Upload
hanhi
View
252
Download
2
Embed Size (px)
Citation preview
1
Session 5
Factors Affecting Eurocode 7Geotechnical Design Triangle
Associated CEN Standards
Implementation and Future Developmentof Eurocode 7
2
Session 5a
Factors Affecting Eurocode 7and
Geotechnical Design Triangle
3
3 Challenges in PreparingEurocode 7
To prepare a geotechnical standard that:
1. Harmonized geotechnical design with structural design - Consistent with EN 1990
2. Took account of special features of soil and geotechnical design
3. Was acceptable to the European geotechnical engineering community- Accommodated different national design practices
4
Consistent with EN 1990
Based on limit state design method
Have partial factors applied to characteristic values
Use partial action factors in EN 1990
Provide partial material factors
Characteristic value and partial factors reliability based
5
Special Features of Soil and Consequences for Eurocode 7
SoilNatural2 or 3 phase
Non-homogeneous
High variability
Frictional
High ductility
Compressible
Non-linear
SteelManufactured Single phase
Homogeneous
Low variability
Non-frictional
Less ductile
Non-compressible
Linear
Comparison between Soil and Steel
Consequences for EC7Properties determined not specifiedNeed to consider water as well as soil – effective stresses control behaviour Characteristic value not 5% fractile of test resultsNeed judgement selecting characteristic valueLoads affect resistances so need care factoring permanent loadsCauses load redistribution in structures so lower partial factors may be appropriate on structural loadsDesign often controlled by SLS – not by ULSSLS calculations often difficult – design using ULS calculation
6
National Design Practice
Throughout Europe, there are different national geotechnical design practices involving:
Ground investigation methodsSoil testing methodsGeotechnical design methods
Due to different:Ground conditionsClimatic conditionsDesign traditions
Due to different regulatory regimes and cultures, e.g.In Germany the calculation methods are prescribed in the national standardsIn the UK, the calculation methods are not prescribed and the standards have no legal status but codes represent good practice
Different design practices needed to be accommodated
National Design Practice accommodated by:Focussing on principles of geotechnical designAllowing each country to produce a National Annex with non-conflicting complementary information
7
Issues in Development of Eurocode 7
Six issues arose during the development of Eurocode7Scope of Eurocode 7
Definition of the characteristic value of a geotechnical parameter
Partial factor on permanent loads
Application of partial factors to material parameters or resistances
Treatment of water pressures and forces
Accommodation of national design practice
8
Scope and Style
Eurocode 7 differs from other Eurocodes in its scope and style because geotechnical design is different from structural design
The importance of geotechnical investigations and testing is emphasised
There is a Part 2 on “Ground investigation and testing”
There are no calculation models in the code text
Important statement in EC7 (2.4.1(2)) concerning knowledge of ground conditions and precision in calculation models:
It should be considered that knowledge of the ground conditions depends on the extent and quality of the geotechnical investigations. Such knowledge and the control of workmanship are usually more significant than is precision in the calculation models or the partial factors
9
Definition of the Characteristic Value
The definition of the characteristic value of a geotechnical parameter is given in Eurocode 7 (Clause 2.4.5.2(2)P):
The characteristic value of a geotechnical parameter shall be selected as a cautious estimate of the value affecting the occurrence of the limit state
The zone of ground governing the behaviour of a geotechnical structure at a limit state is usually much larger than a test sample or the zone of ground affected in an in situ test. Consequently the value of the governing parameter is often the mean of a range of values covering a large surface or volume of the ground. The characteristic value should be a cautious estimate of this mean value (Clause 2.4.5.2(7) – Application Rule)
