Earthquake resistant design of levees and adjacent sheet piling

Marcel Visschedijk

Proven earthquakes damage to levees

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Especially if sand in or under the levee liquefies

All pictures from: Y. Sasaki et al. / Soils and Foundations 52 (2012) 1016–1032

Damage caused by liquefaction

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Damage caused by liquefaction

Kobe, picture from http://geot.civil.metro-u.ac.jp/archives/eq/95kobe/index.html

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Proven earthquakes damage to levees

Slide from: Presentation of Ikuo Towhata, at the Second International Conference on Performance‐Based design in Earthquake Geotechnical Engineering, Taormina, Italy on May 29, 2012

Proven earthquake damage in the Netherlands

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Roermond, 1992 (magnitude 5.8)

All pictures from: beeldbank.rws.nl

Groningen levees

Questions for the 2013 study*: • Show the current state of the primary and

regional defences • Give an indication of the required

improvement, differentiating between the situation without and with earthquakes

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Continued studies in 2014/2015 on most critical stretches: • Eemskanaal: levees and sheet-piling • Eemshaven-Delfzijl

*http://www.rijksoverheid.nl/onderwerpen/aardbevingen-in-groningen/documenten-en-publicaties/rapporten/2014/01/17/deltaers-effecten-van-aardbevingen-op-kritische-infrastructuur.html

Important questions for EQ resistant design

• Which mechanisms to consider and which (software) models to use

• Which loading to apply

• (How to reduce liquefaction, or minimize its effect)

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PGA

T

(Picture from: Y. Sasaki et al.)

(Picture from: Y. Sasaki et al.)

(Picture from: I. Towhata)

Further content of the presentation

• Which mechanisms to consider • Recently applied software models for the Groningen levees

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Mechanims caused by earthquakes

• Instability or damage by earthquake force

• Crest settlement or damage by liquefaction of sand

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Content of the presentation

• Which mechanisms to consider • Recently applied software models for the Groningen levees

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AAD: dedicated software for embankments

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AardbevingsAnalyse Dijken

Input: D-Geostability schematizations + cone resistances Output: Fragility curves

AAD v1: Applied Peak Ground Acceleration

Along Eemskanaal

00

01

02

03

04

05

06

07

1 10 100 1000 10000

km31.5

Along Eemshaven-Delfzijl PGA [m/s^2]

Return period [year]

• Probability distribution According to KNMI • Semi-probabilistic determination of design value

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PGA [m/s^2]

Return period [year]

AAD v2: Nonlinear Soil Response

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AAD: Applied Liquefaction model

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EERI MNO-12*: Determines the excess pore pressure ratio 𝑟𝑢= Δ𝑢

𝜎 𝑣.0′ in clean sand as a function of

field stresses, CPT resistance (𝑞𝑐) en Peak Ground Acceleration (PGA)

Example: Sand layer of 10m, without cover layer: 𝑟𝑢 5m below surface

* Idriss, I.M. and Boulanger, R.W., 2008, Soil liquefaction during earthquakes, EERI MNO-12

𝑞c = 12 Mpa 𝑃𝑃𝑃 = 0.1𝑔

Empirical cyclic shear stress ratio resistance

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AAD: models for the embankment

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Displacement by sliding

Settlement by squeezing

Settlement by compaction

F

Displacement by sliding

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Force = Mass * Acceleration Displacement above yield value by double integration

“Newmark Sliding Block” – also mentioned in EC8

Criterion: maximum sliding displacement = 0.15m (Jibson*)

For design: inverse application to determine the critical acceleration value where static stability with D-Geostability has to be preserved to keep displacement below criterion.

* Jibson, R.W., 2011, Methods for assessing the stability of slopes during earthquakes—A retrospective: Engineering Geology, v. 122, p. 43-50.

