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Activity Name:

Full-scale piping experiments Hedwigepolder

Activity Numbre:

183

Activity type

Strength test

Involved Workpackage

Flood defences
Emergency response
Knowledge infrastructure

Objective

Piping experiments on a large scale to test the strength of tidal sand on backward erosion pipnig (BEP).

Activity Brief descriptor

Piping was initiated on two ajacent test-sites by infiltrating water into a completely enclosed body of tidal sand. This was done using infiltration tubes on one side of each test site, while at the other side a ditch was dug down to the tidal sand layer. By gradually increasing water levels in the tubes, an increasingly steep water pressure gradient was formed in the sand initiating backward erosion piping. The piping process was monitored using an array of techniques, including Electrical Resistance Tomography (ERT), Distributed Temperature Sensing (DTS), over 200 piezometers and infrared cameras. After the test the entire site was excavated to track the route of the pipe and to study the subsurface in detail.

Linked to theme(s):

Breaching
Animal- & vegetation-induced anomalies
Erosion processes
Temporary levee repairs
Levee survey & monitoring technique
Prolonged collaboration

Activity Time

Start Date:

June 1, 2020, 3:35 p.m.

End Date:

Nov. 30, 2021, 12:05 p.m.

Active time length:

Days:

None

Hours:

None

Other:

Location

Levee stretch:

Other

Coordinates/ Latitude (WGS):

None

Coordinates/ Longitude (WGS):

None

Coordinates/ Altitude (mTAW):

None

Descriptor:

Test location in hinterland along section XIII.

Other references:

Data

Data: 1

Data type: Factual report full-scale Piping experiments @Hedwigepolder and paper on monitoring set-up
Description: Factual report on Full scale piping experiments in the Hedwigepolder inclusing some prelimanary analyses results. Paper on the multi-monitoring approach as designed for the piping experiments as submitted for the 11th ISFMG '22 (London).
Date availability: Jan. 2, 2023
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Data: 2

Data type: 04_Monitoring piezometers (WSM) and standpipes (PB)
Description: Timeseries of piezometer and standpipe measurements including monitoring plan, installation report and description of data.
Date availability: Jan. 31, 2023
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Data: 3

Data type: 05_Monitoring AH-DTS
Description: Timeseries of AH-DTS measurements using fiber optic cables with active heating.
Date availability: Jan. 31, 2023
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Data: 4

Data type: 06_Monitoring ERT
Description: Timeseries and plots of ERT measurements.
Date availability: Jan. 31, 2023
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Data: 5

Data type: 07_Monitoring DTS (MOW)
Description: Timeseries of DTS measurements using fiber optic cable.
Date availability: Jan. 31, 2023
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Data: 6

Data type: 08_Monitoring IR (heat camera)
Description: Heat and video images during tests. Camera faced sandboil locations @ exit points.
Date availability: Jan. 31, 2023
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Data: 7

Data type: 09_Monitoring rainfall
Description: Timeseries of rainfall measurements.
Date availability: Jan. 31, 2023
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Data: 8

Data type: 03_Soil investigations incl. factual reports
Description: Soil investigations performed on and alongside the Sieperdadijk and hinterland in 4 different phases: different CPT-techniques (also temperature and piezo); HPT-(A)MPT; borings and geophysical survey (EM) results.
Date availability: Jan. 31, 2023
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Relationships with other activities

This activity has no relation with the other activities

Detaled information about the activity

Pre-conditions

Activity Descriptor

Equipments

Equipment: 1

For all equipment used in the Piping expeiments: see factual report of the piping tests. Detailed specifications are available on request at Fugro and Deltares.

Monitoring & Sensors

The piping process was monitored using an array of techniques, including Electrical Resistance Tomography (ERT), Distributed Temperature Sensing (DTS), over 200 piezometers, discharge meters and infrared cameras. After the test the entire site was excavated to track the route of the pipe and to study the subsurface in detail. The combination of different monitoring techniques will allow data fusion and will give complementary insight into the processes that led to piping.
A multi monitoring approach was implemented to steer and adjust the experiment, determine when pipe growth initiated, follow the pipe as it progressed in the subsoil and to analyse the outcomes of the experiment.

this activity does not have sensors

Limits

During Activity

Post-activity conditions

Immediate Results

Results /Conclusion

Full-scale piping experiments were conducted in the Hedwigepolder to determine the resistance of tidal sands to backward erosion piping. A multi monitoring approach was implemented to steer and adjust the experiment, determine when pipe growth initiated, follow the pipe as it progressed in the subsoil and to analyse the outcomes of the experiment. During construction of the piping experiment, extreme measures were taken to minimize the chance of leakage along the monitoring systems and the sheet piles. This paid off since no leakage was observed nor measured during both tests. The monitoring set up worked very well in general and the formation and growth of pipes have been recorded in detail. The monitoring results from the piezometers, ERT, and DTS are in agreement with each other on time and location of the backward erosion process. The results on location of the erosion pipe were validated in the post-test excavation where it was found that the measured path of the pipe matched perfectly with the location of the excavated pipe. Combination of these results give necessary, high-quality input to ultimately determine the resistance of tidal sands to backward erosion piping. The measured critical head for progressive BEP exceeded the calculated critical head using the Sellmeijer rule.

Infrastructure Knowledge

Tidal sand is more resistant to backward erosion piping (BEP) when compared with more homegenious fluvial deposits on which the current Dutch design rule for BEP is based (Sellmeijer 2011).
Critical gradient as calculated with current design rule was compared with measured critical head (progressive erosion process).

Other key information

Results of the full scale experiments are used to come up with a new approach (design rule / strength factor) in evaluating the risk of flooding caused by backward erosion piping (BEP) in tidal sands in the Netherlands.