Agreeing this definition for the characteristic value of a geotechnical parameter was important for the development of Eurocode 7 and was innovative, enabling Eurocode 7 to be consistent with the basis of design in EN 1990 for manufactured structural materials
Characteristic value is not the 5% fractile of a set of test results
10
Partial Factors on Permanent Loads
Originally a partial factor of unity on permanent loads was argued for geotechnical design by the Eurocode 7 committee
Based on geotechnical design experience, particularly in Denmark
Led to introduction of Design Cases A, B and C in ENV with partial factor of unity of on permanent loads for geotechnical designs to Eurocode 7 to be compatible with other structural Eurocodes using Case B with partial factor on permanent loads of 1.35
At the EN stage, Cases B and C became Design Approach 1, Combinations 1 and 2
11
Partial Factors on Material Parameters or Resistances
Partial factors to material parameters or resistancesRequired by some countries in order to have Eurocode 7 acceptedAccommodated by introduction of 3 Design Approaches
DA1DA2DA3
12
Treatment of Water Pressures and Forces
Water pressures and forces very important in geotechnical designs
Can be most significant
Led to introduction of two hydraulic failure ultimate limit states –UPL and HYD - with separate sets of partial factors
Although water pressures are forces, i.e. actions, it is often better to consider worst possible groundwater level – i.e. use a geometric allowance – rather than apply a partial factors to water pressures
This is an area of on-going debate
13
4 Aspects of Soil MechanicsProfessor John Burland, in his Invited Lecture on The Teaching of Soil Mechanics at the IX ECSMGE in Dublin in 1987, identified four aspects of soil mechanics which, by means of the Soil Mechanics Triangle, he showed were linked
The four linked aspects of Soil Mechanics are:
– The ground profile– Soil behaviour– Applied mechanics– Empiricism, well-winnowed
experience
• Well-winnowed experience is a metaphor from grain industry:– Separating grain (good) from chaff (bad) by a current of air– It is experience where only those practices that have proved to be successful and
reliable are retained while those that have proved to be not reliable are rejected
The Soil Mechanics Triangle
14
Interaction between Structural and Geotechnical Engineers
In 2006 Professor John Burland, in the context of a lecture on the interaction between structural and geotechnical engineers, expanded the Concept of the 4 Aspects of Soil Mechanics
Ground profileAdded
• Genesis/geology• Soil description
Soil behaviourAdded
• ObservationApplied Mechanics changed to Appropriate ModelAdded
• EvaluationEmpiricismAdded
• Precedent
GENESIS/GEOLOGY
IDEALISATION FOLLOWED BY EVALUATION
CONCEPTUAL OR PHYSICAL MODELLING ANALYTICAL MODELLING
LAB./FIELD TESTING OBSERVATION/ MEASUREMENT
PRECEDENT EMPIRICISM
WELL-WINNOWED EXPERIENCE
SITE INVESTIGATION SOIL DESCRIPTION
GENESIS / GEOLOGY
PRECEDENT
SOIL DESCRIPTION
EVALUATION
OBSERVATION
The Geotechnical Triangle
15
Geotechnical Design Components
displacements)(imposed loads or
Actions
movements
Geometry
Limiting values for
Ground properties
Code of Practice(safety factors)
Calculation model
Design
Geotechnical design components
GeometryGround propertiesActions (loads)Calculation models
All relevant limit statesULS and SLS
Safety elementsPartial factorsLimiting values of deformations
16
4 Aspects of Geotechnical Design
Similarly the components of geotechnical design can be grouped into 4 aspects:
Problem geometry– To which geometric allowances are applied
Loads and material properties (Actions and Resistances)– To which partial factors are applied
• Calculation models– To which model factors may be applied
• Relevant to all of these is the geotechnical complexity• To which is applied risk analysis• Comparable experience
17
