PILE FOUNDATION DESIGN
OPTIMIZATION
through
Pile Testing
INTRODUCTION
Pile foundations are critical component of deep foundation systems
for tall buildings and heavy infrastructures like bridges, particularly
when surface soils are too weak to support the imposed loads. Pile
foundations are complex and an expensive operations that when
inefficiently deployed could place finacial strain on the entire project.
We want to explore the optimization of pile foundation design
through comprehensive pile testing methods, focusing on reducing
material and construction costs while maintaining structural integrity.
PILE CAPACITY DETERMINATION
Unlike the simple Terzaghi’s Model which is based on single homogeneous soil strata, deep
foundations often cut through multiple layer of different soils. Theoretical design from soil
test data often results in very conservative results:
• Uncertainties in dealing with several soil conditions.
• Many approximations on the side of safety (n values)
• Extra caution from inexperience
Pile design by pile testing—such as static load testing and dynamic load testing—offers
better assessment of pile capacity and allows for a more efficient pile designs.
PILE CAPACITY DETERMINATION MATRIX
Eurocode 7 recognizes four approaches to capacity determinations that can be tabulated thus:
Analysis Method
(Non-Test Methods)
Static Method
Dynamic Method
Comprehensive subsoil
investigation with static
analysis (Alpha or Beta
Methods)
FOS =3
Testing Methods
Full scale static
Load Test.
FOS= 1.5
Comprehensive subsoil
High Strain Dynamic
investigation with Pile Wave Load Test.
Equation Analysis (GRLWEAP)
FOS =2.5
FOS= 2.0
SAMPLE VARIATIONS IN PILE CAPACITY
PILE CAPACITY FACTOR OF SAFETY (FOS)
Factor of safety is not fixed. Eurocode 7
provides for a basic factor of safety
based on the reliability of the design
model, construction methods and
correlation of the adequacy of number
of pile tested. Design FOS are products
of basic factors and correlation factors
based on the number of tests done
PILE TEST DESIGN METHODS
Testing of piles is either for capacity or shaft integrity. Shaft quality is essential for pile performance.
Load tests can either be done to design the pile or verify the pile capcity.
BUT: Using pile load test to determine capacity is expensive and time consuming.
Traditional Pile design Method
EXPENSIVE, REALLY? WHAT IF?
Soil Test  Design Pile Capacity  Determine Number of Piles  Verify Capacity With Load
Test to 150% for the working pile
Pile Tests Design Methods
Soil Test  Estimate Pile Capacity  Install Trail Piles  Test Load trial pile to Failure or
grater 250% of estimated capacity Establish a new Design Load Capacity  Determine
Number of Piles  Verify Capacity With Load Test to 150% for the working pile
POTENTIAL BENEFITS OF PILE DESIGN
METHODS VIA TESTING
Pile testing is really an expensive and time-consuming exercise,
but the possible return on money spent usually outstrip the cost of
trial pile testing. A careful analysis of cost to benefit helps to
better convince a client to adopt this procedure.
A CASE STUDY ON KOFO ABAYOMI VI, LAGOS
This was a proposed office medium rise building development. The piles were initially designed
for a capcity of 500kN. We reckoned with the structural engineer of record, that higher capcity
is possible based on the depth of pile and soil formation. 3 Nos of trail piles were installed and
tested to 750kN and 1,125kN ULS. 750kN was then adopted for the foundation design. A total
of about 200 piles were installed. By simple ratio this would have been about 300 piles in total.
A total cost savings of for about 100 piles was achieved in the process. If we account for cost of
trial piles, a total cost savings is seventy-five million naira (N75,000,000).
The soil profile and load tests for the KOFO ABAYOMI VI,
LAGOS
FURTHER TECHNICS FOR PILE DESIGN BY
TESTING
Dynamic Load Test DLT:
• Dynamic load testing can be used on trial piles. Only a test
load of 2% to 5% of the anticipated capacity is needed.
• It is a non-destructive. It evaluates total capacity without
damaging the tested piles. The piles doesn’t have to
discarded after testing
• Further verifications to 150% can then be made via static
load test.
• DLT offers great cost and time savings for pile design
process
FURTHER TECHNICS (contd)
Comprehensive subsoil Investigation:
• Good subsoil investigation is the step towards
efficient pile design.
• SPTs should be standardized and well supervised
• CPTs are better for pile design.
Experience:
• Consulting with experienced foundation engineer is
critical for some class of projects is essential
Use of Reaction Piles:
• Use of reaction piles instead of kentledge is a faster
and safer method for static load testing.
FURTHER TECHNICS (contd)
Sound Bearing Capacity Definitions:
• 10% diameter of pile as failure does not have a sound basis for bearing capacity
determination. Methods which simulate plastic behaviour of piles offers better
evaluations. Hansen 80% is known to be good for larger diameter bored piles while
Davisson offset criteria works well driven piles. CAPWAP procedure is excellent for
driven and bored tested dynamically provided the test load is big enough to activate
full capacity.
• Extrapolation procedures can be used when piles are not tested to failure. Some
methods are Mazurkiewiczs or Chin-Konder.
FURTHER TECHNICS (contd)
Maintained Load test Procedure:
• Maintained Load Test Procedure is
recommended especial for load tests
on of trials. This makes the load test
curve smooth enough for capacity
analysis, especially if extrapolation is
need. Cyclic load should not be used
Some Technics Methods For Pile Design By Pile
Testing
The 10% criterion by BS and Eurocode does
not have sound theoretical basis. The Hansen
criteria seeks limits of plastic failure are better
recommended for bored piles.
The Davisson offset Criteria have been known
from experience to be better suited for bored
piles.
CASE EXAMPLE 2: EKO ANTLANTIC PROJECT
It was required to carry out load test ascertain working load. The Ultimate test 5475kN is. It was
impractical to work with kentlege for the
load size. So we used the Woking piles as
reaction pile.
CASE EXAMPLE 2: EKO ANTLANTIC PROJECT SLT
RESULTS
It was required to carry out load test ascertain working load. The Ultimate test is 50
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