Requirements on GI (Dr Poh TY)

7/24/2019 Requirements on GI (Dr Poh TY)

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Dr Poh Teoh Yaw

Deep Excavation and Geotechnical Department

Building Engineering Group, BCA

24 April 2015

Requirements on ground investigation and role of

ground investigation in geotechnical design



1. Introduction

2. Requirements on ground investigation

3. Determination of ground types in accordance toEC8

4. Case study on role of ground investigation in

geotechnical design

Contents

2



1. Introduction



4

Transition from BS to EC7

Ground investigation practices

“Malaysia and Singapore, and no doubt other countries,

will no longer be able to specify use of BS5930:1999 as

a basic standard for ground investigation because the

normal logging shorthand of weathering grades is not

part of the revised BS.” - Steve Hencher, professor, University of Leeds



5

Transition from BS to EC7

BS vs EC7

“As a code of practice, the British Standard takes the

form of guidance and recommendations in contrast to

specifications such as BSENISO14688-1;14688-2;14689-3, which take the form of requirements”



6

Ground investigation: EC7

General

1. Designers are responsible for the planning of thegeotechnical investigation and are accountable for their

decisions, i.e. specification of field and laboratory tests,

determination geotechnical design parameters and

characteristic values etc 2. Eurocodes require the rationale behind all geotechnical

parameters used for design to be justified and by inference

this extends to the way in which the parameters were

derived.3. Designer should make use of BS EN ISO 22475-1 to satisfy

themselves that they are comfortable with the sampling and

testing programme that they specify for individual projects



2. Requirements on ground

investigation in accordance to EC7



8

Applicable codes for ground investigation

Field and laboratory works

EC7 Part 2: Ground investigation and testingBS EN ISO 14688 Geotechnical investigation and testing — Identification & classification of soil

BS EN ISO 14689 Geotechnical investigation and testing — Identification & classification of rock

BS EN ISO 22475 Geotechnical investigation and testing — Sampling by drilling and excavation

and groundwater measurements

BS EN ISO 22476 Geotechnical investigation and testing — Field testing

BS EN ISO 22282 Geotechnical investigation and testing — Geohydraulic testing BS EN ISO 17892 Geotechnical investigation and testing — Laboratory testing of soil

BS1377 Parts that are not withdrawn

BS5930 1999: +A2 2010 revised and compliant to Euro codes

Competency criteria for personnel and companies

BS EN ISO 22475-2 – Qualification criteria for enterprises and personnel

BS EN ISO 22475-3 – Conformity assessment of enterprises and personnel by third party



9

Competency criteria for personnel and

companies

General

The Singapore NA to EN1997-2 says that EN 22475-2

and EN 22475-3, which give qualification criteria and

conformity assessment procedures for enterprises and

personnel involved in ground investigation “should befollowed in Singapore practice”.

This is the first time that a code has laid down

competency criteria for personnel and companies.



10


companiesPersonnel

• Qualified operator – documented competence based scheme for lead driller: Skills Evaluation

Certificate (Knowledge) [SEC(K)] for Soil Drilling & instrumentation, issued by the BCA• Responsible expert – degree with 3 years experience or diploma with 5 years experience;

sufficient proven knowledge; Sign the GI report

Companies

• demonstrate adequate competence and have adequate personnel and facilities

• items of equipment conforming to BS EN ISO 22475-1 correctly maintained and

calibrated

• a health and safety system; and

• a quality assurance system

Conformity assessment of enterprises and personnel by third party

• Accreditation scheme by third party

• Annual assessment

• Competency of enterprise and personnel



11


companies

ACCREDITATION OF INSPECTION BODIES FOR SITE INVESTIGATION

Assessment Criteria

An Assessment Team consisting of the Lead Assessor(s) and Technical

Assessor(s) will assess the quality management system and technical

competencies of the inspection bodies against current regulatoryrequirements and the following standards, technical note and accreditation

documents:

• ISO/IEC 17020: 2012 – General Criteria For The Operation Of Various

Types Of Bodies Performing Inspection

• SAC 01 - Terms And Conditions For Accreditation• IB 01 – Accreditation Process

• IB 02 – Fees Schedule

• Technical Note SI:01 - Specific Requirements For The Accreditation Of

Inspection Bodies For Site Investigation – Certified Course for SI Supervisor



12



13

• Singapore geology

• Roles and responsibilities

• Drilling, soil sampling, field test

methods and instrumentation

Topic:



