LimitState:GEO

Eurocode 7 Colin Smith MA(Cantab) PhD Director & LimitState:GEO Product Manager , LimitState Ltd LimitState:GEO launch & technology briefing geo1.0

Contents

Eurocode 7

a. Introduction b. LimitState:GEO functionality c. Examples 20/05/2008 LimitState:GEO launch & technology briefing - ICE London

27/04/2020

Eurocode 7 Introduction

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Eurocode 7

• Eurocode 7 has been under development since 1980.

• Use of Eurocode 7 will be mandatory in the UK in 2010.

20/05/2008 LimitState:GEO launch & technology briefing - ICE London

Eurocode 7

Eurocode 7 moves away from: • working stresses, • overall factors of safety, to: • limit state design approach, • partial factors, • unified approach.

20/05/2008 LimitState:GEO launch & technology briefing - ICE London

Eurocode 7

It introduces a range of separate checks: • Ultimate Limit States (ULS) EQU : loss of equilibrium STR : failure of the structure GEO : failure of the ground UPL : failure by uplift HYD : hydraulic heave • Serviceability Limit States (SLS) 20/05/2008 LimitState:GEO launch & technology briefing - ICE London

Eurocode 7

In the UK the checks against failure in the ground (GEO) and in the structure (STR) must be checked using ‘Design Approach 1’ which specifies 2 calculations :   Design combination 1 Design combination 2 20/05/2008 LimitState:GEO launch & technology briefing - ICE London

Loads

Different factors are applied if loads are: • Permanent • Variable • Accidental Different factors are applied if loads are: • Favourable • Unfavourable i.e assist or resist collapse (this may not be clear at outset) 20/05/2008 LimitState:GEO launch & technology briefing - ICE London

Partial Factors

Permanent unfavourable load Variable unfavourable load Permanent favourable load

c'

tan 

' c

u Overall F.O.S

EC7 DC1 EC7 DC2 Conventional bearing capacity 1.35

1.5

1.0

1.3

1.0

1.0

1.0

1.0

1.0

1.0

N/A 1.0

1.25

1.25

1.4

N/A 1.0

1.0

1.0

1.0

2.5 – 3.0

BS8002 (Retaining walls) 1.0

1.0

1.0

1.2

1.2

1.5

N/A 20/05/2008 LimitState:GEO launch & technology briefing - ICE London

D

Example – footing design

G B Soil properties: c u = 70 kN/m 2 ,  = 20 kN/m 3 Geometry: D = 0.75m, B = 1 m 20/05/2008 LimitState:GEO launch & technology briefing - ICE London

D 20/05/2008

Example – footing design

G Soil properties: c  u = 70, = 20 kN/m 3 B Geometry: D = 0.75m, B = 1 m G fail /B = 5.14 c u +  D = 375 kN/m (unfactored) LimitState:GEO launch & technology briefing - ICE London

Design Combination 1

Design Combination 1

Factors are primarily placed on the loads and the soil properties are unfactored. Factor on: Permanent load = 1.35

Variable load = 1.5 Usually controls failure in the structure 20/05/2008 LimitState:GEO launch & technology briefing - ICE London

Design Combination 1

G D Factor on load = 1.35

B Factor on c u = 1.00

G fail = 278 kN/m = (5.14 x 70 + 0.75 x 20) / 1.35

20/05/2008 LimitState:GEO launch & technology briefing - ICE London

Design Combination 2

Design Combination 2

Factors are primarily placed on the soil properties and loads are unfactored. Factor on: c  tan  c u = 1.25

= 1.25

= 1.4

Usually controls failure in the ground.

20/05/2008 LimitState:GEO launch & technology briefing - ICE London

Design Combination 2

G D Factor on load = 1.00

B Factor on c u = 1.4

G fail = 272 kN/m = 5.14 x (70/1.4) + 0.75 x 20

c.f.

G fail = 278 kN/m for Combination 1 20/05/2008 LimitState:GEO launch & technology briefing - ICE London

Partial Factors

• Different factors are applied for different ULS cases • The purpose of the partial factors is to ensure the probability of failure is sufficiently low.

20/05/2008 LimitState:GEO launch & technology briefing - ICE London

EC7 Challenges

• Multiple ULS cases (e.g. GEO, STR, UPL) each with own set of partial factors • Use of multiple load types (Permanent, Variable, Accidental) • Favourable/unfavourable to be defined and… • Different failure modes to be checked (e.g. local/global, sliding/bearing etc) • Drained / undrained cases to be checked 20/05/2008 LimitState:GEO launch & technology briefing - ICE London

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LimitState:GEO functionality

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Load type specification

20/05/2008 LimitState:GEO launch & technology briefing - ICE London

Multiple scenarios

•

Choose to solve one or many scenarios in one go

•

Select partial factor sets

•

Set long term / short term (drained/undrained) solution mode

20/05/2008 LimitState:GEO launch & technology briefing - ICE London

Scenario solutions

20/05/2008 LimitState:GEO launch & technology briefing - ICE London

27/04/2020

Examples

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Analysis

• At this stage, LimitState:GEO was used to analyse the problem as described in the previous slides

(Hands on demo of Analysis

20/05/2008 LimitState:GEO launch & technology briefing - ICE London

Conclusions

• LimitState:GEO has been designed to maximise ease of use with Eurocode 7:  Permanent, variable and accidental load specification  Unfavourable/favourable load specification   User can specify any partial factor set Multiple scenarios can be solved together • The new unified approach in Eurocode 7 makes use of generic ULS analysis software such as LimitState:GEO directly applicable to all geotechnical problem types.

• Flexible approach makes it easy to utilise partial factors from other design codes.

20/05/2008 LimitState:GEO launch & technology briefing - ICE London

27/04/2020

Thank you for listening

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