Lessons Learned from Ground Modification Program Using Grout in Karst for I-70 in Frederick, Maryland

摘要

The I-70/ MD 85 Interchange, MD 355 and MD 475 Interchange Reconstruction Project is an improvement project for the existing alignment of I-70 as it passes on the south side of the city of Frederick, Maryland. This project occupies an active karst area underlain by Cambrian and Ordovician limestones. Historically, sinkholes have been very problematic for transportation facilities. Consequently, major aspects of this project are ground modification for the sinkhole prone areas and unique storm water management facilities. The storm water management system includes three lined ponds, a 600-foot long earth dam, geotechnical instrumentation, and two pump stations. The past success of Maryland's subsurface grouting program for addressing sinkholes in existing roadways led to the decision to incorporate subsurface grouting as a preventive measure in capital highway projects in sinkhole prone areas. In 2006, the grouting program for the I-70 improvement project included 681 grout holes and 42,227 cubic yards of grout. Management of this program required daily interpretation of a plethora of subsurface data Drill and grout data was entered into a computer with a 3D software program to develop grout hole location maps, depth tb top of rock, and grout-take contdur maps. These maps were used to guide grouting operations, and to determine the need for secondary grout holes. This paper will also cover the geologic setting, the field exploration, and sinkhole-related designs. The subsurface karst conditions encountered during construction were more developed than predicted, resulting in large grout volumes and impacts to the project schedule. Modifications were made to the drilling and grouting strategy. Lessons learned will be discussed. Evaluation is still in progress; however, the grouting program appears to have achieved stabilization at the roadway and structure locations.