Leendert de BoerspolderFailure and pre-failure of a dyke on soft subsoilCristina Jommi, Elisa Ponzoni, Niccolo` Valimberti, Stefano Muraro,

Ludolph Wentholt, Henk van Hemert

2

Leendert de Boerspolder – HH Rijnland

A

C D?Test area

A polder protected by dykes, which had to be flooded, was offered to perform a full scale pre-failure and failure test to assess current models for the geotechnical response of the earth structure

3

Schematic Geotechnical Model

4

Design of the stress testWetting – staged excavation – staged pumping

5

Excavation 3: 12/10/2015Pumping 3: 14/10/2015

N.A.P. [m]

zpolder

water level0

- 1

- 2

- 3

- 4

- 5

- 6 m

dykematerial

peat

organic clay

0 5 m

N.A.P. [m]

zpolder

water level0

- 1

- 2

- 3

- 4

- 5

- 6 m

dykematerial

peat

organic clay

0 5 m

0.5 m0.5 m0.5 m

6

Main questions

Part I: FailureWhen did failure occur?What was the role of pore pressure?How accurately do current models for strength predict failure?

Part II: Pre-failureWhat material models fit the best the subsoil and material behaviour observed in the laboratory?Are laboratory tests representative of the behaviour of the material in the field?Can the pre-failure displacements and pore pressures be predicted accurately with current models?

7

Complementary questions

Part III: Geometry and Geotechnical modelDoes the true 3D geometry of the dyke influence significantly the response of the dyke during the stress test and at failure?

Can we get better prediction of pre-failure and failure including a 3D geometry of the geotechnical system?

Which elements of the models are most affected by uncertainty?

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Available informationGeometry, site investigation, laboratory data, and selected monitoring data on three cross-sections, complete stress test history

A

BC

D?

PwS8

EtS

StS

PtC1

PtC3

PtC2

PmC4

PmC5

PcC9

PcC6

PwC8

EtC

EmC

EcC

PtN1

PtN3

PtN2 Pm

N4

PcN7

PcN6

PmN5

PwN8

EtN

StC

StN

SmC

DPK101

DPK102

DPK103

DPK104

DPK105

DPK106

DPK107

DPK108

DPK109

DPK110

DPK111

DPK112

DPK113

DPK114

DPK115

DPK116

DPK117

DPK118

PB106

PBB

PBC

PBD

PtS1

PtS3

PtS2 Pm

S4

PcS7

PcS6

PmS5

Section South

Section North

Section Mid

0 5 10 15 20m0 5 10 15 20m

polder

canal

AREA B

inner slope

crest

of dy

ke

9

Site investigation: CPTu

A

BC

D?

SECTION SOUTH

PEAT

SILT-ORGANIC CLAY

CLAY

DYKE MATERIAL

0.01 MPa

fs0.01 MPa

fs

DPK1

01

DPK1

02

DPK1

03

DPK1

04

DPK1

05

DPK1

06

NAP

0.01 MPa

fs

0.01 MPa

fs

0.01 MPa

fs

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

12.0

13.0

14.0

15.0

16.0

17.00.01 MPa

fs

1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0 17.0 18.0 19.0 20.0 21.0 22.0

10

Laboratory testingSoil classification data, Triaxial CU, Direct Simple Shear, Constant Rate of Strain and Incremental Loading Oedometer Tests

A

BC

D?

11

Relevant monitoring dataInclinometers – Extensometers - Piezometers

0 1 2 3 4 5

m

0 1 2 3 4 5

m

12

AcknowledgmentsFounded in the framework of the STW “Reliable Dykes” research project by Water Boards and Provinces in The Netherlands