HomeMy WebLinkAbout1027 Campfire Dr - Special Inspections/Engineering - 09/28/2012A.G.
2180 South Ivanhoe Street, Suite 5
Denver. Colorado 80222-5710
Geotechnical and Environmental Consultants
l D,9-7 Ca inY{ie- -de—
D R Horton
9555 South Kingston Court, Suite 200
Englewood, Colorado 80112-5943
Attention: Mr. Kyle Gunther
Subject: Soil and Foundation Study
Proposed Residential Structure
Lot 10, Block 6
Trail Head
Fort Collins, Colorado
Project Number 121931
Purpose
303-759-8100 Fax 303-756-2920
www.agwassenaar.com
September 24, 2012
As requested, we have performed a soil and foundation study at the subject site. The purpose of our
study was to observe subsurface conditions encountered and to recommend geotechnical design
criteria for the design and construction of the foundation for the proposed residence. This letter
presents a summary of our findings and recommendations.
Subsurface Conditions
The field exploration included drilling a 4-inch diameter auger boring near the center of the lot to a
depth of approximately 30 feet. The subsurface materials encountered consisted of:
0' to 6'/2'
6'/z' to 18'
18' to 24'
24' to 30'
Date of drilling:
Depth to water:
Laboratory Testing
Fill, clay, very stiff, silty, sandy, slightly moist to moist, mottled brown
Clay, stiff, silty, moist, brown
Sand, medium dense, silty, moist, light red brown
Sand, medium dense, wet, red brown
August 20, 2012
26 feet at the time of drilling
24 feet 2 days after drilling
Samples obtained during drilling were returned to the laboratory. They were visually classified and
testing was assigned to selected samples in an effort to evaluate the engineering properties of the
subsurface materials encountered. Site specific laboratory swell/consolidation tests exhibited low,
to moderate measured swell (3.0% at a depth of 2 feet and 0.3% at a depth of 7 feet) upon an
Imo, ii (�j
D R Horton
Project Number 121931
September 24, 2012
Page 2
increase in moisture content under a load of 1,000 pounds per square foot (psf). Based upon visual
observation of the subsurface conditions encountered and laboratory testing for this and/or adjacent
lots, it is our opinion that the subsurface materials generally exhibit moderate potential for expansion.
Refer to the Colorado Geological Survey Special Publication 43 for a description of expansive soils
and their impact on structure performance.
Foundation Recommendations
Based on our evaluation of the subsurface conditions, the proposed residence may be founded upon
spread or pad -type footings bearing on the natural undisturbed soils or on properly placed and
compacted fill at a minimum depth of 6 feet below the existing lot grade.
Soil Modification
Overexcavation or another soil modification process will be necessary in order to utilize a spread or
pad type foundation for non -basement foundations unless it is desired to construct all footings at
least 6 feet below the existing lot grade. The following recommendations should be followed during
overexcavation operations in order to enable the placement of a moisture treated fill that can be used
for foundation support. These recommendations may be modified during construction if soil
conditions differing from those anticipated are encountered.
The existing soil should be excavated to a depth of at least 6 feet below the existing lot
grade. The base of the excavation should extend to a width of at least 5 feet beyond
the potential foundation footprint (including any counterforts). The excavation should
be sloped following current OSHA regulations. A licensed surveyor must verify the
depth and width of the excavation prior to any fill placement.
2. Once the excavation limits have been verified, fill placement may begin. The bottom
of the excavation should be scarified and moistened prior to fill placement. The
replacement fill should be placed in maximum 8-inch, loose lifts. If the replacement fill
consists of cohesive soils, the fill should be moistened and thoroughly mixed to obtain
a moisture content between 0% and +4% of optimum moisture content and then
compacted to a minimum of 95% of ASTM D 698 maximum dry density. If the
replacement fill will consist of granular soils, the fill should be moistened to a moisture
content of t2% of optimum moisture content and then compacted to a minimum of 95%
of ASTM D 1557 maximum dry density. It is recommended that a grading compactor
suited for such a fill be utilized to aid in compaction of the fill. Optimum moisture
content and maximum dry density should be obtained from appropriate laboratory
Proctor tests.
3. Observation and testing of fill placement must be performed by this firm on a full-time
basis. Testing should include in -place moisture content and dry density as well as
periodic swell -consolidation testing.
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