative error
Global check	FailedFailFailed	Fail	OK
Detailed check	FailedFailFailed	Fail	OK

2.2. Spui dike at km 65.0 (between Oud Beijerland and Nieuw Beijerland)

Description

The dike profile at km 65.0 is given in the figure below.

The soil profile and the material properties are the same as for the profile at km 63.9 (see paragraph 2.1).

Benchmark results

According to the by hand calculation, both Global and Advanced checks pass.

D-FLOW SLIDE results

By lack of information, the following values are chosen:

• A state parameter (for Global step 5 and Detailed checks) of -0.05
• A critical retrogression length of 10.930 m (which corresponds to the foreland length = 36.817 m - 25.887 m)
• A migration velocity foreshore of 100 mm/year
• For the state parameter per layer, a value of -0.04 is used for sand layers and -0.06 for the other layers.

D-FLOW SLIDE results are in not in accordance with the results by hand as show in the table below.

However, by lack of information about the hand calculation, it can't be concluded that the program gives incorrect results.

2.3. Spui dike at km 67.8 (oud Beijerland)

Description

The dike profile at km 67.8 is given in the figure below.

The soil profile and the material properties are given in the following table:

Benchmark results

According to the by hand calculation, the Global check fails and the Advanced check passes.

D-FLOW SLIDE results

By lack of information, the following values are chosen:

• A state parameter (for Global step 5 and Detailed checks) of -0.05
• A critical retrogression length of 42.098 m (which corresponds to the foreland length = 97.460 m - 55.362 m)
• a migration velocity foreshore of 100 mm/year
• For the state parameter per layer, a value of -0.04 is used for sand layers and -0.06 for the other layers.

D-FLOW SLIDE results differ from are in accordance with the results by hand for the Detailed check, as show in the table below. According to D-FLOW SLIDE, the Detailed check fails even if P(ZV) < P(ZV)_allowable .