Engineers Day, 15.09.2015
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.com
Prof. V.S. Raju
1
Geotechnical Engineering Practice
S.No
Best Practice
(Mostly followed by
developed world)
Most Situations in India at
present
After Site Selection
1
Contour Survey
Sometimes available
2
Geology of site by expert
By the Geotechnical Agency
as part of the Geotechnical
Investigation
Preliminary Geotechnical
Investigation by an accredited
Agency
Rarely Done
3
Prof. V.S. Raju
2
Geotechnical Engineering Practice Contd…
S.No
Best Practice
(Mostly followed by
developed world)
4.
Project layout with location of
important structures made
available to Geotechnical
consultant.
5.
Most Situations in India at
present
Generally not made available to
Investigation Agency
Scope of Detailed Geotechnical Investigation:
Geotechnical Consultant in
Consultation with structural
consultant and on the basis of
structural details.
Prof. V.S. Raju
• 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.
3
Geotechnical Engineering Practice Contd…
S.N
o
Best Practice
(Mostly followed by
developed world)
6.
• Detailed Soil Investigation by • Lack of accreditation
an accredited and qualified
process.
investigation agency.
• Most investigation agencies
• Investigations done under
are not accredited.They do
independent supervision by a
not have trained manpower.
qualified person.
• Mostly not supervised
7.
Report containing
Investigation report by the
• Results of Field and
agency giving the results of field
Laboratory Tests
and laboratory tests only. No
• Recommendations for
Foundation Recommendations.
Foundations
• Safe Bearing Capacity and
Pile Capacities without
having full details of the
structures
Prof. V.S. Raju
Most Situations in India at
present
4
Geotechnical Engineering Practice Contd…
S.No Best Practice
(Mostly followed by
developed world)
8.
Interpretation of the results
by a Specialist Foundation
Consultant and
recommendation for type
of foundation and
foundation parameters.
9.
Interaction between
Foundation and Structural
Consultant and finalisation
of Foundation Design.
Prof. V.S. Raju
Most Situations in
India at present
Very rarely the case.
Investigation Agency hardly
has qualified and
experienced Foundation
Engineers.
Mostly Absent.
5
Geotechnical Engineering Practice Contd…
S.N
o
Ideal/ International
Practice
10.
Involvement of Foundation
Consultant during
Very Rare.
execution, review of
results of further tests.
Ex. Pile Load Tests (Initial
& Routine)
11.
Settlement Observations
and information to
Foundation Consultant.
Very Rare.
Foundation Performance
assessment and report by
Foundation Consultant
Absent.
12.
Prof. V.S. Raju
Most Situations in
India at present
6
QUALITY OF INVESTIGATION
World Standard
India
o Poor quality
equipment.
of
the
o Highly sophisticated and
mechanised equipment.
o Shell & Auger, Wash
Boring is also common
o Continuous core sampling
(in soils as well).
o SPT Equipment manual operation
o SPT equipment with
automatic hammer release.
o Static cone
penetration equipment
with Mechanical cone.
o Static cone test with
electric cone and
piezocone (crucial for
assessment of
liquefaction)
Prof. V.S. Raju
7
Pic.1.1. Non Standard Equipment
No safety measures
Prof. V.S. Raju
Pic. 1.2. Global Standard
8
Pic. 1.3 SPT Hammer
Dropped Manually (2013)
Prof. V.S. Raju
Pic. 1.4. SPT with Auto Trip Hammer
+ Standard Rig
9
Pic.1.5 Static Cone Penetration Reaction with Sand bags
Prof. V.S. Raju
Pic. 1.6 Crawler Mounted SCPT
Equipment
10
CASE STUDIES
Prof. V.S. Raju
11
Delhi International Airport – Terminal T3
Prof. V.S. Raju
12
Terminal T3 at Delhi
International Airport, DIAL
• 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
Prof. V.S. Raju
13
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.
Prof. V.S. Raju
14
Results of Footing Load Tests for Delhi
International Airport
1st Footing load test:
=
SPT N =
50
Size of footing =
Sandy silt
0
𝑬𝒔 = 𝟒 ∗ 𝟏𝟓𝟎
10
20
30
40
50
60
70
80
90
0
1.5 m x 1.5 m
Load Intensity, q = 40 t/m2, S = 4 mm
𝟏− 𝟎.𝟑𝟐
𝟎.𝟒
Load Intensity (t/m2)
* 0.82
Settlement (mm)
Soil type
Load Vs Settlement Curve for DIAL
5
10
15
= 1119 Kg/cm2
20
As per Shultze and Muhs
For SPT N = 50, Es = 800
Kg/cm2
25
Ratio = 1119/800 = 1.4
Prof. V.S. Raju
15
2nd Footing load test:
Type of soil
=
Silt with fine sand
SPT N
=
22
Size of footing =
Load Vs Settlement Curve for DIAL
1.5 m x 1.5 m
Load Intensity (t/m2)
For Load Intensity,
0
𝑬𝒔 = 𝟑. 𝟖 ∗ 𝟏𝟓𝟎
= 787
* 0.82
Kg/cm2
As per Shultze and Muhs
For SPT N = 22, Es = 530 Kg/cm2
Ratio = 787/530 = 1.48
Settlement (mm)
q = 38 t/m2, S=5.4 mm
𝟏− 𝟎.𝟑𝟐
𝟎.𝟓𝟒
10
20
30
40
50
60
70
80
0
5
10
15
20
25
Prof. V.S. Raju
16
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.
Prof. V.S. Raju
17
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.
Prof. V.S. Raju
18
51 storey building for IREO
at Sector 67, Gurgaon
(46 storeys completed)
Prof. V.S. Raju
19
Pile Assisted Raft for 51 Storey Tower continued….
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.
Prof. V.S. Raju
20
Pile Assisted Raft for 51 Storey Tower continued….
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.
Prof. V.S. Raju
21
Pile Assisted Raft for 51 Storey Tower continued….
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)
Prof. V.S. Raju
22
Pile Assisted Raft for 51 Storey Tower continued….
• 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.
Prof. V.S. Raju
23
Pile Assisted Raft for 51 Storey Tower continued….
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
Prof. V.S. Raju
24
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.
Prof. V.S. Raju
25
Summer Palms– Artistic View
Prof. V.S. Raju
26
Summer Palms continued…
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.
Prof. V.S. Raju
27
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
Prof. V.S. Raju
28
Settlement Monitoring Points
Monitoring Points
Prof. V.S. Raju
29
Settlement observations: Predicted 67 to 75 mm
Tower No.
Current Updates of each Tower
Settlement (Measured)
Remarks
(1st Week-August’15)
(4 points on 4 corners)
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
Prof. V.S. Raju
30
L&T Serene County
Hyderabad
Prof. V.S. Raju
31
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?
30 m
75 m
Hard Rock
SBC 400 t/m2
Hard Murrum
80 t/m2
Soft Clay
4 m thick
0 t/m2
Tower Foot Print
Prof. V.S. Raju
32
Acknowledgements
 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
Prof. V.S. Raju
33
Prof. V.S. Raju
34