Role of Foundation Consultants in optimizing time and cost

in large projects – Case Studies

Prof. V.S.Raju

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

Madras)

Email: rajuvs_b@yahoo.com1Prof. V.S. Raju

Engineers Day, 15.09.2015

Geotechnical Engineering Practice

S.No Best Practice(Mostly followed by developed world)

Most Situations in India at present

After Site Selection

1Contour Survey Sometimes available

2Geology of site by expert By the Geotechnical Agency

as part of the Geotechnical Investigation

3Preliminary Geotechnical Investigation by an accredited Agency

Rarely Done

2Prof. V.S. Raju

Geotechnical Engineering Practice Contd…

3

S.No Best Practice(Mostly followed by developed world)

Most Situations in India at present

4. Project layout with location of important structures made available to Geotechnical consultant.

Generally not made available to Investigation Agency

5.Scope of Detailed Geotechnical Investigation:

Geotechnical Consultant in Consultation with structural consultant and on the basis of structural details.

• Not the common practice.• Most often a bill of quantities

and a standard set of laboratory tests are given to the agency by Architect/Structural Designer.

• Inappropriate also because the laboratory tests are a function of the type of soil strata.

Prof. V.S. Raju

Geotechnical Engineering Practice Contd…

4

S.No Best Practice(Mostly followed by developed world)

Most Situations in India at present

6. • Detailed Soil Investigation by an accredited and qualified investigation agency.

• Investigations done under independent supervision by a qualified person.

• Lack of accreditation process.

• Most investigation agencies are not accredited.They do not have trained manpower.

• Mostly not supervised

7.Investigation report by the agency giving the results of field and laboratory tests only. No Foundation Recommendations.

Report containing• Results of Field and

Laboratory Tests• Recommendations for

Foundations• Safe Bearing Capacity and

Pile Capacities without having full details of the structures

Prof. V.S. Raju

Geotechnical Engineering Practice Contd…

5

S.No Best Practice(Mostly followed by developed world)

Most Situations in India at present

8. Interpretation of the results by a Specialist Foundation Consultant and recommendation for type of foundation and foundation parameters.

Very rarely the case.Investigation Agency hardly has qualified and experienced Foundation Engineers.

9. Interaction between Foundation and Structural Consultant and finalisation of Foundation Design.

Mostly Absent.

Prof. V.S. Raju

6

S.No Ideal/ International Practice

Most Situations in India at present

10. Involvement of Foundation Consultant during execution, review of results of further tests.Ex. Pile Load Tests (Initial & Routine)

Very Rare.

11. Settlement Observations and information to Foundation Consultant.

Very Rare.

12. Foundation Performance assessment and report by Foundation Consultant

Absent.

Geotechnical Engineering Practice Contd…

Prof. V.S. Raju

World StandardWorld StandardIndiaIndia

o Poor quality of the equipment.

o Shell & Auger, Wash Boring is also common

o SPT Equipment - manual operation

o Static cone penetration equipment with Mechanical cone.

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 (crucial for assessment of liquefaction)

QUALITY OF INVESTIGATION

7Prof. V.S. Raju

Pic.1.1. Non Standard EquipmentNo safety measures

Pic. 1.2. Global Standard

8Prof. V.S. Raju

Pic. 1.3 SPT Hammer Dropped Manually (2013)

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

9Prof. V.S. Raju

Pic.1.5 Static Cone Penetration - Reaction with Sand bags

Pic. 1.6 Crawler Mounted SCPT Equipment

10Prof. V.S. Raju

CASE STUDIES

Prof. V.S. Raju 11

Delhi International Airport – Terminal T3

Prof. V.S. Raju 12

• Terminal T1 was on Pile Foundation• Soil Investigation report recommends

pile foundation for T3

• EPC contract awarded on the basis of pile foundation.

• Review by Prof. V.S. Raju

13

Terminal T3 at Delhi International Airport, DIAL

Prof. V.S. Raju

Terminal T3 Continued..

• Soil Strata : Sandy silt and silty sand.

• SPT N value at Founding level is 22 to 33 and increases with depth

• For conforming adequacy of raft, 2 footing load tests were done at Founding level.

- Footing size - 1.5 m x 1.5 m

• In first case, settlements (S) at 40 t/m2 is

4 mm

• In second case, S at 38 t/m2 is 5.4 mm.

14Prof. V.S. Raju

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

Load Intensity, q = 40 t/m2, S = 4 mm

* 0.82

= 1119 Kg/cm2

As per Shultze and Muhs

For SPT N = 50, Es = 800 Kg/cm2

Ratio = 1119/800 = 1.4

0 10 20 30 40 50 60 70 80 900

5

10

15

20

25

Load Vs Settlement Curve for DIALLoad Intensity (t/m2)

Sett

lem

ent (

mm

)

15Prof. V.S. Raju

2nd Footing load test:

Type of soil = Silt with fine sand

SPT N = 22

Size of footing = 1.5 m x 1.5 m

For Load Intensity,

q = 38 t/m2, S=5.4 mm

* 0.82

= 787 Kg/cm2

As per Shultze and Muhs

For SPT N = 22, Es = 530 Kg/cm2 Ratio = 787/530 = 1.48

0 10 20 30 40 50 60 70 800

5

10

15

20

25

Load Vs Settlement Curve for DIALLoad Intensity (t/m2)

Sett

lem

ent (

mm

)

16Prof. V.S. Raju

Delhi Airport – T3

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

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

• Direct cost savings as well.

• Raft settlements were monitored and were found well with in limits.

17Prof. V.S. Raju

3. Pile Assisted Raft for a 51 Storey Tower at Gurgaon

• High rise tower with 51 storeys and 2 Basements.

• Strata : Predominantly Sandy Silt with water table 25 m below Ground level

• Founding Level: 12 m below Ground Level

• SPT N value is 35 & above below Founding level.

18Prof. V.S. Raju

51 storey building for IREO at Sector 67, Gurgaon (46 storeys completed)

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Preliminary Design proposed by a Singapore Structural Consultant:

- A Large Piled Raft of size 54 m x 68 m (3672 m2) with 600 mm dia bored piles of varying length

- Total number of piles = 345.

- Total Settlement of the Piled Raft is restricted to 50 mm.

- In Piled Raft, Raft is the main bearing element

and piles are used as settlement reducers.

Pile Assisted Raft for 51 Storey Tower continued….

20Prof. V.S. Raju

Review by Prof. V.S. Raju:

• Additional Investigations were proposed by us with 2 additional boreholes, 50 m depth.

• Fresh Assessment and Analysis led to a solution of reduced raft size and number of piles.

Pile Assisted Raft for 51 Storey Tower continued….

21Prof. V.S. Raju

Revised Pile Assisted Raft Design based on Fresh Analysis:

• Raft Area = 1740 m2 (reduction 50%)• Bored Piles of 600 mm diameter and 18 m

long• Total number of piles = 94 (reduction 70%) • Settlements restricted to 50 mm (as desired

by the client)

Pile Assisted Raft for 51 Storey Tower continued….

22Prof. V.S. Raju

• Approximately 25 % of total load will be transferred to piles from raft.

• Initially load will be predominantly transferred to the piles.

• At allowable settlement of 50 mm, the ultimate capacity of the piles will be fully mobilized.

- Hence Piles are designed for ultimate capacity.

Pile Assisted Raft for 51 Storey Tower continued….

23Prof. V.S. Raju

Settlement Observations.

• Settlements of the tower are monitored at 5 points on the raft.

• As of July 2014, 35 floors are completed

• Estimated load transferred = 47 %

• The maximum observed settlement is only 10 mm.

• FIRST TIME ADOPTION Of PILED RAFT IN INDIA

Pile Assisted Raft for 51 Storey Tower continued….

24Prof. V.S. Raju

Project: Summer Palms, Sector 4A, Bahadurgarh, Haryana.

13 Blocks, G+14

Original Investigation:

- 11 Boreholes

- Strata- Silty sand and sandy silt layers with water table at 2 m below GL.

- SPT N values – 2 to 10 up to 7 m below Ground Level

- Layers up to 7 m below ground level are prone to liquefaction.

- Pile Foundation recommended.25Prof. V.S. Raju

Summer Palms– Artistic View

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Review by Prof. V.S. Raju

Supplementary Investigation:

• 14 Static Cone penetration Tests (SCPT)

• 8 SCPTs using Mechanical Cone

• 6 SCPTs using Electric Cone with Pore Pressure sensors.

Confirmation of weak strata up to 7 m below ground level.

27Prof. V.S. Raju

Summer Palms continued…

Foundation Adopted:

Vibrostone columns to mitigate liquefaction

and improve soil stiffness

900 mm diameter Stone Columns installed at

2 m c/c spacing using bottom dry feed method

Raft Foundation on improved ground. Trial with Footing load tests on vibro stone columns

- 2 m x 2 m Footing (Single Column)- 4 m x 4 m Footing (4 columns)

SCPT tests between columns after installation.

Significant ground improvement

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Summer Palms continued…

Prof. V.S. Raju

Settlement Monitoring Points

Monitoring Points

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Tower No. Current Updates of each Tower Settlement (Measured)

(1st Week-August’15)

(4 points on 4 corners)

Remarks

F G+14 casted and Brickwork is in progress 58 to 60 mm Monitoring started from raft construction

G G+14 casted and Brickwork is in progress 49 to 50 mm Monitoring started after construction of ground floor

H G+5 casted and 6th floor is in progress  24 to 25 mm Monitoring started after construction of Raft

I G+5 casted and 6th floor is in progress  23 to 25 mm Monitoring started after construction of Raft

Settlement observations: Predicted 67 to 75 mm

Prof. V.S. Raju 30

L&T Serene CountyHyderabad

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Extreme Issue with one of the 10 towers, 14 storeyed

Tower Dimension : 75 m x 30 m

Recommended SBC by the soil Investigation Agency 30 t/m2?

Hard Rock SBC 400 t/m2

Hard Murrum 80 t/m2

Soft Clay 4 m thick0 t/m2

75 m

30 m

Tower Foot PrintProf. V.S. Raju 32

Acknowledgements

33Prof. V.S. Raju

Larsen & Toubro Limited

IREO, New Delhi

UMANG Realtech Pvt Ltd., New Delhi

M/s Keller Ground Engineering India Pvt. Ltd

Who carried out the Ground Improvement and Monitoring Settlements

THANK YOU

Jai Hind

34Prof. V.S. Raju