El Niño Landslides of 1998

This article describes two "groundbreaking" applications of Applied Geomechanics instrumentation and the TDR method, as performed by KANE GeoTech, Inc. for the California Department of Transportation (Caltrans).

KANE GeoTech designed, programmed, installed, and monitored these systems under a contract with Caltrans. Text and photo courtesy of Dr. William Kane. The winter of 1998 brought devastating rain and landslides to California. Several remote systems were designed to monitor the stability of the slopes during clean-up. Personnel safety during reconstruction and that of the future motorists were the primary concerns. State Highway 25 in Hollister County was devastated when Tres Piños Creek eroded its banks and caused a massive slide.

A coaxial cable was installed to a depth of approximately 180 feet through the upper slide area. A remote TDR system using a datalogger was programmed to set off an alarm if the cable severed due to reactivation of the slide. A vibrating wire piezometer was coupled with the TDR to monitor fluctuations in groundwater levels. In addition, the system was programmed to allow remote access and data collection over a hardwire telephone line when desired. Along the Big Sur coast, Highway 1 experienced many landslides.

In Monterey County, a combination of TDR and in-place electrolytic tiltmeters was used in one large slide. Budget constraints, however, prevented using a remote TDR system. Instead, a single 200 feet borehole was instrumented with a TDR cable. Tiltmeters were attached to the cable at the depths of 150 feet, 100 ft, 50 feet and 10 feet.

The datalogger was programmed to monitor the tiltmeters for rotation and initiate phone calls to several pagers notifying personnel of movement. If movement occurred, the TDR cable could be read manually to locate the depth of such movement.

Figure 1 shows the installed monitoring system.

Attached Documents:

ElNinoLandslides1998.pdf