Florida Department of

TRANSPORTATION

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• Current Florida Department of Transportation Practice to estimate static pile capacity during driving is to employ GRL’s suite of hardware and software: PDA, WEAP, and CAPWAP.   The process is both expensive (> $50,000+ for equipment), interferes with the contractor’s construction (i.e. attachment of leads to pile, delays) and time consuming (i.e. 1 to 7 days to perform CAPWAP analysis).  In addition, the present capacity assessment is conducted on less than 10 % of the piles with the other lengths being set with a driving criterion (i.e. blows/ft) based on the former tests.  The latter fails to consider variability of
  the site, or monitor stresses within all the piles.

• Consequently, the focus of this research is to develop less expensive equipment which is non intrusive, and software which can determine static pile capacities including skin and tip resistance real time (i.e. as pile is being driven).   The former and latter will allow every pile to be monitored without interfering with the contractor and eliminate the need of a driving criterion.   

            Shown in Figure 1 is schematic of the proposed pile driving process.

Figure 1.  Pile Driving Monitoring Equipment

 

The equipment, which generates the signal (i.e. strain gauges, and accelerometers), along with the transmitter equipment (shown in Figure 2), is cast into each prestressed concrete pile.    The latter equipment is non-reusable for pile driving, but is of nominal cost (less than $300).

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2.  Instrumentation and Transmitter which is Cast Into the Pile 

 

Shown in Figure 3. is the receiver for the data signal, along with the lap top computer which processes the data.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3. Receiver with Lap Top Computer 

The real time capacity is assessed from either the energy passing into the pile (i.e. FHWA approach) or the stress wave traveling down and up the pile.   In the latter approach, the dynamic skin to tip ratio is used to assess Case damping, Jc, and the static skin to tip resistance.    The work has progressed to the start of field-testing. 

• Static and Dynamic Field Testing of Drilled Shafts: Suggested Guidelines on Their Use for FDOT Structures

   

  The Florida Department of Transportation supports over ninety percent of their bridge structures on deep foundations.  Due to geology and loading, an increasing number are being supported on drilled shafts.   As part of the design and construction, a number of “field tests: Osterberg and Statnamic” have been specified to verify either design assumptions (i.e. skin, tip resistance, etc.) or contractors’ construction techniques.  The latter number may vary from as little as one to over ten (vertical and lateral) on any given site.  In addition, the tests may occur on production shafts or on sacrificial shafts.

              The focus of this research is to develop suggested guidelines on their use (i.e. number and local) for FDOT structures.   This will be accomplished by optimizing the benefits (i.e. evaluating design assumptions, construction ability, etc.) vs. the costs of the tests.  The costs will consider both direct (i.e. price of test: equipment, engineering, etc.) and indirect (delays in construction, etc.) numbers.  The benefits, such as validating the design assumptions will involve reducing the field test data (i.e. Osterberg and Statnamic) and comparing it to the design data.   The latter will also consider spatial variability of the sites by predicting shaft capacities from all the boring logs vs. variability of the Osterberg and Statnamic data over the sites. The investigation will involve all of the major FDOT bridges over the past 5 to 7 years: Victory, Apalachicola, 17^th, Gandy, Port Orange, West 47^th, McArthur, Christa, Acosta, Victoria, and Venetian Causeway.  Other options besides load tests (i.e. increasing length of shafts) will considered along with current impact of load testing (i.e. as built lengths) .

•             Recently a research project on the "Evaluation and Analysis of Current Compaction Methods for FDOT Pipe Trench Backfills in Areas of High Water Table" was completed.. Florida International University in Miami conducted the investigation with input from FDOT ( Central Office, District - 4 and District-6). The general finding is that the density obtained by dewatering with no compaction yielded similar results as compaction (by hand-tamping) with no dewatering. In addition, densities obtained by both these conditions gave values similar to that of the condition when neither dewatering nor compaction was done. On the other hand, both dewatering and compaction done simultaneously showed significant improvement in the density.
  
•             Final phase of the FDOT project " The Effect of Vibrations and Sound Induced during Installation of Deep Foundations" consisted in measuring the effect of acoustic curtain in mitigating pile driving noise. Florida Atlantic University . In addition to Laboratory Testing, a full-scale field test was conducted to determine the actual sound pressure level reduction through the use of an acoustic curtain in an on-site application. The acoustic curtain is a noise reduction blanket which is a combination of absorptive and reflective materials. Preliminary results indicate that acoustic curtain provides about 20 decibel reduction in noise.