Performance of Settled Bridge-Approach Slabs with Polyurethane-Foam Injection

摘要

Bridge-approach settlement costs hundreds of millions of dollars in repairs annually. Polyurethane-foam injection by two different processes: (1) a patented deep-injection process, and (2) a non-patented process (directly under the slab) were investigated to study the effectiveness of the slab lifting and leveling. A method of evaluating localized roughness by using areas bound by deviation curves was developed. Three field projects were investigated, one of which was repaired over 6 years ago. The deviation curves from these sites are very repeatable, as the plots often overlap. Evaluating the localized roughness, such as the bridge-approach settlement, using the areas bound by deviation curves seems to be a reasonable approach. The slab lifting with polyurethane foam, using either process, was successful at all three sites. The slabs were all raised to the desired elevation, improving safety and ride quality. The roughness was reduced by as much as 70 %. The falling weight deflectometer (FWD) deflections were reduced by as much as 60 % at many monitored locations. It is believed that when there are no other factors to cause the embankment to lose soil, the polyurethane-foam injection can be used to lift the settled approach slabs. Flowable fill should be used to fill any visible voids prior to the polyurethane-foam injection. The advantage of the patented deep injection process over the non-patented process is inconclusive.