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Bridge/Bent No
1Penetration in PWR
(ft)
N values in PWR
2Top of Layer Bottom of Layer
-Auger Refusal
Bridge A, Bent 10 17.41 34-50/4" 50/1"
Bridge B-Bent 1 20.84 5-23-50/3" 50/1"
Bridge C-Bent 3 7.5 12-24-50/4" 50/5"
Bridge D-Bent 20 0.81 50/5" 50/0"
Bridge E-Bent 1 5.47 35-50/5" 50/1"
1Penetration values are obtained from CAPWAP results
2The blow counts are based on borings located at or near the bents and they show the strength
of PWR materials varied from top to bottom
TECHNICAL
From the Table 2 results, following comments
can be made:
1. Actual geotechnical capacities
(CAPWAP results, total capacities
in Table 1) in hard PWR exceed the
MFSLSLs that were provided by the
project structural engineer. These
results are anticipated considering
the properties of hard PWR materials
tend to behave like rock in the
local geology.
2. Average stroke = 10.3 feet is based on
values of maximum stroke in Table 2.
The stroke of 10± feet in a high fuel
setting indicate practical refusal by
hard PWR.
3. Maximum compressive stress recorded
is 37.3 ksi, which is within the
tolerable limit, 45 ksi. Therefore, piles
are not damaged even though geotechnical
capacity exceeds the MFSR.
Hence, pile sizes can be chosen using
MFSR without limiting the controlling
load NDR ≤ MFSR.
4. Blows per inch required to record the
maximum capacity in hard PWR range
from 10 to 20 blows per inch. Based on
our review of ICE I30 v2 Bearing Chart
and comments, 10 blows per inch
should be considered practical refusal
and driving in excess of 20 blows per
inch should be considered “improper
use” and will void the hammer warranty.
FHWA-NHI-16-003, Volume 2
includes definitions of both practical
and absolute refusals which generally
agree with ICE Bearing Chart
comments. Therefore, blows per inch
recorded in five tests indicate the
bearing materials (PWR with 50/5" ≤
N ≤ 50/1") can be considered “practical
refusal materials.”
5. The varying depths of penetration of
piles into the PWR (0.81 feet to 20.84
feet) presents various consistencies
of the PWR layers with SPT values as
given in Table 3. From these depths of
penetration, it can be concluded that
PWR with 12-24-50/4" ≤ N ≤ 34-50/4"
can be considered penetrable.
6. It should be noted that subsurface
conditions at each test location were
reviewed using the boring data at or
near the respective bents. The conditions
of PWR such as penetrable or
not penetrable/practical refusal (in
hard PWR) can be considered generally
correct; see Table 3. But depths of
penetration may vary at other locations
that are unexplored at other pile
locations of the respective bent.
Table 3: Blow counts in PWR layers at test locations
7. The BTA factor 100 percent shows
none of the piles were damaged, which
is reflected by the maximum compressive
stress values remaining less than
45 ksi during driving.
Continued on page 125
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