SOLVING A ROCKFALL PROBLEM IN NEVADA COUNTY, CALIFORNIA

A SIDEHILL CUT ON THE NORTHWEST SIDE OF I-80 IS COMPOSED OF MESOZOIC GRANITIC RODS OF THE SIERRA NEVADA BOTHOLITH. ORIGINALLY CONSTRUCTED IN 1958, IT HAS A 1:1 SLOPE WITH THE TOE AT THE EDGE OF THE SHOULDER AND A 15-FOOT-WIDE BENCH 40 FEET ABOVE GRADE. ADT AT THIS LOCATION IN 1971 WAS 10,600; DURING THE PEAK MONTH, ADT WAS 16,900. A GLACIAL MORAINE OVERLIES THE ROCKS AND IS COMPOSED OF UNCONSOLIDATED AND UNCEMENTED MATERIAL RANGING FROM CLAY SIZE TO BOUNDERS 3--4 FEET IN DIAMETER. ROCKFALLS RESULTED IN HAZARDOUS DRIVING AN DAMAGE TO BOTH THE PAVEMENT AND POWERHOUSE ACROSS THE ROAD. DURING THE SUMMER OF 1970 THE SLOPE WAS RECONSTRUCTED ON THE BASIS OF RESEARCH CONDUCTED BY THE WASHINGTON DEPARTMENT OF HIGHWAYS. THE BENCH WAS REMOVED, AND THE NEW SLOPE WAS BROUGHT DOWN ON A 0.9:1 SLOPE TO AN ELEVATION 6 FEET BELOW GRADE, RESULTING IN A 2-FOOT-WIDE TRENCH AT GRADE FOR CATCHING FALLING ROCKS. IT WAS FOUND THAT SOME ROCKS STILL ROLLED OUT OF THE TRENCH INTO THE TRAVELLED WAY, SO A FOOT- THICK SAND BLANKET WAS PUT IN THE BOTTOM OF THE TRENCH TO ACT AS AN ENERGY ABSORBER. IN THE INTERVENING TWO YEARS, NO ROCKS HAVE FALLEN ONTO THE ROADWAY, AND THE NUMBER REACHING THE TRAVELLED WAY HAS BEEN REDUCED BY ABOUT 80%. MAINTENANCE COSTS HAVE BEEN REDUCED BY ABOUT 25%. AS THE SAND BLANKET SOMETIMES BECOMES SATURATED AND FREEZES (THE ELEVATION IS ONE MILE), IT IS THOUGHT THAT PEA GRAVEL MIGHT PROVIDE MORE RELIABLE ENERGY OBSORPTION.

• Record URL:
  • https://onlinepubs.trb.org/Onlinepubs/hrnews/hr-news-49-01.pdf
• Supplemental Notes:
  • Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved.
• Authors:
  • Mearns, R
• Publication Date: 1972

Media Info

• Media Type: Digital/other
• Features: Figures; Tables;
• Pagination: p. 14-7
• Serial:
  • Highway Research News
  • Issue Number: 49

Subject/Index Terms

• TRT Terms: Embankments; Rockfalls; Slopes; Trenches
• Subject Areas: Geotechnology; Highways; Maintenance and Preservation;

Filing Info

• Accession Number: 00219036
• Record Type: Publication
• Files: TRIS, TRB
• Created Date: May 7 1973 12:00AM