Laser Scanner Survey to Document Grouting-Induced Highway Surface Elevation Change (05-1002) - MP-03
Jeffrey R. Keaton, AMEC Environment and Infrastructure, Inc.
Brian Stutzman, AMEC Infrastructure
Jeffrey Geraci, Moore & Taber

Two pipelines were installed approximately 10 years apart as bored crossings under a divided highway. Sinkholes discovered locally above both lines alerted the pipeline company to a problem with subsurface voids and loose soils around the cased crossings. The sinkholes were filled initially with surface soils or flowable fill, but limited-mobility displacement grout was needed to fill voids and compact loose soil. The road surfaces were scanned before and after grouting to provide a basis for documenting elevation change that might have been caused by the grouting. Arbitrary coordinates were used for the scanner surveys, the locations of which were related to distinctive features on nearby steel lattice electrical transmission towers. Grouting was accomplished in vertical pipes in the northbound lanes and parts of the median and shoulder. Grout-pressure criteria and manometer readings at two locations on the road surface adjacent to each grout injection point were used to minimize expected heave. The two sets of scanner survey data showed that the grouting caused no detectible change in the road surface elevation. Error in the scanner data, which varied with distance away from the scanner setup location, was attributed to windy conditions and air blasts generated by passing vehicles. The scanner survey revealed a slight depression over one of the pipelines in the southbound left lane, which was treated with a supplemental grouting program.