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 CASE G8 - Pile Driving Problems, A. H. Wu
Problem:
Difficulty in driving piles as required by the specification.
Symptoms: The following difficulties were encountered during installation of
cast-in-place pipe pile at Physical Education Center, U.S. Naval Academy.
Pile damage resulting from overdriving.
1.
Piles cannot be driven to anticipated depth.
2.
Piles do not achieve anticipated resistance.
3.
Collection of Facts:
1. The pile driving criteria was excessive and resulted in overdriving of
the piles. Consequently, damage occurred in some piles.
2. There were three pile load tests available for this project. However,
the load test results and the associated pile driving records were not fully
used to develop the driving criteria. The existing criteria relied heavily on
very high dynamic blow counts. This tends to overstress the shell pile during
deep driving which causes pile deformations and driving difficulties.
3. The pile driving criteria, even though it is excessive, was
established for a pile to carry 60 ton allowable bearing capacity. However,
it appears that only a few of the piles are requiring 60 ton bearing capacity
(many of them require between 40 to 50 ton capacities. Tension piles in the
pool areas to resist uplift force are believed to need lesser capacity). It
is incorrect to use a 60 ton pile driving criteria to control all the pile
installation when many of the piles do not require 60 ton capacity.
Causes:
Excessive pile driving criteria.
1.
Unusual and/or inhomogeneous site conditions.
2.
Improper test pile program and interpretation of test results.
3.
Solution: It is important to correct the pile driving criteria so that
overdriving can be avoided and pile damage can be eliminated. This, of
course, will result in a government cost saving. In this regard, it is
suggested that:
a. Driving criteria should be adjusted to accommodate actual bearing
capacity needed. Namely, different driving criteria for 40, 50, and 60 ton
piles can be used.
b. For 60 ton pile capacity, the driving criteria should be modified to
read that: "Piles shall be driven to a depth where the dynamic blow counts
shall be greater than 10 blows per foot for at least 20 feet."
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