Investigation of Settlement at Bridge Approach Slab Expansion Joint: Survey and Site Investigations (0-4147-1)

Researchers investigated the bump at the end of the bridge by conducting a literature survey, distributing a questionnaire to the 25 districts of the Texas Department of Transportation, and by investigating two bridge sites in Houston, Texas. Some of the most important conclusions from the surveys are : 1. On the average, 25 percent of all bridges in the USA are affected by the bump problem; this is also the number for Texas Bridges. 2. The maintenance cost for the bump problem in the USA is estimated at 100 million dollars per year (1997) and 6.3 million dollars per year in Texas (2001), 3. A tolerable bump has a slope of 1/200 or less, 4. In Texas, the number one reason for the bump is the settlement of the embankment fill followed by the loss of fill by erosion, 5. The problem is worse when the embankment is high and the fill is clay, 6. The problem is minimized when an approach slab is used and the fill behind the abutment is cement stabilized. The investigations at the two bridge sites with significant bumps indicated that : 1. The soil near the abutment was weaker and wetter than the soil away from the abutment, 2. The soil near the abutment had a relatively high PI for an embankment fill, 3. There were no voids under the pavement. A bump rating number, BR, and a bump index number, Bl, are proposed to document the severity of existing bumps and to evaluate the likelihood of developing a bump at a site, respectively. The recommendations for the soil within 100 ft of the abutment are to: 1. Use controlled quality backfill : PI less than 15, less than 20 percent passing sieve #200, coefficient of uniformity larger than 3, 2. Compact the soil to 95 percent of Modified Proctor controlled by inspection with a measurement every 50 ft2, 3. If such a backfill cannot be achieved, the embankment fill within that 100 ft zone should be cement stabilized.