Chap. 23 Piles—The Design Process
23.1 You are the foundation engineer for a new baseball stadium that is now under construction. The
design drawings indicate the stadium will be supported on a series of steel H–piles, and provides
the “estimated toe elevation” for each pile. However, during construction it became necessary to
drive many of the piles to greater depths, which resulted in a significant increase in the
construction cost. The owner (who knows a great deal about baseball, but little about
foundations) is very unhappy about this additional cost. His construction manager has advised
the owner to pay the invoice, but so far the owner has refused. Therefore, the construction
manager has asked you to write a 300– to 500–word letter to the owner explaining the situation
and encouraging him to pay for the extra pile expense.
Keep in mind that the owner is a layperson who should trust the judgment of his construction
manager but is too strong–willed to stay in the background. At the moment he does not intend to
approve the extra payment to the foundation contractor, which could eventually lead to an
expensive and time–consuming lawsuit. A well–written letter by you could diffuse the situation
and avoid litigation.
Solution
Dear Mr. Jones:
At the request of Mr. Smith of ABC Construction Management Company, I have prepared this
summary and discussion of the construction cost overrun on the baseball stadium project. This
stadium is supported on a foundation consisting of ___ steel H–piles which were constructed
Chap. 23 Piles—The Design Process
Chap. 23 Piles—The Design Process
23.2 What are indicator piles, and how do they benefit the foundation design process?
Solution
Indicator piles are prototype piles that are constructed before the production piles. These
Chap. 23 Piles—The Design Process
23.3 Explain the advantages of using wave equation analysis and static load tests in the design-
construction process for driven piles for both ASD and LRFD methods.
Solution
Wave equation analyses provide important information on both the load capacity and
Chap. 23 Piles—The Design Process
23.4 Many engineers believe the only disadvantage to overdesigning pile foundations is the additional
cost of the pile materials. However, there is another important consequence of overdesign which
can significantly affect construction cost and may even make the foundation impossible to build.
What is this consequence and how can it be avoided?
Solution
In addition to increasing materials costs, overdesigned piles are more difficult to install, thus
increasing labor and equipment costs. In some cases, the additional labor and equipment costs,
Chap. 23 Piles—The Design Process
23.5 Under what circumstances would you most likely require integrity testing of newly–constructed
drilled shaft foundations?
Solution
Chap. 23 Piles—The Design Process
23.6 Describe a condition where downdrag loads might be a problem.
Solution
Downdrag can be a problem when a fill is placed over soft soils, then piles are driven through
Chap. 23 Piles—The Design Process
23.7 A proposed bridge is to be supported on a series of steel pipe piles which are to be designed in
accordance with the AASHTO bridge code. The engineer has designed these piles using static
methods, and intends to verify the capacity during construction using the FHWA modified Gates
dynamic pile formula with the end of driving blow counts. The estimated pile construction cost
(not including pile caps) is $250,000.
In an effort to reduce the total cost, the engineer is considering the following additional activities:
• A static pile load test (cost = $10,000)
• Dynamic testing of 5% of the production piles using a pile driving analyzer (cost =
$3,000)
• Dynamic testing of all the production piles using a pile driving analyzer (cost = $7,000)
Evaluate the expected construction cost savings from these additional activities, both
individually and in combination, and determine the most cost–effective course of action. Hint:
Review the AASHTO resistance factors in Table 13.3.
Solution
Assume construction cost is proportional to total pile footage.
Option Description AASHTO
φ
Construction Cost
Additional
Analysis
Cost Total Cost
A
Gates
0.40
$250,000
0
$250,000