The Geotechnical Design Triangle
Four Aspects of Geotechnical Design
Geometrical DataGround profile, structural dataNominal values, Geometrical allowances
Loads (Actions), Geotechnical ParametersGeotechnical investigations, Lab./field testing, Derived parametersCharacteristic values, Correlation factors
Limit State DesignConsideration of limit statesCalculations, Prescriptive measures,Load or model tests, An Observational methodPartial factors, Combination factors, Allowable deformations
Design ComplexityComparable experienceRisk assessmentGeotechnical Categories
- GROUND PROFILE - STRUCTURAL GEOMETRY
- CONSIDERATION OF LIMIT STATES - CALCULATIONS - PRESCRIPTIVE MEASURES - LOAD OR MODEL TESTS - AN OBSERVATIONAL METHOD
- GEOTECHNICAL INVESTIGATIONS - LAB./FIELD TESTING - DERIVED PARAMETERS
DESIGN COMPLEXITY
NOMINAL VALUES
GEOMETRIC ALLOWANCES e.g OVERDIG
GEOTECHNICALPARAMETERS
GEOMETRICALDATA
LOADS
- COMPARABLE EXPERIENCE
CHARACTERISTIC VALUES CORRELATION FACTORS, ξ
PARTIAL FACTORS, γ COMBINATION FACTORS, ψ ALLOWABLE DEFORMATIONS
LIMIT STATE
DESIGN
RISK ASSESSMENT
GEOTECHNICAL CATEGORIES
The Geotechnical Design Triangle
GROUND PROFILE /STRUCTRURAL DATA
NOMINAL VALUES/GEOMETRICAL ALLOWANCES
- GEOTECHNICAL INVESTIGATIONS- LAB./FIELD TESTING- DERIVED PARAMETERS
CHARACTERISTIC VALUES/CORRELATION FACTORS, ξ
PARTIAL FACTORS, γCOMBINATION FACTORS, ΨALLOWABLE DEFORMATIONS
- CONSIDERATION OF LIMIT STATES- CALCULATIONS- PRESCRIPTIVE MEASURES- LOAD OR MODEL TESTS- AN OBSERVATIONAL METHOD
RISK ASSESSEMENTGEOTECHNICAL
CATEGORIES
DESIGN COMPLEXITY
- COMPARABLE EXPERIENCE
18
Experience“Experience” is in both The Geotechnical Triangle and The Geotechnical Design Triangle
“Experience” is a term very commonly used term in geotechnics
However it is not well-defined
Eurocode 7 provides the following definition for comparable experience:
– Documented or other clearly established information related to the ground being considered in design, involving the same types of soil and rock and for which similar geotechnical behaviour is expected, and involving similar structures. Information gained locally is considered to be particularly relevant
Experience is linked to “Precedent”, which is also in the Geotechnical Triangle
Many existing national geotechnical codes contain valuable information and design practices that are based on national experiences – this is well-winnowed experience
It was considered important that this experience should not be lost with the introduction of Eurocode 7
Hence it has been agreed that the Eurocodes may be supported by national standard providing non-conflicting complementary information (NCCI)
19
Well-Winnowed Experienceand Eurocode 7
Since work on Eurocode 7 started in 1981, it has progressed through a number of stages
Model codeENV Stage (trial code)EN Stage
Many geotechnical engineersFrom different parts of EuropeWith different experiences
Many drafts preparedMany comments receivedMany design examples
Based on more geotechnical experience than any previous geotechnical code
Hence it is now well-winnowed
20
Discussion
Any Questions
21
Session 5b
Related CEN Standards
22
Related CEN Standards
Parts 1 and 2 of EN 1997 refer to many CEN standards for:Geotechnical investigation and testing
Execution of special geotechnical works
23
The CEN Standards for
Geotechnical Investigations and Testing
24
CEN and ISO StandardsCEN has three committees preparing standards covering different aspects of geotechnical engineering– TC 250/SC7: Geotechnical design
– TC 341: Geotechnical investigation and testing
– TC 288: Execution of special geotechnical works
Under Vienna Agreement, CEN and ISO (International Standards Organisation) cooperate in preparation of standards – i.e. do not produce separate standards for same area
– Hence some geotechnical and investigation standards are being produced by ISO TC 182: Geotechnics and are also being published as CEN standards
Many CEN geotechnical standards have already been published as ENs, and hence as Polish and other national standards, while others are still being prepared
25
