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17-11-2014
1
Advances in Field Testing Methods and Code of Practice
Prof. V.S.Raju
(Formerly: Director, IIT Delhi & Professor and Dean, IIT Madras)
Email: [email protected] 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….
4 Prof. V.S. Raju
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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.
5 Prof. V.S. Raju
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
6 Prof. V.S. Raju
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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
13
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
Prof. V.S. Raju
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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
Prof. V.S. Raju
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Pic.1.6 Static Cone Penetration - Reaction with Sand bags
Pic. 1.7 Crawler Mounted SCPT Equipment
17 Prof. V.S. Raju
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
Prof. V.S. Raju
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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
43 Prof. V.S. Raju
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.
44 Prof. V.S. Raju
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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
45 Prof. V.S. Raju
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
48 Prof. V.S. Raju
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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:
49 Prof. V.S. Raju
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
51 Prof. V.S. Raju
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.
53 Prof. V.S. Raju
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.
55 Prof. V.S. Raju
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
57 Prof. V.S. Raju
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
59 Prof. V.S. Raju
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
60 Prof. V.S. Raju
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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
63 Prof. V.S. Raju
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
65 Prof. V.S. Raju
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
67 Prof. V.S. Raju
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
69 Prof. V.S. Raju
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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