Foundation Reuse: Length, Condition, and Capacity of Existing Driven Piles

Reusing existing bridge foundations is an appealing design alternative for many bridge projects, but methods for investigating and analyzing existing foundations vary widely. Researchers from the University of Missouri performed research to evaluate various methods for predicting the installed length, assessing the condition, and predicting the load capacity of existing foundations. The methods were evaluated via application to two MoDOT bridges, both built in the 1960s and replaced in 2017. One bridge was founded on driven closed-end steel pipe piles backfilled with concrete (CIP piles), and the other was founded on octagonal precast concrete piles. The foundations were not actual candidates for reuse, but were selected for study because of the age and type of piles. To perform the evaluations, researchers gathered and made predictions from historical records, performed various geophysical test methods to predict pile length and potentially identify deterioration, performed static load testing, performed high-strain dynamic analyses of pile restrikes, and exhumed the piles to assess true pile length and condition.

The research found that historical pile driving records could be used to predict pile length within 3 percent of the exhumed length whereas values from as-built plans were as much as 30 percent less than the exhumed length. Results from parallel seismic testing produced estimates of pile length that were within 8 percent of the exhumed length. Parallel seismic results were more accurate when the sensor was located within 5 ft of the pile. MoDOT’s seismic cone penetration test (SCPT) rig was effective for parallel seismic tests. Sonic Echo / Impulse Response test methods performed after bridge demolition were effective in predicting pile lengths for the CIP piles, but application to the precast piles underpredicted lengths by as much as 20 percent, most likely because of the taper in the precast piles. SE/IR tests performed prior to bridge demolition were mostly inconclusive, mostly because of complex vibrations between the pile and connected superstructure. Observations of exhumed piles for both CIP and precast piles revealed no significant deterioration. CIP piles had visible surface corrosion, but caliper measurements of wall thickness at sections cut through the most corroded portions were not significantly different from measurements through portions without visible corrosion. Estimates of axial load capacity of the existing foundations varied widely. Values listed on historical documents were the least, and quite conservative compared to values from static load testing. The CIP test pile was loaded to four times the historical design capacity, and the precast test pile was loaded to seven times the historical design capacity. Maximum load test values can be considered lower bound values since the tests terminated upon failure of the capping beam for the existing bridge, which was used as the reaction. Dynamic analysis of restrike data yielded estimates of axial capacity similar to the maximum loads applied during static load testing. The dynamic values are also lower bound values because the restrike hammer had insufficient energy to transfer significant load to the pile tips.

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Report number: cmr18-008
Published: May 2018
Project number: TR201714
Authors: Andrew Z. Boeckmann, Brent L. Rosenblad, and John J. Bowders
Performing organization: University of Missouri-Columbia Dept. of Civil and Environmental Engineering

Missouri's Bond Strength Investigation

Delamination or debonding between asphalt layers is a persistent problem often encountered when analyzing pavement cores taken from Missouri’s roadways.  Delaminated asphalt layers are suspected to be the primary cause of premature pavement deterioration that dramatically decreases the pavement’s service life. After a thorough review, the Missouri Department of Transportation (MoDOT) increased their minimum tack coat application rates to more closely follow national recommendations and guidelines in order to mitigate the issues with delaminated asphalt lifts.  This report presents the findings of a tack coat investigation conducted by MoDOT to evaluate and verify the effects of the tack coat specification change.  The source of the data and information presented in the report is from a laboratory study and field studies that evaluated the bond strength of asphalt overlays between different surface types, tack coat products, varied application rates, and environmental conditions. The laboratory study evaluated different tack coat products for bond strength between two lifts of new asphalt and between new asphalt and concrete.  The laboratory study subjected a set of each tack product to freezing temperatures to monitor the effects of cold temperature.  Also, the application rates were varied to determine the most optimal rate for adequate bond strength.


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Report number: CM 2018-01
Published: May 2018 (originally submitted January 2015)
Project number: Internal research
Authors: Jason M. Blomberg and Paul T. Denkler
Performing organization: Missouri Department of Transportation Construction and Materials Division Pavements Section

Evaluation of Green Lights on TMAs

The use of green versus traditional amber lights on Truck Mounted Attenuators (TMAs) was investigated to see if their use could help to improve safety in mobile work zones. Four light color configurations were evaluated via a combination of simulator and field study: amber/white, green only, green/white, and green/amber. The TMAs were used as shadow vehicles representing mobile work zones and were equipped with flashing light bars, an arrow board, and a checkerboard sign with steady light bulbs. Driver behavior measures, including first blinker distance and speed, merge distance and speed, work zone and arrow direction recognition distance, and disability glare were captured in simulator tests. Vehicle speeds as they passed TMAs were recorded in both the simulator and field studies. The simulator study results indicated that the amber/white combination had the highest visibility of work zone but created the highest level of concern with disability glare. The green only configuration yielded the least disability glare but also low overall visibility. The study findings implied an inverse relationship between visibility (awareness of work zone) and arrow board recognition (easy on eyes). The green/amber TMA light configuration performed roughly between the two aforementioned configurations and was the configuration preferred by the participants in a post simulator survey. The field study found that the green only TMA slowed drivers down when they passed the mobile work zone, and lower TMA speeds led to lower vehicle speeds. The results did not point in a single direction for both the simulator and field tests, and all four configurations appear to be viable.

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Report number: cmr18-007
Published: May 2018
Project number: TR201722
Authors: Henry Brown, Carlos Sun, Praveen Edara, Siyang Zhang, and Zhu Qing
Performing organization: University of Missouri-Columbia Dept. of Civil and Environmental Engineering