Standards for Geotechnical Design and Investigation and Testing
TC 250/SC7: Geotechnical Design– 1997 Geotechnical Design 2 Parts
• Part 1: General rules• Part 2: Ground investigation and testing
TC 341: Geotechnical investigation and testing– 14688 Identification and classification of soil 3 Parts– 14689 Identification and classification of rock 2 Parts– 17892 Laboratory testing of soil 12 Parts– 22282 Geohydraulic testing 6 Parts– 22475 Sampling methods and groundwater measurements 3 Parts– 22476 Field testing 13 Parts– 22477 Testing of geotechnical structures 8 Parts
Total of 47 parts
26
CEN Standards forExecution of Special Geotechnical Works
TC 288: Execution of special geotechnical works13 standards:
– 1536 Bored piles– 1537 Ground anchors– 1538 Diaphragm walls– 12063 Sheet pile walls– 12699 Displacement piles– 12715 Grouting– 12716 Jet grouting– 14199 Micropiles– 14475 Reinforced fill– 14490 Soil nailing– 14679 Deep mixing– 14731 Ground treatment by deep vibration– 15237 Vertical drainage
Hence the total planned number of new CEN geotechnical standards from these three TCs is
– 2 (TC 250) + 47 (TC 341) + 13 (TC 288) = 62
27
Other Related CEN StandardsCEN has established four other committees whose work is related to geotechnical engineering– TC 89: Thermal performance of buildings– TC 154: Aggregates– TC 277: Road Materials– TC 396: Earthworks
TC 89 has produced one standard part:– EN ISO 13793 Thermal design of foundations to avoid frost heave 1 Part
TC 154 and TC 277 have produced many standards which have already been published as ENs
TC 396 only formed in 2009 and so has not yet produced any standards– 5 Working groups established
- General matters- Classification systems for Earthwork purposes and characterisation of
excavatability- Construction procedures- Quality control and monitoring - Hydraulic fill
28
Road Material and Aggregate StandardsTC 154 Aggregates
– 932 Tests for general properties of aggregates 6 parts– 933 Tests for geometrical properties of aggregates 11 parts– 1097 Tests for mechanical and physical properties of aggregates 10 parts– 1367 Tests for thermal and weathering properties of aggregates 6 parts– 1744 Tests for chemical properties of aggregates 6 parts– 13242 Aggregates for unbound and hydraulically bound materials
for use in civil engineering work and road construction 1 part– 13383 Armourstone 2 parts
TC 277: Road Materials– 13285 Unbound mixtures – specification 1 part– 13286 Unbound and hydraulically bound mixtures 20 parts
Part 1: Test methods for laboratory reference density and water content –Introduction, general requirements and sampling
Part 2: Test methods for the determination of the laboratory reference density and water content – Proctor compaction
Part 46: Test method for the determination of the Moisture Condition Value
TC 89, TC 154 and TC 277 give 64 more standard parts
29
Standards for Identificationand Classification of Soil
CEN ISO Standards3 parts of 14688: Geotechnical investigation and testing - Identification and classification of soil
– EN ISO 14688-1:2002/AC:2005 - Part 1: Identification and description– EN ISO 14688-2:2004 - Part 2: Principles for a classification– prCEN ISO/TS 14688-3 - Part 3: Electronic exchange of data on
(Under drafting) identification and description of soil
30
Standards for Identificationand Classification of Rock
CEN ISO Standards2 parts of 14689: Geotechnical investigation and testing - Identification and classification of rock
– EN ISO 14689-1:2003 - Part 1: Identification and description– prCEN ISO/TS 14689-2 - Part 2: Electronic exchange of data on (Under
drafting) identification and description of rock
31
Standards for Laboratory Testing of SoilCEN ISO Standards
12 parts of 17892: Geotechnical investigation and testing - Laboratory testing of soil
