CPT Installation of Fiber Optic Cable for Settlement Monitoring

Researchers: Andrew Yeskoo, Peter Hubbard

Client/Owner: ENGEO

Technologies: Distributed Fiber Optic Sensing

The UC Berkeley team performed strain monitoring of soil vertical displacements using distributed fiber optic sensing for a surcharge pre-load program on Treasure Island in the San Francisco Bay. Unlike previous installations performed by the UC Berkeley team, the fiber optic cable for this project was installed via CPT push using a sacrificial anchor tip and pretensioning frame. The result is an instrument that can be installed in an afternoon and localize the development of vertical displacement in the subsurface with time. The fiber optic data set was correlated with construction records of fill thickness of the surcharge in the area, as well as vertical settlement of a plate settlement point monitored by an Automated Motorized Total Station. Readings were performed over several months, measuring over 2 inches of settlement n the native materials before the localized strain around the fiber reached a threshold level and the fiber optic cable decoupled from the soil movements. Prior to the decoupling, the settlements shown by the fiber optic system were in close agreement with the survey results.