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Advances in Field Testing Methods and Code of Practice

Prof. V.S.Raju

(Formerly: Director, IIT Delhi & Professor and Dean, IIT Madras)

Email: rajuvs_b@yahoo.com 1 Prof. V.S. Raju

Started in 1965, as a doctoral student in University of Karlsruhe Germany. The Consultancy services involved a variety of projects all over the

country and abroad.

Fertilizer plants, Power Stations, Harbour structures involving all major ports in the country, Airports, Residential Towers and Industrial Structures.

Consultant to Larsen & Toubro, ECC for over 35 years.

With APGENCO, for all their Power Stations for 30 years

Expert Consultant to Hyderabad Metro on Foundations.

Over the last 3 years, to 30 Gated Communities in the NCR Region, Delhi.

My background as a Foundation Consultant over 45 years

Prof. V.S. Raju

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GEOTECHNICAL DESIGN

Extract from Eurocode 7,

BS EN 1997-1:2004 The provisions of this standard are based on

the assumptions given below:

1.Data required for design are collected, recorded and interpreted by appropriately qualified personnel;

2.Structures are designed by appropriately qualified and

experienced personnel; 3 Prof. V.S. Raju

3. Adequate continuity and communication exist between the personnel involved in data collection, design and construction;

4. Adequate supervision and quality control are provided in

factories, in plants, and on site; 5. Execution is carried out according to the relevant standards

and specifications by personnel having the appropriate skill and experience;

6. construction materials and products are used as specified in this standard or in the relevant material or product specifications;

Continued….

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Continued….

7. The structure will be adequately maintained to ensure its safety and serviceability for the designed service life;

8. The structure will be used for the purpose defined for

the design. 9. These assumptions need to be considered both by the

designer and the client. To prevent uncertainty, compliance with them should be documented, E.g. in the geotechnical design report.

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Eurocode 7 is the latest and best code of practise. It helps in evolving Optimum Designs –Safety and Economy Ensuring this standard will benefit India significantly

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Planning Subsoil Investigation

• Number of Boreholes • One for each important structure

• Information for every 50m of loaded area

• Borehole for medium size structure only if variations

• Few boreholes for future expansion

• Depth of Boreholes • 1.5 to 2 times times the width of foundation

• Few up to hard strata( N > 100 ) or rock

• 5 to 10m beyond foundation level on rock

Selection of Agency

• Not by lowest quotation

• Short listing of Agencies based on equipments’ condition and laboratory

facilities

• Qualified/Trained manpower

• Constant supervision at site

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Methods of Investigation

• Open Pits

• Bore Holes

• Geophysical Investigation

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QUALITY OF INVESTIGATION

High quality is the very basis for excellence in practice.

In spite of detailed standard specifications (IS-codes), the range of practices vary very widely in the country.

For field investigations, most primitive to fairly sophisticated equipments are in use. Unfortunately, in majority of cases the practice is nearer to the primitive. Similarly laboratory testing practices vary widely, with little or no

standardization.

GEOTECHNICAL INVESTIGATIONS

Prof. V.S. Raju

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World Standard India o Poor quality of the equipment.

o Wash Boring mostly,

o SPT Equipment - manual operation

o Conventional static cone penetration equipment.

o Highly sophisticated and mechanised equipment.

o Continuous core sampling (in soils as well).

o SPT equipment with automatic hammer release.

o Static cone test with electric cone and piezocone

QUALITY OF INVESTIGATION

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Pic.1.1. Non Standard Equipment

No safety measures Prof. V.S. Raju

Pic. 1.2 International Standard

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Pic. 1.3 SPT Hammer Dropped Manually (2013)

Pic. 1.4. SPT with Auto Trip Hammer + Standard Rig

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Pic.1.6 Static Cone Penetration - Reaction with Sand bags

Pic. 1.7 Crawler Mounted SCPT Equipment

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CPT Truck

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Prof. V.S. Raju

Pic. 1.8 Electric Cone plus pore pressure sensor

Pic. 1.7 Conventional Static Cone Penetrometer-

Mechanical Cone 21

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Dimensions of Platform: 18mx8m

Counter weight = 10 ton

Diameter of Counter weight = 3.4 m

Counter Weight - Tower

Control room

Marine cone penetration system

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Insufficient Appreciation with regard to the Quality and Importance of Soil Investigation at all Levels. Responsibility Geotechnical community of the country; it is a major failure on our part.