– Part 1: Determination of water content– Part 2: Determination of density of fine-grained soil– Part 3: Determination of particle density - Pycnometer method– Part 4: Determination of particle size distribution– Part 5: Incremental loading oedometer test– Part 6: Fall cone test– Part 7: Unconfined compression test on fine-grained soils– Part 8: Unconsolidated undrained triaxial test– Part 9: Consolidated trail compression tests on water-saturated soils– Part 10: Direct shear tests– Part 11: Determination of permeability by constant and falling head– Part 12: Determination of Atterberg limits
– All parts published as CEN ISO/TS with same date: 2004/AC:2005– CEN defines a TS as a normative document where the state-of-the-art is not yet
stable enough for confirmation as an EN
32
Standards for Geohydraulic Testing
CEN ISO Standards6 parts of 22282: Geotechnical investigation and testing - Geohydraulic testing
– Part 1: General rules– Part 2: Water permeability tests in a borehole without packer– Part 3: Water pressure test in rock– Part 4: Pumping test– Part 5: Infiltrometer test– Part 6: Water permeability tests in a borehole with packer and pulse -
litre stimulation
They have been published in 2008 (Parts 1 and 2) and in 2007 (Parts 3, 4, 5 and 6) by CEN as prEN (draft European Standard – a standard under development) and by ISO as DIS (Draft International Standard) for approval). They all have a Foreseen Date of Availability (FDAV) of 07-2010
Since the 22282 parts have not yet been published by CEN as ENs or TSs, they are not referred to in EN 1997 Parts 1 or 2
33
Standards for Sampling Methods and Groundwater Measurements
CEN ISO Standards
3 parts of 22475: Geotechnical investigation and testing - Laboratory testing of soil
EN ISO 22475-1:2006 Technical principles for execution
CEN ISO/TS 22475-2:2006 Qualification criteria for enterprises and personnel
CEN ISO/TS 22475-3:2007 Conformity assessment of enterprises and personnel by third party
34
Standards for Field Testing of Soil
CEN ISO Standards13 parts of 22476: Geotechnical investigation and testing: Field testing
– prEN ISO 22476-1 Electrical cone and piezocone penetration tests– EN ISO 22476-2:2005 Dynamic probing– EN ISO 22476-3:2005 Standard penetration test– prEN ISO/DIS 22476-4:2007 Ménard pressuremeter test– prEN ISO/DIS 22476-5:2008 Flexible dilatometer test– 22476-6 Self-Boring pressuremeter test– prEN ISO/DIS 22476-7:2008 Borehole jacking test– 22476-8 Full displacement pressuremeter test– prEN ISO/DIS 22476-9:2009 Field vane test– CEN ISO/TS 22476-10:2005 Weight sounding test– CEN ISO/TS 22476-11:2005 Flat dilatometer test– EN ISO 22476-12:2009 Part 12: 2004 Mechanical cone penetration test (CPTM)– 22476-13 Plate loading test
– The parts of 22476 are at different stages of development
35
Status of CEN/ISO Field Testing StandardsThree parts, 2, 3 and 12, as full EN standards
– 2: Dynamic probing– 3: Standard penetration test– 12: Mechanical cone penetration test (CPTM)
Two parts as CEN ISO TSs– 10: Weight sounding test– 11: Flat dilatometer test
Three parts as prEN and ISO/DIS, “Under approval” with Foreseen Dates of Availability (FDAVs)
– 5: Flexible dilatometer test - FDAV 11-2010– 7: Borehole jacking test - FDAV 11-2010– 9: Field vane test - FDAV 01-2012
One part as prEN and ISO/DIS, “Under approval” with no FDAV– 4: Ménard pressuremeter test
One part as prEN ISO “Under drafting” with an FDAV– 1: Electrical cone and piezocone penetration tests - FDAV 01-2012
Three parts not yet listed by CEN– 6: Self Boring pressuremeter test– 8: Full displacement pressuremeter test– 13: Plate loading test
36
Execution Standards13 standards with the umbrella title Execution of special geotechnical workshave been prepared by TC 288 and published by CEN– EN 1536:1999 Bored piles– EN 1537:1999/AC 2000 Ground anchors– EN 1538:2000 Diaphragm walls– EN 12063:1999 Sheet pile walls– EN 12699:2000 Displacement piles– EN 12715:2000 Grouting– EN 12716:2001 Jet grouting– EN 14199:2005 Micropiles– EN 14475:2006/AC:2006 Reinforced fill– FprEN 14490 Soil nailing– EN 14679:2005/AC:2006 Deep mixing– EN 14731:2005 Ground treatment by deep vibration– EN 15237:2007 Vertical drainage
All parts are current ENs except 14490 Soil Nailing, so should be national standards Status of 14490 is “Under approval” and FDAV is 05-2010The execution standards have only been published by CEN, not by ISO, and so are not under the Vienna Agreement