14

Geotechnical categories

EN 1997-1 C2.1(8) to C2.1(21)

• To establish geotechnical design, structures are

classified into Geotechnical Categories 1, 2 or 3

according to:

- complexity of the structure,- complexity of the ground conditions

- complexity of the loading

- level of risk that is acceptable for the purpose of the

structure



15


Geotechn ical Categor ies related to geotech nical hazard and vulnerabil ity levels (Geotechn ical Design to Euroc ode 7; Orr & Farrell, 1999)

Factors to be

Considered

Geotechnical Categories

GC1 GC2 GC3

Geotechnical

Hazards/risk

Low Moderate High

Ground

conditions

Known from comparable experience

to be straightforward. Not involving

soft, loose or compressible soil,

loose fill or sloping ground.

Ground conditions and properties

can be determined from routine

investigation and tests.

Unusual or exceptionally difficult

ground conditions requiring non

routine investigations and tests.

Groundwater

situation

No excavations below water table,

except where experience indicates

this will not cause problems.

No risk of damage without prior

warning to structures due to

groundwater lowering or drainage.

No exceptional water tightness

requirements

High groundwater pressures and

exceptionally groundwater conditions,

e.g. multi-layered strata with variable

permeability.

Regional

seismicity

Areas with no or vary low

earthquake hazard

Moderate earthquake hazard

where seismic design code (EC8)

may be used

Areas of high earthquake hazard

Influence of the

environment

Negligible risk of problems due to

surface water, subsidence,

hazardous chemicals, etc

Environmental factors covered

routine design methods

Complex or difficult environmental

factors requiring special design

methods

Vulnerability Low Moderate High

Natural and sizeof the structure

and its

elements

Small and relatively simplestructures or construction.

Insensitive structures in seismic

areas

Conventional types of structureswith no abnormal risks

Very large or unusual structures andstructures involving abnormal risks.

Very sensitive structures in seismic

areas

Surroundings Negligible risk of damage to or from

neighbouring structures or services

and negligible risk of life

Possible risk of damage to

neighbouring structures or services

due, for example, to excavation or

piling

High risk of damage to neighbouring

structures or services



16

Local example: GC1

Description of category

Example of projects

GC1

small and relatively simple

structures:

for which it is possible to ensure

that the fundamental requirements

will be satisfied on the basis ofexperience and qualitative

geotechnical investigations;

with negligible risk.

Landed housing on shallow foundations in

firm residual soil;

Single storey sheds;

Link-ways;Minor roadside drain;




17

Local example: GC2


Example of projects

GC2

conventional types of structure

and foundation with no

exceptional risk or difficult

ground or loading conditions

- canal

- conventional buildings on

- shallow or raft foundations;

- pile foundations;

- walls and other structures retaining or supporting soil

or water < 6m height;- excavations < 6m depth

- bridge piers and abutments;

- embankments and earthworks;

- ground anchors and other tied-back systems;

- tunnels in hard, non-fractured rock/ competent soils,

and not subjected to special water tightness or other

requirements.




18

Local example: GC3


Example of projects

GC3

fall outside the limits of

Geotechnical Categories

1 and 2

- very large structure such as infrastructure projects for rail

and road tunnels

- utilities tunnels of more than 3 m in diameter - airport

terminal buildings

- foundation for building of 30 storey or more; - unusualstructures such as port structures in poor ground

conditions;

- structures involving abnormal risks such as dam, dikes

- GBW(ERSS) in close proximity to existing buildings

except for single unit landed housing development,

- unusual or exceptionally difficult ground such as

foundation in limestone areas for more than 6 storey orunusually loading conditions

-foundation for high-rise of more than 10 storey on

reclaimed land, or soft soils with combined thickness of soft

soils of more than 8 m

-GBW (ERSS) in soft soil ground conditions

- special buildings subjected to seismic risks (according

BC3);