Owners, Structural Consultants – Lack of appreciation.

Whole hearted commitment towards excellence needed.

MAIN PROBLEM

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Benefits of Good Quality Investigations Factor of Safety adopted in Pile Foundations

Based on Initial Pile Load Tests

Implication: For the same situation as per IS, We provide 33 % more number of piles.

Pile Capacity

Minimum Factor of Safety

IS:2911 Eurocode 7 (Simplified)

2 1.5

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Case Study

Terminal T3 at Delhi International Airport

• Terminal T1 was on Pile Foundation

• T3 was originally planned with Pile Foundation. However later changed to a raft through reassessment.

• Additionally 2 footing load tests (1.5 m x 1.5 m) were conducted at Founding Level.

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Results of Footing Load Tests for Delhi International Airport

1st Footing load test:

Soil type = Sandy silt

SPT N = 50

Size of footing = 1.5 m x 1.5 m

For q = 40 t/m2 = 4 Kg/cm2,

Settlement (S) = 4 mm

𝑬𝒔 = 𝟒 ∗ 𝟏𝟓𝟎 𝟏− 𝟎.𝟑𝟐

𝟎.𝟒 * 0.82

= 1119 Kg/cm2

As per Shultze and Muhs for SPT N = 50

Es = 800 Kg/cm2

Ratio = 1119/800 = 1.4

0

5

10

15

20

25

0 10 20 30 40 50 60 70 80 90

Sett

lem

ent

(mm

)

Load Intensity (t/m2)

Load Vs Settlement Curve for DIAL

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Pic. 1.5 Bent SPT Sampler

In one of the sites in 2013

Prof. V.S. Raju

Project: 10 Towers, 15 storeys each

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Source of Disturbance

• During drilling operations

• Improper cleaning of the borehole bottom

• During driving of the sampler tube

• Stress release due to removal of overburden

• During ejecting the sample from sampling tube

• During storage of sample

• During preparation of sample for testing

2nd Footing load test:

Type of soil = Silt with fine sand

SPT N = 22

Size of footing = 1.5 m x 1.5 m

q = 38 t/m2 = 3.8 Kg/cm2

Settlement (S) = 5.4 mm

𝑬𝒔 = 𝟑. 𝟖 ∗ 𝟏𝟓𝟎 𝟏− 𝟎.𝟑𝟐

𝟎.𝟓𝟒 * 0.82

= 787 Kg/cm2

As per Shultze and Muhs for

SPT N = 22

Es = 530 Kg/cm2 Ratio = 787/530 = 1.48

0

5

10

15

20

25

0 10 20 30 40 50 60 70 80

Sett

lem

ent

(mm

)

Load Intensity (t/m2)

Load Vs Settlement Curve for DIAL

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S. No SPT N Es in kg/cm2

As per Bowles

book

As per IS Code

As per Schultze

and Muhs

From Footing

Load test at DIAL

1 50 208 820*** 800 1119

2 22 118 710+++ 530 787

Es values calculated from Bowles book are for corrected N values. ***However, for the same N value at a depth of 8 m, the Es value would be only 400 kg/cm2 as per IS. +++ However, for the same N value at a depth of 8 m, the Es value would be only 320 kg/cm2 as per IS.

Comparison of Soil Modulus (Es) values in kg/cm2 from SPT correlations and from load test results:

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Delhi Airport – T3

• Based on these results, Raft Foundation was found fully satisfactory and adopted.

• 6 months of Time Saving – A huge advantage, on total investment of 12,000 crores.

• Direct cost savings as well.

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As compared to a full pile solution, pile assisted raft has a major advantage of substantial reduction in number of piles, which in turn results in savings of cost and time.

It also to some extent removes uncertainties associated with bored piles and driven cast in situ piles. Extensively used world wide.

PILED RAFT

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Conventional Pile Design Method

Disregards the capacity of Pile caps/Rafts

Increased number of piles or length of piles

Very small allowable settlement

Pile factor of safety (FS ≈ 2)

Piled Raft Design Method

Raft is the main bearing element

Design for full utilization of pile capacity (FS ≥1)

Piles are Settlement reducers

Consideration of the optimal location of piles to decrease the

differential settlement and bending moment of raft.

Design Philosophy of Piled Rafts

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Concept of Piled Raft :

• A very good reference

“The Piled Raft Foundation for The Burj Dubai – Design and

Performance “, IGS-Ferroco Terzaghi Oration – 2008, by Prof.Harry

Poulos.

