Roller Coaster Highways: The Implementation and Execution of a Settlement Monitoring Program at Two Colorado Highway Projects

摘要

We are all familiar with the infamous "bump" at the end of a bridge. After recent highway projects experienced significant differential settlement at bridge abutments, the Colorado Department of Transportation (CDOT) updated their specifications to address the problem. CDOT now requires contractors to monitor embankment settlement and verify the completion of primary settlement prior to allowing roadway paving. Kleinfelder, as part of design-build teams, was selected to provide geotechnical services for two highway interchange projects requiring settlement monitoring, and consulted each contractor on the implementation and execution of a settlement monitoring program. Instruments were installed at the subgrade/foundation soils elevation, middle depth of the embankments, and at the final grade to determine the rate of settlement at each location within the embankment fill. Four instrument types were chosen based on subgrade soils and the installation height within the fill. Installation of the instruments required planning, cooperation, and communication with the prime contractor, sub-contractors, and CDOT representatives, to address the challenges of location selection during the fluid design-build process, avoiding and repairing damage to instruments, and field installation of the instruments. Settlement data was collected for analysis and submitted regularly throughout the construction process. Observed settlement data was compared to predicted and theoretical models. The settlement monitoring programs discussed are unique for Colorado highway projects, and presented are the challenges and lessons learned in implementing and executing settlement monitoring programs on two highway interchange projects.