19

Geotechnical investigations

EN 1997-1

EN 1997-2



20

Geotechnical investigations

EC7-1 Section 3: Geotechnical Data

EC7-2 Section 2: Planning of ground investigations

Gathering of all relevant information about the site

Ground investigation

Preliminary investigation (conceptual design) – desk

studies & site inspection

Design investigation (detailed design) – specify relevant

investigation methods i.e. field tests/ lab tests to justify

choice of foundations, geotechnical works

Control investigation (construction stage) - Verification of

choice of foundation method and design procedure,

control of ground improvement works and stability during

construction



21

Preliminary investigations

EN 1997-2 C2.3

• Assess suitability of site in comparison with alternative

sites

• Assess suitable positioning of structure

• Evaluate the possible effects of the proposed works onsurroundings, such as neighbouring buildings,

structures and sites

• Walk-over surveys, desk studies of previous site

investigations• Plan the design and control investigations



22

Design investigations

EN 1997-1 C3.2.3



23


EN 1997-2 C2.4

• To provide all the information required for the design oftemporary and permanent works

• Identify any difficulties that may arise during construction

• Include drilling, field tests, laboratory tests, groundwater

measurement



24


EN 1997-2 C2.4



25

Adequacy of boreholes investigation points

Suggested minimum number of boreholes for local practices

Structures Type Number of BH required

Buildings –

Up to 10 stories high

(excluding landed housings)

More than 10 stories high

15m to 40m grid, minimum 1 BH per block, and 3

BHs per site

10m to 30m grid, 1 BH per 300sqm, minimum 2

BHs per block, and 3 BHs per site

Large area ≤ 60 m grid per BH, at designer’s discretion

Roads, railways, canals, pipelines,

inland dikes

1 BH every 20 to 200m

ERSS, retaining wall < 6m high

ERSS, retaining wall >= 6m high



Tunnelling in built-up area

Tunnelling in green field area



Dam, costal dikes, weirs 1 BH every 25 to 75m along vertical sections

Road Bridges, tower stacks, heavy

machinery foundation

2 to 6 BHs per foundation

*GC3 projects should adopt the more onerous number of boreholes



26

Design investigations:- sampling

EN 1997-2



27

Design investigations:- sampling

EN 1997-2



28

Guide on ground investigation

GeoSS Guide



29

Guide on ground investigation

Reclassification of soil of soil and

rock from BS to EC

Suggested number of samples



30

FAQ

When should I adopt EC-compliant GI work?

All new ground investigation works carried out after 1Apr 2015 should be complied with EC standards.

Can I submit ST plan based on EC with GI report based on BS?

As ground investigation may be conducted in advance

of ST plan submission, designer may still submit ST

plan in EC with GI report based on BS. However,

designer need to produce an ground interpretative report based on EC and include it as part of their GDR.

All new ground investigation works carried out after 1

Apr 2015 should be based on EC standards.



31

How to select an EC-compliant company to carry out your GI work?

Designers to ensure that the GI firm is able to complywith EC on both field and laboratory requirements. In

additions, the firm is also able to meet the competency

criteria for personnel and companies.

Alternatively, designers may adopt firms accredited by

Singapore Accreditation council (SAC) under

accreditation scheme for “Accreditation Scheme for

Inspection Bodies for Site Investigation” Companies accredited by SAC for the above mentioned

scheme can be deemed as EC-compliant companies.

FAQ



32

FAQ

Can designer adopt existing GI report of immediate neighbour

plots for his EC design without the need to carry out borehole?

For GC1 project, where the values are obtained

from the GI of a neighbouring plot and issupplemented by available literature such as

geological map and or published ground

parameters, the determined characteristic value

should be reduced by a further factor of 1.2



33

FAQ

Can designer used existing GI report based on BS standard for his

EC design?

For project where the ground investigation was

conducted prior to 1 Apr 2015 based on British

Standard, the ground investigation still can be

used for plan submission. However, designersneed to produce an interpretive reports on design

parameters based on Euro codes and include

them as part of their GDR.

All new ground investigation works carried out after 1

Apr 2015 should be based on EC standards.

Q



34

FAQ

Which value should be reported in the borehole log, corrected or

uncorrected SPT N value?

Uncorrected SPT N value should be reported in the

borehole log.

Corrected SPT N value should be used when the

designer assessing the potential liquefaction of the

ground.



