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Dynamic
pile testing has been in use in more
than 40 countries and is a part of
various code specifications worldwide
including ASTM D4945. Geo Dynamics
provides this service in India using
the latest Pile Driving Analyzer sourced
from Pile Dynamics, Inc., USA pioneers
in this form of testing worldwide.
The test can be used to evaluate various
pile parameters, few of those important
for cast-in-place bored piles are
mentioned below.
- True static
capacity of the pile at the time
of testing.
- Static load
test curve
- Total skin
friction and end bearing of the
pile
- Skin friction
variation along the length of
the pile
- Compressive
and tensile stresses developed
in the pile during testing
- Net and total
displacement of the pile.
- Pile integrity
and changes in cross-section if
any.
Applicable
For :
- Jetties &
Container Terminals
(e.g. JNPT, Gujarat Maritime Board
Jetties, Port Trusts etc)
- Bridges &
Flyovers
(e.g. Delhi Noida Bridge, JJ Flyover
Mumbai, Bangalore Flyovers,
- Railway ROBs
& Metro Rail Projects
(e.g. Delhi Metro, Western Railway
ROBs)
- Multistory
Buildings & Towers
(10 to 30 storey towers in Mumbai
& Pune for major real estate
developers)
Principle
of Testing :
The
basic purpose of high strain dynamic
pile testing is to evaluate pile static
capacity and its structural integrity
using measurement of both force and
velocity. Unless, any method uses
an instrumentation to measure force
it cannot be called dynamic testing
as such, since the basic requirement
of the test is to measure dynamic
impact and convert it to static capacity.
The
method involves attaching a minimum
of two pairs of strain transducers
and accelerometers on diagonally opposite
sides of the pile that is built upto
1.5 times pile diameter. These are
fixed minimum 1.5 times the pile diameter
below pile top & impact generated
using a hammer weight equal to 1%
to 2% of static test load. Note
that it is desirable that dynamic
testing confirms to ASTM D4945 or
other such relevant codes.
Strains
induced under the impact of a heavy
falling hammer from a pre-determined
height are measured with the help
of strain transducers attached to
the pile, whereas accelerometers record
the accelerations generated in the
pile. The Pile Driving Analyzer converts
strain to force, and acceleration
records are converted to velocities.
The resistance developed by the pile
is then a function of force and velocity
and includes few assumed factors such
as the quake and damping parameters
as inputs based on the soil type.
The maximum pile top compression is
obtained by integrating the pile top
velocity. A more accurate value of
these parameters is then obtained
from CAPWAP analysis conducted on
field data.
Benefits
of PDA Testing :
- Significantly
faster and economical than static
tests; with proper setup arrangements
can test atleast 2 bored piles
and even more driven piles per
day.
- Very effective
for large diameter bored piles
with huge capacity & applicable
for both offshore & onshore
piling
- Applicable
to almost all kinds of piles includes
bored, driven, micro, steel piles
etc.
- Reduces or
eliminates static load testing
especially in case of jetties,
flyovers, bridges, multistory
buildings where space is a constraint.
- Provides information
on friction, end-bearing, pile
integrity, hammer performance
etc. and plot simulated load test
curve for comparison with static
testing.
- Reduces controversies
and eliminates risk enabling a
safe foundation.
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