Quality assurance for deep bored piles

1. 1
QUALITY ASSURANCE
FOR DEEP BORED PILES
- A CASE STUDY
Indian Geotechnical Conference, 2012
IIT Delhi
Paper No. E-545
Sanjay Gupta, Ravi Sundaram & Sorabh Gupta
CENGRS GEOTECHNICA PVT. LTD.
[Presented by Sorabh Gupta]

2. 2
Project Location – Noida, U.P.
7 km
2 km
7 km
2 km
7 km7 km
2 km
7 km
2 km
7 km
2 km
7 km
2 km

3. 3
Project Details
66-story residential tower-
240 m high
Double Basement (9m
below grade)
3,400 m2 circular footprint
Foundation System
Piled-raft;
2.5m thick Raft @ 9m
depth
298 bored piles of 1m dia
and 48m length
Construction is presently
underway!

4. 4
Presentation Flow
Geotechnical Investigations
• 1 borehole to 50m depth
• 1 cross-hole seismic test (CHST) to 50m depth
• 12 pressuremeter tests @ 5m interval to 60m depth
Construction Monitoring & Foundation QA
• 298 Low-strain Pile Integrity Tests (PIT)
• Cross-hole Sonic Logging (CSL)
• Pile Coring
Pile Load Tests
• 2 Initial + 3 Routine Static Pile Load Tests
•6 High-Strain Dynamic Load Tests (HSDLT) using PDA
Final Foundation Design & Construction
Initial Design
• Compute Theoretical Safe Pile Capacities
• Initial Foundation Analysis

5. 5
Plan of Field Investigations

6. 6
Borehole Data
Medium dense to
dense alluvial sand to
37m depth
Hard clay to 41-50m
depth
Very dense sands /
silt (N>100) to 60 m
depth
GW at 11m depth
below OGL

7. 7
Pressuremeter Test Data

8. 8
Cross-hole Seismic Test
Olson® Freedom Data PC with
PSV Source and down-hole
triaxial geophones Test Setup

9. 9
Freedom NDT PC with DS/CS-2 Data Collection System
Olson Instruments’ Triaxial Geophone
Output Manifold and Air Compressor

10. 10
Time Domain Data FromCh: 5 , x= 16200 ,y =-1
0 20000 40000 60000 80000 100000
-10
-5
0
5
10
Time Domain Data fromCh: 6 x= 4980.
0 20000 40000 60000 80000 100000
-2
0
2
Time Domain Data FromCh: 8 , x =2340 , y =0
0 20000 40000 60000 80000 100000
-0.05
0
0.05
SV-Shear Wave
Arrival
P- Compressional
Wave Arrival
P-SV Source
Trigger Pulse

11. 11
Cross-hole Seismic Test Results
Direct Measurements:
•Compression Wave Velocity (Vp)
•Shear Wave Velocity (Vs)
Computed Parameters:
•Dynamic Young’s Modulus (E)
•Dynamic Shear Modulus (G)
•Poisson’s Ratio (μ)
•Coefficient of elastic uniform compression (cu),
•Coefficient of elastic uniform shear (cτ),
•Coefficient of elastic non-uniform compression (cφ)
•Coefficient of coefficient of elastic non-uniform shear (cΨ)
s
p
V
V
mwhere
m
m
=
−
−
= ,
)1(2
2
2
2
μ
2
)1(2
Vs
E
G ρ
μ
=
+
=
μ
μμ
ρ
−
−+
=
1
)21()1(2
VpE
A
E
cu
1
1
13.1 2
×
−
×=
μ
uc0.5~0.67 ×=τc
τφ c×=. 46.3c
τϕ c×=. 5.1c

12. 12
Cross-hole Seismic Test Results

13. 13
Design Profiles

14. 14
Theoretical Pile Capacities
Boundary Conditions:
1m dia bored piles
COL @ 10m depth (Basement Level)
GWT considered @ COL
Pile length
below COL, m
Ultimate Pile Capacity, MN
Compression Pullout
44 11.6 4.0
46 12.2 4.3
48 13.2 4.5

15. 15
Initial (Static Load Tests)
1m dia
25m long test piles
COL ~ 2-3m below
OGL
<25mm settlement at
10 MN compressive
load
Note: Test results provided by client

16. 16
Routine Static Load Tests
Concrete blocks used as kentledge
1m dia, 48m long production
piles @ COL of 10m Hydraulic Jacks
with
synchronized
pumping unit

17. 17
High-Strain Dynamic Load Tests
20 MT drop hammer
0.5-3m drop heights
4-strain transducers,
2 accelerometers
(recommended)
20 MT guided drop weight6 HSDLT were performed using PDA

18. 18
Routine Pile Load Test Results
Load test results are fairly
consistent
However, pile performance is
very poor as compared to
theoretical estimates (13MN)
and initial pile load test
results on 25m long piles
Settlement of 48m long piles
is almost twice as much as
25m test piles
Structural defects & ‘soft-toe
condition’ suspected

19. 19
Low-Strain Pile Integrity Tests (PIT)
Customized equipment
manufactured by Pile
Dynamics, Inc. (USA)
298 Piles
8 lbs hand-
held hammer

20. 20
PIT Results
PIT on 298 production
piles
Generally speaking:
Significant impedance
changes along the pile
shaft
Bulging at shallow
depths (2.5-4.5m)-
confirmed by pile
exposures
Weak toe response-
possible ‘soft toe
condition’ and low pile
end bearing Pile 1103

21. 21
PIT: Profile Analysis- Pile 1079
Pile No. 1079

22. 22
Pile Coring- 1079
0m to 7.5m depth

23. 23
Pile Coring- 1079
7.5m to 13.5m depth
Nil recovery 11.5m-12m

24. 24
Pile Coring- 1079
13.5m to 19.5m depth

25. 25
Pile Coring- 1079
19.5m to 28.5m depth

26. 26
Pile Coring- 1079
28.5m to 35.0m depth

27. 27
Pile Coring- 1079
35.0m to 44.5m depth
Slush encountered below 44.5m depth- confirms suspected ‘soft
toe’ condition

28. 28
PIT vs. Pile Coring- 1079
NeckingNecking
‘Soft Toe’
NeckingNecking

29. 29
Design Ramifications
Lowered pile stiffness was considered in
the analysis (nil end bearing)
Final design of the piled-raft system was
updated with reduced ultimate pile
capacities / stiffness
Additional piles were constructed under
the raft

30. 30
Conclusions
“There is many a slip twixt the cup and the lip”
A well-planned, comprehensive Foundation QA program is
essential to deliver foundation performance and avert disaster
Keep the geotechnical and structural engineers involved
throughout the foundation construction process
Just doing the tests is not enough!
Proper interpretation of the test results by an independent
agency of repute
Correlate all information and test results- geotechnical data,
pour card information, test results, etc.
Improve the design as well as the construction methodology in
parallel to get maximum benefit

31. 31
Let us Strive to Achieve..
Quality in Pile Construction
THANK YOU…
31
Cengrs Geotechnica Pvt. Ltd