Atch 11 Bridge DCP blow counts.pdf

This document is an email correspondence regarding Standard Penetration Test (SPT) blow count data collected for the Sand Pond Trail Bridge project. Jonathan Berry, PE and Public Services Staff Officer with the Plumas National Forest, reports geotechnical findings from subsurface investigations conducted at the bridge site.

The SPT data was collected at depths of 7 feet below ground surface and deeper using previously established bore holes. At Hole 1, the Drive probe achieved refusal after progressing only half an inch with 90 blows, indicating either very dense soil or obstruction. At Hole 3, two measurements were recorded: 67 blows at the 7.5-8 foot depth interval and 103 blows at the 8.0-8.2 foot depth interval. Advancement beyond 8.2 feet was not possible; a large one-inch gravel clast was retrieved by auger, with uncertainty regarding whether the material represents glacial till or bedrock. The high blow counts and refusal conditions suggest increasingly dense or resistant soil and subsurface conditions at depth.