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Fig. 1 Load settlement curves for piles and Raft on cohesion-less soils. Rafts have large settlements before failure (sands & non plastic silts)

Loa

d (

t)

Settlement (mm)

RaftPiles

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Schematic Model of Burj Kalifa on Piled Raft World’s tallest building. 160 storey high rise tower.

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As per IS – 1904, 1986 (Reaffirmed1995): For spread foundation resting on Sand and Hard clay

Permissible settlements:

Type of structureIsolated

foundationRaft

foundationFor reinforced concrete structures 50 75

Maximum settlement (mm)

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Structure

Messe Torhaus Messeturm

DG-Bank (Westend Strasse 1)

American Express

Max Height above ground surface (m)

130 256.5 208 74.7

Basement floors 0 2 3 4 Foundation area (m2) 2 x 430 3457 2940 3570 Foundation level below GL (m)

-3 -14 -12.0/-14.0 -14

Raft thickness (m) 2.5 3.0-6.0 3.0-4.5 2 Number of piles 2 x 42 64 40 35 Observed pile load (MN) 1.7-6.9 5.8-20.1 9.2-14.9 2.7-5.1

Observed Max. settlements (mm)

150 144 110 55

Details of piled raft foundation of the buildings in Germany (Katzenbach,et.al., 2000)

Contd…

Settlement Observations from Literature

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Structure Taunustor Japan-Centre

Forum(Kastor and pollux)

Congress centre Messe

Frankfurt

Main Tower

Eurotheum

Max Height above ground surface (m)

115.3 94/130 51.6 198 110

Basement floors 4 3 2 5 3 Foundation area (m2) 1920 14000 10200 3800 1830 Foundation level below GL (m)

-15.8 -13.5 -8 -21 -13

Raft thickness (m) 1.0-3.5 1.0-3.0 0.8-2.7 3.0-3.8 1.0-2.5 Number of piles 25 26/22 141 112 25

Observed pile load (MN)

7.9-13.8 7.4-11.7/5.0-

12.6 4.2-6.5 1.4-8.0 1.8-6.1

Observed Max. settlements (mm)

60 80 40-60 25 32

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Settlement of the piled raft foundation of the

Burj Kalifa: 160 storey high rise tower

Founded on 3.7 m thick raft supported on bored piles (1.5

m diameter, 50 m long).

Estimated total settlement is 45 mm to 75 mm.

Settlements under dead load (February 2008) 43 mm.

Extrapolated to full load is 55 mm to 60 mm

Predicted final settlement is 70 to 75 mm

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Adoption of Piled Rafts in National Capital Region (NCR)

Starting in 2009, we have consulted to 32 projects in the NCR.

Except in 2 cases, foundation is either a raft or a pile assisted raft including a 50 storey tower.

In about 6 cases we got a fresh soil investigation done.

A proper analysis has lead to a very economical foundation designs.

The details are given in the following slides

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PROJECTS NEAR DELHI:

Sector Area Number of storeys Ground Water

Table (m)

Liquefaction Potential

Foundation Recommendations

103 Cosmocity 1

Gurgaon 1B + S + 14 1B+S+30

2 Yes Raft Foundations

103 Cosmocity 2

Gurgaon 1B + S + 14

2.7 to 4.5 Yes Raft Foundations

103 Cosmocity 3

Gurgaon 1B + S + 22

4.5 Yes

Pile Assisted Raft Foundations

68 Gurgaon 1B + G+ 13 to 25 2B + G+ 25 to 33

21 No Raft Foundations

86 Gurgaon 1B + G+ 13 to 17 28 No Raft Foundations

16 B Gurgaon 3B + G+ 17 to 39 11 No Pile Assisted Raft, Raft Foundations

67 Gurgaon 2B + G+ 18 to 33 20 No Raft Foundations

62 Gurgaon 3B + G+ 29 to 37 8 No Pile Assisted Raft Foundations

Contd… 61 Prof. V.S. Raju

Sector Area Number of storeys

Ground Water

Table (m)

