Bridge Approach Polymer Grouting

Challenge:

Exploratory geotechnical borings as part of bridge rehabilitation planning discovered very loose to loose sandy micaceous silt.  Consolidation of this material was identified as the cause of continued flexible pavement settlement and deterioration on the both ends of the bridge, which carried a 4 lane parkway over a deep ravine.  Performing bridge approach polymer grouting or other soil consolidating grouting was required.

Limits:

Repairs had to be completed in fewer than 7 total days on site due to an exceptionally compressed time schedule for the entire project.  The roadway is an arterial commuter road into Washington, DC, so a compressed schedule was required to minimize traffic disruptions.  

The Solution:

The project’s geotechnical consultant recommended polymer grouting to stabilize the loose sandy silt material behind the abutments.  Polymer grouting was recommended over cementitious grouting due to rapid cure, compact equipment, minimal environmental risk, and low unit weight.  CJGeo proposed a 5lb/cuft polyurethane formulated specifically for compaction grouting.  The Terrathane grout is cures to 90% of ultimate strength within 15 minutes, weighs 95% less than the same volume of cementitious grout, and is environmentally inert.  

From a logistics standpoint, given the very tight site, polyurethane grouting is superior in that all 178 cubic yards of in place material were delivered and processed onsite via a single box truck and support pickup.

CJGeo proposed grouting in three stages (5′, 10′, & 15′ below grade) on a 4′ grid pattern. 

Result:

CJGeo mobilized to the site two different times; once to grout the approach & departure areas of the southbound lanes, and again to threat the approach & departure areas of the northbound lanes.  Pre & post DCP testing was performed by Schnabel Engineering to confirm the increase in bearing capacity of the treated soils.  CJGeo placed more than 23,000 pounds of Terrathane to complete the bridge approach polymer grouting in fewer than 60 hours onsite.  Significant improvements in soil characteristics were documented.  After the polymer grouting was completed, the general contractor removed the top 3′ of soil (fill material) and replaced it with 57 stone, then repaved the roadway.

CJGeo worked alongside the general contractor’s team to schedule polymer grouting around the hydrodemolition and latex overlay work being done on the bridge deck.  Crews worked seamlessly and CJGeo’s scope was completed ahead of schedule and below budget.