Displacement by sliding in case of liquefaction

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Reduced tangent of the angle of friction tan(𝜙) by (partial) liquefaction • 50 % reduction during earthquake: tan𝜙reduced = 1 − 0.5ru ⋅ tan𝜙initial • 100 % reduction after earthquake: tan𝜙reduced = max (0.06, 1 − ru ⋅ tan𝜙initial) (analogous to draft Dutch National Application Document – NPR 9989)

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Scaling of measured accelerogram

Derivation of (horizontal) design accelerograms

1. EC8: use at least 3 representative ground signals (4 used)

2. Scale measured signals for acceleration and time* with the Peak Ground Acceleration ratio: 𝑃𝑃𝑃design/𝑃𝑃𝑃measured

PGA

Crest settlement by squeezing

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h_levee

d_top

d_liquefied

Finite Element results were used to fit an approximate (!) function between crest settlement and ℎlevee ⋅

𝑑liquefied𝑑top2 (inspired by Finn*)

* Finn, W. (2000). State-of-the-art of geotechnical earthquake engineering practice. Soil Dynamics and Earthquake Engineering, 20, pp 1-15.

Crest settlement by compaction

Accepted empirical function of cyclic Factor of Safety against liquefaction and Relative Density 𝐷𝑟 (based on Ishihara & Yoshimine*)

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* Ishihara, K., & Yoshimine, M. (1992). Evaluation of settlements in sand deposits following liquefaction during earthquakes. Soils and Foundations, Vol. 32, No.1, March 1992, pp 173-188.

Factor of safety is cyclic shear ratio (CSR) divided by cyclic resistance ratio (CRR)

Example of resulting Fragility Curves

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FoS Slope Stability versus PGA

Crest Settlement versus PGA

Models for Sheet-Piling: before and after EQ

Before earthquake: D-Sheetpiling

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After earthquake: D-Sheetpiling with 100 % reduced strength by (partial) liquefaction

Models for Sheet-Piling: during EQ

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Comparison of bending moments between generalized Mononobe-Okabe method (also suited for cohesive soil) and Finite Element Method (FEM)

FEM is preferred: Mononobe-Okabe method is too conservative, and not able to find solutions for larger PGA values

M-O

M-O

M-O

FEM

• Used to derive an approximate factor between static and dynamic moments and anchor forces (load and site specific)

• Liquefaction modeling by manual strength reduction (using 50 % of the final 𝑟𝑢) in combination with (damping) Hardening Soil Small Strain model

• In progress: comparison with implicit pore pressure generation by

constitutive models such as UBC-Sand or Hypoplasticity.

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Current usage for Groningen levees:

Dynamic FEM for sheetpiling during EQ

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Dynamic FEM for sheetpiling during EQ

Derivation of (horizontal) base acceleration

1. EC8: use at least 3 representative ground signals (4 used)

2. Translate measured surface signals to the base at the location of the measurement, using the local soil profile and for example the EERA* software

3. Scale the base signals for acceleration and time with the ratio 𝑃𝑃𝑃design/𝑃𝑃𝑃measured (see Newmark Sliding Block)

*A Computer Program for Equivalent linear Earthquake site Response Analyses of Layered Soil Deposits. Bardett et all, 2000

surface base

Finite Element simulation of liquefaction

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• Hypoplasticity model is more generic than UBC-Sand model (initial state, different CSR values), but parameter determination is more difficult

• Models are sensitive to variations of dominant parameters (HP: blow count, UBC-Sand: initial void ratio)

• Current models can determine the undrained onset of liquefaction, but don’t supply reliable post-liquefaction deformations

Cyclic DSS test simulation on Loose sand

0.08

0.1

0.12

Green: UBCSAND Green: Hypoplastic

Excess Pore Pressure Ratio

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Shear Stress Ratio

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Expected further application of Finite Elements

• Liquefiability of Groningen sand with “single pulse” signals, compared to tectonic signals

• Nonlinear response of subsoil plus levee, incl. pore pressure

generation • Effectivity of mitigating measures

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