United States Department of Transportation
i
Resistance factors for 100% dynamic testing, with and without static load tests.
-
2011-05-01
[PDF-1.33 MB]
Details:
-
Creators:
-
Corporate Creators:
-
Subject/TRT Terms:
-
Resource Type:
-
Geographical Coverage:
-
Edition:Final report; 09/24/09-06/30/11.
-
Corporate Publisher:
-
Abstract:Current department of transportation (DOT) and Federal Highway Administration (FHWA) practice has highly
variable load and resistance factor design (LRFD) resistance factors, Φ, for driven piles from design (e.g., Standard
Penetration Tests (SPT), Cone Penetrometer Test (CPT)) to construction (e.g., pile monitoring). Complicating the
construction effort, are the number of piles monitored (e.g., 10% versus 100%), as well as the type of monitoring (e.g., high
strain rate: Embedded Data Collector (EDC), Pile Driving Analyzer (PDA), static load test, etc.). Of great interest are
quantifying the influence of number of piles within a group, number of piles monitored, as well as spatial variability on a
pile group’s uncertainty and associated LRFD Φ factors.
The work started with an investigation of probability of failure (POF) of a bridge in terms of its piers and underlying
piles. It was discovered that the number of piles in a pier may have a large impact on POF of a pier, which is why the
development of LRFD Φ should occur with respect to pier (i.e., pile group) level and include the total number of piles
within the group as well as the distribution of monitored and unmonitored piles within the group. Next, the total
uncertainty of the pier including spatial variability and error of the method (e.g., SPT, EDC/PDA, etc.) was investigated. The work started with spatial uncertainty of single pile resistance (side plus tip) from SPT data and then extended through
kriging (considering different weights for individual borings) to group layouts (e.g., double, triple, quads, etc.) for assessing
group resistance uncertainty, CVR. Subsequently, the kriging group work was carried over to assessing uncertainty, i.e.,
spatial and method error (predicted versus static load test) for high strain rate field measurements. Equations and charts
were developed to quantify group uncertainty, CVR, and LRFD Φ for typical group layouts and monitoring. The latter
approach was considered to be inflexible, and the spatial uncertainty (i.e., kriging) was replaced with hammer monitoring
in conjunction with high strain rate monitoring. Using the uncertainty of monitoring method (CV εm) and a measured
uncertainty of blow count regression (CVεh) versus high strain rate monitoring, an LRFD Φ equation was developed for pile
groups considering the numbers of monitored and unmonitored piles. The developed expression was evaluated at two sites
and gave reasonable predictions compared to current practice.
-
Format:
-
Funding:
-
Collection(s):
-
Main Document Checksum:
-
Download URL:
-
File Type:
