Howard Concrete Pumping, Inc.

Scope Of Work

During a routine bridge inspection, it was discovered that the 6-span, 5 pier , bridge over the Sangamon River on I-72 was experiencing differential settlement, compromising the integrity of the bridge and the safety of motorists. Piers 3, 4, and 5 were all experiencing differential settlement with pier 3 experiencing the most, at approximately -3.5 cm of movement. Upon further investigation, it was determined that the differential settlement was caused by mine subsidence due to 2 abandoned coal mines beneath the bridge, approximately 200 feet below ground surface.

Howard Concrete Pumping was contracted to perform the first phase in mine stabilization by drilling and grouting beneath pier 3 under an emergency contract let by the Illinois Department of Natural Resources (IDNR). We drilled 60 grout injection bore holes beneath and adjacent to pier 3, and 2,839 cubic yards of grout were injected through the bore holes into the mine below. Survey of the structure indicated that movement of pier 3 had ceased upon placement of the grout.

Soon after completion of Phase I, we were again contracted for Phase II, which involved stabilization of the abandoned mine below piers 4 and 5. We drilled 48 grout injection bore holes, and 4,463 cubic yards of grout were injected through the bore holes into the mine below. As with pier 3, movement of piers 4 and 5 ceased upon placement of the grout.

We overcame numerous challenges during the project to save the bridge, including: extreme cold weather, flooding of the Sangamon River, and drilling the grout injection bore holes through the alluvial deposits adjacent to the river. Our vast experience in mine stabilization along with a superior equipment fleet, and partnering with the agencies involved, allowed this project to be a success and keep the bridge open and safe for the motoring public.