Combining Automatic Monitoring of Grouting Performance Parameters and Geotechnical Instrumentation for Risk Reduction in Complex Grouting Projects

The paper describes two case histories of compaction grouting projects where geotechnical instrumentation was required in parallel to automatic monitoring of grouting performance parameters in order to prevent damages to adjacent structures. Both projects involved compaction grouting in very close proximity to water lines. The first project involved six 18-foot (5.5-m) diameter discharge pipes below the siphon house of a pumping plant on the California Aqueduct. The joint between steel lined pipes and concrete pipes had gradually opened due to piping and seepage and ground improvement by compaction grouting under the pipe joints was required. Submersible 3D crackmeters for quick installation by divers across the contact joints between the pipes were developed for this project and were read automatically in parallel to compaction grouting pressures, flows and total injected volumes. The second project involved three 4-foot (1.2-m) diameter HDPE water inlet conduits at a lift station of a city near Los Angeles. Very loose soil zones and possible open voids were known to exist around the lift station structures as a result of shoring removal and flooding of the excavations during construction. Therefore ground improvement by compaction grouting around and below the conduits was needed and combined settlement and diameter sensors were specifically developed to be installed in the water conduits and were read automatically in parallel to compaction grouting pressures, flows and total injected volumes. In both of those projects, grouting could not have proceeded safely without monitoring of the water lines. All parties recognized that monitoring was essential because of the high consequences and costs that would have resulted from damages to the water lines and disruption of service.