3. Determination of ground types inaccordance to EC8



36

Classification of ground types

Suggested investigation/tests for classification of ground types

Test Measurement/correlated value

Down-hole/cross-hole/PS logging seismic

wave test

Shear wave

piezocone test (CPTU)

(Note: should be carried whenever feasible for building of

important Class I)

In situ relative density

Correlated shear wave and

maximum shear modulus

In-situ permeability tests Field permeability

SPT tests SPT N value

in-situ density tests In-situ density

Laboratory tests; sieve analysis, Atterberg

limits, moisture content, specific gravity, bulk

and dry densities, and maximum and minimum

dry densities tests; constant head permeability

tests on sand, one-dimensional consolidation

tests on clayey soils, and unconsolidatedundrained (UU) triaxial tests on clayey soils

Basic soil properties



37


Suspension P-S velocity logging system

Cl ifi ti f



38

Ground types based

on EC8(+A1:2013)

Classification of

ground types

Cl ifi ti f d t



39



Cl ifi ti f d t



40

Worked example

Depth (m) Description of soil layer SPT

1.5 Fill 4 3.0 Fill 4

4.5 Firm sandy clay/silt 7

6.0 Firm sandy clay/silt 8

7.5 Firm to very stiff sandy silt 22



12.0 Firm to very stiff sandy silt 22 13.5 Firm to very stiff sandy silt 24








25.5 Hard sandy silt 42

27.0 Hard sandy silt 75

28.5 Moderately highly weatheredsandstone 100

30.0 Moderately highly weathered

sandstone 100


Soil profile

Cl ifi ti f d t



41

Worked example

Should equation (3-1) be also used for SPT N or cu values?


?

Cl ifi ti f d t



42

Worked example

Using SPT Using correlated Vs from SPT N values

Depth (m) Description of soil layer SPT Depth/SPT Average value

(m/s)

Depth/Vs Lower bound

value (m/s)

Depth/Vs

1.5 Fill 4 0.375 146 0.0102 146 0.0102

3.0 Fill 4 0.375 146 0.0102 146 0.0102

4.5 Firm sandy clay/silt 7 0.214 164 0.0092 164 0.0092

6.0 Firm sandy clay/silt 8 0.188 168 0.0089 168 0.0089

7.5 Firm to very stiff sandy silt 22 0.068 311 0.0048 259 0.0058



12.0 Firm to very stiff sandy silt 22 0.068 311 0.0048 259 0.0058 13.5 Firm to very stiff sandy silt 24 0.063 320 0.0047 266 0.0056








25.5 Hard sandy silt 42 0.036 384 0.0039 316 0.0048

27.0 Hard sandy silt 75 0.020 466 0.0032 378 0.0040


sandstone 100 0.015 512 0.0029 413 0.0036


sandstone 100 0.015 512 0.0029 413 0.0036

2.240 0.1132 0.1283

Avg SPT

13.4

265

m/s 234 m/s Class D

Class C

Class C


Cl ifi ti f d t



43


Sand Fill

Sand Fill

Sand Fill

Residualsoil

Residual

soil

Sample of shear wave

measurements usingPS logging in

compacted sand fill




44

Suggested notes for designer considerations:

The shear wave velocity is the preferred parameter if it is available.

• Most rational

• Provide the best estimate of the site class

Alternatively, test results from piezocone test (CPTu), SPT N profile orundrained shear strength profile in the upper 30m should be converted to

shear wave velocities for assessment of site class.

For soft clayey materials with SPT-N value less than or equal to 5, SPT N

values should not be used to derive shear wave velocities. This is because

for these soft clays the SPT N values are often very low (frequently zero)

and not representative for the strengths expected for these materials.





45

FAQ

Can designer used Singapore Geological Map for site classification?

The above example showed that for an area within the same geological

formation, there could be big variation in ground type classification. Assuch, the designer cannot just solely rely on the geological map.

Each project should use its own boreholes to determine the site

classification




4. Case study on role of groundinvestigation in geotechnical design

46

Adequacy of ground investigation




2 block of high-rise building

Stage investigation

Obstruction by existing buildings

Stage 1 investigation

Stage 2 investigation

47





Sufficient information for the intended design

GI for design of ERSS

GI for design of permanent structures

48





Boreholes

Probed holes

Use of probe holes to supplement boreholes

49




Case Study

Hard soil above

tunnel crown

Plan of cross passage

Section

Design of cross-passage: Original ground investigation BH1

TunnelTunnel CP


50




Plan of cross passage

Section

Design of cross-passage: Verification

by new boreholeBH1BH2

Weaker soilabove tunnel

crown

New borehole

TunnelTunnel CP


51



End of presentation

52

Documents

Requirements on GI (Dr Poh TY)