PILE DRIVING PROCESS
Abstract
A seven-step process for selecting driving
criteria has proven successful for the
installation of driven piles. The process
incorporates static analysis of pile capacity,
wave equation analyses, dynamic load
testing and static load testing in a rational
and consistent sequence resulting in
reliable and cost-effective driving criteria.
The process can be used successfully on
relatively small projects to projects with
several thousand piles. Experience shows
this process avoids excessive conservatism
in design and unnecessary cost.
Introduction
The need for deep foundations on any
project results from many factors, including
subsurface conditions, foundation
loads and allowable foundation settlement.
The decision to use piles typically
results from having soft/loose soil
conditions near the surface that would
result in unacceptable settlement or
inadequate bearing capacity for shallow
foundations. Once a decision is made
to use deep foundations – in particular,
driven piles – the type of pile, pile dimensions
and the design load of the pile must
be chosen. The pile type and diameter are
often chosen based on cost, availability
and local experience and practice.
The pile loading conditions in compression,
tension and lateral loading are
needed to select the type and size, or
range of types and sizes, of pile to be analyzed.
Obviously, the loading per pile will
depend on the number of piles selected
for the foundation. The loading conditions
also influence this selection – displacement
piles provide more shaft resistance
and thus larger uplift loading. Piles
with high bending stiffness provide larger
lateral resistance.
Pile driving criterion
In its simplest form, a pile driving criterion
is defined as a specified pile driving
resistance when the driving operation
can be stopped. The criterion in the
United States is generally expressed in
a minimum number of blows per foot
or blows per inch at a certain hammer
stroke or energy transfer. In other parts
of the world, the criterion is expressed
typically as a minimum number of blows
per 250 mm. A properly chosen criterion
ensures each production pile will have
adequate capacity.
Understating the driving criterion can
result in a pile with less than adequate
capacity. Overstating the driving criterion
can result in an unnecessarily high capacity
and excess depth, resulting in additional
cost, schedule delays and a higher
risk of pile damage.
The process
Although the process outlined here contains
no new tools or unique methods,
it details a logical method to simply link
several established tools to optimize the
final driving criterion.
The steps of the process are:
1. Evaluate subsurface data and perform
static pile capacity analysis.
2. Select preliminary driving criterion
using wave equation analysis.
3. Drive probe piles across the site area
using a Pile Driving Analyzer® (PDA)
to evaluate capacity, driving stresses
and hammer performance, including
retapping of selected piles after
initial setup.
4. Evaluate and adjust the driving criterion
based on the PDA results.
5. Drive test pile(s) using the revised
driving criterion.
6. Statically load the test pile(s).
7. Perform a final evaluation of the driving
criterion for the production piles
based on the load test results.
A brief discussion of each step is
included below.
Evaluate subsurface data and perform
static pile capacity analysis. It is
essential to have an adequate subsurface
investigation with sufficient exploration
points, along with an adequate laboratory
testing program.
There are numerous methods for performing
static pile capacity analysis,
The original article, published in the Fall 2002 issue of PileDriver, then known as PileDrivers.org
90 | ISSUE 4 2020 www.piledrivers.org
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