SUPPORTING_DOCUMENT__C_-_TEST_HOLE_EXCAVATION_SUMMARY-GEO_TECH_REPORT.pdf

SUPPORTING DOCUMENT – C

AG-0261-S-17-0091

REDFISH LAKE ROAD PHASE 2 – NUMBER 2

PROJECT 2017

TEST HOLE EXCAVATION SUMMARY &

GEO TECH REPORT

7 Pages (including this header page)

Test Hole Excavation Summary Redfish Lake Road Improvements (Phase 2) Project Sawtooth National Forest Performed on August 12, 2016

Objective On August 12, 2016, five (5) test holes were excavated along the proposed road alignment as part of the Redfish Lake Road Improvements (Phase 2) project. The purpose of the excavation work was to determine the likelihood of encountering large boulders as part of the roadway earthwork installations in locations where the greatest excavations would be occurring. A large excavator was used to perform the test hole digging, with depths varying between eight (8) feet and ten (10) feet below the existing ground surface.

Findings The soil information collected is informational and is meant to provide an approximate idea of what material likely exists onsite, at the locations and to the depths excavated. Material encountered consisted of a topsoil layer of mostly fine silt/clay at the surface with underlying decomposed granitic gravelly-sand material below with cobbles and boulders of varying sizes intermixed through-out. Boulders varied in size from 6” up to 7’, in their smallest and largest dimensions, respectively. Larger boulders should be expected based on those that are present on the surface at various location along the alignment.

No gradations, moisture-density relations, or California Bearing Ratio tests were performed on these soils sampled from the test holes. Interpretation of the soil descriptions for each test hole is based solely on observations made of the spoils and cross sections of each site during the time of excavation. These soil descriptions are further explained below:

• Test Hole #1

Total depth below existing ground was about eight (8) feet.

Material is consistently gravelly-sand intermixed with boulders, some measuring over 30 inches in the largest dimension, with the majority being less that one foot in the greatest dimension.

• Test Hole #2

Total depth below existing ground was about eight (8) feet.

Material is consistently gravelly-sand intermixed with boulders, some measuring over 30 inches in the largest dimension, with the majority being less that one foot in the greatest dimension.

• Test Hole #3

Total depth below existing ground was about ten (10) feet.

Material is consistently gravelly-sand intermixed with boulders. Three large boulders measuring 4’- 7’ in their largest dimension were encountered. About 30%-35% large boulders.

• Test Hole #4

Material is consistently gravelly-sand intermixed with boulders, one measuring about 3’ in the largest dimension. About 20% cobble/boulder material, most of which were smaller than a bowling ball.

Very favorable backfill material

• Test Hole #5

Total depth below existing ground was about eight and a half (8.5) feet.

Material is consistently gravelly-sand intermixed with boulders. Larger boulders measuring between 2’-4’ in their largest dimension were removed from the bottom of the hole.