Methodology:

The Caltrans GeoResearch Group (GRG) initiated a research project to test innovative mapping technologies. GRG acquired two field mapping systems and evaluated them during deployments in response to more than 30 landslides from October 2001 through October 2002.

• The first system relied on differential Global Positioning System (GPS) and laser ranging hardware, providing accuracy within 1 meter.
• The second system employed real-time kinematic GPS hardware with centimeter-level accuracy.

With both systems, a GPS antenna, receiver, and laser ranging device were used to acquire the relative coordinates of surrounding points. A digital terrain model, or topographic map was then generated from the coordinate points. Caltrans engineers used the field mapping system to survey the slope, develop cross sections, perform slope stability analyses, and provide grading recommendations.

Findings:

• The systems helped produce higher quality data and maps.
• The time required for staff to deliver engineering solutions for maintenance and construction work was significantly cut, reducing the delays to traffic.
• Assuming 200 landslides per year, the mapping system would cost $180,000 to deploy for a 3-year period (200 landslides x $300 labor x 3 years); in contrast, conventional surveys would cost $900,000 (200 landslides x $1,500 labor x 3 years). Even including the initial cost of one mapping system ($15,000) and the cost of the research project ($80,000), the potential net savings would be $625,000 over 3 years (or $208,000 per year.)