Liquefaction Potential

Foundation Recommendatio

ns

16 Noida G + 22 to 34

18 No Pile Assisted Raft, Raft

Foundations

Gwalpahari Gurgaon 3B + G+ 17 21 No Raft Foundations

48 Gurgaon 2B + G+ 34

21 No Pile Assisted Raft

Foundations

58 Gurgaon 2B + G+ 23 to 30

7 No Raft Foundations

58 Mixed Use

Gurgaon

1B+G+25 to 29

8 to 13 No

Raft Foundations,

Pile Foundation

Gwalpahari Gurgaon 2B + G+ 28

Not met No Raft Foundations

102 Gurgaon 1B + G+ 26 1.5 Yes Pile Foundations

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Sector Area Number of storeys

Ground Water

Table (m)

Liquefaction Potential

Foundation Recommendati

ons

128 Noida 2B + G+ 35 to 38

8 No Pile Assisted Raft

Foundations

60 Gurgaon

2B+G+8 25 No

Raft Foundations

66 Gurgaon

2B+G+23 25 No Raft Foundations

67 Gurgaon

2B+G+26 26 No Raft Foundations

River Heights

Ghaziabad 3B+G+15 12.5 No Raft Foundations

Golf Links Ghaziabad

2B+G+29 20 No

Raft Foundations

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Sector Area Number of storeys

Ground Water

Table (m)

Liquefaction Potential

Foundation Recommendat

ions

88 A Center Court

Gurgaon 2B+G+27 9.2 No Raft Foundations

Solitairian City

Greater Noida

1B+G+29 4.5 No Pile Assisted Rafts &

Raft Foundations

Kristal Court, Wish

Town

NOIDA 1B+G+20 t0 26

10 No Pile Assisted Raft

Foundation

5A Palwal

Haryana G+4 1.5 Yes Raft Foundation

4A Bahadurgar

h

Haryana S+14 1.7 to 2.7 Yes Raft Foundation on

Vibro Stone Columns

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Sector Area Number of storeys

Ground Water

Table (m)

Liquefaction Potential

Foundation Recommendati

ons

77 Winter Hills

Gurgaon 1B+G+15 to 17

37 No Raft Foundation

78 Monsoon

Breeze

Gurgaon S+13 to 18 18 No Raft Foundation

Iconic Tower Kanpur 2B+G+28 20 No Pile Assisted Raft Foundation

DDA EWS Kalkaji S+14 Not Met No Strip Rafts

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Importance of Settlement Observations

The settlement information is most valuable, as these measurements will significantly contribute to improvements in design procedures, ensuring economy along with safety

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Settlement Observations Method:

Any precision leveling will be O.K

Fix plates on the floor or to the columns ( basement is

ideal), ground floor level is also adequate.

It is adequate if the measurements are done from stilt level

or ground floor level. This may be much easier than

transferring the level from the reference mark on the

ground to the basement level

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Examples in Delhi Region –Settlements of Rafts

1. DIAL – Terminal 3 on Raft

Settlements measured and reported as not significant.

2. Sector 58, Gurgaon

Structure : Residential building 2B+30 floor on Raft.

Frame completed

Dead load settlements = 32 mm

Estimated total settlement = 40 mm

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Settlements observations are being carried out for 6 structures One structure in Noida is fully instrumented, where load on the piles, reactions of the base raft and the settlements are being measured. For one more structure in Noida, pile loads and settlements are planned to be observed. My Recommendation: Make Settlement Observations mandatory for all structures with more than 10 storeys

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THE WAY FORWARD ON GEOTECHNICAL INVESTIGATIONS: Recognise the importance of a good Geotechnical

Investigations and educate Geotechnical, Structural Consultants, Architects and the owners

Soil Investigations have to be of International Standards and have to be supervised by an Independent qualified / trained persons. Prequalify the soil investigation agency based on standard

norms, Highly desirable that the agency is suitably accredited.

Involve a specialist Foundation Engineer / Consultant (Preferable in-house in case of a big consulting office) right from the start. Prof. V.S. Raju

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Specialist Consultant has to decide the scope of investigations, in consultation with Structural Consultants who has to give inputs with regard to Structures to be designed / built.

While engaging a geotechnical investigation agency, their scope

could be given in 2 parts, viz Part A – Field and Laboratory Investigations and Part B – Foundation Analysis and Recommendations.

Part B could be made optional depending on expertise of the

agency, should be done only when all the Structural details are available.

The Foundation and Structural Consultants should work very closely to arrive at a safe and optimum solutions.

During execution, the Foundation Consultant has to visit the site to ensure that foundation work is being done as per specifications. Prof. V.S. Raju

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