37
Standards for Testing of Structures
EN ISO Standards
8 parts of 22477: Geotechnical investigation and testing - Testing of geotechnical structures
– ISO/DIS 22477-1 Pile load test by static axially loaded compression test – 22477-2 Pile load test by static axially loaded tension test – 22477-3 Pile load test by static transversely loaded tension test – 22477-4 Pile load test by dynamic axially loaded compression test – prEN ISO 22477-5 Testing of anchorages – 22477-6 Testing of nailing – 22477-7 Testing of reinforced fill – 22477-8 Pile testing - Statnamic testing
All parts of 22477 are under development. Only Part 5 listed on CEN website and listed as “under drafting”
Not referred to in EN 1997 Parts 1 or 2
38
CEN Standards Referred to in Eurocode 7
Part 1: Geotechnical design– EN 1536 Bored piles
– EN 1537 Ground anchors
– EN 12063 Sheet pile walls
– EN 12699 Displacement piles
– EN 13793 Thermal design of foundations to avoid frost heave
Part 2: Ground investigation and testing– EN ISO 14688 Identification and classification of soil (Parts 1 and 2)
– EN ISO 14689 Identification and classification of rock (part 1)
– EN ISO 22475 Sampling methods and groundwater measurements (Part 1)
– EN ISO 22476 Field testing (Parts 1, 2, 3, 4, 5, 6, 8, 9, 12, 13)
39
Conclusions
Eurocode 7 will become the geotechnical design code for all public works in Europe from March ’09
Many supporting referenced CEN investigation, testing and execution standards have already been published as national standards
Existing standards will no longer be maintained but may be revised to provide NCCI
40
Session 5c
Implementation and Future Developmentof Eurocode 7
41
Implementation of Eurocode 7
To use Eurocode 7 (EN 1997) in practice, each country has to select values of the partial factors for geotechnical designs in its country
These, and any other aspects of Eurocode 7 left for national determination – e.g. which Design Approach to use - are known as nationally Determined Parameters – NDPs
The NPDs are published in a country’s National Annex to a Eurocode
42
Planned Implementation of the Eurocodes
Plan:From 31st March 2010 the Eurocodes will be implemented in all 29 CEN countries as national standards, with National Annexes giving the nationally determined parameters (NDPs) - next month !
Eurocodes will supersede and take precedence over existing national geotechnical standards
Hence, from 31st March 2010, all publicly funded projects must be designed to the Eurocodes
It is likely that all private projects will also be designed to the Eurocodes after 31st March 2010
Existing national standards may be revised to provide non-conflicting complementary information (NCCI)
It is intended that most of the other CEN standards referred to in the Eurocodes will also be published as national standards by 31st March 2010
43
Actual Implementation of Eurocodes
Joint Research Council (CEN and EU) set up to manage the implementation of the Eurocodes is determined to implement them on 31st March 2010
BUT Austria and Germany (and other countries?) have requested a postponement of the date of withdrawal of existing standards due to:
the many corrigenda and amendments that have been made to the Eurocode parts since they were published, and
the need to have so many supporting CEN supporting standards to be implemented as national standards
44
Selection of DAs by 29 CEN Countries
after Schuppener, July 2008
Total
Slopes
Retaining structures
Piles
Shallow foundations
DA3DA2*DA2DA1ALLNo or
Incomplete answers
Design Situation
IRL
IRL
IRL
IRL
BG, CY, CZ, IS, LV, H, MN
EST, F, I
L, SF
A, D, E, GR, PL, SK, SLO CH, DK, NL, S
NA
NL, S, SK
E, FB, EST, LT, P, UK
A, CH, D, E, EST, F, GR, I, L, NL, PL, S, SF, SK, SLO
A, CH, D, GR, L, NL, PL, RO, S, SF, SK, SLO
B, I, LT, P, RO, UK
B, LT, P, RO, UK
A,CH, D, E, EST, F, GR, L, SF, SLO
7 1 5-6 2-16 4-14
DK
DK
DK
DK
B, LT, RO, P, UK
* Partial action factor applied to action effect rather than to the actions
PL
PL
PL PL
45
Thank You
Thank you
Any questions?
Discussion
46